lib/pthreadpool/pthreadpool.c

   1 /*
   2  * Unix SMB/CIFS implementation.
   3  * thread pool implementation
   4  * Copyright (C) Volker Lendecke 2009
   5  *
   6  * This program is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License as published by
   8  * the Free Software Foundation; either version 3 of the License, or
   9  * (at your option) any later version.
  10  *
  11  * This program is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  * GNU General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU General Public License
  17  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  18  */
  19
  20 #include "replace.h"
  21 #include "system/time.h"
  22 #include "system/wait.h"
  23 #include "system/threads.h"
  24 #include "system/filesys.h"
  25 #include "pthreadpool.h"
  26 #include "lib/util/dlinklist.h"
  27
  28 #ifdef NDEBUG
  29 #undef NDEBUG
  30 #endif
  31
  32 #include <assert.h>
  33
  34 struct pthreadpool_job {
  35         int id;
  36         void (*fn)(void *private_data);
  37         void *private_data;
  38 };
  39
  40 struct pthreadpool {
  41         /*
  42          * List pthreadpools for fork safety
  43          */
  44         struct pthreadpool *prev, *next;
  45
  46         /*
  47          * Control access to this struct
  48          */
  49         pthread_mutex_t mutex;
  50
  51         /*
  52          * Threads waiting for work do so here
  53          */
  54         pthread_cond_t condvar;
  55
  56         /*
  57          * Array of jobs
  58          */
  59         size_t jobs_array_len;
  60         struct pthreadpool_job *jobs;
  61
  62         size_t head;
  63         size_t num_jobs;
  64
  65         /*
  66          * Indicate job completion
  67          */
  68         int (*signal_fn)(int jobid,
  69                          void (*job_fn)(void *private_data),
  70                          void *job_fn_private_data,
  71                          void *private_data);
  72         void *signal_fn_private_data;
  73
  74         /*
  75          * indicator to worker threads to stop processing further jobs
  76          * and exit.
  77          */
  78         bool stopped;
  79
  80         /*
  81          * indicator to the last worker thread to free the pool
  82          * resources.
  83          */
  84         bool destroyed;
  85
  86         /*
  87          * maximum number of threads
  88          * 0 means no real thread, only strict sync processing.
  89          */
  90         unsigned max_threads;
  91
  92         /*
  93          * Number of threads
  94          */
  95         unsigned num_threads;
  96
  97         /*
  98          * Number of idle threads
  99          */
 100         unsigned num_idle;
 101
 102         /*
 103          * Condition variable indicating that helper threads should
 104          * quickly go away making way for fork() without anybody
 105          * waiting on pool->condvar.
 106          */
 107         pthread_cond_t *prefork_cond;
 108
 109         /*
 110          * Waiting position for helper threads while fork is
 111          * running. The forking thread will have locked it, and all
 112          * idle helper threads will sit here until after the fork,
 113          * where the forking thread will unlock it again.
 114          */
 115         pthread_mutex_t fork_mutex;
 116 };
 117
 118 static pthread_mutex_t pthreadpools_mutex = PTHREAD_MUTEX_INITIALIZER;
 119 static struct pthreadpool *pthreadpools = NULL;
 120 static pthread_once_t pthreadpool_atfork_initialized = PTHREAD_ONCE_INIT;
 121
 122 static void pthreadpool_prep_atfork(void);
 123
 124 /*
 125  * Initialize a thread pool
 126  */
 127
 128 int pthreadpool_init(unsigned max_threads, struct pthreadpool **presult,
 129                      int (*signal_fn)(int jobid,
 130                                       void (*job_fn)(void *private_data),
 131                                       void *job_fn_private_data,
 132                                       void *private_data),
 133                      void *signal_fn_private_data)
 134 {
 135         struct pthreadpool *pool;
 136         int ret;
 137
 138         pool = (struct pthreadpool *)malloc(sizeof(struct pthreadpool));
 139         if (pool == NULL) {
 140                 return ENOMEM;
 141         }
 142         pool->signal_fn = signal_fn;
 143         pool->signal_fn_private_data = signal_fn_private_data;
 144
 145         pool->jobs_array_len = 4;
 146         pool->jobs = calloc(
 147                 pool->jobs_array_len, sizeof(struct pthreadpool_job));
 148
 149         if (pool->jobs == NULL) {
 150                 free(pool);
 151                 return ENOMEM;
 152         }
 153
 154         pool->head = pool->num_jobs = 0;
 155
 156         ret = pthread_mutex_init(&pool->mutex, NULL);
 157         if (ret != 0) {
 158                 free(pool->jobs);
 159                 free(pool);
 160                 return ret;
 161         }
 162
 163         ret = pthread_cond_init(&pool->condvar, NULL);
 164         if (ret != 0) {
 165                 pthread_mutex_destroy(&pool->mutex);
 166                 free(pool->jobs);
 167                 free(pool);
 168                 return ret;
 169         }
 170
 171         ret = pthread_mutex_init(&pool->fork_mutex, NULL);
 172         if (ret != 0) {
 173                 pthread_cond_destroy(&pool->condvar);
 174                 pthread_mutex_destroy(&pool->mutex);
 175                 free(pool->jobs);
 176                 free(pool);
 177                 return ret;
 178         }
 179
 180         pool->stopped = false;
 181         pool->destroyed = false;
 182         pool->num_threads = 0;
 183         pool->max_threads = max_threads;
 184         pool->num_idle = 0;
 185         pool->prefork_cond = NULL;
 186
 187         ret = pthread_mutex_lock(&pthreadpools_mutex);
 188         if (ret != 0) {
 189                 pthread_mutex_destroy(&pool->fork_mutex);
 190                 pthread_cond_destroy(&pool->condvar);
 191                 pthread_mutex_destroy(&pool->mutex);
 192                 free(pool->jobs);
 193                 free(pool);
 194                 return ret;
 195         }
 196         DLIST_ADD(pthreadpools, pool);
 197
 198         ret = pthread_mutex_unlock(&pthreadpools_mutex);
 199         assert(ret == 0);
 200
 201         pthread_once(&pthreadpool_atfork_initialized, pthreadpool_prep_atfork);
 202
 203         *presult = pool;
 204
 205         return 0;
 206 }
 207
 208 size_t pthreadpool_max_threads(struct pthreadpool *pool)
 209 {
 210         if (pool->stopped) {
 211                 return 0;
 212         }
 213
 214         return pool->max_threads;
 215 }
 216
 217 size_t pthreadpool_queued_jobs(struct pthreadpool *pool)
 218 {
 219         int res;
 220         int unlock_res;
 221         size_t ret;
 222
 223         if (pool->stopped) {
 224                 return 0;
 225         }
 226
 227         res = pthread_mutex_lock(&pool->mutex);
 228         if (res != 0) {
 229                 return res;
 230         }
 231
 232         if (pool->stopped) {
 233                 unlock_res = pthread_mutex_unlock(&pool->mutex);
 234                 assert(unlock_res == 0);
 235                 return 0;
 236         }
 237
 238         ret = pool->num_jobs;
 239
 240         unlock_res = pthread_mutex_unlock(&pool->mutex);
 241         assert(unlock_res == 0);
 242         return ret;
 243 }
 244
 245 static void pthreadpool_prepare_pool(struct pthreadpool *pool)
 246 {
 247         int ret;
 248
 249         ret = pthread_mutex_lock(&pool->fork_mutex);
 250         assert(ret == 0);
 251
 252         ret = pthread_mutex_lock(&pool->mutex);
 253         assert(ret == 0);
 254
 255         while (pool->num_idle != 0) {
 256                 unsigned num_idle = pool->num_idle;
 257                 pthread_cond_t prefork_cond;
 258
 259                 ret = pthread_cond_init(&prefork_cond, NULL);
 260                 assert(ret == 0);
 261
 262                 /*
 263                  * Push all idle threads off pool->condvar. In the
 264                  * child we can destroy the pool, which would result
 265                  * in undefined behaviour in the
 266                  * pthread_cond_destroy(pool->condvar). glibc just
 267                  * blocks here.
 268                  */
 269                 pool->prefork_cond = &prefork_cond;
 270
 271                 ret = pthread_cond_signal(&pool->condvar);
 272                 assert(ret == 0);
 273
 274                 while (pool->num_idle == num_idle) {
 275                         ret = pthread_cond_wait(&prefork_cond, &pool->mutex);
 276                         assert(ret == 0);
 277                 }
 278
 279                 pool->prefork_cond = NULL;
 280
 281                 ret = pthread_cond_destroy(&prefork_cond);
 282                 assert(ret == 0);
 283         }
 284
 285         /*
 286          * Probably it's well-defined somewhere: What happens to
 287          * condvars after a fork? The rationale of pthread_atfork only
 288          * writes about mutexes. So better be safe than sorry and
 289          * destroy/reinit pool->condvar across a fork.
 290          */
 291
 292         ret = pthread_cond_destroy(&pool->condvar);
 293         assert(ret == 0);
 294 }
 295
 296 static void pthreadpool_prepare(void)
 297 {
 298         int ret;
 299         struct pthreadpool *pool;
 300
 301         ret = pthread_mutex_lock(&pthreadpools_mutex);
 302         assert(ret == 0);
 303
 304         pool = pthreadpools;
 305
 306         while (pool != NULL) {
 307                 pthreadpool_prepare_pool(pool);
 308                 pool = pool->next;
 309         }
 310 }
 311
 312 static void pthreadpool_parent(void)
 313 {
 314         int ret;
 315         struct pthreadpool *pool;
 316
 317         for (pool = DLIST_TAIL(pthreadpools);
 318              pool != NULL;
 319              pool = DLIST_PREV(pool)) {
 320                 ret = pthread_cond_init(&pool->condvar, NULL);
 321                 assert(ret == 0);
 322                 ret = pthread_mutex_unlock(&pool->mutex);
 323                 assert(ret == 0);
 324                 ret = pthread_mutex_unlock(&pool->fork_mutex);
 325                 assert(ret == 0);
 326         }
 327
 328         ret = pthread_mutex_unlock(&pthreadpools_mutex);
 329         assert(ret == 0);
 330 }
 331
 332 static void pthreadpool_child(void)
 333 {
 334         int ret;
 335         struct pthreadpool *pool;
 336
 337         for (pool = DLIST_TAIL(pthreadpools);
 338              pool != NULL;
 339              pool = DLIST_PREV(pool)) {
 340
 341                 pool->num_threads = 0;
 342                 pool->num_idle = 0;
 343                 pool->head = 0;
 344                 pool->num_jobs = 0;
 345                 pool->stopped = true;
 346
 347                 ret = pthread_cond_init(&pool->condvar, NULL);
 348                 assert(ret == 0);
 349
 350                 ret = pthread_mutex_unlock(&pool->mutex);
 351                 assert(ret == 0);
 352
 353                 ret = pthread_mutex_unlock(&pool->fork_mutex);
 354                 assert(ret == 0);
 355         }
 356
 357         ret = pthread_mutex_unlock(&pthreadpools_mutex);
 358         assert(ret == 0);
 359 }
 360
 361 static void pthreadpool_prep_atfork(void)
 362 {
 363         pthread_atfork(pthreadpool_prepare, pthreadpool_parent,
 364                        pthreadpool_child);
 365 }
 366
 367 static int pthreadpool_free(struct pthreadpool *pool)
 368 {
 369         int ret, ret1, ret2;
 370
 371         ret = pthread_mutex_lock(&pthreadpools_mutex);
 372         if (ret != 0) {
 373                 return ret;
 374         }
 375         DLIST_REMOVE(pthreadpools, pool);
 376         ret = pthread_mutex_unlock(&pthreadpools_mutex);
 377         assert(ret == 0);
 378
 379         ret = pthread_mutex_lock(&pool->mutex);
 380         assert(ret == 0);
 381         ret = pthread_mutex_unlock(&pool->mutex);
 382         assert(ret == 0);
 383
 384         ret = pthread_mutex_destroy(&pool->mutex);
 385         ret1 = pthread_cond_destroy(&pool->condvar);
 386         ret2 = pthread_mutex_destroy(&pool->fork_mutex);
 387
 388         if (ret != 0) {
 389                 return ret;
 390         }
 391         if (ret1 != 0) {
 392                 return ret1;
 393         }
 394         if (ret2 != 0) {
 395                 return ret2;
 396         }
 397
 398         free(pool->jobs);
 399         free(pool);
 400
 401         return 0;
 402 }
 403
 404 /*
 405  * Stop a thread pool. Wake up all idle threads for exit.
 406  */
 407
 408 static int pthreadpool_stop_locked(struct pthreadpool *pool)
 409 {
 410         int ret;
 411
 412         pool->stopped = true;
 413
 414         if (pool->num_threads == 0) {
 415                 return 0;
 416         }
 417
 418         /*
 419          * We have active threads, tell them to finish.
 420          */
 421
 422         ret = pthread_cond_broadcast(&pool->condvar);
 423
 424         return ret;
 425 }
 426
 427 /*
 428  * Stop a thread pool. Wake up all idle threads for exit.
 429  */
 430
 431 int pthreadpool_stop(struct pthreadpool *pool)
 432 {
 433         int ret, ret1;
 434
 435         ret = pthread_mutex_lock(&pool->mutex);
 436         if (ret != 0) {
 437                 return ret;
 438         }
 439
 440         if (!pool->stopped) {
 441                 ret = pthreadpool_stop_locked(pool);
 442         }
 443
 444         ret1 = pthread_mutex_unlock(&pool->mutex);
 445         assert(ret1 == 0);
 446
 447         return ret;
 448 }
 449
 450 /*
 451  * Destroy a thread pool. Wake up all idle threads for exit. The last
 452  * one will free the pool.
 453  */
 454
 455 int pthreadpool_destroy(struct pthreadpool *pool)
 456 {
 457         int ret, ret1;
 458         bool free_it;
 459
 460         assert(!pool->destroyed);
 461
 462         ret = pthread_mutex_lock(&pool->mutex);
 463         if (ret != 0) {
 464                 return ret;
 465         }
 466
 467         pool->destroyed = true;
 468
 469         if (!pool->stopped) {
 470                 ret = pthreadpool_stop_locked(pool);
 471         }
 472
 473         free_it = (pool->num_threads == 0);
 474
 475         ret1 = pthread_mutex_unlock(&pool->mutex);
 476         assert(ret1 == 0);
 477
 478         if (free_it) {
 479                 pthreadpool_free(pool);
 480         }
 481
 482         return ret;
 483 }
 484 /*
 485  * Prepare for pthread_exit(), pool->mutex must be locked and will be
 486  * unlocked here. This is a bit of a layering violation, but here we
 487  * also take care of removing the pool if we're the last thread.
 488  */
 489 static void pthreadpool_server_exit(struct pthreadpool *pool)
 490 {
 491         int ret;
 492         bool free_it;
 493
 494         pool->num_threads -= 1;
 495
 496         free_it = (pool->destroyed && (pool->num_threads == 0));
 497
 498         ret = pthread_mutex_unlock(&pool->mutex);
 499         assert(ret == 0);
 500
 501         if (free_it) {
 502                 pthreadpool_free(pool);
 503         }
 504 }
 505
 506 static bool pthreadpool_get_job(struct pthreadpool *p,
 507                                 struct pthreadpool_job *job)
 508 {
 509         if (p->stopped) {
 510                 return false;
 511         }
 512
 513         if (p->num_jobs == 0) {
 514                 return false;
 515         }
 516         *job = p->jobs[p->head];
 517         p->head = (p->head+1) % p->jobs_array_len;
 518         p->num_jobs -= 1;
 519         return true;
 520 }
 521
 522 static bool pthreadpool_put_job(struct pthreadpool *p,
 523                                 int id,
 524                                 void (*fn)(void *private_data),
 525                                 void *private_data)
 526 {
 527         struct pthreadpool_job *job;
 528
 529         if (p->num_jobs == p->jobs_array_len) {
 530                 struct pthreadpool_job *tmp;
 531                 size_t new_len = p->jobs_array_len * 2;
 532
 533                 tmp = realloc(
 534                         p->jobs, sizeof(struct pthreadpool_job) * new_len);
 535                 if (tmp == NULL) {
 536                         return false;
 537                 }
 538                 p->jobs = tmp;
 539
 540                 /*
 541                  * We just doubled the jobs array. The array implements a FIFO
 542                  * queue with a modulo-based wraparound, so we have to memcpy
 543                  * the jobs that are logically at the queue end but physically
 544                  * before the queue head into the reallocated area. The new
 545                  * space starts at the current jobs_array_len, and we have to
 546                  * copy everything before the current head job into the new
 547                  * area.
 548                  */
 549                 memcpy(&p->jobs[p->jobs_array_len], p->jobs,
 550                        sizeof(struct pthreadpool_job) * p->head);
 551
 552                 p->jobs_array_len = new_len;
 553         }
 554
 555         job = &p->jobs[(p->head + p->num_jobs) % p->jobs_array_len];
 556         job->id = id;
 557         job->fn = fn;
 558         job->private_data = private_data;
 559
 560         p->num_jobs += 1;
 561
 562         return true;
 563 }
 564
 565 static void pthreadpool_undo_put_job(struct pthreadpool *p)
 566 {
 567         p->num_jobs -= 1;
 568 }
 569
 570 static void *pthreadpool_server(void *arg)
 571 {
 572         struct pthreadpool *pool = (struct pthreadpool *)arg;
 573         int res;
 574
 575         res = pthread_mutex_lock(&pool->mutex);
 576         if (res != 0) {
 577                 return NULL;
 578         }
 579
 580         while (1) {
 581                 struct timespec ts;
 582                 struct pthreadpool_job job;
 583
 584                 /*
 585                  * idle-wait at most 1 second. If nothing happens in that
 586                  * time, exit this thread.
 587                  */
 588
 589                 clock_gettime(CLOCK_REALTIME, &ts);
 590                 ts.tv_sec += 1;
 591
 592                 while ((pool->num_jobs == 0) && !pool->stopped) {
 593
 594                         pool->num_idle += 1;
 595                         res = pthread_cond_timedwait(
 596                                 &pool->condvar, &pool->mutex, &ts);
 597                         pool->num_idle -= 1;
 598
 599                         if (pool->prefork_cond != NULL) {
 600                                 /*
 601                                  * Me must allow fork() to continue
 602                                  * without anybody waiting on
 603                                  * &pool->condvar. Tell
 604                                  * pthreadpool_prepare_pool that we
 605                                  * got that message.
 606                                  */
 607
 608                                 res = pthread_cond_signal(pool->prefork_cond);
 609                                 assert(res == 0);
 610
 611                                 res = pthread_mutex_unlock(&pool->mutex);
 612                                 assert(res == 0);
 613
 614                                 /*
 615                                  * pthreadpool_prepare_pool has
 616                                  * already locked this mutex across
 617                                  * the fork. This makes us wait
 618                                  * without sitting in a condvar.
 619                                  */
 620                                 res = pthread_mutex_lock(&pool->fork_mutex);
 621                                 assert(res == 0);
 622                                 res = pthread_mutex_unlock(&pool->fork_mutex);
 623                                 assert(res == 0);
 624
 625                                 res = pthread_mutex_lock(&pool->mutex);
 626                                 assert(res == 0);
 627                         }
 628
 629                         if (res == ETIMEDOUT) {
 630
 631                                 if (pool->num_jobs == 0) {
 632                                         /*
 633                                          * we timed out and still no work for
 634                                          * us. Exit.
 635                                          */
 636                                         pthreadpool_server_exit(pool);
 637                                         return NULL;
 638                                 }
 639
 640                                 break;
 641                         }
 642                         assert(res == 0);
 643                 }
 644
 645                 if (pthreadpool_get_job(pool, &job)) {
 646                         int ret;
 647
 648                         /*
 649                          * Do the work with the mutex unlocked
 650                          */
 651
 652                         res = pthread_mutex_unlock(&pool->mutex);
 653                         assert(res == 0);
 654
 655                         job.fn(job.private_data);
 656
 657                         ret = pool->signal_fn(job.id,
 658                                               job.fn, job.private_data,
 659                                               pool->signal_fn_private_data);
 660
 661                         res = pthread_mutex_lock(&pool->mutex);
 662                         assert(res == 0);
 663
 664                         if (ret != 0) {
 665                                 pthreadpool_server_exit(pool);
 666                                 return NULL;
 667                         }
 668                 }
 669
 670                 if (pool->stopped) {
 671                         /*
 672                          * we're asked to stop processing jobs, so exit
 673                          */
 674                         pthreadpool_server_exit(pool);
 675                         return NULL;
 676                 }
 677         }
 678 }
 679
 680 static int pthreadpool_create_thread(struct pthreadpool *pool)
 681 {
 682         pthread_attr_t thread_attr;
 683         pthread_t thread_id;
 684         int res;
 685         sigset_t mask, omask;
 686
 687         /*
 688          * Create a new worker thread. It should not receive any signals.
 689          */
 690
 691         sigfillset(&mask);
 692
 693         res = pthread_attr_init(&thread_attr);
 694         if (res != 0) {
 695                 return res;
 696         }
 697
 698         res = pthread_attr_setdetachstate(
 699                 &thread_attr, PTHREAD_CREATE_DETACHED);
 700         if (res != 0) {
 701                 pthread_attr_destroy(&thread_attr);
 702                 return res;
 703         }
 704
 705         res = pthread_sigmask(SIG_BLOCK, &mask, &omask);
 706         if (res != 0) {
 707                 pthread_attr_destroy(&thread_attr);
 708                 return res;
 709         }
 710
 711         res = pthread_create(&thread_id, &thread_attr, pthreadpool_server,
 712                              (void *)pool);
 713
 714         assert(pthread_sigmask(SIG_SETMASK, &omask, NULL) == 0);
 715
 716         pthread_attr_destroy(&thread_attr);
 717
 718         if (res == 0) {
 719                 pool->num_threads += 1;
 720         }
 721
 722         return res;
 723 }
 724
 725 int pthreadpool_add_job(struct pthreadpool *pool, int job_id,
 726                         void (*fn)(void *private_data), void *private_data)
 727 {
 728         int res;
 729         int unlock_res;
 730
 731         assert(!pool->destroyed);
 732
 733         res = pthread_mutex_lock(&pool->mutex);
 734         if (res != 0) {
 735                 return res;
 736         }
 737
 738         if (pool->stopped) {
 739                 /*
 740                  * Protect against the pool being shut down while
 741                  * trying to add a job
 742                  */
 743                 unlock_res = pthread_mutex_unlock(&pool->mutex);
 744                 assert(unlock_res == 0);
 745                 return EINVAL;
 746         }
 747
 748         if (pool->max_threads == 0) {
 749                 unlock_res = pthread_mutex_unlock(&pool->mutex);
 750                 assert(unlock_res == 0);
 751
 752                 /*
 753                  * If no thread are allowed we do strict sync processing.
 754                  */
 755                 fn(private_data);
 756                 res = pool->signal_fn(job_id, fn, private_data,
 757                                       pool->signal_fn_private_data);
 758                 return res;
 759         }
 760
 761         /*
 762          * Add job to the end of the queue
 763          */
 764         if (!pthreadpool_put_job(pool, job_id, fn, private_data)) {
 765                 unlock_res = pthread_mutex_unlock(&pool->mutex);
 766                 assert(unlock_res == 0);
 767                 return ENOMEM;
 768         }
 769
 770         if (pool->num_idle > 0) {
 771                 /*
 772                  * We have idle threads, wake one.
 773                  */
 774                 res = pthread_cond_signal(&pool->condvar);
 775                 if (res != 0) {
 776                         pthreadpool_undo_put_job(pool);
 777                 }
 778                 unlock_res = pthread_mutex_unlock(&pool->mutex);
 779                 assert(unlock_res == 0);
 780                 return res;
 781         }
 782
 783         if (pool->num_threads >= pool->max_threads) {
 784                 /*
 785                  * No more new threads, we just queue the request
 786                  */
 787                 unlock_res = pthread_mutex_unlock(&pool->mutex);
 788                 assert(unlock_res == 0);
 789                 return 0;
 790         }
 791
 792         res = pthreadpool_create_thread(pool);
 793         if (res == 0) {
 794                 unlock_res = pthread_mutex_unlock(&pool->mutex);
 795                 assert(unlock_res == 0);
 796                 return 0;
 797         }
 798
 799         if (pool->num_threads != 0) {
 800                 /*
 801                  * At least one thread is still available, let
 802                  * that one run the queued job.
 803                  */
 804                 unlock_res = pthread_mutex_unlock(&pool->mutex);
 805                 assert(unlock_res == 0);
 806                 return 0;
 807         }
 808
 809         /*
 810          * No thread could be created to run job, fallback to sync
 811          * call.
 812          */
 813         pthreadpool_undo_put_job(pool);
 814
 815         unlock_res = pthread_mutex_unlock(&pool->mutex);
 816         assert(unlock_res == 0);
 817
 818         return res;
 819 }
 820
 821 size_t pthreadpool_cancel_job(struct pthreadpool *pool, int job_id,
 822                               void (*fn)(void *private_data), void *private_data)
 823 {
 824         int res;
 825         size_t i, j;
 826         size_t num = 0;
 827
 828         assert(!pool->destroyed);
 829
 830         res = pthread_mutex_lock(&pool->mutex);
 831         if (res != 0) {
 832                 return res;
 833         }
 834
 835         for (i = 0, j = 0; i < pool->num_jobs; i++) {
 836                 size_t idx = (pool->head + i) % pool->jobs_array_len;
 837                 size_t new_idx = (pool->head + j) % pool->jobs_array_len;
 838                 struct pthreadpool_job *job = &pool->jobs[idx];
 839
 840                 if ((job->private_data == private_data) &&
 841                     (job->id == job_id) &&
 842                     (job->fn == fn))
 843                 {
 844                         /*
 845                          * Just skip the entry.
 846                          */
 847                         num++;
 848                         continue;
 849                 }
 850
 851                 /*
 852                  * If we already removed one or more jobs (so j will be smaller
 853                  * then i), we need to fill possible gaps in the logical list.
 854                  */
 855                 if (j < i) {
 856                         pool->jobs[new_idx] = *job;
 857                 }
 858                 j++;
 859         }
 860
 861         pool->num_jobs -= num;
 862
 863         res = pthread_mutex_unlock(&pool->mutex);
 864         assert(res == 0);
 865
 866         return num;
 867 }