Explicit parallelism

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In computer programming, explicit parallelism is the representation of concurrent computations by means of primitives in the form of special-purpose directives or function calls. Most parallel primitives are related to process synchronization, communication or task partitioning. As they seldom contribute to actually carry out the intendend computation of the program, their computational cost is often condsidered as parallelization overhead.

The advantage of explicit parallel programming is the absolute programmer control over the parallel execution. A skilled parallel programmer takes advantage of explicit parallelism to produce very efficient code. However, programming with explicit parallelism is often difficult, especially for non computing specialists, because of the extra work involved in planning the task division and synchronization of concurrent processes.

In some instances, explicit parallelism may be avoided with the use of an optimizing compiler that automatically extracts the parallelism inherent to computations (see implicit parallelism).

[edit] Programming with explicit parallelism

Topics in Parallel Computing  v • d • e 
General High-performance computing
Parallelism Data parallelism • Task parallelism
Theory Speedup • Amdahl's law • Flynn's Taxonomy • Cost efficiency • Gustafson's Law • Karp-Flatt Metric
Elements Process • Thread • Fiber • Parallel Random Access Machine
Coordination Multiprocessing • Multithreading •Multitasking • Memory coherency • Cache coherency • Barrier • Synchronization • Distributed computing • Grid computing
Programming Programming model • Implicit parallelism • Explicit parallelism
Hardware Computer cluster • Beowulf • Symmetric multiprocessing • Non-Uniform Memory Access • Cache only memory architecture • Asymmetric multiprocessing • Simultaneous multithreading • Shared memory • Distributed memory • Massively parallel processing • Superscalar processing • Vector processing • Supercomputer
Software Distributed shared memory • Application checkpointing
APIs Pthreads • OpenMP • Message Passing Interface (MPI)
Problems Embarrassingly parallel • Grand Challenge
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