README file for GASNet
by: Dan Bonachea <bonachea@cs.berkeley.edu>

This is a combination user manual and design document for GASNet. Anyone
planning on using, modifying or adding to the GASNet code base should read this
file.

Other documentation:
 * In this README the "docs directory" means either docs/ in the source
   directory or ${prefix}/share/doc/gasnet/ in an installation of GASNet.
 * For GASNet licensing and usage terms, see license.txt.
 * For documentation on a particular GASNet conduit, see the README file in the
   conduit directory (also installed as README-<conduit> in the docs directory).
 * For documentation on the communication-independent GASNet-tools library,
   see README-tools.
 * Additional information, including the GASNet specification and our bug
   tracking database, is available from http://gasnet.lbl.gov
 * Anyone planning to modify or add to the GASNet code base should also read
   + README-devel: rules developers are expected to follow when committing
   + README-git: overview and examples of GASNet's recommended git workflow
   README-git has instructions for obtaining the latest GASNet source code.

Contents of this file:
 * Building and Installing GASNet
 * Basic Usage Information
 * Conduit Status
 * Supported Platforms
 * Recognized Environment Variables
 * GASNet tracing & statistical collection
 * GASNet Collectives
 * GASNet debug malloc services
 * MPI Interoperability
 * GASNet Design Information
 * System Organization
 * GASNet coding standards
 * GASNet porting guide
 * Source Control and GASNet

Building and Installing GASNet
==============================
Here are the steps to build GASNet:

* optional: ./Bootstrap  
  Runs the autoconf tools to build a configure script (this can be done on any
system and may already have been done for you).
  If you are keeping a copy of the GASNet sources in your own source control
repository (CVS, svn, Hg, Git, etc.), then please also see "Source Control and
GASNet", below.

* ./configure (options)
  Generate the Makefiles tailored to your system, creating a build tree in the
current working directory.  You can run configure from a different directory to
place your build files somewhere other than inside the source tree (a nice
option when maintaining several build trees on the same source tree). 
  Unlike many other configure-based software, GASNet's configure will ignore
any setting of CFLAGS or CXXFLAGS.  Therefore, any flags that are required
(e.g. for the correct ABI) must be included in the values of CC, CXX and MPI_CC.
For example to build 64-bit code when your gcc and g++ default to 32-bit:
  CC='gcc -m64' CXX='g++ -m64'

  Some of the useful configure options:

    --help - display all available configure options
    --prefix=/install/path - set the directory where GASNet will be installed
    --enable-debug - build GASNet in a debugging mode. This turns on C-level
      debugger options and also enables extensive error and sanity checking 
      system-wide, which is highly recommended for developing and debugging 
      GASNet clients (but should not be used for performance testing). 
    --enable-trace - turn on GASNet tracing (see usage info below)
    --enable-stats - turn on GASNet statistical collection (see usage info below)
    --enable-debug-malloc - use GASNet debugging malloc (see usage info below)
    --enable-segment-{fast,large,everything} - select a GASNet segment 
      configuration (see the GASNet spec for more info)
    --enable-strict-prototypes - Use strict prototypes in GASNet headers
      At the expense of slight deviation from the GASNet specification, this
      option will ensure GASNet's public headers use prototypes that are
      compatible with the -Wstrict-prototypes flag to gcc and work-alikes.
    --{enable,disable}-smp-safe - Build GASNet for an SMP or uni-processor.
      These options are not normally necessary, since by default configure
      will probe the machine to determine if it is an SMP.  However:
      1) If you configure on a uni-processor and intend to use the resulting
         libraries on an SMP, then you MUST specify --enable-smp-safe to
         ensure correctness.
      2) If you configure on an SMP for execution ONLY on uniprocessors, then
         you MAY specify --disable-smp-safe for a performance improvement.
    --enable-pshm - Build GASNet with inter-Process SHared Memory (PSHM) support.
      This feature uses shared memory communication among the processes (aka
      GASNet nodes) within a single compute node (where the other alternatives
      are multi-threading via a PAR or PARSYNC build; or use of the conduit's
      API to perform the communication).
      Note that not all conduits and operating systems support this feature.
      For more information, see the file pshm-design.txt in the docs directory.
    --with-segment-mmap-max=<n>GB - configure maximum segment size.
      Many of the GASNet network conduits obtain memory for the shared segment
      (in FAST and LARGE segment configurations) using mmap().  By default
      GASNet will use a very conservative (2GB minus pagesize) maximum value
      for calls to mmap().  This configure option allows one to raise that
      to a value more appropriate to your platform.  See also the description
      below for the GASNET_MAX_SEGSIZE environment variable, for information
      on the two setings which take precedence over this configure setting.

  Configure will detect various interesting features about your system and
compilers, including which GASNet conduits are supported.

  For cross-compilation support, look for an appropriate cross configure
script in other/contrib/ and link it into your top-level source directory and
invoke it in place of configure.  Example for the IBM BlueGene/Q:
     cd <path-to-gasnet-src>
     ln -s other/contrib/cross-configure-bgq .
     cd <your-build-dir>
     <path-to-gasnet-src>/cross-configure-bgq (configure_options)

  For cross-compilation support on platforms without scripts in other/contrib
see the instructions in other/cross-configure-help.c.
[NOTE: We currently don't distribute the cross-configure-help.c in our
normal distribution.  If you think you need it, contact us at upc@lbl.gov]

* make all
  Build the GASNet libraries. A number of other useful makefile targets 
  are available from the top-level:
    make {seq,par,parsync}
      build the conduit libraries in a given mode
    make tests-{seq,par,parsync}  
      build all the GASNet tests in a given mode
    make run-tests-{seq,par,parsync}  
      build and run all the GASNet tests in a given mode
    make run-tests
      run whatever tests are already built in the conduit directories
    make run-tests TESTS="test1 test2..."
      run specifically-listed tests that are already built in the conduit directories
    make DO_WHAT="<makefile target>"
      build selected makefile target in all supported conduit directories
  Each conduit directory also has several useful makefile targets:
    make {seq,par,parsync}
      build the conduit libraries in a given mode
    make tests-{seq,par,parsync}  
      build the conduit tests in a given mode
    make testXXX 
      build just testXXX, in SEQ mode
    make testXXX-{seq,par,parsync}
      build just testXXX, in a given mode
    make run-tests-{seq,par,parsync}  
      build and run the conduit tests in a given mode
    make run-tests
      run whatever tests are already built in the conduit directory
    make run-tests TESTS="test1 test2..."
      run specifically-listed tests that are already built in the conduit directory
    make run-testexit
      build a script to run the testexit tester and run it
  Compilation and linker flags for the GASNet libraries and tests can be
  augmented from the command-line by setting the following variables in the make
  command, as described in more detail in the next section:
    make MANUAL_CFLAGS=...    Flags to add on the C compile for GASNet libs, clients & tests
    make MANUAL_CXXFLAGS=...  Flags to add on the C++ compile for GASNet libs, clients & tests
    make MANUAL_MPICFLAGS=... Flags to add on the mpicc compile for GASNet libs, clients & tests
    make MANUAL_DEFINES=...   Flags to add on all compiles for GASNet libs, clients & tests
    make MANUAL_LDFLAGS=...   Linker flags to add for GASNet clients & tests
    make MANUAL_LIBS=...      Linker library flags to add for GASNet clients & tests
  The following misc make variables can also be set to affect GASNet compilation:
    make SEPARATE_CC=1        
      Build libgasnet using separate C compiler invocations, rather than one big one.
    make KEEPTMPS=1           
      Keep temporary files generated by the C compiler, if supported.

* make install
  Install GASNet to the directory chosen at configure time. This will create an
include directory with a sub-directory for each supported conduit, and a lib
directory containing a library file for each supported conduit, as well as any
supporting libraries.

Manual control over compile and link flags
===================

As described in the previous section, the recommended mechanism for passing
flags to the compilers used by GASNet is to include them in the definition of
the compiler variable itself (e.g. CC='gcc -m64').  These will be followed on
the command line by flags chosen by GASNet's configure script instead of using
the standard CFLAGS and CXXFLAGS make variables.  If there is a need to pass
flags that override ones chosen by configure, then one may set MANUAL_CFLAGS,
MANUAL_CXXFLAGS and MANUAL_MPICFLAGS on the 'make' command line, and these are
guaranteed to appear on the compilation command line after the ones chosen by
configure.  Additionally, MANUAL_DEFINES is provided to pass flags to all
three compilers, but its order on the command line is not guaranteed (since it
is intended for position-independent command line options such as '-Dfoo=10').

Note that GASNet does not assume that MPI_CC is the same compiler as CC
(though that is recommended), and therefore invokes it using a distinct
MANUAL_MPICFLAGS, instead of MANUAL_CFLAGS.  The MPI C compiler is used to
compile a portion of mpi-conduit (AMMPI) and the MPI-based spawner code used
by several conduits; and to link executables for mpi-conduit and any conduit
in which the MPI-based spawner is enabled.  Similarly, the C++ compiler is
used to compile a portion of udp-conduit (AMUDP) and to link udp-conduit
executables.

Finally, the make variables MANUAL_LDFLAGS and MANUAL_LIBS are provided to add
to the link command lines, after the respective configure-detected settings.
They are intended for flags such as '-Ldir' and '-lfoo', respectively.  Since
they do not have compiler-specific variants, their use is limited to
compiler-independent flags unless special care is taken with the selection of
the make target to ensure that make only invokes one compiler as a linker.

All of the MANUAL_* make variables described above are honored by the Makefile
infrastructure used to build GASNet's libraries and tests.  Additionally, the
makefile fragments (next section) use these variables when compiling client
code.

Basic Usage Information
=================
See the README for each GASNet core implementations for specific usage
information, but generally client programs should #include <gasnet.h>
(and nothing else), and use the conduit-provided compilation settings.

The best way to get the correct compiler flags for your GASNet client is to 
"include" the appropriate makefile fragment for the conduit and configuration 
you want in your Makefile, and use the variables it defines in the Makefile 
rules for your GASNet client code.

For example:
  ----------------------------
  include /install/path/include/mpi-conduit/mpi-seq.mak 

  .c.o:
	  $(GASNET_CC) $(GASNET_CPPFLAGS) $(GASNET_CFLAGS) -c -o $@ $<

  .cxx.o:
	  $(GASNET_CXX) $(GASNET_CXXCPPFLAGS) $(GASNET_CXXFLAGS) -c -o $@ $<

  myprog: myprog.o
	  $(GASNET_LD) $(GASNET_LDFLAGS) -o $@ $< $(GASNET_LIBS)
  ----------------------------

See tests/Makefile for another example of compiling GASNet client code.

For more fine-grained control, the flags variables break-down as follows:
  GASNET_CFLAGS is an alias for:
     $(GASNET_OPT_CFLAGS) $(GASNET_MISC_CFLAGS)
  GASNET_CPPFLAGS is an alias for:
     $(GASNET_MISC_CPPFLAGS) $(GASNET_DEFINES) $(GASNET_INCLUDES)
  GASNET_CXXFLAGS is an alias for:
     $(GASNET_OPT_CXXFLAGS) $(GASNET_MISC_CXXFLAGS)
  GASNET_CXXCPPFLAGS is an alias for:
     $(GASNET_MISC_CXXCPPFLAGS) $(GASNET_DEFINES) $(GASNET_INCLUDES)

Conduit Status
==============

The GASNet distribution includes multiple complete implementations of the GASNet API
targeting particular lower-level networking layers. Each of these implementations 
is called a 'conduit'. In some cases the lower-level layer is a proprietary or 
hardware-specific network API, whereas in other cases the target API is a
portable standard (although in some cases this distinction is blurred). The corresponding 
GASNet conduits can be loosely categorized as either 'native' or 'portable' conduits.

Below is the list of conduits in the current distribution, and their high-level status.
Many conduits are supported on multiple platforms (CPU architectures, operating systems 
and compilers) - see the 'Supported Platforms' section for more details on platforms.
For more detailed info about each conduit, please consult the corresponding conduit README.

Portable conduits:
-----------------

smp-conduit: SMP loopback (shared memory)
 The conduit of choice for GASNet operation within a single shared-memory node.
 Rigorously tested and supported on all current platforms. 
  
udp-conduit: UDP/IP (part of the TCP/IP protocol suite)
 The conduit of choice for GASNet over Ethernet, supported on any TCP/IP-compliant network.
 Rigorously tested over Ethernet and supported on most current platforms (see below).
 
mpi-conduit: MPI (Message Passing Interface)
 A portable implementation of GASNet over MPI-1.1 or later.
 Intended as a reference implementation for systems lacking native conduit support.
 Rigorously tested and supported on most current platforms (see below).

ofi-conduit: Open Fabrics Interfaces
 GASNet over the Open Fabrics Interface framework (libfabric).
 Rigorously tested and supported over the portable/reference OFI sockets Provider.
 Believed to also work over the Intel Truescale and Omni-Path Providers.

portals4-conduit: Portals4   *BETA*
 GASNet over the Portals4 network API developed at Sandia National Lab.
 The core GASNet developers have been unable to test this conduit recently.
  
Native, high-performance conduits:
---------------------------------

pami-conduit: IBM Parallel Active Messaging Interface (PAMI)
 The conduit of choice for GASNet on the IBM BlueGene/Q.
 Rigorously tested on BlueGene/Q, also supported on other select IBM systems.

gemini-conduit: Cray XE/XK Gemini
aries-conduit:  Cray XC Aries
 The conduit of choice for GASNet on the Gemini and Aries networks in recent Cray X* systems.
 Rigorously tested and supported.

ibv-conduit: InfiniBand Verbs
 GASNet over the OpenFabrics Verbs API.
 Rigorously tested and supported over InfiniBand hardware on all supported systems (see below).
 Believed to also work on other hardware offering a standard-compliant Verbs layer.

mxm-conduit: Mellanox InfiniBand Messaging Accelerator (MXM)
 GASNet over the MXM API for recent Mellanox InfiniBand adapters.
 The core GASNet developers have limited access to this hardware, but have completed 
 minimal validation on x86_64/Linux.

psm-conduit: Intel Omni-Path PSM2
 GASNet over the PSM2 API for Intel Omni-Path adapters.
 The core GASNet developers have limited access to this hardware, but have completed 
 minimal validation on x86_64/Linux. 
 
shmem-conduit: SGI Altix / Cray X1 Shmem   *DEPRECATED*
 GASNet over proprietary (hardware-supported) SHMEM. Does not function over OpenSHMEM.
 The core GASNet developers have been unable to test this conduit recently,
 and it is officially deprecated. 
 If you have interest in this conduit please contact us!

Supported Platforms
===================

Platforms where GASNet and Berkeley UPC have been successfully tested:

      OS/Architecture/compiler/ABI: network conduits
      ----------------------------------------------
    * Linux/x86-Ethernet/{gcc,clang}32: smp, mpi, udp
    * Linux/x86-Mellanox/gcc/32:     smp, mpi, udp, ibv
    * Linux/x86/IntelC/32:           smp, mpi, udp
    * Linux/x86/PortlandGroupC/32:   smp, mpi, udp
    * Linux/x86_64-Ethernet/{gcc,PortlandGroup,SunC}/{32,64}: smp, mpi, udp
    * Linux/x86_64-Mellanox/{gcc,PathScale,IntelC,SunC}/64: smp, mpi, udp, ibv, mxm
    * Linux/x86_64/x86-Open64/64:   smp, udp, #

    * Linux/PowerPC-Ethernet/{gcc,xlc,clang}/{32,64}: smp, mpi, udp
    * Linux/PowerPC-HFI/{xlc,gcc}/32: smp, mpi, udp, pami &
    * Linux/PPC64le/gcc/{32,64}:     smp, udp, #

    * Linux/MIPS/gcc/{32,n32,64}:       smp, udp, #
    * Linux/MIPS64el/gcc/{32,n32,64}:   smp, udp, #

    * Linux/SGI-Altix-IA64/{gcc,IntelC}/64: smp, mpi, udp, shmem
    * Linux/SGI-Altix-Xeon/{gcc,IntelC}/64: smp, mpi, udp, shmem

    * FreeBSD/{x86,amd64}/{gcc,clang}/{32,64}: smp, mpi, udp
    * OpenBSD/{x86,amd64}/{gcc,clang}/{32,64}: smp, mpi, udp
    * NetBSD/{x86,amd64}/{gcc,clang}/{32,64}:  smp, mpi, udp

    * Solaris10/SPARC/gcc,SunProC/{32,64}: smp, udp, mpi
    * Solaris10/x86/gcc,SunProC/{32,64}:   smp, udp, mpi
    * OpenSolaris/x86/gcc,SunStudio12/{32,64}: smp, udp, #
    * Solaris11Express/x86/gcc,SunStudio12/{32,64}: smp, udp, mpi, ibv
    * Solaris11/x86/gcc,SunStudio12/{32,64}: smp, udp, mpi, ibv

    * MSWindows-Cygwin/x86/gcc/32: smp, udp, mpi (MPICH.NT,MPICH2)

    * MacOSX/PowerPC/{gcc,xlc}/{32,64}: smp, udp, mpi
    * MacOSX/{x86,x86_64}/{gcc,icc,clang}/{32,64}: smp, udp, mpi
    * MacOSX/{x86,x86_64}/{PGI}/{32,64}: smp, udp, #

    * CNL/Cray-XT/{gcc,PGI,PathScale,Intel}/64: smp, mpi &

    * CNL/Cray-XE/{gcc,PGI,PathScale,Intel}/64: smp, mpi, gemini
    * CNL/Cray-XK/{gcc,PGI,PathScale,Intel}/64: smp, mpi, gemini

    * CNL/Cray-XC/{gcc,Intel}/64: smp, mpi, aries

    * Linux/Cray-XD1/{gcc,PGI}/64: smp, mpi &

    * CNK/IBM-BlueGeneQ-PowerPC/{gcc,xlc,clang}/64: smp, mpi, pami
 
    * MTX/Cray-MTA/CrayMTAC/64: smp, udp &
 
    * ucLinux/Microblaze/gcc/32: smp, udp, #%&

    * Linux/ARM/gcc/32:               smp, udp, #
    * Linux/AARCH64/{gcc,clang}/64:   smp, udp, #

# = No working MPI implementation available, although we have every
    reason to believe mpi conduit would work if one was available.
% = System lacks pthreads or they are broken
& = System has not been tested in recent releases due to lack of access.
    Reports of success or failure on this system are strongly encouraged.

This list is not meant to be exhaustive.
Other combinations of the platforms above are likely to also work, these are
just the systems we've personally tested. Several of the systems listed using a
vendor-specific C compiler can also use gcc as the underlying C compiler,
although we generally recommend the vendor C compiler for performance reasons.

Recognized Environment Variables
================================

Users of language- or application-specific wrappers for job launch should also
consult the wrapper's documentation.  Such wrappers often have options to set
these environment variables while also enabling any corresponding language- or
application-specific support.

* GASNET_VERBOSEENV: set to 1 to output information about environment variable settings
 read by the conduit that affect conduit behavior.

* GASNET_FREEZE: set to 1 to make GASNet pause and wait for a debugger to attach on
 startup

* GASNET_FREEZE_ON_ERROR: set to 1 to make GASNet pause and wait for a debugger
 to attach on any fatal errors or fatal signals

* GASNET_FREEZE_SIGNAL: set to a signal name (e.g. "SIGINT" or "SIGUSR1") to
 specify a signal that will cause the process to freeze and await debugger attach.

* GASNET_TRACEFILE, GASNET_TRACEMASK, GASNET_STATSFILE, GASNET_STATSMASK, 
  GASNET_TRACEFLUSH, GASNET_TRACELOCAL, GASNET_TRACENODES, GASNET_STATSNODES:
   control tracing & statistical features, if enabled at configure time.
   See usage information below.

* GASNET_TEST_POLITE_SYNC: set to 1 to enable polite-mode synchronization
  for the GASNet tests (only), for running with overcommitted CPUs.

* GASNET_MALLOC_* : control the GASNet debug malloc features, if enabled at configure time.
 See usage information below.

* GASNET_MAX_SEGSIZE - control the upper limit for FAST/LARGE segment size on most conduits
 This setting defaults to the value passed to configure: --with-segment-mmap-max=XGB
 or the one provided by the GASNet client at link-time with a definition like:
   uint64_t gasnet_max_segsize = ((uint64_t)8) << 30; /* set to 8GB */

* GASNET_DISABLE_MUNMAP - requests the use of mallopt() on glibc systems to disable
 mmap-based allocation for satisfying malloc. This can be used to work-around a
 known bug in firehose (bug 495) that could lead to incorrect behavior after 
 free()ing out-of-segment memory areas previously used for communication. Note that
 on some systems (32-bit Linux in particular) the disable is only partly effective
 because once the sbrk()-controlled heap reaches the bottom of shared libraries,
 glibc will use mmap() used to obtain memory regardless of any options one can
 control.

* GASNET_MAX_THREADS - per-node limit on the number of GASNet client pthreads 
  (in PAR and PARSYNC modes) that can simultaneously be live on each GASNet node.
  This is subject to the hard limit established by configure --with-max-pthreads-per-node,
  and pthread limits that may be imposed by specific conduits (see conduit README).

* GASNET_SUPERNODE_MAXSIZE - limit on size of a GASNet "supernode".
 This is the maximum number of processes (GASNet "nodes") that will be grouped
 into a shared-memory "supernode", as reported by gasnet_getNodeInfo() and used
 by shared-memory communication (PSHM).  A value of zero means no limit.

* GASNET_PSHM_BARRIER_HIER - enable/disable hierarchical shared-memory barrier.
 When shared-memory communication (PSHM) is enabled, the default behavior of
 most of GASNet's barrier implementations is to use a two-stage barrier which
 coordinates within each supernode before communicating across the network.
 This variable can be set to 0 to disable this optimization.

* GASNET_NO_CATCH_SIGNAL - specify a comma separated list of signals
 to exclude from GASNet default signal handling. Formats "SIGSEGV",
 "SEGV", "sigsegv", "segv", and "11" are accepted. If the value of
 this environment variable is "*" (alone, with no leading or trailing
 whitespace), GASNet will not register the default handler for any
 signal.
 
 The default handler provides GASNet's backtrace support and ensures clean
 exits when fatal signals are received.  Disabling this handler may
 allow use of other tools for debugging of signals, but is not intended
 for production use.

* GASNET_BACKTRACE - requests the generation of stack backtraces on most fatal
 errors.  The format/content of these backtraces varies by platform.  On some
 platforms no backtrace support is available and this variable will be
 ignored.  Backtraces are sent to stderr and to the trace file if tracing is
 active (see below).
 WARNING: Some fatal errors may involve memory corruption or other abnormal
 conditions that could cause the backtrace code to hang. For this reason we
 do not recommend setting GASNET_BACKTRACE by default (though there is no
 performance penalty for doing so).
 When reporting bugs, one is strongly encouraged to include a backtrace if
 possible.  The backtrace is almost always more detailed if GASNet is built
 with debugging enabled, but may still be useful to a GASNet developer in a
 non-debug build.  If tracing is active (see below) then a copy of the
 backtrace will be sent to the trace file.  This file may provide developers
 with potentially useful information about activities prior to the error.

* GASNET_BACKTRACE_NODES - if enabled by GASNET_BACKTRACE then this provides
 an optional list of nodes on which to permit backtraces.  The list may
 contain one or more integers or ranges separated by commas, such as "0,2-4,6".
 If unset, empty, or equal to "*" then all nodes may generate backtraces.

* GASNET_BACKTRACE_SIGNAL: set to a signal name (e.g. "SIGINT" or "SIGUSR1") to
 specify a signal that will cause the process to generate an immediate backtrace,
 and then continue executing. This is useful for getting a convenient
 backtrace for a "hung" process.

* GASNET_BACKTRACE_TYPE - set to a comma-delimited, ordered list of mechanisms 
 (i.e. different debugger tools) to try when generating a backtrace for
 GASNET_BACKTRACE. The default value (visible via GASNET_VERBOSEENV) includes
 all mechanisms detected as supported on the current platform.

* GASNET_DISABLE_ENVDECODE/GASNET_DISABLE_ARGDECODE - disable the automatic decoding 
 of environment variable values/command-line arguments. Some GASNet spawners 
 automatically encode shell meta-characters passing through non-GASNet spawn scripts, 
 in to order to ensure their safe delivery to the GASNet client program.

* GASNET_BARRIER - select the communication algorithm for use in GASNet barriers.
 The following values are available on all conduits:
  AMCENTRAL - uses Active Messages to manipulate a single centralized counter.
  AMDISSEM - uses Active Messages to implement the Dissemination barrier
   algorithm as described in section 3.3 of
    John M. Mellor-Crummey and Michael L. Scott. "Algorithms for scalable
    synchronization on shared-memory multiprocessors." ACM ToCS, 9(1):21 65, 1991.
  RDMADISSEM - uses Put operations to implement the Dissemination algorithm.
  DISSEM - auto-selects either AMDISSEM or RDMADISSEM
   The AMDISSEM or RDMADISSEM algorithm is selected automatically based on
   conduit-specific criteria.  In general RDMADISSEM is favored when the GASNet
   Extended API is implemented natively.
 In addition to those choices, many conduits have additional network-specific
 barrier algorithms documented in the corresponding conduit READMEs.
 The default is DISSEM, unless the conduit README documents another default.

* GASNET_PSHM_BARRIER_RADIX - set radix for intra-node barrier algorithm
 For configurations using PSHM (a function of OS and conduit) the GASNet barrier
 is performed in intra-node and inter-node stages.  This environment variable
 is the radix of the tree-based intra-node (shared-memory) barrier.
   If zero (default) then radix = size - 1, resulting in a "flat tree" (linear time)
   If positive, then the given value is the out-degree of an N-ary tree.
   If negative, then a tree is built with the processes in groups of size = -radix.
     The first process in each group is the parent of the others in that group.
     The rank==0 process is the parent of the other group-representatives (in
     addition to being the parent of the others in its own group).
 The default is 0 (linear) on most platforms.

* GASNET_PSHM_NETWORK_DEPTH - set depth of the intra-node AM network
 For configurations using PSHM (a function of OS and conduit) GASNet implements
 intra-node Active Messages using a shared-memory queue.  This variable sets the
 "network depth" of this implementation: the minimum number of outgoing AMs it
 must be capable of buffering before possibly stalling.
 The default is 32 and the minimum is 4.

* GASNET_NODEMAP_EXACT - enables exact algorithm for discovery of shared memory nodes.
 Several GASNet conduits use mmap() and/or conduit-specific memory registration
 resources to establish the GASNet segment.  When multiple GASNet nodes (processes)
 run on the same O/S node, there is a potential for competition for resources which
 can be managed by coordinating among the processes.
 When PSHM support is enabled, multiple processes on the same O/S node must be
 identified so they can cross-mmap() their GASNet segments.
 By default processes sharing the same O/S node are discovered using an algorithm
 that runs in time linear in the number of GASNet nodes, and which is sufficient
 for all common process layout patterns.  However, the default may fail to discover
 sharing in unusual cases.  Setting this variable to 1 enables an algorithm that is
 certain to find all sharing of memory, but has an expected running time
 proportional to N*log(N).
 The default is currently 0 for all but udp-conduit, which has an unpredictable
 process layout.

* GASNET_VIS_AMPIPE - set to 1 to enable packing of most non-contiguous
 put/gets into AMMediums, with each packet of size approx MaxMedium (the only
 exception being cases where both sides happen to be fully contiguous, in
 which case we skip packing). This support is currently experimental, and thus
 disabled by default.

* GASNET_VIS_MAXCHUNK - limits the max size of a strided or indexed chunk which
 will be packed by AM pipelining. Defaults to the size that will fit in one MaxMedium

* GASNET_VIS_REMOTECONTIG - enables a pack & RDMA algorithm for gather puts and
 scatter gets - i.e. cases that are locally non-contiguous but remotely
 contiguous. Currently unsafe for use on many conduits, thus disabled by default.
 (Currently ibv is known or suspected to be unsafe).

* GASNET_COLL_OPT - set to 1 to enable the optimized versions of 
 the collectives. These include binomial trees for the rooted collectives 
 (broadcast, scatter, and gather) and Bruck's algorithm for the non-rooted ones
 (gather all, and exchange) for small enough message sizes. Defaults to 1 if no 
 value is specified.

* GASNET_COLL_BROADCAST_OPT - set to 1 to enable optimized binomial tree broadcast. 
 Defaults to GASNET_COLL_OPT.

* GASNET_COLL_SCATTER_OPT - set to 1 to enable optimized binomial tree scatter.
 Defaults to GASNET_COLL_OPT.

* GASNET_COLL_GATHER_OPT - set to 1 to enable optimized binomial tree gather.
 Defaults to GASNET_COLL_OPT.

* GASNET_COLL_GATHER_ALL_OPT - set to 1 to enable optimized gather all. Defaults to 
 GASNET_COLL_OPT.

* GASNET_COLL_EXCHANGE_OPT - set to 1 to enable optimized exchange. Defaults to 
 GASNET_COLL_OPT

* GASNET_COLL_SCRATCH_SIZE - specifies the size of the GASNet auxiliary scratch space 
 per node. Most of the optimized collectives rely on this auxiliary space to enable 
 optimized communication schedules. If the size is set too low, then the collectives 
 will send a lot more control messages which could adversely affect performance. 
 Defaults to 2MB per node.

* GASNET_COLL_ENABLE_SEARCH - enable autotuning of collectives
* GASNET_COLL_TUNING_FILE - file to read and/or write collective autotuning data
 For usage information, see the file autotuner.txt in the docs directory.

* GASNET_FS_SYNC - set to 1 enable a sync() call (or equivalent) at exit time.
 Default is 0.  Try this setting if you experience truncated output.

* GASNET_TMPDIR: if set to a valid directory name this is used instead of TMPDIR
 or "/tmp" as a location for creating temporary files.

* OPTIONAL: GASNET_EXITTIMEOUT, GASNET_EXITTIMEOUT_MAX, GASNET_EXITTIMEOUT_MIN, and
 GASNET_EXITTIMEOUT_FACTOR - control exit-coordination timeout.  Some conduits use a
 timeout to distinguish orderly job exit from uncoordinated failure of one or more
 nodes.  This is important to help avoid leaving "orphan" processes on the nodes.
 These environment variables allow the user to adjust the length of time that the
 conduit will wait to establish contact among all nodes before deciding that an exit
 is uncoordinated.  By default, the timeout is computed as
   GASNET_EXITTIMEOUT = min(GASNET_EXITTIMEOUT_MAX,
                            GASNET_EXITTIMEOUT_MIN + nodes * GASNET_EXITTIMEOUT_FACTOR)
 Setting GASNET_EXITTIMEOUT provides a specific value, ignoring this formula.
 Setting one or more of the others will compute a value for GASNET_EXITTIMEOUT using
 the formula above (and defaults for any variables not set in the environment).
 Currently most conduits honor these settings.
 Smp-conduit honors these settings only when PSHM-support is enabled.
 Default values differ among these conduits.

* OPTIONAL: GASNET_THREAD_STACK_MIN, GASNET_THREAD_STACK_PAD
 Some conduits spawn additional threads internally for various purposes, which may
 include running client's AM handlers.  If such AM handlers have unusually large
 stack space requirements, a mechanism is required to ensure these internal threads
 will have large enough stacks.
 These settings allow one to control the stack sizes of these internal threads.
 The stack size requested from the system will be computed as
    stack_size = MAX(GASNET_THREAD_STACK_MIN,
                     GASNET_THREAD_STACK_PAD + default) 
 where "default" denotes the system's default thread stack size, and values
 of both variables have been rounded-up to a multiple of the page size.
 The actual stack size may be smaller (e.g. to satisfy rlimits) or larger
 (for instance, the next power of two in some implementations).
 The default for both settings is zero, which results in using the system
 default size for thread stacks.

* see conduit-specific documentation in conduit directories for more settings
 
GASNet tracing & statistical collection
=======================================

GASNet includes an extensive tracing and statistical collection 
utility for monitoring communication events in GASNet applications.
To use, configure with --enable-stats and/or --enable-trace, and
run your program as usual. In order to see the trace/stats output, 
you must set the environment variable GASNET_TRACEFILE and/or 
GASNET_STATSFILE as explained below.

Note that system performance is likely to be degraded as a result of tracing and 
statistical collection. This is still true even when output is disabled
by not setting this GASNET_TRACEFILE/GASNET_STATSFILE (so production platforms 
should not enable tracing/stats at GASNet configure time).

Optional environment variable settings:

 GASNET_TRACEFILE - specify a file name to receive the trace output
   may also be "stdout" or "stderr", (or "-" to indicate stderr)
   each node may have its output directed to a separate file, 
   and any '%' character in the value is replaced by the node number at runtime
   (e.g. GASNET_TRACEFILE="mytrace-%")
   unsetting this environment variable (or setting it to empty) disables 
   tracing output (although the trace code still has performance impact)

 GASNET_TRACENODES - specify an optional list of nodes on which to generate
   tracing output (if enabled by GASNET_TRACEFILE).  List may contain one
   or more integers or ranges separated by commas, such as "0,2-4,6".
   If empty or equal to "*" then all nodes may generate tracing output.

 GASNET_STATSFILE - specify a filename to receive statistical output
   operates analogously to GASNET_TRACEFILE

 GASNET_STATSNODES - limit nodes to generate statistical output
   operates analogously to GASNET_TRACENODES

 GASNET_TRACEMASK - specify the types of trace messages to report
   A string containing one or more of the following letters:
     G - gets
     P - puts
     S - non-blocking synchronization
     W - collective operations (excluding barriers)
     X - collective synchronization (excluding barriers)
     B - barriers
     L - locks
     A - AM requests/replies (and handler execution, if conduit-supported)
     I - informational messages about system status or performance alerts
     C - conduit-specific (low-level) messages
     D - Detailed message data for gets/puts/AMreqrep
     N - Line number information from client source files
     H - High-level messages from the client
     U - Unsuppressable messages, which are always output (use with caution)
  default: (all of the above)

 GASNET_STATSMASK - specify the types of statistics to collect and report
   operates analogously to GASNET_TRACEMASK

 GASNET_TRACEFLUSH - set this variable to force a file system flush 
   after every write to the tracefile. This seriously degrades tracing
   performance, but ensures any final trace messages before a crash
   are flushed into the tracefile.
 
 GASNET_TRACELOCAL - set to control whether the PG trace messages for
   local (i.e. loopback) put/get operations are entered into the trace file 
   or suppressed (they are included by default). This can be used to reduce 
   tracing overhead and trace file size for clients with a large number of 
   local put/get operations which are not of interest.

GASNet Collectives
==================

GASNet includes interfaces for collective operations, which is still
evolving.  The design for the interfaces is located under the source directory
in docs/collective_notes.txt.  Anyone planning to implement a client that
uses these collective should contact us (upc@lbl.gov) first to determine
the completeness and stability of the relevant portions of the implementation.

In GASNet 1.14.0 we introduce a mechanism for auto-tuning of collectives
in which a variety of algorithms are tried for each collective operation in
a user's application and the best choice can be recorded in a file for use
in future runs.  For more information, see the file autotuner.txt in the
docs directory.

GASNet debug malloc services
============================

GASNet includes a debug malloc implementation that can be used to find local
heap corruption bugs in GASNet itself and also in GASNet client applications
(notably Berkeley UPC). To use, configure GASNet with --enable-debug-malloc
(or --enable-debug which implies --enable-debug-malloc), and run your
program as usual.  GASNet will regularly scan the heap for corruption at malloc
events and AMPoll's and report any detected problems.  If you're a GASNet
client writer, you should see the gasnett_debug_malloc functions in
gasnet_tools.h to tie your applications into the GASNet debug malloc services.

Note the debug malloc implementation imposes some CPU and memory consumption
overhead relative to the system malloc implementation (it's implemented as a
thin wrapper around the system malloc).  This means heap behavior is likely to
be somewhat perturbed relative to the normal mode of operation, however the
overhead is probably less than it would be with third-party heap corruption
tools such as efence or purify (at some cost in lost precision).

Optional environment variable settings (recognized only when debugging
malloc is enabled):

GASNET_MALLOC_INIT: When set to 1, every byte of allocated memory is
 initialized to the value specified by GASNET_MALLOC_INITVAL. This can be useful
 for detecting use of uninitialized data.

GASNET_MALLOC_CLOBBER: When set to 1, every byte of freed memory is overwritten
 with the value specified by GASNET_MALLOC_CLOBBERVAL. This can be useful for
 detecting inadvertent use of freed data.

GASNET_MALLOC_INITVAL, GASNET_MALLOC_CLOBBERVAL: The data value to use for
 allocation init or free clobbering, respectively. The value may be specified
 as a decimal integer matching the pattern: "-?[0-9]+" or a hexadecimal integer
 matching the pattern: "0x[0-9A-F]+".  If the value is between 0 and 255
 (inclusive) it is taken to be an 8-bit value which is used to overwrite every
 byte in the given region. Otherwise, it is taken to be a 64-bit value which is
 used to overwrite the given region in 8-byte chunks.  The value may also be one
 of "NAN", "sNAN" or "qNAN", which select a double-precision signaling or quiet
 NAN, which is likely to propagate through floating point calculations and cause
 segmentation faults when used as a pointer. Both values default to "NAN". 

GASNET_MALLOC_LEAKALL: set to 1 to leak all freed objects, ensuring they are
 not re-allocated during subsequent mallocs. This has an obvious cost in memory
 consumption, but can be helpful for tracking bugs in conjunction with
 GASNET_MALLOC_CLOBBER for tracking usage of dead objects.

GASNET_MALLOC_SCANFREED: set to 1 to enable scanning of freed objects, to
 detect write-after-free errors. This option implies GASNET_MALLOC_LEAKALL and
 GASNET_MALLOC_CLOBBER.

GASNET_MALLOC_EXTRACHECK: set to 1 to enable more frequent checking for memory
 corruption (at a cost in performance)

GASNET_MALLOCFILE: specify a file name to receive a report of malloc heap
 behavior and utilization at process exit. Includes a list of leaked objects.
 The filename may also be "stdout" or "stderr", (or "-" to indicate stderr)
 Each node may have its output directed to a separate file,
 and any '%' character in the value is replaced by the node number at runtime
 (e.g. GASNET_MALLOCFILE="mallocreport-%"). These output files are
 human-readable, but can be passed to gasnet_trace for summarization.

GASNET_MALLOCNODES: limit which nodes will generate a malloc report.
   operates analogously to GASNET_TRACENODES

MPI Interoperability
====================

The Message Passing Interface (MPI) is a ubiquitous portable interface for
communication in scientific computing and is used both directly and indirectly
by various applications and libraries.  In most cases GASNet is implemented
natively on the various SAN interconnects, bypassing the MPI layer in order to
provide the best possible performance. This means that in general GASNet does
NOT use MPI for performing communication (the only notable exception being
mpi-conduit, which is a portable implementation of GASNet over MPI).  In some
cases GASNet can use MPI to assist in parallel job creation and termination
(thereby taking advantage of the existing MPI infrastructure), but in those
cases it will not use MPI during the steady state of operation - only at
startup and shutdown.

Although GASNet is not implemented using MPI, it is *compatible* with MPI -
GASNet and MPI can be used together within the same network and even within the
same program.  However, there are a few subtle issues to be dealt with when
using both communication systems in the same process, because in those cases
GASNet and MPI must both be initialized properly and cooperate to "share" the
resources of the network and physical memory. This section describes issues
that arise when combining the use of MPI-based communication and GASNet
communication within a single process. The information described here applies
to any case where a single process attempts to access the network hardware
using both GASNet and MPI, even when such usage occurs at different levels
within a layered application (for example, a UPC application which uses GASNet
via the Berkeley UPC compiler and makes calls to a helper library that
communicates using MPI).

MPI requires exactly one initialization call before MPI communication can be used
within a process.  The GASNet implementation may or may not automatically
initialize the MPI library, depending on the conduit and various configuration
settings. Therefore, processes using both communication libraries must be
prepared to correctly handle either situation - the recommended way to
arbitrate this is using the MPI_Initialized() call which reports whether or not
the MPI layer has been initialized.  Here is some example code for
accomplishing this:

int isMPIinit;
int main(int argc, char **argv) {
  size_t segment_size = 64*1024*1024; /* want 64MB segment in this example */
  size_t segment_max;

  gasnet_init(&argc, &argv);

  segment_max = gasnet_getMaxGlobalSegmentSize();
  if (segment_size > segment_max) segment_size = segment_max;

  gasnet_attach(NULL, 0, segment_size, 0);

  gasnet_barrier_notify(0, GASNET_BARRIERFLAG_ANONYMOUS);
  gasnet_barrier_wait(0, GASNET_BARRIERFLAG_ANONYMOUS);

  if (MPI_Initialized(&isMPIinit) != MPI_OK) { /* test if MPI already init */
    fprintf(stderr, "Error calling MPI_Initialized()\n");
    abort();
  }
  if (!isMPIinit) MPI_Init(argc, argv); /* MPI not init, so do it */

  /* ... use MPI as usual ... */

  MPI_Barrier(MPI_COMM_WORLD);

  /* ... use GASNet as usual ... */

  gasnet_barrier_notify(0, GASNET_BARRIERFLAG_ANONYMOUS);
  gasnet_barrier_wait(0, GASNET_BARRIERFLAG_ANONYMOUS);

  ...

  if (!isMPIinit) MPI_Finalize(); 
  return 0;
}

The MPI_Initialized call checks to make sure MPI hasn't already been
initialized by GASNet, which will be the case on mpi-conduit and possibly on
other conduits that use MPI for job startup. Any MPI usage internal to GASNet
uses a private MPI communicator, preventing any potential interference with MPI
use by the GASNet client. The code which initializes the MPI layer is also
responsible for finalizing it before exit.

An extensive example is available in tests/testmpi.c, which implements various
interoperability tests between GASNet and MPI.

There are a few other important caveats to be aware of when mixing GASNet and MPI:

* GASNet must be configured with MPI_CC set to the exact *same* MPI
 installation that will be used when building any GASNet client code using MPI.
 Note that many MPI implementations are not binary-compatible across versions,
 so upgrading the MPI compiler usually requires a fresh configure/build/install
 of GASNet with the new MPI implementation if you intend to mix GASNet and MPI.

* When a node is inside a blocking MPI call, most conduits will be prevented
 from servicing many GASNet requests from remote nodes. Similarly, GASNet
 blocking calls will generally not ensure progress of MPI communication. This
 means that arbitrarily interleaving blocking MPI calls with GASNet calls
 (e.g. UPC shared accesses) can easily lead to deadlock. In order to ensure
 safety and portably correct operation across networks, GASNet communication
 operations and user MPI calls should be isolated from each other by barriers, 
 by strictly adhering to the following protocol:

   - When the application starts, the first MPI or GASNet call issued from any
     node should be considered to put the application in 'MPI' or 'GASNet'
     mode, respectively. 

   - When an application is in 'MPI' mode, and needs to switch to using GASNet,
     it should collectively execute an 'MPI_Barrier()' as the last MPI call
     before issuing any GASNet communication calls. Once any GASNet communication has
     occurred from any node, the program should be considered to have switched to
    'GASNet' mode. 

   - When an application is in 'GASNet' mode, and an MPI call that may cause
     network traffic is needed, a collective call to 'gasnet_notify()' followed
     by a 'gasnet_wait()' should be executed as the last GASNet communication
     before any MPI calls are made. Once any MPI functions have been called from any
     thread, the program should be considered to be in 'MPI' mode. 

 If this simple construct--GASNet code must be followed by a GASNet barrier,
 and MPI code must be followed by an MPI_Barrier--is followed, deadlock should
 not occur. This usage is demonstrated in the code above.

* GASNet and MPI both number processes with a unique non-negative index (i.e. gasnet_mynode()
  and MPI_Comm_rank(MPI_COMM_WORLD)). Every attempt is made to ensure this
  numbering matches between layers, but it might not always be possible to ensure this. 
  To maximize portability, apps using both layers should use a GASNet or MPI collective 
  (e.g. AllGather) to build a table of ids and translate rank identifiers as needed.

* Note that GASNet language clients such as UPC or Titanium might include 
  compilation modes where multiple language-level threads are implemented as pthreads
  within a single process, which will map to a single GASNet node id (and hence
  a single MPI rank). Clients using such threading should ensure they are using
  a pthread-safe implementation of MPI (GASNet is thread-safe by virtue of PAR mode),
  and be aware that MPI messages sent to a particular node might be received by any
  pthread at the target (unless steps are taken to avoid this, e.g. using an MPI tag).

* There are various network-specific issues that may arise when combining
 GASNet with specific MPI implementations, most notably related to job creation
 and spawning mechanisms. Please see the README file in each conduit directory
 for network-specific discussion of issues with MPI interoperability.


GASNet Design Information
=========================

See the GASNet specification for information about the GASNet API. A copy is
included with this archive in docs/, and the definitive version is located on
the GASNet webpage here:

  http://gasnet.lbl.gov/

The GASNet API is a two-level interface consisting of the lower-level "core API"
and the upper-level "extended API". All of the functions in the extended API can
be implemented using the core API, but some implementations may choose to
implement them directly for performance reasons. We use the term "conduit" to
refer to any complete implementation of the GASNet API (both layers), which
targets a specific network device or lower-level networking layer. A conduit
is comprised of any required headers, source files and supporting libraries
necessary to provide the functionality of the GASNet API to GASNet clients. Some
conduits may be monolithic - implementing the entire GASNet API directly on the
lower-level network system, and others may be layered - directly implementing
just the GASNet core API and borrowing a reference implementation of the
extended API which is written using the core primitives.

This distribution provides several conduits for different networks that are
packaged together for convenience because they share some code and general
infrastructure. However, each conduit is logically a stand-alone implementation
of the GASNet API. Note there may eventually be other GASNet conduits (e.g.
provided by vendors) which need not be included as part of this distribution -
all that's required of a conduit is that it implements the standardized GASNet API.

System Organization
===================

The directory tree for this distribution looks something like this:

top-level/
 \__ config-aux/
 \__ tests/
 \__ docs/
 \__ extended-ref/
 \__ {conduitname1}-conduit/
 \__ {conduitname2}-conduit/
 \__ template-conduit/
 \__ other/

* top-level: contains the GASNet configuration scripts and master Makefile and
GASNet headers.

  When making changes to GASNet (esp the configure script), please remember that
GASNet is not only a communication system for UPC, but also a self-contained
product used as the communication system for other languages (like Titanium) so
the configuration scripts, header files, etc. should not rely on anything from
outside directories not included in this distribution (other than basic system
headers and lower-level networking libraries).

* Header files: The GASNet master header file (gasnet.h) #includes
several files which should be provided by each conduit:

<gasnet.h> includes the following files:
   <gasnet_config.h> Created by the configure script, this header helps in
		     customizing gasnet for site-specific and platform-specific
		     information.
   <gasnet_basic.h>  Defines various basic and optimizing compiler macros,
                     platform-independent integer types and c++ binding macros.
   <gasnet_help.h> Extended and core API platform independent helpers
                    (providing services which aren't part of GASNet API, but are
		     required by code in gasnet.h)
   <gasnet_trace.h> Implements GASNet's sophisticated
                    internal tracing and statistical collection system
   <gasnet_core_fwd.h> definitions of basic constants and types used by the
		       core API and included early in the gasnet.h file
		       (gasnet.h provides some default values for various
		       constants and types that can be overridden here)
   <gasnet_extended_fwd.h>  Allows a specific extended implementation to
			    override the default gasnet types such as handles
			    and threadinfo.
   <gasnet_core.h> Provides the public interface for the GASNet core API
		   (function prototypes and/or inline functions for
		   implementing the core API).
      .. <gasnet_core_help.h> This is the core's entry point to provide access
			      to private symbols which might be required by the 
			      core header (e.g.: node's node id, number of nodes
			      in job), but which should not really be publicly
			      visible to client code (i.e. not part of GASNet API)
   <gasnet_extended.h> Provides the public interface for the GASNet extended API
      .. <gasnet_extended_help.h> Extended API's entry point to define private symbols
				  used by the extended header (e.g.segment info, 
				  thread info) but which should not really be publicly
			          visible to client code (i.e. not part of GASNet API)

Many conduits also have <gasnet_core_internal.h> and <gasnet_extended_internal.h> files
which are _not_ included by gasnet.h (and therefore not visible to client code) and
are exclusively for use in building the conduit libraries. 
<gasnet_internal.h> is the conduit-independent version of these files at the top level.
Internal GASNet implementation should include <gasnet_internal.h> instead of <gasnet.h>.

<gasnet_coll.h> and <gasnet_vis.h> are headers providing a set of proposed additions
to the GASNet spec (for collective operations and non-contiguous put/get,
respectively).  Since these interfaces are not finalized in a written specification,
we strongly recommend you contact us before using them.

<gasnet_tools.h> is header providing a set of conduit-independent general system 
utilities which are not specified by the GASNet spec. The header can and is used 
independently of libgasnet*.a (even on systems with no supported conduits) - 
all that's required is a successful configure and #include <gasnet_tools.h>.
See README-tools for documentation on the GASNet Tools interface.

* config-aux: helper scripts for configure

* {conduitname}-conduit: the complete implementation for a particular GASNet conduit. 
This directory is in charge of providing/installing the headers listed above,
compiling any appropriate tests and building/installing the following libraries:

 libgasnet-conduitname-seq.a - GASNET_SEQ implementation of GASNet
 libgasnet-conduitname-par.a - GASNET_PAR implementation of GASNet
 libgasnet-conduitname-parsync.a - GASNET_PARSYNC implementation of GASNet

* template-conduit: A conduit template which should be used as a starting point for 
new conduit implementations. See the README.template file in this directory for detailed 
instructions.

* other: A container directory for any external supporting libraries or
utilities used by one or more conduits.

* extended-ref: the reference implementation of the GASNet extended API. Conduits
can optionally use some or all of the files in this directory by compiling the
sources into the conduit library and installing the headers into the appropriate
conduit include directory. See mpi-conduit for an example of how to use the
reference extended API implementation (the template-conduit is setup to use the
extended-ref implementation by default).

* tests: basic tests written to the GASNet API that should run on any GASNet
conduit. These can be sucked in and compiled in each conduit directory (see
mpi-conduit for an example).

* docs: documentation on GASNet and various conduits

GASNet coding standards
=======================
All GASNet conduit code is required to meet the following coding standards:

* Naming Conventions for macros and identifiers:
  - All entry points required by GASNet spec are lower-case identifiers with
    the prefix gasnet_ 
  - All constants or macros required by GASNet spec are upper-case and preceded
    with the prefix GASNET_
  - All private symbols in the reference extended API implementation are
    prefixed with gasnete_ (or GASNETE_ for macros)
  - All private symbols in a core API implementation are prefixed with gasnetc_
    (or GASNETC_ for macros)
  - All private symbols shared throughout GASNet are prefixed with gasneti_ (or
    GASNETI_ for macros)
  - All GASNET_ or GASNETI_ configuration selection macros are either #defined
    to 1 or #undef'd

* All non-normative identifiers appearing in public header files should use
  either one of the GASNet internal name-space prefixes from the previous rule,
  or a _ prefix to reduce the possibility of identifier name capture (eg
  -Dfoo= before the #include of gasnet.h). This especially applies to
  macro/function names, function arguments, local variables declared in macros
  or inline functions, type/enum names, and struct field names.
  This rule was added in July 2016 and applies to all new code.

* GASNet code should be as close to C89 as possible (i.e. never differing without
  good reason), because many C compilers still do not provide full C99 support,
  and differ quite widely in the supported features. 
  The following is the COMPLETE list of features introduced by C99 we PERMIT:
   1. C++/C99-style // comments
   2. Mid-block declarations (mixing declarations and code)
   3. Conditional expression declarations, only in for loop headers, 
      ie: for (int i=...) { ..i.. }
  All GASNet code should otherwise adhere to C89 restrictions.
  Most notably, we PROHIBIT: (incomplete list)
   - Do not use variable-length array declarations
   - Do not use zero-length structure fields (aka flexible array member)
   - Do not use compound literals or named struct field initializers
   - Do not use printf format specifiers added in C99, such as: ll,j,z,t,L
   - Do not include any header files introduced by C99 or any features they introduce
   - Do not use restrict, __func__ or _Pragma/#pragma directly
     (use GASNETI_RESTRICT, GASNETI_CURRENT_FUNCTION, and the various attribute
      wrapper macros defined in gasnet_basic.h using configure detection)
   - Do not use other GNU or vendor extensions (unless properly #ifdef protected w/ fallback)

* GASNet code should use full prototypes whenever possible:
    NO:  extern void foo();
    YES: extern void foo(void);
    NO:  int bar() { return xyz; }
    YES: int bar(void) { return xyz; }
  Configuring with --enable-strict-prototypes and compiling with the GNU or
  PathScale compilers will give you warnings for violations of this rule.

* All code in public header files should be C++98-compliant to support C++
  GASNet clients. Most notably this means using GASNETI_{BEGIN,END}_EXTERNC
  around all extern function prototypes, and ensuring any inline function code
  or macro code passes the C++ type checker.  It is especially important for
  code in public headers to avoid the few dozen C constructs which are not
  present in the C subset of the C++98 standard. Most notably: (incomplete list)
   - Do not use C++ keywords in identifiers
   - Do not use long long types or printf specifiers
   - Do not use tentative definitions
   - Do not use empty preprocessor function macro arguments FOO(,,,)
  See bug 3296 for a complete list.
  Run a "make testcxx" to verify compliance.

* GASNet conduit code should never call any of the following functions 
  directly:
   malloc, calloc, realloc, free, str(n)dup, assert, sched_yield, 
   getenv, (un)setenv, mmap, pthread_*
  Instead, you should use the gasneti_* wrapper functions of the same name.

* GASNet code may leak "permanent" data structures with a lifetime that extends
  through gasnet_exit(), such as frequently re-used structures kept on freelists.
  Any such dynamic allocation should be annotated with calls to gasneti_leak()
  or gasneti_leak_aligned() to preserve the value of GASNET_MALLOCFILE for the
  identification of unintended leaks.

* The calls gasneti_malloc(), _calloc and _realloc all return NULL for zero-byte
  allocations.  Correspondingly, gasneti_free() and gasneti_realloc() accept NULL
  for the pointer argument, and GASNet code should therefore NOT make an
  unnecessary check for NULL before calling these functions.

* The calls gasneti_malloc(), _calloc, _realloc and str(n)dup all check for
  NULL return, and GASNet code should therefore NOT make a redundant check.
  The call gasneti_malloc_allowfail() exists for the rare occasion when the
  caller is prepared to respond to a NULL return with something better than
  a fatal error.
  However, as noted above, a NULL return is expected for a zero-byte allocation.

* Use gasneti_fatalerror() to signal fatal errors - the arguments work
  just like printf. NEVER use "gasneti_assert(0)" (it will be compiled away), 
  and gasneti_fatalerror() with a useful message is always preferable to abort().

* Conditional compilation for platform-specific features should be done using
  the standardized platform macros provided by other/portable_platform.h, not ad-hoc
  vendor or compiler-provided preprocessor macros.

* Code should never make assumptions about integer data type sizes. In cases that
  call for a specific size integral type, the (u)int(sz)_t types provided by
  other/portable_inttypes.h should always be used (e.g. "uint64_t" = unsigned 64-bit int).

* Do NOT make assumptions about the width of values stored in type "gasneti_atomic_t".
  On some platforms the width may be neither 32 nor 64 bits.
  See README-tools for complete documentation. 

* Conduit code may use any of the GASNet tools documented in README-tools, but should
  use the gasneti_ version when referring to these tools in public headers, because
  gasnet_tools.h is not included by gasnet.h.

* Learn how to use the tracing macros and use them to trace interesting
  events in your conduit. They're invaluable for debugging mysterious behavior.
  See the comments in gasnet_trace.h for usage information.

* Do NOT make trivial and/or non-meaningful changes to the code or
  makefile framework inherited from template-conduit or cloned from
  the extended-ref directory (e.g. re-indenting lines, 
  moving code into different files, renaming existing identifiers, etc.)
  as this makes it more difficult to patch your conduit if a bug is 
  discovered in template-conduit or a GASNet-wide change is required.

* Do NOT use tab characters in GASNet code files. Use spaces to ensure correct
  formatting in any editor. 
    Emacs users should: (setq-default indent-tabs-mode nil)
    Vim users should: :set expandtab

* Do NOT commit gratuitous changes to whitespace, even to remove tab characters.
  Such changes have no semantic content and can make use of revision history more
  difficult.  You can preview your changes with the following two commands:
     git diff -u | wc -l
     git diff -u -b | wc -l
  and if the outputs differ, then your changes include lines that have changed
  in only the whitespace characters.

* Do not make any conduit-specific changes to the files in the
  extended-ref or tests directories.  They do not have any Makefiles because they
  just provide a centralized place for files used in other directories.

* When implementing the extended API for your conduit, please clone only the
  necessary files from the extended-ref directory that you need to change 
  (and continue to include the unchanged files) to reduce maintenance headache
  (this applies especially to gasnet_extended.h, gasnet_extended_help.h, and
  gasnet_extended_common.c. which should never be cloned).

* Makefiles should never use GNU-make specific features (vanilla BSD make only).
  Makefile commands and configure scripts should adhere strictly to simple
  Bourne shell usage (not bash).
  Currently there are some violations of this rule, but these should NOT be
  taken as license to create additional dependencies on GNU-make.

* Perl code should only use features and modules available in all installations
  of Perl 5.005+.

* Test code should follow these standards and also those listed in tests/README
  Only the tests are currently using GNU-make specific features, and we'd stop
  doing so if we could.

GASNet porting guide
====================

This section documents the list of changes usually required when porting GASNet
to a new, UNIX-like operating system, CPU and/or C compiler. Porting existing 
GASNet conduits to a new system is usually a 1-2 day effort. Writing a new 
conduit is more complicated (and is not covered in this section), although the
"fill-in-the-blanks" template-conduit framework is very helpful - given high
degree of familiarity with the target network hardware, a functional conduit
can usually be constructed within a week.  Subsequent tuning can take up to
several months, depending on the level of NIC hardware support available to be
exploited.

Required porting steps:

* For a new OS, add OS detection to configure.in and acconfig.h, with 
  appropriate settings for GASNET_MACHINE_DEFINES, GASNET_THREAD_DEFINES,
  GASNET_THREAD_LIBS.  If the system supports MPI, add appropriate configure.in
  defaults for MPI_CC, MPI_CFLAGS, MPI_LIBS and MPIRUN_CMD. 

* For a new C/C++ compiler, add a detection check for the new compiler to 
  acinclude.m4:GASNET_FAMILY_CACHE_CHECK. Add configure.in settings for 
  MISC_CFLAGS and MISC_CXXFLAGS if appropriate. 

* For a new CPU, OS or C/C++ compiler, update portable_platform.h to create
  an appropriate canonical platform identifier for that component. You will
  need the canonical identifier(s) for most of the steps that follow.

* For a new C/C++ compiler, implement GASNETI_ASM for inline assembly 
  in gasnet_asm.h, if supported by the compiler. Ensure configure
  inline modifier detection worked, otherwise tweak it in gasnet_basic.h.

* For a new CPU, implement atomic increment/decrement operations in 
  gasnet_atomic_bits.h, or enable GASNETI_USE_GENERIC_ATOMICOPS if the CPU does
  not support atomic operations. Implement atomic compare-and-swap, if supported
  by the system.
  For an outline of the yet-to-be-written "Atomic OPS HOWTO" see
  http://upc-bugs.lbl.gov/bugzilla/show_bug.cgi?id=1607

* For a new CPU, implement appropriate memory barriers in gasnet_membar.h:
  gasneti_local_wmb and gasneti_local_rmb (one or both may be no-ops, depending
  on the memory consistency semantics enforced by hardware).

* Fix any misc compile errors that arise.

* Run the gasnet tests for all supported conduits (gmake run-tests-seq run-tests-par).
  Pay special attention to testtools, which tests the functionality above and
  is the most likely to fail on a new system.

Optional porting steps:

* Implement GASNet high-performance timers (gasneti_tick_t) in gasnet_timer.h,
  if supported by the system.

* Implement a new conduit for the network hardware (see template-conduit/README.template).

Source Control and GASNet
=========================

If you are using GASNet in your own project and wish to track any
local changes you make, then you'll probably keep a copy of the GASNet
sources in your project's Source Control repository (CVS, svn, Hg, Git,
etc.).  If so, you should be aware of potentially undesirable
interactions between timestamps as maintained by your Source Control
software and the files generated by GASNet's Bootstrap script.  The
issues are well described here:
  http://www.gnu.org/software/hello/manual/automake/CVS.html

To summarize the link above, you must decide whether or not to commit to
Source Control those files generated by GASNet's Bootstrap script.
Each approach has arguments for and against.  We do not dictate
that users of GASNet must use one approach or the other, and we provide
the tools to implement either approach.

* If you keep Bootstrap-generated files under Source Control

You need a mechanism to ensure that the files you checkout will be
treated as being up-to-date by the rules in GASNet's Makefiles,
regardless of what your Source Control software has done with
timestamps.  Running
    ./Bootstrap -T
will touch the generated files in an order that ensures that they
appear to be up-to-date.

Caution: This is intended to correct for lost timestamp information
when you retrieve files.  Using "./Bootstrap -T" in the presence of
locally modified versions of Bootstrap's input files will prevent
those changes from being propagated to the dependent files.  Inputs
include configure.in, and all acinclude.m4 and Makefile.am files (and
possibly others).

* If you omit Bootstrap-generated files from Source Control

You need a way to identify the files generated by Bootstrap to ignore
or delete them.  Running
    ./unBootstrap
will remove the generated files.  One may examine the contents of
unBootstrap to identify files that Source Control software may be
configured to ignore.  Note that the set of Bootstrap-generated files
may change from one release of GASNet to the next, but unBootstrap
will be kept current in each release.