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Loop parallelism is a very common type of parallelism in scientific codes, so OpenMP has an easy mechanism for it. OpenMP parallel loops are a first example of. Jun 4, 2005 - FILE: omp_hello.c * DESCRIPTION: * OpenMP Example - Hello World - C/C++ Version * In this simple example, the master thread forks a.
OPENMP - FORTRAN90 Examples of Parallel Programming with OpenMP OPENMP FORTRAN90 Examples of Parallel Programming with OpenMP OPENMP is a directory of FORTRAN90 examples which illustrate the use of the OpenMP application program interface for carrying out parallel computations in a shared memory environment. The directives allow the user to mark areas of the code, such as do, while or for loops, which are suitable for parallel processing. The directives appear as a special kind of comment, so the program can be compiled and run in serial mode. However, the user can tell the compiler to 'notice' the special directives, in which case a version of the program will be created that runs in parallel. Thus the same program can easily be run in serial or parallel mode on a given computer, or run on a computer that does not have OpenMP at all.
OpenMP is suitable for a shared memory parallel system, that is, a situation in which there is a single memory space, and multiple processors. If memory is shared, then typically the number of processors will be small, and they will all be on the same physical machine. By contrast, in a distributed memory system, items of data are closely associated with a particular processor.
There may be a very large number of processors, and they may be more loosely coupled and even on different machines. Such a system will need to be handled with MPI or some other message passing interface. FORTRAN90 Issues OpenMP includes a number of functions whose type must be declared in any program that uses them. To avoid having to declare these functions, you can use the command use omplib in any routine that invokes OpenMP functions. 'Pretend' Parallelism OpenMP allows you to 'request' any number of threads of execution. This is a request, and it's not always a wise request.
If your system has four processors available, and they're not busy doing other things, or serving other users, maybe 4 threads is what you want. But you can't guarantee you'll get the undivided use of those processors. Moreover, if you run the same program using 1 thread and 4 threads, you may find that using 4 threads slows you down, either because you don't actually have 4 processors, (so the system has the overhead of pretending to run in parallel), or because the processors you have are also busy doing other things. For this reason, it's wise to run the program at least once in single thread mode, so you have a benchmark against which to measure the speedup you got (or didn't get!) versus the speedup you hoped for. Compiler Support The compiler you use must recognize the OpenMP directives in order to produce code that will run in parallel. Here are some of the compilers available that support OpenMP:. The GNU compilers gcc/g (version 4.2 or later) and gfortran (version 2.0 or later).
The IBM compilers xlc and xlf. The Intel compilers icc, icpc and ifort. The Microsoft Visual C compiler. The Portland Group C/C and Fortran compilers.
Sun Studio C/C and Fortran95 compilers. Licensing: The computer code and data files described and made available on this web page are distributed under Languages: OPENMP examples are available in. Related Data and Programs:, a FORTRAN90 program which uses OpenMP to parallelize a simple example of Dijkstra's minimum distance algorithm for graphs., a FORTRAN90 program which demonstrates the computation of a Fast Fourier Transform in parallel, using OpenMP., a FORTRAN90 program which solves the steady (time independent) heat equation in a 2D rectangular region, using OpenMP to run in parallel., a FORTRAN90 program which prints out 'Hello, world!'
OPENMP - C Examples of Parallel Programming with OpenMP OPENMP C Examples of Parallel Programming with OpenMP OPENMP is a directory of C examples which illustrate the use of the OpenMP application program interface for carrying out parallel computations in a shared memory environment. The directives allow the user to mark areas of the code, such as do, while or for loops, which are suitable for parallel processing. The directives appear as a special kind of comment, so the program can be compiled and run in serial mode.
However, the user can tell the compiler to 'notice' the special directives, in which case a version of the program will be created that runs in parallel. Thus the same program can easily be run in serial or parallel mode on a given computer, or run on a computer that does not have OpenMP at all. OpenMP is suitable for a shared memory parallel system, that is, a situation in which there is a single memory space, and multiple processors. If memory is shared, then typically the number of processors will be small, and they will all be on the same physical machine.
By contrast, in a distributed memory system, items of data are closely associated with a particular processor. There may be a very large number of processors, and they may be more loosely coupled and even on different machines. Such a system will need to be handled with MPI or some other message passing interface.
OpenMP descended in part from the old Cray microtasking directives, so if you've lived long enough to remember those, you will recognize some features. C Issues OpenMP includes a number of functions whose type must be declared in any program that uses them. A user program calling OpenMP must have the statement # include 'Pretend' Parallelism OpenMP allows you to 'request' any number of threads of execution.
This is a request, and it's not always a wise request. If your system has four processors available, and they're not busy doing other things, or serving other users, maybe 4 threads is what you want. But you can't guarantee you'll get the undivided use of those processors.
Moreover, if you run the same program using 1 thread and 4 threads, you may find that using 4 threads slows you down, either because you don't actually have 4 processors, (so the system has the overhead of pretending to run in parallel), or because the processors you have are also busy doing other things. For this reason, it's wise to run the program at least once in single thread mode, so you have a benchmark against which to measure the speedup you got (or didn't get!) versus the speedup you hoped for. Compiler Support The compiler you use must recognize the OpenMP directives in order to produce code that will run in parallel. Here are some of the compilers available that support OpenMP:.
The GNU compilers gcc/g (version 4.2 or later) and gfortran (version 2.0 or later). The IBM compilers xlc and xlf. The Intel compilers icc, icpc and ifort. The Microsoft Visual C compiler. The Portland Group C/C and Fortran compilers. Sun Studio C/C and Fortran95 compilers. Licensing: The computer code and data files described and made available on this web page are distributed under Languages: OPENMP examples are available in.
Related Data and Programs:, a C program which uses OpenMP to parallelize a simple example of Dijkstra's minimum distance algorithm for graphs., a C program which demonstrates the computation of a Fast Fourier Transform in parallel, using OpenMP., a C program which demonstrates the behavior of a few of the OpenMP library functions., a C program which solves the steady (time independent) heat equation in a 2D rectangular region, using OpenMP to run in parallel., a C program which prints out 'Hello, world!'