computer science Computer science is the study of computation, automation, and information. Computer science spans theoretical disciplines (such as algorithms, theory of computation, information theory, and automation) to practical disciplines (includi ...

, partitioned global address space (PGAS) is a

parallel programming model In computing, a parallel programming model is an abstraction of parallel computer architecture, with which it is convenient to express algorithms and their composition in programs. The value of a programming model can be judged on its ''generality ...

paradigm. PGAS is typified by communication operations involving a global memory address space abstraction that is logically partitioned, where a portion is local to each process, thread, or

processing element This glossary of computer hardware terms is a list of definitions of terms and concepts related to computer hardware, i.e. the physical and structural components of computers, architectural issues, and peripheral devices. A ...

. The novelty of PGAS is that the portions of the

shared memory In computer science, shared memory is memory that may be simultaneously accessed by multiple programs with an intent to provide communication among them or avoid redundant copies. Shared memory is an efficient means of passing data between progr ...

space may have an affinity for a particular process, thereby exploiting

locality of reference In computer science, locality of reference, also known as the principle of locality, is the tendency of a processor to access the same set of memory locations repetitively over a short period of time. There are two basic types of reference localit ...

in order to improve performance. A PGAS memory model is featured in various parallel programming languages and libraries, including:

Coarray Fortran Coarray Fortran (CAF), formerly known as F--, started as an extension of Fortran 95/2003 for parallel processing created by Robert Numrich and John Reid in the 1990s. The Fortran 2008 standard (ISO/IEC 1539-1:2010) now includes coarrays (spel ...

Unified Parallel C Unified Parallel C (UPC) is an extension of the C programming language designed for high-performance computing on large-scale parallel machines, including those with a common global address space ( SMP and NUMA) and those with distributed memory ...

Split-C
Fortress,

Chapel A chapel is a Christian place of prayer and worship that is usually relatively small. The term has several meanings. Firstly, smaller spaces inside a church that have their own altar are often called chapels; the Lady chapel is a common ty ...

, X10
UPC++Coarray C++

Global Arrays Global Arrays, or GA, is the library developed by scientists at Pacific Northwest National Laboratory for parallel computing. GA provides a friendly API for shared-memory programming on distributed-memory computers for multidimensional arrays. T ...

DASH
and

SHMEM SHMEM (from Cray Research’s “shared memory” library) is a family of parallel programming libraries, providing one-sided, RDMA, parallel-processing interfaces for low-latency distributed-memory supercomputers. The SHMEM acronym was subsequent ...

. The PGAS paradigm is now an integrated part of the Fortran language, as of Fortran 2008 which standardized coarrays. The various languages and libraries offering a PGAS memory model differ widely in other details, such as the base programming language and the mechanisms used to express parallelism. Many PGAS systems combine the advantages of a

SPMD In computing, single program, multiple data (SPMD) is a technique employed to achieve parallelism; it is a subcategory of MIMD. Tasks are split up and run simultaneously on multiple processors with different input in order to obtain results fast ...

programming style for distributed memory systems (as employed by MPI) with the data referencing semantics of shared memory systems. In contrast to

message passing In computer science, message passing is a technique for invoking behavior (i.e., running a program) on a computer. The invoking program sends a message to a process (which may be an actor or object) and relies on that process and its support ...

, PGAS programming models frequently offer one-sided communication operations such as Remote Memory Access (RMA), whereby one processing element may directly access memory with affinity to a different (potentially remote) process, without explicit semantic involvement by the passive target process. PGAS offers more efficiency and scalability than traditional shared-memory approaches with a flat address space, because hardware-specific

data locality In computer science, locality of reference, also known as the principle of locality, is the tendency of a processor to access the same set of memory locations repetitively over a short period of time. There are two basic types of reference localit ...

can be explicitly exposed in the semantic partitioning of the address space. A variant of the PGAS paradigm, asynchronous partitioned global address space (APGAS) augments the programming model with facilities for both local and remote asynchronous task creation. Two programming languages that use this model are

and X10.

Examples

now an integrated part of the language as of Fortran 2008 *

an explicitly parallel SPMD dialect of the ISO C programming language *

a parallel language originally developed by Cray under the DARPA HPCS project
UPC++
A

C++ C++ (pronounced "C plus plus") is a high-level general-purpose programming language created by Danish computer scientist Bjarne Stroustrup as an extension of the C programming language, or "C with Classes". The language has expanded significan ...

template library that provides PGAS communication operations designed to support

high-performance computing High-performance computing (HPC) uses supercomputers and computer clusters to solve advanced computation problems. Overview HPC integrates systems administration (including network and security knowledge) and parallel programming into a mult ...

exascale Exascale computing refers to computing systems capable of calculating at least "1018 IEEE 754 Double Precision (64-bit) operations (multiplications and/or additions) per second ( exa FLOPS)"; it is a measure of supercomputer performance. Exasca ...

supercomputers, including Remote Memory Access (RMA) and

Remote Procedure Call In distributed computing, a remote procedure call (RPC) is when a computer program causes a procedure ( subroutine) to execute in a different address space (commonly on another computer on a shared network), which is coded as if it were a normal ( ...

(RPC)
Coarray C++
a

library developed by Cray, providing a close analog to Fortran coarray functionality *

a library supporting parallel scientific computing on distributed arrays
DASH
a

template library for distributed data structures with support for hierarchical locality *

a family of libraries supporting parallel scientific computing on distributed arrays * X10 a parallel language developed by IBM under the DARPA HPCS project * Fortress a parallel language developed by Sun Microsystems under the DARPA HPCS project
Titanium
an explicitly parallel dialect of

Java Java (; id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 151.6 million people, Java is the world's mos ...

developed at UC Berkeley to support scientific

on large-scale multiprocessors
Split-C
a parallel extension of the C programming language that supports efficient access to a global address space * The

Adapteva Zero ASIC Corporation, formerly Adapteva, Inc., is a fabless semiconductor company focusing on low power many core microprocessor design. The company was the second company to announce a design with 1,000 specialized processing cores on a single ...

Epiphany architecture is a

manycore Manycore processors are special kinds of multi-core processors designed for a high degree of parallel processing, containing numerous simpler, independent processor cores (from a few tens of cores to thousands or more). Manycore processors are use ...

network on a chip A network on a chip or network-on-chip (NoC or )This article uses the convention that "NoC" is pronounced . Therefore, it uses the convention "a" for the indefinite article corresponding to NoC ("a NoC"). Other sources may pronounce it as a ...

processor with

scratchpad memory Scratchpad memory (SPM), also known as scratchpad, scratchpad RAM or local store in computer terminology, is a high-speed internal memory used for temporary storage of calculations, data, and other work in progress. In reference to a microprocess ...

addressable between cores.

External links

*
An Introduction to the Partitioned Global Address Space Model

Programming in the Partitioned Global Address Space Model
(2003)
GASNet Communication System
- provides a software infrastructure for PGAS languages over high-performance networksBonachea D, Hargrove
GASNet-EX: A High-Performance, Portable Communication Library for Exascale
Proceedings of Languages and Compilers for Parallel Computing (LCPC'18). Oct 2018. https://doi.org/10.25344/S4QP4W

References

{{Parallel Computing

Programming model A programming model is an execution model coupled to an API or a particular pattern of code. In this style, there are actually two execution models in play: the execution model of the base programming language and the execution model of the prog ...

Programming paradigms

Examples

See also

External links

References