Most software distributed shared memory systems (SW-DSMs) lack industry standard interfaces that limit their applicability to a small set of shared-memory applications. In order to gain general acceptance, SW-DSMs should support the same look-and-feel of shared memory as hardware DSMs. This paper presents a runtime system concept that enables unmodified POSIX P1003.1c (Pthreads) compliant binaries to run transparently on clustered hardware. The key idea is to extend the single process model of multi-threading to a multi-process model where threads are distributed to processes executing in remote nodes. The distributed threads execute in a global shared address space made coherent by a fine-grain SW-DSM layer. We also present THROOM, a proof-of-concept implementation that runs unmodified Pthread binaries on a virtual cluster modeled as standard UNIX processes. THROOM runs on top of the DSZOOM fine-grain SW-DSM system with limited OS support.
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