ESMF_GridCompSetVMMaxThreads Subroutine

  subroutine ESMF_GridCompSetVMMaxThreads(gridcomp, keywordEnforcer, &
    maxPetCountPerVas, prefIntraProcess, prefIntraSsi, prefInterSsi, &
    pthreadMinStackSize, forceChildPthreads, rc)
!
! !ARGUMENTS:
    type(ESMF_GridComp), intent(inout)         :: gridcomp
type(ESMF_KeywordEnforcer), optional:: keywordEnforcer ! must use keywords below
    integer,             intent(in),  optional :: maxPetCountPerVas
    integer,             intent(in),  optional :: prefIntraProcess
    integer,             intent(in),  optional :: prefIntraSsi
    integer,             intent(in),  optional :: prefInterSsi
    integer,             intent(in),  optional :: pthreadMinStackSize
    logical,             intent(in),  optional :: forceChildPthreads
    integer,             intent(out), optional :: rc
!
! !DESCRIPTION:
!   Set characteristics of the {\tt ESMF\_VM} for this {\tt ESMF\_GridComp}.
!   Attempts to provide {\tt maxPetCountPerVas} threaded PETs in each
!   virtual address space (VAS). Only as many threaded PETs as there are PEs
!   located on the single system image (SSI) can be associated with the VAS.
!   Within this constraint the call tries to get as close as possible to the
!   number specified by {\tt maxPetCountPerVas}.
!
!   The other constraint to this call is that the number of PETs is preserved.
!   This means that the child Component in the end is associated with as many
!   PETs as the parent Component provided to the child. The threading level of
!   the child PETs however is adjusted according to the above rule.
!
!   The typical use of {\tt ESMF\_GridCompSetVMMaxThreads()} is to run a
!   Component multi-threaded with groups of PETs executing within a common
!   virtual address space.
!
! The arguments are:
! \begin{description}
! \item[gridcomp]
!   {\tt ESMF\_GridComp} to set the {\tt ESMF\_VM} for.
! \item[{[maxPetCountPerVas]}]
!   Maximum number of threaded PETs in each virtual address space (VAS).
!   Default for each SSI is the local number of PEs.
! \item[{[prefIntraProcess]}]
!   Communication preference within a single process.
!   {\em Currently options not documented. Use default.}
! \item[{[prefIntraSsi]}]
!   Communication preference within a single system image (SSI).
!   {\em Currently options not documented. Use default.}
! \item[{[prefInterSsi]}]
!   Communication preference between different single system images (SSIs).
!   {\em Currently options not documented. Use default.}
! \item[{[pthreadMinStackSize]}]
!   Minimum stack size in byte of any child PET executing as Pthread. By default
!   single threaded child PETs do {\em not} execute as Pthread, and their stack
!   size is unaffected by this argument. However, for multi-threaded child PETs,
!   or if {\tt forceChildPthreads} is {\tt .true.}, child PETs execute
!   as Pthreads with their own private stack.
!
!   For cases where OpenMP threads
!   are used by the user code, each thread allocates its own private stack. For
!   all threads {\em other} than the master, the stack size is set via the 
!   typical {\tt OMP\_STACKSIZE} environment variable mechanism. The PET itself,
!   however, becomes the {\em master} of the OpenMP thread team, and is not
!   affected by {\tt OMP\_STACKSIZE}. It is the master's stack that can be
!   sized via the {\tt pthreadMinStackSize} argument, and a large enough size
!   is often critical.
!
!   When {\tt pthreadMinStackSize}
!   is absent, the default is to use the system default
!   set by the {\tt limit} or {\tt ulimit} command. However, the stack of a
!   Pthread cannot be unlimited, and a shell {\em stacksize} setting of
!   {\em unlimited}, or any setting below the ESMF implemented minimum,
!   will result in setting the stack size to 20MiB (the ESMF minimum).
!   Depending on how much private data is used by the user code under
!   the master thread, the default might be too small, and
!   {\tt pthreadMinStackSize} must be used to allocate sufficient stack space.
! \item[{[forceChildPthreads]}] 
!   For {\tt .true.}, force each child PET to execute in its own Pthread.
!   By default, {\tt .false.}, single PETs spawned from a parent PET
!   execute in the same thread (or MPI process) as the parent PET. Multiple
!   child PETs spawned by the same parent PET always execute as their own
!   Pthreads.
! \item[{[rc]}]
!   Return code; equals {\tt ESMF\_SUCCESS} if there are no errors.
! \end{description}
!
!EOP
!------------------------------------------------------------------------------
    integer :: localrc                     ! local error status

    ! initialize return code; assume routine not implemented
    if (present(rc)) rc = ESMF_RC_NOT_IMPL
    localrc = ESMF_RC_NOT_IMPL

    ESMF_INIT_CHECK_DEEP(ESMF_GridCompGetInit,gridcomp,rc)

    ! call Comp method
    call ESMF_CompSetVMMaxThreads(gridcomp%compp, maxPetCountPerVas, &
      prefIntraProcess, prefIntraSsi, prefInterSsi, pthreadMinStackSize, &
      forceChildPthreads, rc=localrc)
    if (ESMF_LogFoundError(localrc, &
      ESMF_ERR_PASSTHRU, &
      ESMF_CONTEXT, rcToReturn=rc)) return

    ! return successfully
    if (present(rc)) rc = ESMF_SUCCESS
  end subroutine ESMF_GridCompSetVMMaxThreads