glib/gthreadpool.c

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/* 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 Lesser 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
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser 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 = (gpointer) &g_thread_pool_new;
/* Here all unused threads are waiting, depending on their priority */
static GAsyncQueue *unused_thread_queue[G_THREAD_PRIORITY_URGENT + 1][2];
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, GError **error);
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;
g_async_queue_lock (pool->queue);
while (TRUE)
{
gpointer task;
gboolean goto_global_pool =
!pool->pool.exclusive && pool->pool.stack_size == 0;
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);
goto_global_pool = TRUE;
}
else if (len >= 0)
/* At this pool there is no thread waiting */
goto_global_pool = FALSE;
if (goto_global_pool)
{
GAsyncQueue *unused_queue =
unused_thread_queue[pool->pool.priority][pool->pool.bound ? 1 : 0];
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);
g_async_queue_unlock (pool->queue);
}
}
else
g_async_queue_unlock (pool->queue);
g_async_queue_lock (unused_queue);
G_LOCK (unused_threads);
if ((unused_threads >= max_unused_threads &&
max_unused_threads != -1) || pool->pool.stack_size != 0)
{
G_UNLOCK (unused_threads);
g_async_queue_unlock (unused_queue);
/* Stop this thread */
return;
}
unused_threads++;
G_UNLOCK (unused_threads);
pool = g_async_queue_pop_unlocked (unused_queue);
G_LOCK (unused_threads);
unused_threads--;
G_UNLOCK (unused_threads);
g_async_queue_unlock (unused_queue);
if (pool == stop_this_thread_marker)
/* Stop this thread */
return;
g_async_queue_lock (pool->queue);
/* 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,
GError **error)
{
gboolean success = FALSE;
GThreadPriority priority = pool->pool.priority;
guint bound = pool->pool.bound ? 1 : 0;
GAsyncQueue *queue = unused_thread_queue[priority][bound];
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);
/* We will not search for threads with other priorities, because changing
* priority is quite unportable */
if (!success)
{
GError *local_error = NULL;
/* No thread was found, we have to start a new one */
g_thread_create (g_thread_pool_thread_proxy, pool,
pool->pool.stack_size, FALSE,
bound, priority, &local_error);
if (local_error)
{
g_propagate_error (error, local_error);
return;
}
}
/* See comment in g_thread_pool_thread_proxy as to why this is done
* here and not there */
pool->num_threads++;
}
/**
* g_thread_pool_new:
* @thread_func: a function to execute in the threads of the new thread pool
* @max_threads: the maximal number of threads to execute concurrently in
* the new thread pool, -1 means no limit
* @stack_size: the stack size for the threads of the new thread pool,
* 0 means using the standard
* @bound: should the threads of the new thread pool be bound?
* @priority: a priority for the threads of the new thread pool
* @exclusive: should this thread pool be exclusive?
* @user_data: user data that is handed over to @thread_func every time it
* is called
* @error: return location for error
*
* This function creates a new thread pool. All threads created within
* this thread pool will have the priority @priority and the stack
* size @stack_size and will be bound if and only if @bound is
* true.
*
* Whenever you call g_thread_pool_push(), either a new thread is
* created or an unused one is reused. At most @max_threads threads
* are running concurrently for this thread pool. @max_threads = -1
* allows unlimited threads to be created for this thread pool. The
* newly created or reused thread now executes the function
* @thread_func with the two arguments. The first one is the parameter
* to g_thread_pool_push() and the second one is @user_data.
*
* The parameter @exclusive determines, whether the thread pool owns
* all threads exclusive or whether the threads are shared
* globally. If @exclusive is @TRUE, @max_threads threads are started
* immediately and they will run exclusively for this thread pool until
* it is destroyed by g_thread_pool_free(). If @exclusive is @FALSE,
* threads are created, when needed and shared between all
* non-exclusive thread pools. This implies that @max_threads may not
* be -1 for exclusive thread pools.
*
* Note, that only threads from a thread pool with a @stack_size of 0
* (which means using the standard stack size) will be globally
* reused. Threads from a thread pool with a non-zero stack size will
* stay only in this thread pool until it is freed and can thus not be
* controlled by the g_thread_pool_set_unused_threads() function.
*
* @error can be NULL to ignore errors, or non-NULL to report
* errors. An error can only occur, when @exclusive is set to @TRUE and
* not all @max_threads threads could be created.
*
* Return value: the new #GThreadPool
**/
GThreadPool*
g_thread_pool_new (GFunc thread_func,
gint max_threads,
gulong stack_size,
gboolean bound,
GThreadPriority priority,
gboolean exclusive,
gpointer user_data,
GError **error)
{
GRealThreadPool *retval;
G_LOCK_DEFINE_STATIC (init);
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;
G_LOCK (init);
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][0] = g_async_queue_new ();
unused_thread_queue[priority][1] = g_async_queue_new ();
}
}
G_UNLOCK (init);
if (retval->pool.exclusive)
{
g_async_queue_lock (retval->queue);
while (retval->num_threads < retval->max_threads)
{
GError *local_error = NULL;
g_thread_pool_start_thread (retval, &local_error);
if (local_error)
{
g_propagate_error (error, local_error);
break;
}
}
g_async_queue_unlock (retval->queue);
}
return (GThreadPool*) retval;
}
/**
* g_thread_pool_push:
* @pool: a #GThreadPool
* @data: a new task for @pool
* @error: return location for error
*
* Inserts @data into the list of tasks to be executed by @pool. When
* the number of currently running threads is lower than the maximal
* allowed number of threads, a new thread is started (or reused) with
* the properties given to g_thread_pool_new (). Otherwise @data stays
* in the queue until a thread in this pool finishes its previous task
* and processes @data.
*
* @error can be NULL to ignore errors, or non-NULL to report
* errors. An error can only occur, when a new thread couldn't be
* created. In that case @data is simply appended to the queue of work
* to do.
**/
void
g_thread_pool_push (GThreadPool *pool,
gpointer data,
GError **error)
{
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 (g_async_queue_length_unlocked (real->queue) >= 0)
/* No thread is waiting in the queue */
g_thread_pool_start_thread (real, error);
g_async_queue_push_unlocked (real->queue, data);
g_async_queue_unlock (real->queue);
}
/**
* g_thread_pool_set_max_threads:
* @pool: a #GThreadPool
* @max_threads: a new maximal number of threads for @pool
* @error: return location for error
*
* Sets the maximal allowed number of threads for @pool. A value of -1
* means, that the maximal number of threads is unlimited.
*
* Setting @max_threads to 0 means stopping all work for @pool. It is
* effectively frozen until @max_threads is set to a non-zero value
* again.
*
* A thread is never terminated while calling @thread_func, as
* supplied by g_thread_pool_new (). Instead the maximal number of
* threads only has effect for the allocation of new threads in
* g_thread_pool_push (). A new thread is allocated, whenever the
* number of currently running threads in @pool is smaller than the
* maximal number.
*
* @error can be NULL to ignore errors, or non-NULL to report
* errors. An error can only occur, when a new thread couldn't be
* created.
**/
void
g_thread_pool_set_max_threads (GThreadPool *pool,
gint max_threads,
GError **error)
{
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--)
{
GError *local_error = NULL;
g_thread_pool_start_thread (real, &local_error);
if (local_error)
{
g_propagate_error (error, local_error);
break;
}
}
g_async_queue_unlock (real->queue);
}
/**
* g_thread_pool_get_max_threads:
* @pool: a #GThreadPool
*
* Returns the maximal number of threads for @pool.
*
* Return value: the maximal number of threads
**/
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;
}
/**
* g_thread_pool_get_num_threads:
* @pool: a #GThreadPool
*
* Returns the number of threads currently running in @pool.
*
* Return value: the number of threads currently running
**/
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;
}
/**
* g_thread_pool_unprocessed:
* @pool: a #GThreadPool
*
* Returns the number of tasks still unprocessed in @pool.
*
* Return value: the number of unprocessed tasks
**/
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);
}
/**
* g_thread_pool_free:
* @pool: a #GThreadPool
* @immediate: should @pool shut down immediately?
* @wait: should the function wait for all tasks to be finished?
*
* Frees all resources allocated for @pool.
*
* If @immediate is #TRUE, no new task is processed for
* @pool. Otherwise @pool is not freed before the last task is
* processed. Note however, that no thread of this pool is
* interrupted, while processing a task. Instead at least all still
* running threads can finish their tasks before the @pool is freed.
*
* If @wait is #TRUE, the functions does not return before all tasks
* to be processed (dependent on @immediate, whether all or only the
* currently running) are ready. Otherwise the function returns immediately.
*
* After calling this function @pool must not be used anymore.
**/
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 immediately, 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));
}
/**
* g_thread_pool_set_max_unused_threads:
* @max_threads: maximal number of unused threads
*
* Sets the maximal number of unused threads to @max_threads. If
* @max_threads is -1, no limit is imposed on the number of unused
* threads.
**/
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;
while (close_down_num > 0)
{
GThreadPriority priority;
guint bound;
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++)
{
for (bound = 0; bound < 2; bound++)
{
GAsyncQueue *queue = unused_thread_queue[priority][bound];
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);
}
/**
* g_thread_pool_get_max_unused_threads:
*
* Returns the maximal allowed number of unused threads.
*
* Return value: the maximal number of 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;
}
/**
* g_thread_pool_get_num_unused_threads:
*
* Returns the number of currently unused threads.
*
* Return value: the number of currently unused threads
**/
guint g_thread_pool_get_num_unused_threads (void)
{
guint retval;
G_LOCK (unused_threads);
retval = unused_threads;
G_UNLOCK (unused_threads);
return retval;
}
/**
* g_thread_pool_stop_unused_threads:
*
* Stops all currently unused threads. This does not change the
* maximal number of unused threads. This function can be used to
* regularly stop all unused threads e.g. from g_timeout_add().
**/
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);
}