task.c

Go to the documentation of this file.

/* Copyright (C) 2007, 2008, 2009 Free Software Foundation, Inc.
   Contributed by Richard Henderson <rth@redhat.com>.

   This file is part of the GNU OpenMP Library (libgomp).

   Libgomp is free software; you can redistribute it and/or modify it
   under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3, or (at your option)
   any later version.

   Libgomp is distributed in the hope that it will be useful, but WITHOUT ANY
   WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
   FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
   more details.

   Under Section 7 of GPL version 3, you are granted additional
   permissions described in the GCC Runtime Library Exception, version
   3.1, as published by the Free Software Foundation.

   You should have received a copy of the GNU General Public License and
   a copy of the GCC Runtime Library Exception along with this program;
   see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
   <http://www.gnu.org/licenses/>.  */

/* This file handles the maintainence of tasks in response to task
   creation and termination.  */

#include "libgomp.h"
#include <stdlib.h>
#include <string.h>


/* Create a new task data structure.  */

void
gomp_init_task (struct gomp_task *task, struct gomp_task *parent_task,
        struct gomp_task_icv *prev_icv)
{
  task->parent = parent_task;
  task->icv = *prev_icv;
  task->kind = GOMP_TASK_IMPLICIT;
  task->in_taskwait = false;
  task->in_tied_task = false;
  task->children = NULL;
  gomp_sem_init (&task->taskwait_sem, 0);
}

/* Clean up a task, after completing it.  */

void
gomp_end_task (void)
{
  struct gomp_thread *thr = gomp_thread ();
  struct gomp_task *task = thr->task;

  gomp_finish_task (task);
  thr->task = task->parent;
}

static inline void
gomp_clear_parent (struct gomp_task *children)
{
  struct gomp_task *task = children;

  if (task)
    do
      {
    task->parent = NULL;
    task = task->next_child;
      }
    while (task != children);
}

/* Called when encountering an explicit task directive.  If IF_CLAUSE is
   false, then we must not delay in executing the task.  If UNTIED is true,
   then the task may be executed by any member of the team.  */

void
GOMP_task (void (*fn) (void *), void *data, void (*cpyfn) (void *, void *),
       long arg_size, long arg_align, bool if_clause,
       unsigned flags __attribute__((unused)))
{
  struct gomp_thread *thr = gomp_thread ();
  struct gomp_team *team = thr->ts.team;

#ifdef HAVE_BROKEN_POSIX_SEMAPHORES
  /* If pthread_mutex_* is used for omp_*lock*, then each task must be
     tied to one thread all the time.  This means UNTIED tasks must be
     tied and if CPYFN is non-NULL IF(0) must be forced, as CPYFN
     might be running on different thread than FN.  */
  if (cpyfn)
    if_clause = false;
  if (flags & 1)
    flags &= ~1;
#endif

  if (!if_clause || team == NULL
      || team->task_count > 64 * team->nthreads)
    {
      struct gomp_task task;

      gomp_init_task (&task, thr->task, gomp_icv (false));
      task.kind = GOMP_TASK_IFFALSE;
      if (thr->task)
    task.in_tied_task = thr->task->in_tied_task;
      thr->task = &task;
      if (__builtin_expect (cpyfn != NULL, 0))
    {
      char buf[arg_size + arg_align - 1];
      char *arg = (char *) (((uintptr_t) buf + arg_align - 1)
                & ~(uintptr_t) (arg_align - 1));
      cpyfn (arg, data);
      fn (arg);
    }
      else
    fn (data);
      if (task.children)
    {
      gomp_mutex_lock (&team->task_lock);
      gomp_clear_parent (task.children);
      gomp_mutex_unlock (&team->task_lock);
    }
      gomp_end_task ();
    }
  else
    {
      struct gomp_task *task;
      struct gomp_task *parent = thr->task;
      char *arg;
      bool do_wake;

      task = gomp_malloc (sizeof (*task) + arg_size + arg_align - 1);
      arg = (char *) (((uintptr_t) (task + 1) + arg_align - 1)
              & ~(uintptr_t) (arg_align - 1));
      gomp_init_task (task, parent, gomp_icv (false));
      task->kind = GOMP_TASK_IFFALSE;
      task->in_tied_task = parent->in_tied_task;
      thr->task = task;
      if (cpyfn)
    cpyfn (arg, data);
      else
    memcpy (arg, data, arg_size);
      thr->task = parent;
      task->kind = GOMP_TASK_WAITING;
      task->fn = fn;
      task->fn_data = arg;
      task->in_tied_task = true;
      gomp_mutex_lock (&team->task_lock);
      if (parent->children)
    {
      task->next_child = parent->children;
      task->prev_child = parent->children->prev_child;
      task->next_child->prev_child = task;
      task->prev_child->next_child = task;
    }
      else
    {
      task->next_child = task;
      task->prev_child = task;
    }
      parent->children = task;
      if (team->task_queue)
    {
      task->next_queue = team->task_queue;
      task->prev_queue = team->task_queue->prev_queue;
      task->next_queue->prev_queue = task;
      task->prev_queue->next_queue = task;
    }
      else
    {
      task->next_queue = task;
      task->prev_queue = task;
      team->task_queue = task;
    }
      ++team->task_count;
      gomp_team_barrier_set_task_pending (&team->barrier);
      do_wake = team->task_running_count + !parent->in_tied_task
        < team->nthreads;
      gomp_mutex_unlock (&team->task_lock);
      if (do_wake)
    gomp_team_barrier_wake (&team->barrier, 1);
    }
}

void
gomp_barrier_handle_tasks (gomp_barrier_state_t state)
{
  struct gomp_thread *thr = gomp_thread ();
  struct gomp_team *team = thr->ts.team;
  struct gomp_task *task = thr->task;
  struct gomp_task *child_task = NULL;
  struct gomp_task *to_free = NULL;

  gomp_mutex_lock (&team->task_lock);
  if (gomp_barrier_last_thread (state))
    {
      if (team->task_count == 0)
    {
      gomp_team_barrier_done (&team->barrier, state);
      gomp_mutex_unlock (&team->task_lock);
      gomp_team_barrier_wake (&team->barrier, 0);
      return;
    }
      gomp_team_barrier_set_waiting_for_tasks (&team->barrier);
    }

  while (1)
    {
      if (team->task_queue != NULL)
    {
      struct gomp_task *parent;

      child_task = team->task_queue;
      parent = child_task->parent;
      if (parent && parent->children == child_task)
        parent->children = child_task->next_child;
      child_task->prev_queue->next_queue = child_task->next_queue;
      child_task->next_queue->prev_queue = child_task->prev_queue;
      if (child_task->next_queue != child_task)
        team->task_queue = child_task->next_queue;
      else
        team->task_queue = NULL;
      child_task->kind = GOMP_TASK_TIED;
      team->task_running_count++;
      if (team->task_count == team->task_running_count)
        gomp_team_barrier_clear_task_pending (&team->barrier);
    }
      gomp_mutex_unlock (&team->task_lock);
      if (to_free)
    {
      gomp_finish_task (to_free);
      free (to_free);
      to_free = NULL;
    }
      if (child_task)
    {
      thr->task = child_task;
      child_task->fn (child_task->fn_data);
      thr->task = task;
    }
      else
    return;
      gomp_mutex_lock (&team->task_lock);
      if (child_task)
    {
      struct gomp_task *parent = child_task->parent;
      if (parent)
        {
          child_task->prev_child->next_child = child_task->next_child;
          child_task->next_child->prev_child = child_task->prev_child;
          if (parent->children == child_task)
        {
          if (child_task->next_child != child_task)
            parent->children = child_task->next_child;
          else
            {
              parent->children = NULL;
              if (parent->in_taskwait)
            gomp_sem_post (&parent->taskwait_sem);
            }
        }
        }
      gomp_clear_parent (child_task->children);
      to_free = child_task;
      child_task = NULL;
      team->task_running_count--;
      if (--team->task_count == 0
          && gomp_team_barrier_waiting_for_tasks (&team->barrier))
        {
          gomp_team_barrier_done (&team->barrier, state);
          gomp_mutex_unlock (&team->task_lock);
          gomp_team_barrier_wake (&team->barrier, 0);
        }
    }
    }
}

/* Called when encountering a taskwait directive.  */

void
GOMP_taskwait (void)
{
  struct gomp_thread *thr = gomp_thread ();
  struct gomp_team *team = thr->ts.team;
  struct gomp_task *task = thr->task;
  struct gomp_task *child_task = NULL;
  struct gomp_task *to_free = NULL;

  if (task == NULL || task->children == NULL)
    return;
  gomp_mutex_lock (&team->task_lock);
  while (1)
    {
      if (task->children == NULL)
    {
      gomp_mutex_unlock (&team->task_lock);
      if (to_free)
        {
          gomp_finish_task (to_free);
          free (to_free);
        }
      return;
    }
      if (task->children->kind == GOMP_TASK_WAITING)
    {
      child_task = task->children;
      task->children = child_task->next_child;
      child_task->prev_queue->next_queue = child_task->next_queue;
      child_task->next_queue->prev_queue = child_task->prev_queue;
      if (team->task_queue == child_task)
        {
          if (child_task->next_queue != child_task)
        team->task_queue = child_task->next_queue;
          else
        team->task_queue = NULL;
        }
      child_task->kind = GOMP_TASK_TIED;
      team->task_running_count++;
      if (team->task_count == team->task_running_count)
        gomp_team_barrier_clear_task_pending (&team->barrier);
    }
      else
    /* All tasks we are waiting for are already running
       in other threads.  Wait for them.  */
    task->in_taskwait = true;
      gomp_mutex_unlock (&team->task_lock);
      if (to_free)
    {
      gomp_finish_task (to_free);
      free (to_free);
      to_free = NULL;
    }
      if (child_task)
    {
      thr->task = child_task;
      child_task->fn (child_task->fn_data);
      thr->task = task;
    }
      else
    {
      gomp_sem_wait (&task->taskwait_sem);
      task->in_taskwait = false;
      return;
    }
      gomp_mutex_lock (&team->task_lock);
      if (child_task)
    {
      child_task->prev_child->next_child = child_task->next_child;
      child_task->next_child->prev_child = child_task->prev_child;
      if (task->children == child_task)
        {
          if (child_task->next_child != child_task)
        task->children = child_task->next_child;
          else
        task->children = NULL;
        }
      gomp_clear_parent (child_task->children);
      to_free = child_task;
      child_task = NULL;
      team->task_count--;
      team->task_running_count--;
    }
    }
}

---