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97 lines
3.5 KiB
TeX
97 lines
3.5 KiB
TeX
\pagebreak
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\section{Utilities}
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\label{sec:utilities}
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This section contains examples of utility routines and features.
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%---------------------------
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\subsection{Timing Routines}
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\label{subsec:get_wtime}
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The \scode{omp_get_wtime} routine can be used to measure the elapsed wall
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clock time (in seconds) of code execution in a program.
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The routine is thread safe and can be executed by multiple threads concurrently.
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The precision of the timer can be obtained by a call to
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the \scode{omp_get_wtick} routine. The following example shows a use case.
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\cexample{get_wtime}{1}
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\ffreeexample{get_wtime}{1}
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%---------------------------
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\subsection{Environment Display}
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\label{subsec:display_env}
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The OpenMP version number and the values of ICVs associated with the relevant
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environment variables can be displayed at runtime by setting
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the \scode{OMP_DISPLAY_ENV} environment variable to either
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\code{TRUE} or \code{VERBOSE}.
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The information is displayed once by the runtime.
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A more flexible or controllable approach is to call
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the \scode{omp_display_env} API routine at any desired
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point of a code to display the same information.
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This OpenMP 5.1 API routine takes a single \plc{verbose} argument.
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A value of 0 or .false. (for C/C++ or Fortran) indicates
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the required OpenMP ICVs associated with environment variables be displayed,
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and a value of 1 or .true. (for C/C++ or Fortran) will include
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vendor-specific ICVs that can be modified by environment variables.
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The following example illustrates the conditional execution of the API
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\scode{omp_display_env} routine. Typically it would be invoked in
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various debug modes of an application.
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An important use case is to have a single MPI process (e.g., rank = 0)
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of a hybrid (MPI+OpenMP) code execute the routine,
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instead of all MPI processes, as would be done by
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setting the \scode{OMP_DISPLAY_ENV} to \code{TRUE} or \code{VERBOSE}.
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\cexample[5.1]{display_env}{1}
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\ffreeexample[5.1]{display_env}{1}
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\clearpage
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\emph{Note}:
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A sample output from the execution of the code might look like:
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{\small\begin{verbatim}
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OPENMP DISPLAY ENVIRONMENT BEGIN
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_OPENMP='202011'
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[host] OMP_AFFINITY_FORMAT='(null)'
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[host] OMP_ALLOCATOR='omp_default_mem_alloc'
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[host] OMP_CANCELLATION='FALSE'
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[host] OMP_DEFAULT_DEVICE='0'
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[host] OMP_DISPLAY_AFFINITY='FALSE'
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[host] OMP_DISPLAY_ENV='FALSE'
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[host] OMP_DYNAMIC='FALSE'
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[host] OMP_MAX_ACTIVE_LEVELS='1'
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[host] OMP_MAX_TASK_PRIORITY='0'
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[host] OMP_NESTED: deprecated; max-active-levels-var=1
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[host] OMP_NUM_THREADS: value is not defined
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[host] OMP_PLACES: value is not defined
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[host] OMP_PROC_BIND: value is not defined
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[host] OMP_SCHEDULE='static'
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[host] OMP_STACKSIZE='4M'
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[host] OMP_TARGET_OFFLOAD=DEFAULT
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[host] OMP_THREAD_LIMIT='0'
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[host] OMP_TOOL='enabled'
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[host] OMP_TOOL_LIBRARIES: value is not defined
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OPENMP DISPLAY ENVIRONMENT END
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\end{verbatim}}
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%---------------------------
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\subsection{\code{error} Directive}
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\label{subsec:error}
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The \code{error} directive provides a consistent method for C, C++, and Fortran to emit a \plc{fatal} or
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\plc{warning} message at \plc{compilation} or \plc{execution} time, as determined by a \code{severity}
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or an \code{at} clause, respectively. When \code{severity(fatal)} is present, the compilation
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or execution is aborted. Without any clauses the default behavior is as if \code{at(compilation)}
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and \code{severity(fatal)} were specified.
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The C, C++, and Fortran examples below show all the cases for reporting messages.
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\cexample[5.1]{error}{1}
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\ffreeexample[5.1]{error}{1}
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