Parallel Programming in Fortran 95 using OpenMP - People

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56 4. The OpenMP run-time library The number of threads imposed by a call to this subroutine has always precedence over the value specified in the OMP NUM THREADS environment variable. 4.1.2 OMP get num threads This function allows to know the number of threads currently in the team executing the parallel region from which it is called. Therefore, this function is meant to be used from inside a parallel region; although when called from a serial region or from inside a serialized nested parallel region, it returns the correct result, namely 1 thread. Its interface declaration is: function OMP_get_num_threads() integer(kind = OMP_integer_kind) :: OMP_get_num_threads end function OMP_get_num_threads where the returned value will be the number of threads in use. 4.1.3 OMP get max threads This function returns the maximum number of threads that can be used in the program. Its result may differ from the one returned by the function OMP get num threads, ifthe dynamic adjustment of threads is enabled; otherwise, the results will be equal. Its interface declaration is equivalent to the one of the function OMP get num threads: function OMP_get_max_threads() integer(kind = OMP_integer_kind) :: OMP_get_max_threads end function OMP_get_max_threads where the returned value is the maximum allowed number of threads. Since the returned value has nothing to do with the actual number of threads used in a given parallel region, this function can be called from serial regions as well as from parallel regions. 4.1.4 OMP get thread num This function returns the identification number of the current thread within the team. The identification numbers are between 0, the master thread, and OMP get num threads() - 1, inclusive. The interface of this function is: function OMP_get_thread_num() integer(kind = OMP_integer_kind) :: OMP_get_thread_num end function OMP_get_thread_num This function returns 0, when called from inside a serial region or a serialized nested parallel region, which is the identification number of the lonely master thread.
4.1. Execution environment routines 57 4.1.5 OMP get num procs This function returns the number of processors available to the program. Its interface declaration is as follows: function OMP_get_num_procs() integer(kind = OMP_integer_kind) :: OMP_get_num_procs end function OMP_get_num_procs 4.1.6 OMP in parallel This function allows to know, if a given region of the program is being computed in parallel or not. For that purpose, it looks at all the parallel regions which are surrounding the block of source code enclosing the call to OMP in parallel and returns .TRUE., ifatleast one of them is being executed in parallel; otherwise, it returns .FALSE.. The interface declaration of this function is the following one: function OMP_in_parallel() logical(kind = OMP_logical_kind) :: OMP_in_parallel end function OMP_in_parallel Since the returned value will be .TRUE. as soon as one of the enclosing parallel regions is being executed in parallel, this function returns .TRUE. from any point inside the dynamic extent of that parallel region, even inside nested serialized parallel regions (which are not considered as being executed in parallel!). 4.1.7 OMP set dynamic The OMP set dynamic subroutine enables or disables dynamic adjustment of the number of threads available for execution of parallel regions. Its interface is: subroutine OMP_set_dynamic(enable) logical(kind = OMP_logical_kind), intent(in) :: enable end subroutine OMP_set_dynamic When enable is set equal to .TRUE., the number of threads to be used by subsequent parallel regions can be adjusted automatically by the run-time environment in order to maximize the use of the SMP machine; otherwise, if enable is equal to .FALSE., the dynamic adjustment is disabled. As a consequence, the number of threads specified through the environment variable OMP NUM THREADS or by a call to the run-time library subroutine OMP set num threads represents the maximum allowed number of threads which can be assigned to the program by the run-time environment. The working conditions specified in a call to OMP set dynamic have precedence over the settings in the OMP DYNAMIC environment variable. The default for dynamic thread adjustment is OpenMP-implementation dependent, therefore a program needing a specific number of threads to run correctly should explicitly
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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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4 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 !$OMP SECTI
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Page 24 and 25: 20 2. OpenMP constructs • If the
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Page 32 and 33: 28 2. OpenMP constructs !$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
Page 46 and 47: 42 3. PRIVATE, SHARED & Co. In this
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Page 54 and 55: 50 3. PRIVATE, SHARED & Co. DYNAMIC
Page 56 and 57: 52 3. PRIVATE, SHARED & Co. Pieces
Page 58 and 59: 54 3. PRIVATE, SHARED & Co.
Page 62 and 63: 58 4. The OpenMP run-time library d
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Parallel Programming in Fortran 95 using OpenMP - People

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