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Unified Parallel C
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<p>Unified Parallel C (UPC) is an extension of the <a href="/facts/C_(programming_language)/Ky2No763">C programming language</a> designed for <a href="/facts/High-performance_computing/HT9NwGAN">high-performance computing</a> on large-scale <a href="/facts/Parallel_machine/nQzcpzQt">parallel machines</a>, including those with a common global <a href="/facts/Address_space/EscyYKkP">address space</a> (<a href="/facts/Symmetric_multiprocessing/T9CahUsN">SMP</a> and <a href="/facts/Non-Uniform_Memory_Access/MpmN5mN0">NUMA</a>) and those with <a href="/facts/Distributed_memory/AxVfko1b">distributed memory</a> (e. g. <a href="/facts/Computer_cluster/mT7S1BcX">clusters</a>). The <a href="/facts/Programmer/WGTS1Jv9">programmer</a> is presented with a single <a href="/facts/Partitioned_global_address_space/wE3AwgJL">partitioned global address space</a>; where shared variables may be directly read and written by any <a href="/facts/Central_processing_unit/Jxp1bqMV">processor</a>, but each variable is physically associated with a single processor. UPC uses a <i>single program, multiple data</i> (<a href="/facts/SPMD/SEDIrB0l">SPMD</a>) model of computation in which the amount of parallelism is fixed at program startup time, typically with a single <a href="/facts/Thread_(computer_science)/hh8WHyPd">thread</a> of execution per processor. </p><p>In order to express parallelism, UPC extends <a href="/facts/C_(programming_language)/Ky2No763">ISO C 99</a> with the following constructs: </p> <ul><li>An explicitly parallel execution model</li> <li>A shared address space (shared storage qualifier) with thread-local parts (normal variables)</li> <li>Synchronization primitives and a memory consistency model</li> <li>Explicit communication primitives, e. g. upc_memput</li> <li><a href="/facts/Memory_management/vthLkUpz">Memory management</a> primitives</li></ul> <p>The UPC language evolved from experiences with three other earlier languages that proposed parallel extensions to ISO C 99: AC, <a href="/facts/Split-C/9nlRonEg">Split-C</a>, and Parallel C preprocessor (PCP). UPC is not a <a href="/facts/Superset/SJGERmbA">superset</a> of these three languages, but rather an attempt to distill the best characteristics of each. UPC combines the programmability advantages of the shared memory programming paradigm and the control over data layout and performance of the <a href="/facts/Message_passing/RYf3hD3J">message passing</a> <a href="/facts/Programming_paradigm/7LwgRpB3">programming paradigm</a>. </p>