glib/gthreadpool.c

/* GLIB - Library of useful routines for C programming
 * Copyright (C) 1995-1997  Peter Mattis, Spencer Kimball and Josh MacDonald
 *
 * GAsyncQueue: thread pool implementation.
 * Copyright (C) 2000 Sebastian Wilhelmi; University of Karlsruhe
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library 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
 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public
 * License along with this library; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, USA.
 */

/*
 * MT safe
 */

#include "glib.h"

typedef struct _GRealThreadPool GRealThreadPool;

struct _GRealThreadPool
{
  GThreadPool pool;
  GAsyncQueue* queue;
  gint max_threads;
  gint num_threads;
  gboolean running;
  gboolean immediate;
  gboolean waiting;
};

/* The following is just an address to mark the stop order for a
 * thread, it could be any address (as long, as it isn;t a valid
 * GThreadPool address) */
static const gpointer stop_this_thread_marker = &g_thread_pool_new;

/* Here all unused threads are waiting, depending on their priority */
static GAsyncQueue *unused_thread_queue[G_THREAD_PRIORITY_URGENT + 1];
static gint unused_threads = 0;
static gint max_unused_threads = 0;
G_LOCK_DEFINE_STATIC (unused_threads);

static GMutex *inform_mutex = NULL;
static GCond *inform_cond = NULL;

static void g_thread_pool_free_internal (GRealThreadPool* pool);
static void g_thread_pool_thread_proxy (gpointer data);
static void g_thread_pool_start_thread (GRealThreadPool* pool);
static void g_thread_pool_wakeup_and_stop_all (GRealThreadPool* pool);

#define g_thread_should_run(pool, len) \
  ((pool)->running || (!(pool)->immediate && (len) > 0))

static void 
g_thread_pool_thread_proxy (gpointer data)
{
  GRealThreadPool *pool = data;
  GThread* self = g_thread_self ();

  g_async_queue_lock (pool->queue);
  while (TRUE)
    {
      gpointer task; 
      gboolean goto_global_pool = !pool->pool.exclusive;
      gint len = g_async_queue_length_unlocked (pool->queue);
      
      if (g_thread_should_run (pool, len))
	{
	  task = g_async_queue_pop_unlocked (pool->queue);

	  if (pool->num_threads > pool->max_threads && pool->max_threads != -1)
	    /* We are in fact a superfluous threads, so we go to the
	     * global pool and just hand the data further to the next one
	     * waiting in the queue */
	    {
	      g_async_queue_push_unlocked (pool->queue, task);
	      goto_global_pool = TRUE;
	    }
	  else if (pool->running || !pool->immediate)
	    {
	      g_async_queue_unlock (pool->queue);
	      pool->pool.thread_func (task, pool->pool.user_data);
	      g_async_queue_lock (pool->queue);
	    }

	  len = g_async_queue_length_unlocked (pool->queue);
	}

      if (!g_thread_should_run (pool, len))
	g_cond_broadcast (inform_cond);
      
      if (!pool->running && (pool->immediate || len <= 0))
	goto_global_pool = TRUE;
      else if (len >= 0)
	/* At this pool there is no thread waiting */
	goto_global_pool = FALSE; 
      
      if (goto_global_pool)
	{
	  GThreadPriority priority = pool->pool.priority;
	  pool->num_threads--; 

	  if (!pool->running && !pool->waiting)
	    {
	      if (pool->num_threads == 0)
		{
		  g_async_queue_unlock (pool->queue);
		  g_thread_pool_free_internal (pool);
		}		
	      else if (len == - pool->num_threads)
		g_thread_pool_wakeup_and_stop_all (pool);
	    }
	  else
	    g_async_queue_unlock (pool->queue);
	  
	  g_async_queue_lock (unused_thread_queue[priority]);

	  G_LOCK (unused_threads);
	  if (unused_threads >= max_unused_threads)
	    {
	      G_UNLOCK (unused_threads);
	      g_async_queue_unlock (unused_thread_queue[priority]);
	      /* Stop this thread */
	      return;      
	    }
	  unused_threads++;
	  G_UNLOCK (unused_threads);

	  pool = 
	    g_async_queue_pop_unlocked (unused_thread_queue[priority]);

	  G_LOCK (unused_threads);
	  unused_threads--;
	  G_UNLOCK (unused_threads);

	  g_async_queue_unlock (unused_thread_queue[priority]);
	  
	  if (pool == stop_this_thread_marker)
	    /* Stop this thread */
	    return;
	  
	  g_async_queue_lock (pool->queue);

	  if (pool->pool.priority != self->priority)
	    g_thread_set_priority (self, pool->pool.priority);

	  /* pool->num_threads++ is not done here, but in
           * g_thread_pool_start_thread to make the new started thread
           * known to the pool, before itself can do it. */
	}
    }
}

static void
g_thread_pool_start_thread (GRealThreadPool* pool)
{
  gboolean success = FALSE;
  GThreadPriority priority = pool->pool.priority;
  GAsyncQueue *queue = unused_thread_queue[priority];
  
  if (pool->num_threads >= pool->max_threads && pool->max_threads != -1)
    /* Enough threads are already running */
    return;

  g_async_queue_lock (queue);

  if (g_async_queue_length_unlocked (queue) < 0)
    {
      /* First we try a thread with the right priority */
      g_async_queue_push_unlocked (queue, pool);
      success = TRUE;
    }

  g_async_queue_unlock (queue);

  if (!success)
    {
      /* Now we search for threads with other priorities too, but
       * only, when there is more than one unused thread with that
       * priority. */
      GThreadPriority priority;
      for (priority = G_THREAD_PRIORITY_LOW; 
	   priority < G_THREAD_PRIORITY_URGENT + 1; priority++)
	{
	  queue = unused_thread_queue[priority];
	  g_async_queue_lock (queue);
	  
	  if (g_async_queue_length_unlocked (queue) < -1)
	    {
	      g_async_queue_push_unlocked (queue, pool);
	      success = TRUE;
	    }
	  
	  g_async_queue_unlock (queue);
	}      
    }

  if (!success)
    /* No thread was found, we have to start one new */
    g_thread_create (g_thread_pool_thread_proxy, pool, pool->pool.stack_size, 
		     FALSE, pool->pool.bound, priority);

  /* See comment in g_thread_pool_thread_proxy as to why this is done
   * here and not there */
  pool->num_threads++;
}

GThreadPool* 
g_thread_pool_new (GFunc            thread_func,
		   gint             max_threads,
		   gulong           stack_size,
		   gboolean         bound,
		   GThreadPriority  priority,
		   gboolean         exclusive,
		   gpointer         user_data)
{
  GRealThreadPool *retval;

  g_return_val_if_fail (thread_func, NULL);
  g_return_val_if_fail (!exclusive || max_threads != -1, NULL);
  g_return_val_if_fail (max_threads >= -1, NULL);
  g_return_val_if_fail (g_thread_supported (), NULL);

  retval = g_new (GRealThreadPool, 1);

  retval->pool.thread_func = thread_func;
  retval->pool.stack_size = stack_size;
  retval->pool.bound = bound;
  retval->pool.priority = priority;
  retval->pool.exclusive = exclusive;
  retval->pool.user_data = user_data;

  retval->queue = g_async_queue_new ();
  retval->max_threads = max_threads;
  retval->num_threads = 0;
  retval->running = TRUE;

  if (!inform_mutex)
    {
      inform_mutex = g_mutex_new ();
      inform_cond = g_cond_new ();
      for (priority = G_THREAD_PRIORITY_LOW; 
	   priority < G_THREAD_PRIORITY_URGENT + 1; priority++)
	unused_thread_queue[priority] = g_async_queue_new ();
    }

  if (retval->pool.exclusive)
    {
      g_async_queue_lock (retval->queue);

      while (retval->num_threads < retval->max_threads)
	g_thread_pool_start_thread (retval);

      g_async_queue_unlock (retval->queue);
    }

  return (GThreadPool*) retval;
}

void 
g_thread_pool_push (GThreadPool     *pool,
		    gpointer         data)
{
  GRealThreadPool *real = (GRealThreadPool*) pool;

  g_return_if_fail (real);

  g_async_queue_lock (real->queue);
  
  if (!real->running)
    {
      g_async_queue_unlock (real->queue);
      g_return_if_fail (real->running);
    }

  if (!pool->exclusive && g_async_queue_length_unlocked (real->queue) >= 0)
    {
      /* No thread is waiting in the queue */
      g_thread_pool_start_thread (real);
    }
  g_async_queue_push_unlocked (real->queue, data);
  g_async_queue_unlock (real->queue);
}

void
g_thread_pool_set_max_threads (GThreadPool     *pool,
			       gint             max_threads)
{
  GRealThreadPool *real = (GRealThreadPool*) pool;
  gint to_start;

  g_return_if_fail (real);
  g_return_if_fail (real->running);
  g_return_if_fail (!real->pool.exclusive || max_threads != -1);
  g_return_if_fail (max_threads >= -1);

  g_async_queue_lock (real->queue);

  real->max_threads = max_threads;
  
  if (pool->exclusive)
    to_start = real->max_threads - real->num_threads;
  else
    to_start = g_async_queue_length_unlocked (real->queue);
  
  for ( ; to_start > 0; to_start--)
    g_thread_pool_start_thread (real);
    
  g_async_queue_unlock (real->queue);
}

gint
g_thread_pool_get_max_threads (GThreadPool     *pool)
{
  GRealThreadPool *real = (GRealThreadPool*) pool;
  gint retval;

  g_return_val_if_fail (real, 0);
  g_return_val_if_fail (real->running, 0);

  g_async_queue_lock (real->queue);

  retval = real->max_threads;
    
  g_async_queue_unlock (real->queue);

  return retval;
}

guint
g_thread_pool_get_num_threads (GThreadPool     *pool)
{
  GRealThreadPool *real = (GRealThreadPool*) pool;
  guint retval;

  g_return_val_if_fail (real, 0);
  g_return_val_if_fail (real->running, 0);

  g_async_queue_lock (real->queue);

  retval = real->num_threads;
    
  g_async_queue_unlock (real->queue);

  return retval;
}

guint
g_thread_pool_unprocessed (GThreadPool     *pool)
{
  GRealThreadPool *real = (GRealThreadPool*) pool;
  gint unprocessed;

  g_return_val_if_fail (real, 0);
  g_return_val_if_fail (real->running, 0);

  unprocessed = g_async_queue_length (real->queue);

  return MAX (unprocessed, 0);
}

void
g_thread_pool_free (GThreadPool     *pool,
		    gboolean         immediate,
		    gboolean         wait)
{
  GRealThreadPool *real = (GRealThreadPool*) pool;

  g_return_if_fail (real);
  g_return_if_fail (real->running);
  /* It there's no thread allowed here, there is not much sense in
   * not stopping this pool immediatly, when it's not empty */
  g_return_if_fail (immediate || real->max_threads != 0 || 
		    g_async_queue_length (real->queue) == 0);

  g_async_queue_lock (real->queue);

  real->running = FALSE;
  real->immediate = immediate;
  real->waiting = wait;

  if (wait)
    {
      g_mutex_lock (inform_mutex);
      while (g_async_queue_length_unlocked (real->queue) != -real->num_threads)
	{
	  g_async_queue_unlock (real->queue); 
	  g_cond_wait (inform_cond, inform_mutex); 
	  g_async_queue_lock (real->queue); 
	}
      g_mutex_unlock (inform_mutex); 
    }

  if (g_async_queue_length_unlocked (real->queue) == -real->num_threads)
    {
      /* No thread is currently doing something (and nothing is left
       * to process in the queue) */
      if (real->num_threads == 0) /* No threads left, we clean up */
	{
	  g_async_queue_unlock (real->queue);
	  g_thread_pool_free_internal (real);
	  return;
	}

      g_thread_pool_wakeup_and_stop_all (real);
    }
  
  real->waiting = FALSE; /* The last thread should cleanup the pool */
  g_async_queue_unlock (real->queue);
}

static void
g_thread_pool_free_internal (GRealThreadPool* pool)
{
  g_return_if_fail (pool);
  g_return_if_fail (!pool->running);
  g_return_if_fail (pool->num_threads == 0);

  g_async_queue_unref (pool->queue);

  g_free (pool);
}

static void
g_thread_pool_wakeup_and_stop_all (GRealThreadPool* pool)
{
  guint i;
  
  g_return_if_fail (pool);
  g_return_if_fail (!pool->running);
  g_return_if_fail (pool->num_threads != 0);
  g_return_if_fail (g_async_queue_length_unlocked (pool->queue) == 
		    -pool->num_threads);

  pool->immediate = TRUE; 
  for (i = 0; i < pool->num_threads; i++)
    g_async_queue_push_unlocked (pool->queue, GUINT_TO_POINTER (1));
}

void
g_thread_pool_set_max_unused_threads (gint max_threads)
{
  g_return_if_fail (max_threads >= -1);  

  G_LOCK (unused_threads);
  
  max_unused_threads = max_threads;

  if (max_unused_threads < unused_threads && max_unused_threads != -1)
    {
      guint close_down_num = unused_threads - max_unused_threads;
      GThreadPriority priority;

      while (close_down_num > 0)
	{
	  guint old_close_down_num = close_down_num;
	  for (priority = G_THREAD_PRIORITY_LOW; 
	       priority < G_THREAD_PRIORITY_URGENT + 1 && close_down_num > 0; 
	       priority++)
	    {
	      GAsyncQueue *queue = unused_thread_queue[priority];
	      g_async_queue_lock (queue);
	      
	      if (g_async_queue_length_unlocked (queue) < 0)
		{
		  g_async_queue_push_unlocked (queue, 
					       stop_this_thread_marker);
		  close_down_num--;
		}
	      
	      g_async_queue_unlock (queue);
	    }

	  /* Just to make sure, there are no counting problems */
	  g_assert (old_close_down_num != close_down_num);
	}
    }
    
  G_UNLOCK (unused_threads);
}

gint
g_thread_pool_get_max_unused_threads (void)
{
  gint retval;
  
  G_LOCK (unused_threads);
  retval = max_unused_threads;
  G_UNLOCK (unused_threads);

  return retval;
}

guint g_thread_pool_get_num_unused_threads (void)
{
  guint retval;
  
  G_LOCK (unused_threads);
  retval = unused_threads;
  G_UNLOCK (unused_threads);

  return retval;
}

void g_thread_pool_stop_unused_threads (void)
{ 
  guint oldval = g_thread_pool_get_max_unused_threads ();
  g_thread_pool_set_max_unused_threads (0);
  g_thread_pool_set_max_unused_threads (oldval);
}