Cray OpenSHMEMX is a Remote Memory Access (RMA) library. It is a proprietary software implementation of the OpenSHMEM standards specification and released as part of the Cray Programming Environment software package. The Cray OpenSHMEMX software stack is available as a standard compliant software package on different architectures of Cray and HPE supercomputer systems.

OpenSHMEM is a Partitioned Global Address Space (PGAS) library interface specification, which is the culmination of a standardization effort among many implementers and users of SHMEM programming model. Refer for more details on the OpenSHMEM programming model.

SHMEM has a long history as a parallel programming model. It is extensively used since 1993, starting from Cray T3D systems. For the past two decades the SHMEM library implementation in Cray supercomputer systems have evolved through different generations. The current generation of the SHMEM implementation on Cray XC and XK systems is called Cray SHMEM. Cray SHMEM is a proprietary SHMEM implementation from Cray Inc., which is OpenSHMEM standards compliant. The next evolution of OpenSHMEM implementation for current and future generation exascale Cray supercomputer systems is called Cray OpenSHMEMX.

This document contains public announcement information about the Cray OpenSHMEMX software stack including release informations, updated API references, information on performance optimization and tuning parameters, supported environments and systems, and general backward compatibility details.



Cray OpenSHMEMX software stack provides support for the OpenSHMEM standard specific features as well as Cray-specific features. The examples of the supported features includes teams and library management operations, one-sided data transfer operations including RMA, AMO, and put-with-signal (PWS), collective communication operations, symmetric memory management routines, memory ordering and point-to-point synchronization routines, and support for distributed locks.

All the supported features are accessed using standard OpenSHMEM C and Fortran interfaces. These features are implemented over different transport options like XPMEM, Cross Memory Attach (CMA), Libfabric and DMAPP. While XPMEM and CMA are used for moving data across processing elements within the same node, Libfabric and DMAPP are used to move data across nodes. The SMP transport combines two transports one for inter-node and another for intra-node data transfers. Cray OpenSHMEMX software stack is usable across different Cray and HPE system architectures.

Latest News

Latest Release Updates
System Architecture Release Version Release Date
Cray Shasta Cray OpenSHMEMX v11.1.0 August 2020
Cray XC Cray OpenSHMEMX v9.1.1 August 2020

The following changes were made in the latest release of Cray OpenSHMEMX v11.1.0 on Cray Shasta systems:

  1. Enabling manual-progress by default for OFI “verbs;ofi_rxm” provider
  2. Allow using Cray OpenSHMEMX on HPE Apollo systems as a beta release. The initial beta release is not performant and it is provided as a functional test library
  3. Fix padding issues on the symmetric heaps, to avoid internal library usage memory buffers to use the user-allocated symmetric heaps

The following changes were made in the latest release of Cray OpenSHMEMX v9.1.1 on Cray XC systems:

  1. Fix issues in supporting lmod-based cray-openshmemx modules

For more details on the different released versions of Cray OpenSHMEMX, please refer the link.

System Architectures

Cray OpenSHMEMX is supported on both Cray XC and Cray Shasta systems. The current support for Cray OpenSHMEMX on Cray XC systems are in maintenance mode, only bugfixes are provided and no new functional additions are planned. Active functional additions and performance tuning is done on Cray Shasta systems.

The following table shows the availability of Cray OpenSHMEMX on different Cray systems.

Availability of Cray OpenSHMEMX on Different Cray Systems
System Architecture Processor Type Availability
Cray XC x86_64 Available as evaluation library
Cray XC aarch64 Available as primary library
Cray Shasta x86_64 Available as primary library

On X86_64 based Cray XC systems, Cray SHMEM is still the production-ready implementation. Early access to Cray OpenSHMEMX library is provided for users to start migrating their existing applications to the new library.

On AARCH64 based Cray XC systems, Cray OpenSHMEMX is the only available and supported SHMEM implementation by Cray Inc.

Transport Options

The following table shows the support for different transport options in Cray OpenSHMEMX software stack on different system architectures.

Supported Transport Options in Cray OpenSHMEMX
System Architecture Inter-node Transport Option Intra-node Transport Option
Cray XC using Aries-Interconnect DMAPP XPMEM
Cray Shasta using Ethernet OFI (verbs;ofi_rxm provider) XPMEM (default)/CMA


The proper citation of Cray OpenSHMEMX software stack is: Naveen Namashivayam, Bob Cernohous, Dan Pou, and Mark Pagel, “OpenSHMEM 2018: Fifth Workshop on OpenSHMEM and Related Technologies.” Baltimore, MD, August, 2018. “Introducing Cray OpenSHMEMX- A Modular Multi-Communication Layer OpenSHMEM Implementation.”

The corresponding Bibtex is:

author = {Naveen Namashivayam and Bob Cernohous and Dan Pou and Mark
title = {Introducing Cray OpenSHMEMX - A Modular Multi-Communication
Layer OpenSHMEM Implementation},
booktitle = {OpenSHMEM 2018: Fifth Workshop on OpenSHMEM and
Related Technologies},

month = Aug, year = {2018}, location = {Baltimore, MD, USA},



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