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<pre>
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Using HDF5 with OpenMP
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----------------------
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1. Introduction to OpenMP
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-------------------------
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- For shared-memory parallelism
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- A combination of library and directives
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- Available for C/C++ and Fortran
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- SGI leading effort
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- Information at http://www.openmp.org and
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http://www.sgi.com/software/openmp
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2. Programming(SGI MPISpro compiler and C language)
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---------------------------------------------------
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- Turn on compiler '-mp' option
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- Include 'omp.h' library in program
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- Use library functions, directives and environment variables
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3. Sample Programs
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------------------
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Appendix A contains four OpenMP-HDF5 test programs. (They are derived from
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the hdf5/examples/h5_write.c). The purpose of these program is to
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test OpenMP parallelism with the HDF5 library.
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All tests were run on modi4 with SGI MPISpro compiler(cc) and make.
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Program 1 and Program 2 are the working programs. Program 3 and Program 4
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work occasionally due to racing conditions.
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Follow the following steps to try the programs.
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a. have your hdf5 library compiled,
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b. go to hdf5/examples directory,
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c. add -mp option to the end of the CFLAGS list in the Makefile. If you
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have the compiled program in another directory, you should go to the
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examples in that directory.
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d. modify the hdf5/examples/h5_write.c according to the program attached
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here.
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e. use hdf5/tools/h5dump to examine the output file.
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4. Conclusion
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-------------
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It is not safe to invoke HDF5 library calls via multiple threads in an
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OpenMP program. But if one serializes HDF5 calls as illustrated in Program 1,
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the HDF5 library works correctly with the OpenMP programs.
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The serialization of HDF5 calls will slow down the OpenMP program unnecessarily.
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Future study is needed to check possible ways to "un-seralize" the HDF5 calls.
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One possibility is that the HDF5 library has a beta-version of Thread-safe
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implmentation though it is for Pthreads environment. One can check on the
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feasibility of running OpenMP programs with this version of HDF5 Thread-safe
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library.
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<A HREF="openmp-hdf5.c">Appendix A: OpenMP-HDF5 Programs</A>
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-------
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Updated: 2000/11/28
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Contact: hdfhelp@ncsa.uiuc.edu
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</pre>
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