libgomp/doc/openmp-environment-variables/gomprtemsthreadpools.rst

   1 ..
   2   Copyright 1988-2022 Free Software Foundation, Inc.
   3   This is part of the GCC manual.
   4   For copying conditions, see the copyright.rst file.
   5
   6 .. index:: Environment Variable, Implementation specific setting
   7
   8 .. _gomp_rtems_thread_pools:
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  10 GOMP_RTEMS_THREAD_POOLS -- Set the RTEMS specific thread pools
  11 **************************************************************
  12
  13 Description:
  14   This environment variable is only used on the RTEMS real-time operating system.
  15   It determines the scheduler instance specific thread pools.  The format for
  16   :envvar:`GOMP_RTEMS_THREAD_POOLS` is a list of optional
  17   ``<thread-pool-count>[$<priority>]@<scheduler-name>`` configurations
  18   separated by ``:`` where:
  19
  20   * ``<thread-pool-count>`` is the thread pool count for this scheduler
  21     instance.
  22
  23   * ``$<priority>`` is an optional priority for the worker threads of a
  24     thread pool according to ``pthread_setschedparam``.  In case a priority
  25     value is omitted, then a worker thread will inherit the priority of the OpenMP
  26     primary thread that created it.  The priority of the worker thread is not
  27     changed after creation, even if a new OpenMP primary thread using the worker has
  28     a different priority.
  29
  30   * ``@<scheduler-name>`` is the scheduler instance name according to the
  31     RTEMS application configuration.
  32
  33   In case no thread pool configuration is specified for a scheduler instance,
  34   then each OpenMP primary thread of this scheduler instance will use its own
  35   dynamically allocated thread pool.  To limit the worker thread count of the
  36   thread pools, each OpenMP primary thread must call ``omp_set_num_threads``.
  37
  38 Example:
  39   Lets suppose we have three scheduler instances ``IO``, ``WRK0``, and
  40   ``WRK1`` with :envvar:`GOMP_RTEMS_THREAD_POOLS` set to
  41   ``"1@WRK0:3$4@WRK1"``.  Then there are no thread pool restrictions for
  42   scheduler instance ``IO``.  In the scheduler instance ``WRK0`` there is
  43   one thread pool available.  Since no priority is specified for this scheduler
  44   instance, the worker thread inherits the priority of the OpenMP primary thread
  45   that created it.  In the scheduler instance ``WRK1`` there are three thread
  46   pools available and their worker threads run at priority four.