nptl/pthread_mutex_trylock.c

   1 /* Copyright (C) 2002-2015 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3    Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 #include <assert.h>
  20 #include <errno.h>
  21 #include <stdlib.h>
  22 #include "pthreadP.h"
  23 #include <lowlevellock.h>
  24
  25 #ifndef lll_trylock_elision
  26 #define lll_trylock_elision(a,t) lll_trylock(a)
  27 #endif
  28
  29 #ifndef FORCE_ELISION
  30 #define FORCE_ELISION(m, s)
  31 #endif
  32
  33 int
  34 __pthread_mutex_trylock (mutex)
  35      pthread_mutex_t *mutex;
  36 {
  37   int oldval;
  38   pid_t id = THREAD_GETMEM (THREAD_SELF, tid);
  39
  40   switch (__builtin_expect (PTHREAD_MUTEX_TYPE_ELISION (mutex),
  41                             PTHREAD_MUTEX_TIMED_NP))
  42     {
  43       /* Recursive mutex.  */
  44     case PTHREAD_MUTEX_RECURSIVE_NP|PTHREAD_MUTEX_ELISION_NP:
  45     case PTHREAD_MUTEX_RECURSIVE_NP:
  46       /* Check whether we already hold the mutex.  */
  47       if (mutex->__data.__owner == id)
  48         {
  49           /* Just bump the counter.  */
  50           if (__glibc_unlikely (mutex->__data.__count + 1 == 0))
  51             /* Overflow of the counter.  */
  52             return EAGAIN;
  53
  54           ++mutex->__data.__count;
  55           return 0;
  56         }
  57
  58       if (lll_trylock (mutex->__data.__lock) == 0)
  59         {
  60           /* Record the ownership.  */
  61           mutex->__data.__owner = id;
  62           mutex->__data.__count = 1;
  63           ++mutex->__data.__nusers;
  64           return 0;
  65         }
  66       break;
  67
  68     case PTHREAD_MUTEX_TIMED_ELISION_NP:
  69     elision: __attribute__((unused))
  70       if (lll_trylock_elision (mutex->__data.__lock,
  71                                mutex->__data.__elision) != 0)
  72         break;
  73       /* Don't record the ownership.  */
  74       return 0;
  75
  76     case PTHREAD_MUTEX_TIMED_NP:
  77       FORCE_ELISION (mutex, goto elision);
  78       /*FALL THROUGH*/
  79     case PTHREAD_MUTEX_ADAPTIVE_NP:
  80     case PTHREAD_MUTEX_ERRORCHECK_NP:
  81       if (lll_trylock (mutex->__data.__lock) != 0)
  82         break;
  83
  84       /* Record the ownership.  */
  85       mutex->__data.__owner = id;
  86       ++mutex->__data.__nusers;
  87
  88       return 0;
  89
  90     case PTHREAD_MUTEX_ROBUST_RECURSIVE_NP:
  91     case PTHREAD_MUTEX_ROBUST_ERRORCHECK_NP:
  92     case PTHREAD_MUTEX_ROBUST_NORMAL_NP:
  93     case PTHREAD_MUTEX_ROBUST_ADAPTIVE_NP:
  94       THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending,
  95                      &mutex->__data.__list.__next);
  96
  97       oldval = mutex->__data.__lock;
  98       do
  99         {
 100         again:
 101           if ((oldval & FUTEX_OWNER_DIED) != 0)
 102             {
 103               /* The previous owner died.  Try locking the mutex.  */
 104               int newval = id | (oldval & FUTEX_WAITERS);
 105
 106               newval
 107                 = atomic_compare_and_exchange_val_acq (&mutex->__data.__lock,
 108                                                        newval, oldval);
 109
 110               if (newval != oldval)
 111                 {
 112                   oldval = newval;
 113                   goto again;
 114                 }
 115
 116               /* We got the mutex.  */
 117               mutex->__data.__count = 1;
 118               /* But it is inconsistent unless marked otherwise.  */
 119               mutex->__data.__owner = PTHREAD_MUTEX_INCONSISTENT;
 120
 121               ENQUEUE_MUTEX (mutex);
 122               THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
 123
 124               /* Note that we deliberately exist here.  If we fall
 125                  through to the end of the function __nusers would be
 126                  incremented which is not correct because the old
 127                  owner has to be discounted.  */
 128               return EOWNERDEAD;
 129             }
 130
 131           /* Check whether we already hold the mutex.  */
 132           if (__glibc_unlikely ((oldval & FUTEX_TID_MASK) == id))
 133             {
 134               int kind = PTHREAD_MUTEX_TYPE (mutex);
 135               if (kind == PTHREAD_MUTEX_ROBUST_ERRORCHECK_NP)
 136                 {
 137                   THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending,
 138                                  NULL);
 139                   return EDEADLK;
 140                 }
 141
 142               if (kind == PTHREAD_MUTEX_ROBUST_RECURSIVE_NP)
 143                 {
 144                   THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending,
 145                                  NULL);
 146
 147                   /* Just bump the counter.  */
 148                   if (__glibc_unlikely (mutex->__data.__count + 1 == 0))
 149                     /* Overflow of the counter.  */
 150                     return EAGAIN;
 151
 152                   ++mutex->__data.__count;
 153
 154                   return 0;
 155                 }
 156             }
 157
 158           oldval = atomic_compare_and_exchange_val_acq (&mutex->__data.__lock,
 159                                                         id, 0);
 160           if (oldval != 0 && (oldval & FUTEX_OWNER_DIED) == 0)
 161             {
 162               THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
 163
 164               return EBUSY;
 165             }
 166
 167           if (__builtin_expect (mutex->__data.__owner
 168                                 == PTHREAD_MUTEX_NOTRECOVERABLE, 0))
 169             {
 170               /* This mutex is now not recoverable.  */
 171               mutex->__data.__count = 0;
 172               if (oldval == id)
 173                 lll_unlock (mutex->__data.__lock,
 174                             PTHREAD_ROBUST_MUTEX_PSHARED (mutex));
 175               THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
 176               return ENOTRECOVERABLE;
 177             }
 178         }
 179       while ((oldval & FUTEX_OWNER_DIED) != 0);
 180
 181       ENQUEUE_MUTEX (mutex);
 182       THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
 183
 184       mutex->__data.__owner = id;
 185       ++mutex->__data.__nusers;
 186       mutex->__data.__count = 1;
 187
 188       return 0;
 189
 190     /* The PI support requires the Linux futex system call.  If that's not
 191        available, pthread_mutex_init should never have allowed the type to
 192        be set.  So it will get the default case for an invalid type.  */
 193 #ifdef __NR_futex
 194     case PTHREAD_MUTEX_PI_RECURSIVE_NP:
 195     case PTHREAD_MUTEX_PI_ERRORCHECK_NP:
 196     case PTHREAD_MUTEX_PI_NORMAL_NP:
 197     case PTHREAD_MUTEX_PI_ADAPTIVE_NP:
 198     case PTHREAD_MUTEX_PI_ROBUST_RECURSIVE_NP:
 199     case PTHREAD_MUTEX_PI_ROBUST_ERRORCHECK_NP:
 200     case PTHREAD_MUTEX_PI_ROBUST_NORMAL_NP:
 201     case PTHREAD_MUTEX_PI_ROBUST_ADAPTIVE_NP:
 202       {
 203         int kind = mutex->__data.__kind & PTHREAD_MUTEX_KIND_MASK_NP;
 204         int robust = mutex->__data.__kind & PTHREAD_MUTEX_ROBUST_NORMAL_NP;
 205
 206         if (robust)
 207           /* Note: robust PI futexes are signaled by setting bit 0.  */
 208           THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending,
 209                          (void *) (((uintptr_t) &mutex->__data.__list.__next)
 210                                    | 1));
 211
 212         oldval = mutex->__data.__lock;
 213
 214         /* Check whether we already hold the mutex.  */
 215         if (__glibc_unlikely ((oldval & FUTEX_TID_MASK) == id))
 216           {
 217             if (kind == PTHREAD_MUTEX_ERRORCHECK_NP)
 218               {
 219                 THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
 220                 return EDEADLK;
 221               }
 222
 223             if (kind == PTHREAD_MUTEX_RECURSIVE_NP)
 224               {
 225                 THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
 226
 227                 /* Just bump the counter.  */
 228                 if (__glibc_unlikely (mutex->__data.__count + 1 == 0))
 229                   /* Overflow of the counter.  */
 230                   return EAGAIN;
 231
 232                 ++mutex->__data.__count;
 233
 234                 return 0;
 235               }
 236           }
 237
 238         oldval
 239           = atomic_compare_and_exchange_val_acq (&mutex->__data.__lock,
 240                                                  id, 0);
 241
 242         if (oldval != 0)
 243           {
 244             if ((oldval & FUTEX_OWNER_DIED) == 0)
 245               {
 246                 THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
 247
 248                 return EBUSY;
 249               }
 250
 251             assert (robust);
 252
 253             /* The mutex owner died.  The kernel will now take care of
 254                everything.  */
 255             int private = (robust
 256                            ? PTHREAD_ROBUST_MUTEX_PSHARED (mutex)
 257                            : PTHREAD_MUTEX_PSHARED (mutex));
 258             INTERNAL_SYSCALL_DECL (__err);
 259             int e = INTERNAL_SYSCALL (futex, __err, 4, &mutex->__data.__lock,
 260                                       __lll_private_flag (FUTEX_TRYLOCK_PI,
 261                                                           private), 0, 0);
 262
 263             if (INTERNAL_SYSCALL_ERROR_P (e, __err)
 264                 && INTERNAL_SYSCALL_ERRNO (e, __err) == EWOULDBLOCK)
 265               {
 266                 THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
 267
 268                 return EBUSY;
 269               }
 270
 271             oldval = mutex->__data.__lock;
 272           }
 273
 274         if (__glibc_unlikely (oldval & FUTEX_OWNER_DIED))
 275           {
 276             atomic_and (&mutex->__data.__lock, ~FUTEX_OWNER_DIED);
 277
 278             /* We got the mutex.  */
 279             mutex->__data.__count = 1;
 280             /* But it is inconsistent unless marked otherwise.  */
 281             mutex->__data.__owner = PTHREAD_MUTEX_INCONSISTENT;
 282
 283             ENQUEUE_MUTEX (mutex);
 284             THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
 285
 286             /* Note that we deliberately exit here.  If we fall
 287                through to the end of the function __nusers would be
 288                incremented which is not correct because the old owner
 289                has to be discounted.  */
 290             return EOWNERDEAD;
 291           }
 292
 293         if (robust
 294             && __builtin_expect (mutex->__data.__owner
 295                                  == PTHREAD_MUTEX_NOTRECOVERABLE, 0))
 296           {
 297             /* This mutex is now not recoverable.  */
 298             mutex->__data.__count = 0;
 299
 300             INTERNAL_SYSCALL_DECL (__err);
 301             INTERNAL_SYSCALL (futex, __err, 4, &mutex->__data.__lock,
 302                               __lll_private_flag (FUTEX_UNLOCK_PI,
 303                                                   PTHREAD_ROBUST_MUTEX_PSHARED (mutex)),
 304                               0, 0);
 305
 306             THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
 307             return ENOTRECOVERABLE;
 308           }
 309
 310         if (robust)
 311           {
 312             ENQUEUE_MUTEX_PI (mutex);
 313             THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
 314           }
 315
 316         mutex->__data.__owner = id;
 317         ++mutex->__data.__nusers;
 318         mutex->__data.__count = 1;
 319
 320         return 0;
 321       }
 322 #endif  /* __NR_futex.  */
 323
 324     case PTHREAD_MUTEX_PP_RECURSIVE_NP:
 325     case PTHREAD_MUTEX_PP_ERRORCHECK_NP:
 326     case PTHREAD_MUTEX_PP_NORMAL_NP:
 327     case PTHREAD_MUTEX_PP_ADAPTIVE_NP:
 328       {
 329         int kind = mutex->__data.__kind & PTHREAD_MUTEX_KIND_MASK_NP;
 330
 331         oldval = mutex->__data.__lock;
 332
 333         /* Check whether we already hold the mutex.  */
 334         if (mutex->__data.__owner == id)
 335           {
 336             if (kind == PTHREAD_MUTEX_ERRORCHECK_NP)
 337               return EDEADLK;
 338
 339             if (kind == PTHREAD_MUTEX_RECURSIVE_NP)
 340               {
 341                 /* Just bump the counter.  */
 342                 if (__glibc_unlikely (mutex->__data.__count + 1 == 0))
 343                   /* Overflow of the counter.  */
 344                   return EAGAIN;
 345
 346                 ++mutex->__data.__count;
 347
 348                 return 0;
 349               }
 350           }
 351
 352         int oldprio = -1, ceilval;
 353         do
 354           {
 355             int ceiling = (oldval & PTHREAD_MUTEX_PRIO_CEILING_MASK)
 356                           >> PTHREAD_MUTEX_PRIO_CEILING_SHIFT;
 357
 358             if (__pthread_current_priority () > ceiling)
 359               {
 360                 if (oldprio != -1)
 361                   __pthread_tpp_change_priority (oldprio, -1);
 362                 return EINVAL;
 363               }
 364
 365             int retval = __pthread_tpp_change_priority (oldprio, ceiling);
 366             if (retval)
 367               return retval;
 368
 369             ceilval = ceiling << PTHREAD_MUTEX_PRIO_CEILING_SHIFT;
 370             oldprio = ceiling;
 371
 372             oldval
 373               = atomic_compare_and_exchange_val_acq (&mutex->__data.__lock,
 374                                                      ceilval | 1, ceilval);
 375
 376             if (oldval == ceilval)
 377               break;
 378           }
 379         while ((oldval & PTHREAD_MUTEX_PRIO_CEILING_MASK) != ceilval);
 380
 381         if (oldval != ceilval)
 382           {
 383             __pthread_tpp_change_priority (oldprio, -1);
 384             break;
 385           }
 386
 387         assert (mutex->__data.__owner == 0);
 388         /* Record the ownership.  */
 389         mutex->__data.__owner = id;
 390         ++mutex->__data.__nusers;
 391         mutex->__data.__count = 1;
 392
 393         return 0;
 394       }
 395       break;
 396
 397     default:
 398       /* Correct code cannot set any other type.  */
 399       return EINVAL;
 400     }
 401
 402   return EBUSY;
 403 }
 404
 405 #ifndef __pthread_mutex_trylock
 406 #ifndef pthread_mutex_trylock
 407 strong_alias (__pthread_mutex_trylock, pthread_mutex_trylock)
 408 #endif
 409 #endif