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 "config.h"
  28
  29 #include "glib.h"
  30
  31
  32 typedef struct _GRealThreadPool GRealThreadPool;
  33
  34 struct _GRealThreadPool
  35 {
  36   GThreadPool pool;
  37   GAsyncQueue* queue;
  38   gint max_threads;
  39   gint num_threads;
  40   gboolean running;
  41   gboolean immediate;
  42   gboolean waiting;
  43 };
  44
  45 /* The following is just an address to mark the stop order for a
  46  * thread, it could be any address (as long, as it isn't a valid
  47  * GThreadPool address) */
  48 static const gpointer stop_this_thread_marker = (gpointer) &g_thread_pool_new;
  49
  50 /* Here all unused threads are waiting  */
  51 static GAsyncQueue *unused_thread_queue;
  52 static gint unused_threads = 0;
  53 static gint max_unused_threads = 0;
  54 G_LOCK_DEFINE_STATIC (unused_threads);
  55
  56 static GMutex *inform_mutex = NULL;
  57 static GCond *inform_cond = NULL;
  58
  59 static void     g_thread_pool_free_internal (GRealThreadPool* pool);
  60 static gpointer g_thread_pool_thread_proxy (gpointer data);
  61 static void     g_thread_pool_start_thread (GRealThreadPool* pool,
  62                                             GError **error);
  63 static void     g_thread_pool_wakeup_and_stop_all (GRealThreadPool* pool);
  64
  65 #define g_thread_should_run(pool, len) \
  66   ((pool)->running || (!(pool)->immediate && (len) > 0))
  67
  68 static gpointer
  69 g_thread_pool_thread_proxy (gpointer data)
  70 {
  71   GRealThreadPool *pool = data;
  72   gboolean watcher = FALSE;
  73
  74   g_async_queue_lock (pool->queue);
  75   while (TRUE)
  76     {
  77       gpointer task;
  78       gboolean goto_global_pool = !pool->pool.exclusive;
  79       gint len = g_async_queue_length_unlocked (pool->queue);
  80
  81       if (g_thread_should_run (pool, len))
  82         {
  83           if (watcher)
  84             {
  85               /* This thread is actually not needed here, but it waits
  86                * for some time anyway. If during that time a new
  87                * request arrives, this saves process
  88                * swicthes. Otherwise the thread will go to the global
  89                * pool afterwards */
  90               GTimeVal end_time;
  91               g_get_current_time (&end_time);
  92               g_time_val_add (&end_time, G_USEC_PER_SEC / 2); /* 1/2 second */
  93               task = g_async_queue_timed_pop_unlocked (pool->queue, &end_time);
  94             }
  95           else
  96             task = g_async_queue_pop_unlocked (pool->queue);
  97
  98           if (task)
  99             {
 100               watcher = FALSE;
 101               if (pool->num_threads > pool->max_threads &&
 102                   pool->max_threads != -1)
 103                 /* We are in fact a superfluous threads, so we go to
 104                  * the global pool and just hand the data further to
 105                  * the next one waiting in the queue */
 106                 {
 107                   g_async_queue_push_unlocked (pool->queue, task);
 108                   goto_global_pool = TRUE;
 109                 }
 110               else if (pool->running || !pool->immediate)
 111                 {
 112                   g_async_queue_unlock (pool->queue);
 113                   pool->pool.func (task, pool->pool.user_data);
 114                   g_async_queue_lock (pool->queue);
 115                 }
 116             }
 117           len = g_async_queue_length_unlocked (pool->queue);
 118         }
 119
 120       if (!g_thread_should_run (pool, len))
 121         {
 122           g_cond_broadcast (inform_cond);
 123           goto_global_pool = TRUE;
 124         }
 125       else if (len > 0)
 126         {
 127           /* At this pool there are no threads waiting, but tasks are. */
 128           goto_global_pool = FALSE;
 129         }
 130       else if (len == 0 && !watcher && !pool->pool.exclusive)
 131         {
 132           /* Here neither threads nor tasks are queued and we didn't
 133            * just return from a timed wait. We now wait for a limited
 134            * time at this pool for new tasks to avoid costly context
 135            * switches. */
 136           goto_global_pool = FALSE;
 137           watcher = TRUE;
 138         }
 139
 140       if (goto_global_pool)
 141         {
 142           pool->num_threads--;
 143
 144           if (!pool->running && !pool->waiting)
 145             {
 146               if (pool->num_threads == 0)
 147                 {
 148                   g_async_queue_unlock (pool->queue);
 149                   g_thread_pool_free_internal (pool);
 150                 }
 151               else
 152                 {
 153                   if (len == - pool->num_threads)
 154                     g_thread_pool_wakeup_and_stop_all (pool);
 155
 156                   g_async_queue_unlock (pool->queue);
 157                 }
 158             }
 159           else
 160             g_async_queue_unlock (pool->queue);
 161
 162           g_async_queue_lock (unused_thread_queue);
 163
 164           G_LOCK (unused_threads);
 165           if ((unused_threads >= max_unused_threads &&
 166                max_unused_threads != -1))
 167             {
 168               G_UNLOCK (unused_threads);
 169               g_async_queue_unlock (unused_thread_queue);
 170               /* Stop this thread */
 171               return NULL;
 172             }
 173           unused_threads++;
 174           G_UNLOCK (unused_threads);
 175
 176           pool = g_async_queue_pop_unlocked (unused_thread_queue);
 177
 178           G_LOCK (unused_threads);
 179           unused_threads--;
 180           G_UNLOCK (unused_threads);
 181
 182           g_async_queue_unlock (unused_thread_queue);
 183
 184           if (pool == stop_this_thread_marker)
 185             /* Stop this thread */
 186             return NULL;
 187
 188           g_async_queue_lock (pool->queue);
 189
 190           /* pool->num_threads++ is not done here, but in
 191            * g_thread_pool_start_thread to make the new started thread
 192            * known to the pool, before itself can do it. */
 193         }
 194     }
 195   return NULL;
 196 }
 197
 198 static void
 199 g_thread_pool_start_thread (GRealThreadPool  *pool,
 200                             GError          **error)
 201 {
 202   gboolean success = FALSE;
 203
 204   if (pool->num_threads >= pool->max_threads && pool->max_threads != -1)
 205     /* Enough threads are already running */
 206     return;
 207
 208   g_async_queue_lock (unused_thread_queue);
 209
 210   if (g_async_queue_length_unlocked (unused_thread_queue) < 0)
 211     {
 212       g_async_queue_push_unlocked (unused_thread_queue, pool);
 213       success = TRUE;
 214     }
 215
 216   g_async_queue_unlock (unused_thread_queue);
 217
 218   if (!success)
 219     {
 220       GError *local_error = NULL;
 221       /* No thread was found, we have to start a new one */
 222       g_thread_create (g_thread_pool_thread_proxy, pool, FALSE, &local_error);
 223
 224       if (local_error)
 225         {
 226           g_propagate_error (error, local_error);
 227           return;
 228         }
 229     }
 230
 231   /* See comment in g_thread_pool_thread_proxy as to why this is done
 232    * here and not there */
 233   pool->num_threads++;
 234 }
 235
 236 /**
 237  * g_thread_pool_new:
 238  * @func: a function to execute in the threads of the new thread pool
 239  * @user_data: user data that is handed over to @func every time it
 240  *   is called
 241  * @max_threads: the maximal number of threads to execute concurrently in
 242  *   the new thread pool, -1 means no limit
 243  * @exclusive: should this thread pool be exclusive?
 244  * @error: return location for error
 245  *
 246  * This function creates a new thread pool.
 247  *
 248  * Whenever you call g_thread_pool_push(), either a new thread is
 249  * created or an unused one is reused. At most @max_threads threads
 250  * are running concurrently for this thread pool. @max_threads = -1
 251  * allows unlimited threads to be created for this thread pool. The
 252  * newly created or reused thread now executes the function @func with
 253  * the two arguments. The first one is the parameter to
 254  * g_thread_pool_push() and the second one is @user_data.
 255  *
 256  * The parameter @exclusive determines, whether the thread pool owns
 257  * all threads exclusive or whether the threads are shared
 258  * globally. If @exclusive is %TRUE, @max_threads threads are started
 259  * immediately and they will run exclusively for this thread pool until
 260  * it is destroyed by g_thread_pool_free(). If @exclusive is %FALSE,
 261  * threads are created, when needed and shared between all
 262  * non-exclusive thread pools. This implies that @max_threads may not
 263  * be -1 for exclusive thread pools.
 264  *
 265  * @error can be %NULL to ignore errors, or non-%NULL to report
 266  * errors. An error can only occur when @exclusive is set to %TRUE and
 267  * not all @max_threads threads could be created.
 268  *
 269  * Return value: the new #GThreadPool
 270  **/
 271 GThreadPool*
 272 g_thread_pool_new (GFunc            func,
 273                    gpointer         user_data,
 274                    gint             max_threads,
 275                    gboolean         exclusive,
 276                    GError         **error)
 277 {
 278   GRealThreadPool *retval;
 279   G_LOCK_DEFINE_STATIC (init);
 280
 281   g_return_val_if_fail (func, NULL);
 282   g_return_val_if_fail (!exclusive || max_threads != -1, NULL);
 283   g_return_val_if_fail (max_threads >= -1, NULL);
 284   g_return_val_if_fail (g_thread_supported (), NULL);
 285
 286   retval = g_new (GRealThreadPool, 1);
 287
 288   retval->pool.func = func;
 289   retval->pool.user_data = user_data;
 290   retval->pool.exclusive = exclusive;
 291   retval->queue = g_async_queue_new ();
 292   retval->max_threads = max_threads;
 293   retval->num_threads = 0;
 294   retval->running = TRUE;
 295
 296   G_LOCK (init);
 297
 298   if (!inform_mutex)
 299     {
 300       inform_mutex = g_mutex_new ();
 301       inform_cond = g_cond_new ();
 302       unused_thread_queue = g_async_queue_new ();
 303     }
 304
 305   G_UNLOCK (init);
 306
 307   if (retval->pool.exclusive)
 308     {
 309       g_async_queue_lock (retval->queue);
 310
 311       while (retval->num_threads < retval->max_threads)
 312         {
 313           GError *local_error = NULL;
 314           g_thread_pool_start_thread (retval, &local_error);
 315           if (local_error)
 316             {
 317               g_propagate_error (error, local_error);
 318               break;
 319             }
 320         }
 321
 322       g_async_queue_unlock (retval->queue);
 323     }
 324
 325   return (GThreadPool*) retval;
 326 }
 327
 328 /**
 329  * g_thread_pool_push:
 330  * @pool: a #GThreadPool
 331  * @data: a new task for @pool
 332  * @error: return location for error
 333  *
 334  * Inserts @data into the list of tasks to be executed by @pool. When
 335  * the number of currently running threads is lower than the maximal
 336  * allowed number of threads, a new thread is started (or reused) with
 337  * the properties given to g_thread_pool_new (). Otherwise @data stays
 338  * in the queue until a thread in this pool finishes its previous task
 339  * and processes @data.
 340  *
 341  * @error can be %NULL to ignore errors, or non-%NULL to report
 342  * errors. An error can only occur when a new thread couldn't be
 343  * created. In that case @data is simply appended to the queue of work
 344  * to do.
 345  **/
 346 void
 347 g_thread_pool_push (GThreadPool     *pool,
 348                     gpointer         data,
 349                     GError         **error)
 350 {
 351   GRealThreadPool *real = (GRealThreadPool*) pool;
 352
 353   g_return_if_fail (real);
 354
 355   g_async_queue_lock (real->queue);
 356
 357   if (!real->running)
 358     {
 359       g_async_queue_unlock (real->queue);
 360       g_return_if_fail (real->running);
 361     }
 362
 363   if (g_async_queue_length_unlocked (real->queue) >= 0)
 364     /* No thread is waiting in the queue */
 365     g_thread_pool_start_thread (real, error);
 366
 367   g_async_queue_push_unlocked (real->queue, data);
 368   g_async_queue_unlock (real->queue);
 369 }
 370
 371 /**
 372  * g_thread_pool_set_max_threads:
 373  * @pool: a #GThreadPool
 374  * @max_threads: a new maximal number of threads for @pool
 375  * @error: return location for error
 376  *
 377  * Sets the maximal allowed number of threads for @pool. A value of -1
 378  * means, that the maximal number of threads is unlimited.
 379  *
 380  * Setting @max_threads to 0 means stopping all work for @pool. It is
 381  * effectively frozen until @max_threads is set to a non-zero value
 382  * again.
 383  *
 384  * A thread is never terminated while calling @func, as supplied by
 385  * g_thread_pool_new (). Instead the maximal number of threads only
 386  * has effect for the allocation of new threads in g_thread_pool_push().
 387  * A new thread is allocated, whenever the number of currently
 388  * running threads in @pool is smaller than the maximal number.
 389  *
 390  * @error can be %NULL to ignore errors, or non-%NULL to report
 391  * errors. An error can only occur when a new thread couldn't be
 392  * created.
 393  **/
 394 void
 395 g_thread_pool_set_max_threads (GThreadPool     *pool,
 396                                gint             max_threads,
 397                                GError         **error)
 398 {
 399   GRealThreadPool *real = (GRealThreadPool*) pool;
 400   gint to_start;
 401
 402   g_return_if_fail (real);
 403   g_return_if_fail (real->running);
 404   g_return_if_fail (!real->pool.exclusive || max_threads != -1);
 405   g_return_if_fail (max_threads >= -1);
 406
 407   g_async_queue_lock (real->queue);
 408
 409   real->max_threads = max_threads;
 410
 411   if (pool->exclusive)
 412     to_start = real->max_threads - real->num_threads;
 413   else
 414     to_start = g_async_queue_length_unlocked (real->queue);
 415
 416   for ( ; to_start > 0; to_start--)
 417     {
 418       GError *local_error = NULL;
 419       g_thread_pool_start_thread (real, &local_error);
 420       if (local_error)
 421         {
 422           g_propagate_error (error, local_error);
 423           break;
 424         }
 425     }
 426
 427   g_async_queue_unlock (real->queue);
 428 }
 429
 430 /**
 431  * g_thread_pool_get_max_threads:
 432  * @pool: a #GThreadPool
 433  *
 434  * Returns the maximal number of threads for @pool.
 435  *
 436  * Return value: the maximal number of threads
 437  **/
 438 gint
 439 g_thread_pool_get_max_threads (GThreadPool     *pool)
 440 {
 441   GRealThreadPool *real = (GRealThreadPool*) pool;
 442   gint retval;
 443
 444   g_return_val_if_fail (real, 0);
 445   g_return_val_if_fail (real->running, 0);
 446
 447   g_async_queue_lock (real->queue);
 448
 449   retval = real->max_threads;
 450
 451   g_async_queue_unlock (real->queue);
 452
 453   return retval;
 454 }
 455
 456 /**
 457  * g_thread_pool_get_num_threads:
 458  * @pool: a #GThreadPool
 459  *
 460  * Returns the number of threads currently running in @pool.
 461  *
 462  * Return value: the number of threads currently running
 463  **/
 464 guint
 465 g_thread_pool_get_num_threads (GThreadPool     *pool)
 466 {
 467   GRealThreadPool *real = (GRealThreadPool*) pool;
 468   guint retval;
 469
 470   g_return_val_if_fail (real, 0);
 471   g_return_val_if_fail (real->running, 0);
 472
 473   g_async_queue_lock (real->queue);
 474
 475   retval = real->num_threads;
 476
 477   g_async_queue_unlock (real->queue);
 478
 479   return retval;
 480 }
 481
 482 /**
 483  * g_thread_pool_unprocessed:
 484  * @pool: a #GThreadPool
 485  *
 486  * Returns the number of tasks still unprocessed in @pool.
 487  *
 488  * Return value: the number of unprocessed tasks
 489  **/
 490 guint
 491 g_thread_pool_unprocessed (GThreadPool     *pool)
 492 {
 493   GRealThreadPool *real = (GRealThreadPool*) pool;
 494   gint unprocessed;
 495
 496   g_return_val_if_fail (real, 0);
 497   g_return_val_if_fail (real->running, 0);
 498
 499   unprocessed = g_async_queue_length (real->queue);
 500
 501   return MAX (unprocessed, 0);
 502 }
 503
 504 /**
 505  * g_thread_pool_free:
 506  * @pool: a #GThreadPool
 507  * @immediate: should @pool shut down immediately?
 508  * @wait: should the function wait for all tasks to be finished?
 509  *
 510  * Frees all resources allocated for @pool.
 511  *
 512  * If @immediate is %TRUE, no new task is processed for
 513  * @pool. Otherwise @pool is not freed before the last task is
 514  * processed. Note however, that no thread of this pool is
 515  * interrupted, while processing a task. Instead at least all still
 516  * running threads can finish their tasks before the @pool is freed.
 517  *
 518  * If @wait is %TRUE, the functions does not return before all tasks
 519  * to be processed (dependent on @immediate, whether all or only the
 520  * currently running) are ready. Otherwise the function returns immediately.
 521  *
 522  * After calling this function @pool must not be used anymore.
 523  **/
 524 void
 525 g_thread_pool_free (GThreadPool     *pool,
 526                     gboolean         immediate,
 527                     gboolean         wait)
 528 {
 529   GRealThreadPool *real = (GRealThreadPool*) pool;
 530
 531   g_return_if_fail (real);
 532   g_return_if_fail (real->running);
 533   /* It there's no thread allowed here, there is not much sense in
 534    * not stopping this pool immediately, when it's not empty */
 535   g_return_if_fail (immediate || real->max_threads != 0 ||
 536                     g_async_queue_length (real->queue) == 0);
 537
 538   g_async_queue_lock (real->queue);
 539
 540   real->running = FALSE;
 541   real->immediate = immediate;
 542   real->waiting = wait;
 543
 544   if (wait)
 545     {
 546       g_mutex_lock (inform_mutex);
 547       while (g_async_queue_length_unlocked (real->queue) != -real->num_threads)
 548         {
 549           g_async_queue_unlock (real->queue);
 550           g_cond_wait (inform_cond, inform_mutex);
 551           g_async_queue_lock (real->queue);
 552         }
 553       g_mutex_unlock (inform_mutex);
 554     }
 555
 556   if (g_async_queue_length_unlocked (real->queue) == -real->num_threads)
 557     {
 558       /* No thread is currently doing something (and nothing is left
 559        * to process in the queue) */
 560       if (real->num_threads == 0) /* No threads left, we clean up */
 561         {
 562           g_async_queue_unlock (real->queue);
 563           g_thread_pool_free_internal (real);
 564           return;
 565         }
 566
 567       g_thread_pool_wakeup_and_stop_all (real);
 568     }
 569
 570   real->waiting = FALSE; /* The last thread should cleanup the pool */
 571   g_async_queue_unlock (real->queue);
 572 }
 573
 574 static void
 575 g_thread_pool_free_internal (GRealThreadPool* pool)
 576 {
 577   g_return_if_fail (pool);
 578   g_return_if_fail (!pool->running);
 579   g_return_if_fail (pool->num_threads == 0);
 580
 581   g_async_queue_unref (pool->queue);
 582
 583   g_free (pool);
 584 }
 585
 586 static void
 587 g_thread_pool_wakeup_and_stop_all (GRealThreadPool* pool)
 588 {
 589   guint i;
 590
 591   g_return_if_fail (pool);
 592   g_return_if_fail (!pool->running);
 593   g_return_if_fail (pool->num_threads != 0);
 594   g_return_if_fail (g_async_queue_length_unlocked (pool->queue) ==
 595                     -pool->num_threads);
 596
 597   pool->immediate = TRUE;
 598   for (i = 0; i < pool->num_threads; i++)
 599     g_async_queue_push_unlocked (pool->queue, GUINT_TO_POINTER (1));
 600 }
 601
 602 /**
 603  * g_thread_pool_set_max_unused_threads:
 604  * @max_threads: maximal number of unused threads
 605  *
 606  * Sets the maximal number of unused threads to @max_threads. If
 607  * @max_threads is -1, no limit is imposed on the number of unused
 608  * threads.
 609  **/
 610 void
 611 g_thread_pool_set_max_unused_threads (gint max_threads)
 612 {
 613   g_return_if_fail (max_threads >= -1);
 614
 615   G_LOCK (unused_threads);
 616
 617   max_unused_threads = max_threads;
 618
 619   if (max_unused_threads < unused_threads && max_unused_threads != -1)
 620     {
 621       guint i;
 622
 623       g_async_queue_lock (unused_thread_queue);
 624       for (i = unused_threads - max_unused_threads; i > 0; i--)
 625         g_async_queue_push_unlocked (unused_thread_queue,
 626                                      stop_this_thread_marker);
 627       g_async_queue_unlock (unused_thread_queue);
 628     }
 629
 630   G_UNLOCK (unused_threads);
 631 }
 632
 633 /**
 634  * g_thread_pool_get_max_unused_threads:
 635  *
 636  * Returns the maximal allowed number of unused threads.
 637  *
 638  * Return value: the maximal number of unused threads
 639  **/
 640 gint
 641 g_thread_pool_get_max_unused_threads (void)
 642 {
 643   gint retval;
 644
 645   G_LOCK (unused_threads);
 646   retval = max_unused_threads;
 647   G_UNLOCK (unused_threads);
 648
 649   return retval;
 650 }
 651
 652 /**
 653  * g_thread_pool_get_num_unused_threads:
 654  *
 655  * Returns the number of currently unused threads.
 656  *
 657  * Return value: the number of currently unused threads
 658  **/
 659 guint g_thread_pool_get_num_unused_threads (void)
 660 {
 661   guint retval;
 662
 663   G_LOCK (unused_threads);
 664   retval = unused_threads;
 665   G_UNLOCK (unused_threads);
 666
 667   return retval;
 668 }
 669
 670 /**
 671  * g_thread_pool_stop_unused_threads:
 672  *
 673  * Stops all currently unused threads. This does not change the
 674  * maximal number of unused threads. This function can be used to
 675  * regularly stop all unused threads e.g. from g_timeout_add().
 676  **/
 677 void g_thread_pool_stop_unused_threads (void)
 678 {
 679   guint oldval = g_thread_pool_get_max_unused_threads ();
 680   g_thread_pool_set_max_unused_threads (0);
 681   g_thread_pool_set_max_unused_threads (oldval);
 682 }