Parallel Programming in Fortran 95 using OpenMP - People

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54 3. PRIVATE, SHARED & Co.
Chapter 4 The OpenMP run-time library In some of the examples presented in previous chapters it has been mentioned the existence of a run-time library. It is the aim of the present chapter to introduce the so called OpenMP Fortran API run-time library, describe the subroutines and functions it includes and to explain its capabilities as well as its limitations. The OpenMP run-time library is meant to serve as a control and query tool for the parallel execution environment, which the programmer can use from inside its program. Therefore, the run-time library is a set of external procedures with clearly defined interfaces. These interfaces are explicitly delivered by the OpenMP-implementation through a Fortran 95 module named omp lib. In the following descriptions of the different routines, interfaces for them are shown: these may vary from one OpenMP-implementation to another in the precision/size of the variables, but in essence will be all equal. 4.1 Execution environment routines The following functions and subroutines, part of the OpenMP Fortran API run-time library, allow to modify, from inside of a program, the conditions of the run-time environment that controls the parallel execution of the program: 4.1.1 OMP set num threads This subroutine sets the number of threads to be used by subsequent parallel regions. Therefore, it can only be called from outside of a parallel region. Its interface declaration looks as follows: subroutine OMP_set_num_threads(number_of_threads) integer(kind = OMP_integer_kind), intent(in) :: number_of_threads end subroutine OMP_set_num_threads where number of threads is the number of threads to be set. If dynamic adjustment is disabled, the value of number of threads is used as the number of threads for all subsequent parallel regions prior to the next call to this subroutine; otherwise, if dynamic adjustment is enabled, number of threads is the maximum number of threads that is allowed. 55
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Parallel Programming in Fortran 95
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ii CONTENTS 3.1.4 FIRSTPRIVATE(list
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2 1. OpenMP Fortran Application Pro
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Page 14 and 15: 10 2. OpenMP constructs • Work-sh
Page 16 and 17: 12 2. OpenMP constructs real(8) ::
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Page 20 and 21: 16 2. OpenMP constructs !$OMP SECTI
Page 22 and 23: 18 2. OpenMP constructs thread 0 th
Page 24 and 25: 20 2. OpenMP constructs • If the
Page 26 and 27: 22 2. OpenMP constructs 2.3 Synchro
Page 32 and 33: 28 2. OpenMP constructs !$OMP DO do
Page 34 and 35: 30 2. OpenMP constructs 2.3.6 !$OMP
Page 36 and 37: 32 2. OpenMP constructs !$OMP END D
Page 38 and 39: 34 2. OpenMP constructs Shared memo
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Page 42 and 43: 38 3. PRIVATE, SHARED & Co. Shared
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Page 54 and 55: 50 3. PRIVATE, SHARED & Co. DYNAMIC
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Page 60 and 61: 56 4. The OpenMP run-time library T
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Page 72 and 73: 68 4. The OpenMP run-time library i
Page 74 and 75: 70 5. The environment variables 5.1
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