\section{\kcode{omp_pause_resource} and \\

\kcode{omp_pause_resource_all} Routines}

\label{sec:pause_resource}

\index{routines!omp_pause_resource@\kcode{omp_pause_resource}}

\index{omp_pause_resource routine@\kcode{omp_pause_resource} routine}

\index{routines!omp_get_max_threads@\kcode{omp_get_max_threads}}

\index{omp_get_max_threads routine@\kcode{omp_get_max_threadsi} routine}

\index{routines!omp_get_initial_device@\kcode{omp_get_initial_device}}

\index{omp_get_initial_device routine@\kcode{omp_get_initial_device} routine}

Sometimes, it is necessary to relinquish resources created or allocated

for the OpenMP runtime environment to avoid interference with subsequent

actions as illustrated by the following example. In the beginning

either a call to the \kcode{omp_get_max_threads} routine

or the subsequent \kcode{parallel} construct may trigger resource allocation

by the OpenMP runtime, which may cause unexpected side effects

for the subsequent \ucode{fork} call.

It is desirable to relinquish OpenMP resources allocated before

the fork by using the \kcode{omp_pause_resource} routine for a given

device, in this case the host device. The host device number is returned by

the \kcode{omp_get_initial_device} routine.

The \kcode{omp_pause_hard} value is used here to free as many

OpenMP resources as possible.

After the fork, the child process will initialize its OpenMP runtime

environment when encountering the \kcode{parallel} construct.

\cexample[5.0]{pause_resource}{1}

\index{routines!omp_pause_resource_all@\kcode{omp_pause_resource_all}}

\index{omp_pause_resource_all routine@\kcode{omp_pause_resource_all} routine}

The following example illustrates a different use case.

After executing the first parallel code (parallel region 1),

the \ucode{relinquish} program switches to executing an external parallel program

(called \ucode{subprogram}, which is compiled from \example{pause_resource.2b}).

In order to make resources available for the external

subprogram, \ucode{relinquish} calls \kcode{omp_pause_resource_all}

to relinquish OpenMP resources used by the current program before

calling \ucode{execute_command_line} to execute \ucode{subprogram}.

The \kcode{omp_pause_soft} value is used here to allow subsequent

OpenMP regions (parallel region 2) to restart more quickly.

\ffreeexample[5.0]{pause_resource}{2a}

\ffreeexample{pause_resource}{2b}