glib/gthreadpool.c

   1 /* GLIB - Library of useful routines for C programming
   2  * Copyright (C) 1995-1997  Peter Mattis, Spencer Kimball and Josh MacDonald
   3  *
   4  * GAsyncQueue: thread pool implementation.
   5  * Copyright (C) 2000 Sebastian Wilhelmi; University of Karlsruhe
   6  *
   7  * This library is free software; you can redistribute it and/or
   8  * modify it under the terms of the GNU Lesser General Public
   9  * License as published by the Free Software Foundation; either
  10  * version 2 of the License, or (at your option) any later version.
  11  *
  12  * This library is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15  * Lesser General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU Lesser General Public
  18  * License along with this library; if not, write to the
  19  * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  20  * Boston, MA 02111-1307, USA.
  21  */
  22
  23 /*
  24  * MT safe
  25  */
  26
  27 #include "glib.h"
  28
  29 typedef struct _GRealThreadPool GRealThreadPool;
  30
  31 struct _GRealThreadPool
  32 {
  33   GThreadPool pool;
  34   GAsyncQueue* queue;
  35   gint max_threads;
  36   gint num_threads;
  37   gboolean running;
  38   gboolean immediate;
  39   gboolean waiting;
  40 };
  41
  42 /* The following is just an address to mark the stop order for a
  43  * thread, it could be any address (as long, as it isn't a valid
  44  * GThreadPool address) */
  45 static const gpointer stop_this_thread_marker = (gpointer) &g_thread_pool_new;
  46
  47 /* Here all unused threads are waiting  */
  48 static GAsyncQueue *unused_thread_queue;
  49 static gint unused_threads = 0;
  50 static gint max_unused_threads = 0;
  51 G_LOCK_DEFINE_STATIC (unused_threads);
  52
  53 static GMutex *inform_mutex = NULL;
  54 static GCond *inform_cond = NULL;
  55
  56 static void     g_thread_pool_free_internal (GRealThreadPool* pool);
  57 static gpointer g_thread_pool_thread_proxy (gpointer data);
  58 static void     g_thread_pool_start_thread (GRealThreadPool* pool,
  59                                             GError **error);
  60 static void     g_thread_pool_wakeup_and_stop_all (GRealThreadPool* pool);
  61
  62 #define g_thread_should_run(pool, len) \
  63   ((pool)->running || (!(pool)->immediate && (len) > 0))
  64
  65 static gpointer
  66 g_thread_pool_thread_proxy (gpointer data)
  67 {
  68   GRealThreadPool *pool = data;
  69   gboolean watcher = FALSE;
  70
  71   g_async_queue_lock (pool->queue);
  72   while (TRUE)
  73     {
  74       gpointer task;
  75       gboolean goto_global_pool = !pool->pool.exclusive;
  76       gint len = g_async_queue_length_unlocked (pool->queue);
  77
  78       if (g_thread_should_run (pool, len))
  79         {
  80           if (watcher)
  81             {
  82               /* This thread is actually not needed here, but it waits
  83                * for some time anyway. If during that time a new
  84                * request arrives, this saves process
  85                * swicthes. Otherwise the thread will go to the global
  86                * pool afterwards */
  87               GTimeVal end_time;
  88               g_get_current_time (&end_time);
  89               g_time_val_add (&end_time, G_USEC_PER_SEC / 2); /* 1/2 second */
  90               task = g_async_queue_timed_pop_unlocked (pool->queue, &end_time);
  91             }
  92           else
  93             task = g_async_queue_pop_unlocked (pool->queue);
  94
  95           if (task)
  96             {
  97               watcher = FALSE;
  98               if (pool->num_threads > pool->max_threads &&
  99                   pool->max_threads != -1)
 100                 /* We are in fact a superfluous threads, so we go to
 101                  * the global pool and just hand the data further to
 102                  * the next one waiting in the queue */
 103                 {
 104                   g_async_queue_push_unlocked (pool->queue, task);
 105                   goto_global_pool = TRUE;
 106                 }
 107               else if (pool->running || !pool->immediate)
 108                 {
 109                   g_async_queue_unlock (pool->queue);
 110                   pool->pool.func (task, pool->pool.user_data);
 111                   g_async_queue_lock (pool->queue);
 112                 }
 113             }
 114           len = g_async_queue_length_unlocked (pool->queue);
 115         }
 116
 117       if (!g_thread_should_run (pool, len))
 118         {
 119           g_cond_broadcast (inform_cond);
 120           goto_global_pool = TRUE;
 121         }
 122       else if (len > 0)
 123         {
 124           /* At this pool there are no threads waiting, but tasks are. */
 125           goto_global_pool = FALSE;
 126         }
 127       else if (len == 0 && !watcher && !pool->pool.exclusive)
 128         {
 129           /* Here neither threads nor tasks are queued and we didn't
 130            * just return from a timed wait. We now wait for a limited
 131            * time at this pool for new tasks to avoid costly context
 132            * switches. */
 133           goto_global_pool = FALSE;
 134           watcher = TRUE;
 135         }
 136
 137
 138       if (goto_global_pool)
 139         {
 140           pool->num_threads--;
 141
 142           if (!pool->running && !pool->waiting)
 143             {
 144               if (pool->num_threads == 0)
 145                 {
 146                   g_async_queue_unlock (pool->queue);
 147                   g_thread_pool_free_internal (pool);
 148                 }
 149               else if (len == - pool->num_threads)
 150                 {
 151                   g_thread_pool_wakeup_and_stop_all (pool);
 152                   g_async_queue_unlock (pool->queue);
 153                 }
 154             }
 155           else
 156             g_async_queue_unlock (pool->queue);
 157
 158           g_async_queue_lock (unused_thread_queue);
 159
 160           G_LOCK (unused_threads);
 161           if ((unused_threads >= max_unused_threads &&
 162                max_unused_threads != -1))
 163             {
 164               G_UNLOCK (unused_threads);
 165               g_async_queue_unlock (unused_thread_queue);
 166               /* Stop this thread */
 167               return NULL;
 168             }
 169           unused_threads++;
 170           G_UNLOCK (unused_threads);
 171
 172           pool = g_async_queue_pop_unlocked (unused_thread_queue);
 173
 174           G_LOCK (unused_threads);
 175           unused_threads--;
 176           G_UNLOCK (unused_threads);
 177
 178           g_async_queue_unlock (unused_thread_queue);
 179
 180           if (pool == stop_this_thread_marker)
 181             /* Stop this thread */
 182             return NULL;
 183
 184           g_async_queue_lock (pool->queue);
 185
 186           /* pool->num_threads++ is not done here, but in
 187            * g_thread_pool_start_thread to make the new started thread
 188            * known to the pool, before itself can do it. */
 189         }
 190     }
 191   return NULL;
 192 }
 193
 194 static void
 195 g_thread_pool_start_thread (GRealThreadPool  *pool,
 196                             GError          **error)
 197 {
 198   gboolean success = FALSE;
 199
 200   if (pool->num_threads >= pool->max_threads && pool->max_threads != -1)
 201     /* Enough threads are already running */
 202     return;
 203
 204   g_async_queue_lock (unused_thread_queue);
 205
 206   if (g_async_queue_length_unlocked (unused_thread_queue) < 0)
 207     {
 208       g_async_queue_push_unlocked (unused_thread_queue, pool);
 209       success = TRUE;
 210     }
 211
 212   g_async_queue_unlock (unused_thread_queue);
 213
 214   if (!success)
 215     {
 216       GError *local_error = NULL;
 217       /* No thread was found, we have to start a new one */
 218       g_thread_create (g_thread_pool_thread_proxy, pool, FALSE, &local_error);
 219
 220       if (local_error)
 221         {
 222           g_propagate_error (error, local_error);
 223           return;
 224         }
 225     }
 226
 227   /* See comment in g_thread_pool_thread_proxy as to why this is done
 228    * here and not there */
 229   pool->num_threads++;
 230 }
 231
 232 /**
 233  * g_thread_pool_new:
 234  * @func: a function to execute in the threads of the new thread pool
 235  * @user_data: user data that is handed over to @func every time it
 236  *   is called
 237  * @max_threads: the maximal number of threads to execute concurrently in
 238  *   the new thread pool, -1 means no limit
 239  * @exclusive: should this thread pool be exclusive?
 240  * @error: return location for error
 241  *
 242  * This function creates a new thread pool.
 243  *
 244  * Whenever you call g_thread_pool_push(), either a new thread is
 245  * created or an unused one is reused. At most @max_threads threads
 246  * are running concurrently for this thread pool. @max_threads = -1
 247  * allows unlimited threads to be created for this thread pool. The
 248  * newly created or reused thread now executes the function @func with
 249  * the two arguments. The first one is the parameter to
 250  * g_thread_pool_push() and the second one is @user_data.
 251  *
 252  * The parameter @exclusive determines, whether the thread pool owns
 253  * all threads exclusive or whether the threads are shared
 254  * globally. If @exclusive is @TRUE, @max_threads threads are started
 255  * immediately and they will run exclusively for this thread pool until
 256  * it is destroyed by g_thread_pool_free(). If @exclusive is @FALSE,
 257  * threads are created, when needed and shared between all
 258  * non-exclusive thread pools. This implies that @max_threads may not
 259  * be -1 for exclusive thread pools.
 260  *
 261  * @error can be NULL to ignore errors, or non-NULL to report
 262  * errors. An error can only occur, when @exclusive is set to @TRUE and
 263  * not all @max_threads threads could be created.
 264  *
 265  * Return value: the new #GThreadPool
 266  **/
 267 GThreadPool*
 268 g_thread_pool_new (GFunc            func,
 269                    gpointer         user_data,
 270                    gint             max_threads,
 271                    gboolean         exclusive,
 272                    GError         **error)
 273 {
 274   GRealThreadPool *retval;
 275   G_LOCK_DEFINE_STATIC (init);
 276
 277   g_return_val_if_fail (func, NULL);
 278   g_return_val_if_fail (!exclusive || max_threads != -1, NULL);
 279   g_return_val_if_fail (max_threads >= -1, NULL);
 280   g_return_val_if_fail (g_thread_supported (), NULL);
 281
 282   retval = g_new (GRealThreadPool, 1);
 283
 284   retval->pool.func = func;
 285   retval->pool.user_data = user_data;
 286   retval->pool.exclusive = exclusive;
 287   retval->queue = g_async_queue_new ();
 288   retval->max_threads = max_threads;
 289   retval->num_threads = 0;
 290   retval->running = TRUE;
 291
 292   G_LOCK (init);
 293
 294   if (!inform_mutex)
 295     {
 296       inform_mutex = g_mutex_new ();
 297       inform_cond = g_cond_new ();
 298       unused_thread_queue = g_async_queue_new ();
 299     }
 300
 301   G_UNLOCK (init);
 302
 303   if (retval->pool.exclusive)
 304     {
 305       g_async_queue_lock (retval->queue);
 306
 307       while (retval->num_threads < retval->max_threads)
 308         {
 309           GError *local_error = NULL;
 310           g_thread_pool_start_thread (retval, &local_error);
 311           if (local_error)
 312             {
 313               g_propagate_error (error, local_error);
 314               break;
 315             }
 316         }
 317
 318       g_async_queue_unlock (retval->queue);
 319     }
 320
 321   return (GThreadPool*) retval;
 322 }
 323
 324 /**
 325  * g_thread_pool_push:
 326  * @pool: a #GThreadPool
 327  * @data: a new task for @pool
 328  * @error: return location for error
 329  *
 330  * Inserts @data into the list of tasks to be executed by @pool. When
 331  * the number of currently running threads is lower than the maximal
 332  * allowed number of threads, a new thread is started (or reused) with
 333  * the properties given to g_thread_pool_new (). Otherwise @data stays
 334  * in the queue until a thread in this pool finishes its previous task
 335  * and processes @data.
 336  *
 337  * @error can be NULL to ignore errors, or non-NULL to report
 338  * errors. An error can only occur, when a new thread couldn't be
 339  * created. In that case @data is simply appended to the queue of work
 340  * to do.
 341  **/
 342 void
 343 g_thread_pool_push (GThreadPool     *pool,
 344                     gpointer         data,
 345                     GError         **error)
 346 {
 347   GRealThreadPool *real = (GRealThreadPool*) pool;
 348
 349   g_return_if_fail (real);
 350
 351   g_async_queue_lock (real->queue);
 352
 353   if (!real->running)
 354     {
 355       g_async_queue_unlock (real->queue);
 356       g_return_if_fail (real->running);
 357     }
 358
 359   if (g_async_queue_length_unlocked (real->queue) >= 0)
 360     /* No thread is waiting in the queue */
 361     g_thread_pool_start_thread (real, error);
 362
 363   g_async_queue_push_unlocked (real->queue, data);
 364   g_async_queue_unlock (real->queue);
 365 }
 366
 367 /**
 368  * g_thread_pool_set_max_threads:
 369  * @pool: a #GThreadPool
 370  * @max_threads: a new maximal number of threads for @pool
 371  * @error: return location for error
 372  *
 373  * Sets the maximal allowed number of threads for @pool. A value of -1
 374  * means, that the maximal number of threads is unlimited.
 375  *
 376  * Setting @max_threads to 0 means stopping all work for @pool. It is
 377  * effectively frozen until @max_threads is set to a non-zero value
 378  * again.
 379  *
 380  * A thread is never terminated while calling @func, as supplied by
 381  * g_thread_pool_new (). Instead the maximal number of threads only
 382  * has effect for the allocation of new threads in g_thread_pool_push
 383  * (). A new thread is allocated, whenever the number of currently
 384  * running threads in @pool is smaller than the maximal number.
 385  *
 386  * @error can be NULL to ignore errors, or non-NULL to report
 387  * errors. An error can only occur, when a new thread couldn't be
 388  * created.
 389  **/
 390 void
 391 g_thread_pool_set_max_threads (GThreadPool     *pool,
 392                                gint             max_threads,
 393                                GError         **error)
 394 {
 395   GRealThreadPool *real = (GRealThreadPool*) pool;
 396   gint to_start;
 397
 398   g_return_if_fail (real);
 399   g_return_if_fail (real->running);
 400   g_return_if_fail (!real->pool.exclusive || max_threads != -1);
 401   g_return_if_fail (max_threads >= -1);
 402
 403   g_async_queue_lock (real->queue);
 404
 405   real->max_threads = max_threads;
 406
 407   if (pool->exclusive)
 408     to_start = real->max_threads - real->num_threads;
 409   else
 410     to_start = g_async_queue_length_unlocked (real->queue);
 411
 412   for ( ; to_start > 0; to_start--)
 413     {
 414       GError *local_error = NULL;
 415       g_thread_pool_start_thread (real, &local_error);
 416       if (local_error)
 417         {
 418           g_propagate_error (error, local_error);
 419           break;
 420         }
 421     }
 422
 423   g_async_queue_unlock (real->queue);
 424 }
 425
 426 /**
 427  * g_thread_pool_get_max_threads:
 428  * @pool: a #GThreadPool
 429  *
 430  * Returns the maximal number of threads for @pool.
 431  *
 432  * Return value: the maximal number of threads
 433  **/
 434 gint
 435 g_thread_pool_get_max_threads (GThreadPool     *pool)
 436 {
 437   GRealThreadPool *real = (GRealThreadPool*) pool;
 438   gint retval;
 439
 440   g_return_val_if_fail (real, 0);
 441   g_return_val_if_fail (real->running, 0);
 442
 443   g_async_queue_lock (real->queue);
 444
 445   retval = real->max_threads;
 446
 447   g_async_queue_unlock (real->queue);
 448
 449   return retval;
 450 }
 451
 452 /**
 453  * g_thread_pool_get_num_threads:
 454  * @pool: a #GThreadPool
 455  *
 456  * Returns the number of threads currently running in @pool.
 457  *
 458  * Return value: the number of threads currently running
 459  **/
 460 guint
 461 g_thread_pool_get_num_threads (GThreadPool     *pool)
 462 {
 463   GRealThreadPool *real = (GRealThreadPool*) pool;
 464   guint retval;
 465
 466   g_return_val_if_fail (real, 0);
 467   g_return_val_if_fail (real->running, 0);
 468
 469   g_async_queue_lock (real->queue);
 470
 471   retval = real->num_threads;
 472
 473   g_async_queue_unlock (real->queue);
 474
 475   return retval;
 476 }
 477
 478 /**
 479  * g_thread_pool_unprocessed:
 480  * @pool: a #GThreadPool
 481  *
 482  * Returns the number of tasks still unprocessed in @pool.
 483  *
 484  * Return value: the number of unprocessed tasks
 485  **/
 486 guint
 487 g_thread_pool_unprocessed (GThreadPool     *pool)
 488 {
 489   GRealThreadPool *real = (GRealThreadPool*) pool;
 490   gint unprocessed;
 491
 492   g_return_val_if_fail (real, 0);
 493   g_return_val_if_fail (real->running, 0);
 494
 495   unprocessed = g_async_queue_length (real->queue);
 496
 497   return MAX (unprocessed, 0);
 498 }
 499
 500 /**
 501  * g_thread_pool_free:
 502  * @pool: a #GThreadPool
 503  * @immediate: should @pool shut down immediately?
 504  * @wait: should the function wait for all tasks to be finished?
 505  *
 506  * Frees all resources allocated for @pool.
 507  *
 508  * If @immediate is #TRUE, no new task is processed for
 509  * @pool. Otherwise @pool is not freed before the last task is
 510  * processed. Note however, that no thread of this pool is
 511  * interrupted, while processing a task. Instead at least all still
 512  * running threads can finish their tasks before the @pool is freed.
 513  *
 514  * If @wait is #TRUE, the functions does not return before all tasks
 515  * to be processed (dependent on @immediate, whether all or only the
 516  * currently running) are ready. Otherwise the function returns immediately.
 517  *
 518  * After calling this function @pool must not be used anymore.
 519  **/
 520 void
 521 g_thread_pool_free (GThreadPool     *pool,
 522                     gboolean         immediate,
 523                     gboolean         wait)
 524 {
 525   GRealThreadPool *real = (GRealThreadPool*) pool;
 526
 527   g_return_if_fail (real);
 528   g_return_if_fail (real->running);
 529   /* It there's no thread allowed here, there is not much sense in
 530    * not stopping this pool immediately, when it's not empty */
 531   g_return_if_fail (immediate || real->max_threads != 0 ||
 532                     g_async_queue_length (real->queue) == 0);
 533
 534   g_async_queue_lock (real->queue);
 535
 536   real->running = FALSE;
 537   real->immediate = immediate;
 538   real->waiting = wait;
 539
 540   if (wait)
 541     {
 542       g_mutex_lock (inform_mutex);
 543       while (g_async_queue_length_unlocked (real->queue) != -real->num_threads)
 544         {
 545           g_async_queue_unlock (real->queue);
 546           g_cond_wait (inform_cond, inform_mutex);
 547           g_async_queue_lock (real->queue);
 548         }
 549       g_mutex_unlock (inform_mutex);
 550     }
 551
 552   if (g_async_queue_length_unlocked (real->queue) == -real->num_threads)
 553     {
 554       /* No thread is currently doing something (and nothing is left
 555        * to process in the queue) */
 556       if (real->num_threads == 0) /* No threads left, we clean up */
 557         {
 558           g_async_queue_unlock (real->queue);
 559           g_thread_pool_free_internal (real);
 560           return;
 561         }
 562
 563       g_thread_pool_wakeup_and_stop_all (real);
 564     }
 565
 566   real->waiting = FALSE; /* The last thread should cleanup the pool */
 567   g_async_queue_unlock (real->queue);
 568 }
 569
 570 static void
 571 g_thread_pool_free_internal (GRealThreadPool* pool)
 572 {
 573   g_return_if_fail (pool);
 574   g_return_if_fail (!pool->running);
 575   g_return_if_fail (pool->num_threads == 0);
 576
 577   g_async_queue_unref (pool->queue);
 578
 579   g_free (pool);
 580 }
 581
 582 static void
 583 g_thread_pool_wakeup_and_stop_all (GRealThreadPool* pool)
 584 {
 585   guint i;
 586
 587   g_return_if_fail (pool);
 588   g_return_if_fail (!pool->running);
 589   g_return_if_fail (pool->num_threads != 0);
 590   g_return_if_fail (g_async_queue_length_unlocked (pool->queue) ==
 591                     -pool->num_threads);
 592
 593   pool->immediate = TRUE;
 594   for (i = 0; i < pool->num_threads; i++)
 595     g_async_queue_push_unlocked (pool->queue, GUINT_TO_POINTER (1));
 596 }
 597
 598 /**
 599  * g_thread_pool_set_max_unused_threads:
 600  * @max_threads: maximal number of unused threads
 601  *
 602  * Sets the maximal number of unused threads to @max_threads. If
 603  * @max_threads is -1, no limit is imposed on the number of unused
 604  * threads.
 605  **/
 606 void
 607 g_thread_pool_set_max_unused_threads (gint max_threads)
 608 {
 609   g_return_if_fail (max_threads >= -1);
 610
 611   G_LOCK (unused_threads);
 612
 613   max_unused_threads = max_threads;
 614
 615   if (max_unused_threads < unused_threads && max_unused_threads != -1)
 616     {
 617       guint i;
 618
 619       g_async_queue_lock (unused_thread_queue);
 620       for (i = unused_threads - max_unused_threads; i > 0; i--)
 621         g_async_queue_push_unlocked (unused_thread_queue,
 622                                      stop_this_thread_marker);
 623       g_async_queue_unlock (unused_thread_queue);
 624     }
 625
 626   G_UNLOCK (unused_threads);
 627 }
 628
 629 /**
 630  * g_thread_pool_get_max_unused_threads:
 631  *
 632  * Returns the maximal allowed number of unused threads.
 633  *
 634  * Return value: the maximal number of unused threads
 635  **/
 636 gint
 637 g_thread_pool_get_max_unused_threads (void)
 638 {
 639   gint retval;
 640
 641   G_LOCK (unused_threads);
 642   retval = max_unused_threads;
 643   G_UNLOCK (unused_threads);
 644
 645   return retval;
 646 }
 647
 648 /**
 649  * g_thread_pool_get_num_unused_threads:
 650  *
 651  * Returns the number of currently unused threads.
 652  *
 653  * Return value: the number of currently unused threads
 654  **/
 655 guint g_thread_pool_get_num_unused_threads (void)
 656 {
 657   guint retval;
 658
 659   G_LOCK (unused_threads);
 660   retval = unused_threads;
 661   G_UNLOCK (unused_threads);
 662
 663   return retval;
 664 }
 665
 666 /**
 667  * g_thread_pool_stop_unused_threads:
 668  *
 669  * Stops all currently unused threads. This does not change the
 670  * maximal number of unused threads. This function can be used to
 671  * regularly stop all unused threads e.g. from g_timeout_add().
 672  **/
 673 void g_thread_pool_stop_unused_threads (void)
 674 {
 675   guint oldval = g_thread_pool_get_max_unused_threads ();
 676   g_thread_pool_set_max_unused_threads (0);
 677   g_thread_pool_set_max_unused_threads (oldval);
 678 }