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UPC++ Installation

The general recipe for building and installing UPC++ is to run the install script found in the top-level (upcxx) source directory:

cd <upcxx-source-path>
./install <upcxx-install-path>

This will build the UPC++ library and install it to the <upcxx-install-path> directory. Users are recommended to use paths to non-existent or empty directories as the installation path so that uninstallation is as trivial as rm -rf <upcxx-install-path>. Note that the install process downloads the GASNet communication library, so an Internet connection is needed. Depending on the platform, additional configuration may be necessary before invoking install. See below.

Installation: Linux

The installation command above will work as is. The default compilers used will be gcc/g++. The CC and CXX environment variables can be set to alternatives to override this behavior. Additional environment variables allowing finer control over how UPC++ is configured can be found in the "Advanced Installer Configuration" section below.

Installation: Mac

The Xcode Command Line Tools need to be installed before invoking install, i.e.:

xcode-select --install

Installation: Cray XC

To run on the compute nodes of a Cray XC, the CROSS environment variable needs to be set before the install command is invoked, i.e. CROSS=cray-aries-slurm. Additionally, because UPC++ does not currently support the Intel compilers (usually the default for these systems), either GCC or Clang must be loaded, e.g.:

module switch PrgEnv-intel PrgEnv-gnu
cd <upcxx-source-path>
CROSS=cray-aries-slurm ./install <upcxx-install-path>

The installer will use the cc and CC compiler aliases of the Cray programming environment loaded.

Advanced Installer Configuration

The installer script tries to pick a sensible default behavior for the platform it is running on, but the install can be customized using the following environment variables:

  • CC, CXX: The C and C++ compilers to use.
  • CROSS: The cross-configure settings script to pull from the GASNet source tree (computed as <gasnet>/other/contrib/cross-configure-${CROSS}).
  • GASNET: Provides the GASNetEx source tree from which the UPC++ install script will build its own version of GASNet. This can be a path to a tarball, url to a tarball, or path to a full source tree. Defaults to a url to a publicly available GASNetEx tarball.
  • GASNET_CONFIGURE_ARGS: List of additional command line arguments passed to GASNet's configure phase.

Compiling Against UPC++

With UPC++ installed, the application's build process can query for the appropriate compiler flags to enable building against upcxx by invoking the <upcxx-install-path>/bin/upcxx-meta <what> script, where <what> indicates which form of flags are desired. Valid values are:

  • PPFLAGS: Preprocessor flags which will put the upcxx headers in the compiler's search path and define macros required by those headers.
  • LDFLAGS: Linker flags usually belonging at the front of the link command line (before the list of object files).
  • LIBFLAGS: Linker flags belonging at the end of the link command line. These will make libupcxx and its dependencies available to the linker.

For example, to build an application consisting of my-app1.cpp and my-app2.cpp:

upcxx="<upcxx-install-path>/bin/upcxx-meta"
<c++ compiler> -std=c++11 $($upcxx PPFLAGS) -c my-app1.cpp
<c++ compiler> -std=c++11 $($upcxx PPFLAGS) -c my-app2.cpp
<c++ compiler> $($upcxx LDFLAGS) my-app1.o my-app2.o $($upcxx LIBFLAGS)

The <c++ compiler> used to build the application must be the same as the one used for the UPC++ installation.

For an example of a Makefile which builds UPC++ applications, look at example/prog-guide/Makefile. This directory also has code for running all the examples given in the programmer's guide. To use that Makefile, first set the UPCXX_INSTALL shell variable to the <upcxx-install-path>.

UPC++ Backends

UPC++ provides multiple "backends" offering the user flexibility to choose the means by which the parallel communication facilities are implemented. Those backends are characterized by three dimensions: conduit, thread-mode, and code-mode. The conduit and thread-mode parameters map directly to the GASNet concepts of the same name (for more explanation, see below). Code-mode selects between highly optimized code and highly debuggable code. The upcxx-meta script will assume sensible defaults for these parameters based on the installation configuration. The following environment variables can be set to influence which backend upcxx-meta selects:

  • UPCXX_GASNET_CONDUIT=[smp|udp|aries]: The GASNet conduit to use. smp is the typical high-performance choice for single-node multi-core runs, udp is a useful low-performance alternative for testing and debugging, and aries is the high-performance Cray XC network. The default value is platform dependent.
  • UPCXX_THREADMODE=[seq|par]: The value seq limits the application to only calling "communicating" upcxx routines from the thread that invoked upcxx::init, and only while that thread is holding the master persona. The benefit is that seq can be synchronization free in much of its internals. A thread-mode value of par allows any thread in the process to issue communication as allowed by the specification, allowing for greater injection concurrency from a multi-threaded application but at the expensive of greater internal synchronization (higher overheads per operation). The default value is always seq.
  • UPCXX_CODEMODE=[O3|debug]: O3 is for highly compiler-optimized code. debug produces unoptimized code, includes extra error checking assertions, and is annotated with the symbol tables needed by debuggers. The default value is always O3.

Running UPC++ Programs

To run a parallel UPC++ application, use the upcxx-run launcher provided in the installation directory:

<upcxx-install-path>/bin/upcxx-run <ranks> <exe> <args...>

This will run the executable and arguments <exe> <args...> in a parallel context with <ranks> number of UPC++ ranks.

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