The OpenTM Transactional Application Programming Interface

Abstract

Transactional Memory (TM) simplifies parallel programming by supporting atomic and isolated execution of user-identified tasks. To date, TM programming has required the use of libraries that make it difficult to achieve scalable performance with code that is easy to develop and maintain. For TM programming to become practical, it is important to integrate TM into familiar, high-level environments for parallel programming. This paper presents OpenTM, an application programming interface (API) for parallel programming with transactions. OpenTM extends OpenMP, a widely used API for shared-memory parallel programming, with a set of compiler directives to express non-blocking synchronization and speculative parallelization based on memory transactions. We also present a portable OpenTM implementation that produces code for hardware, software, and hybrid TM systems. The implementation builds upon the OpenMP support in the GCC compiler and includes a runtime for the C programming language.We evaluate the performance and programmability features of OpenTM. We show that it delivers the performance of fine-grain locks at the programming simplicity of coarsegrain locks. Compared to transactional programming with lower-level interfaces, it removes the burden of manual annotations for accesses to shared variables and enables easy changes of the scheduling and contention management policies. Overall, OpenTM provides a practical and efficient TM programming environment within the familiar scope of OpenMP.

Design and implementation of transactional constructs for C/C++

“…Prior systems support basic mechanisms for C [46,3]. We refine and extend these mechanisms to provide first-class language constructs (rather than compiler pragmas) and to add full support for C++ classes, virtual functions, inheritance, templates, and exception handling.…”

“…Several STM systems have introduced the basic atomic block language construct into C [46,10,3,35,15,28]. Some of these approaches introduce pragmas [46,28] and OpenMP extensions [3,35].…”

“…Much of this work has focused on managed languages such as Java [20], C# [22], Haskell [21], and Caml [39], and on C [46,3,35,15,28]. Only quite recently have TM language proposals for C++ started emerging [10].…”

Towards Transactional Memory for OpenMP

“…Two proposals were presented almost at the same time [22], [6] with the aim of adding transactional memory support within the OpenMP programming interface. The topic has reborn with a more recent proposal [3], presenting results using hardware transactional memory, which can significantly reduce the complexity of shared memory programming while retaining efficiency.…”

Notary: Hardware techniques to enhance signatures

“…Furthermore, researchers recently proposed a transactional version of OpenMP [27], which support the additional keywords exclude and only to denote which variables to exclude and track for conflict detection. Similarly, OpenTM [4] supports the keywords private and shared.…”