nptl/pthread_mutex_trylock.c

   1 /* Copyright (C) 2002-2014 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 DO_ELISION
  30 #define DO_ELISION(m) 0
  31 #endif
  32
  33 /* We don't force elision in trylock, because this can lead to inconsistent
  34    lock state if the lock was actually busy.  */
  35
  36 int
  37 __pthread_mutex_trylock (mutex)
  38      pthread_mutex_t *mutex;
  39 {
  40   int oldval;
  41   pid_t id = THREAD_GETMEM (THREAD_SELF, tid);
  42
  43   switch (__builtin_expect (PTHREAD_MUTEX_TYPE_ELISION (mutex),
  44                             PTHREAD_MUTEX_TIMED_NP))
  45     {
  46       /* Recursive mutex.  */
  47     case PTHREAD_MUTEX_RECURSIVE_NP|PTHREAD_MUTEX_ELISION_NP:
  48     case PTHREAD_MUTEX_RECURSIVE_NP:
  49       /* Check whether we already hold the mutex.  */
  50       if (mutex->__data.__owner == id)
  51         {
  52           /* Just bump the counter.  */
  53           if (__glibc_unlikely (mutex->__data.__count + 1 == 0))
  54             /* Overflow of the counter.  */
  55             return EAGAIN;
  56
  57           ++mutex->__data.__count;
  58           return 0;
  59         }
  60
  61       if (lll_trylock (mutex->__data.__lock) == 0)
  62         {
  63           /* Record the ownership.  */
  64           mutex->__data.__owner = id;
  65           mutex->__data.__count = 1;
  66           ++mutex->__data.__nusers;
  67           return 0;
  68         }
  69       break;
  70
  71     case PTHREAD_MUTEX_TIMED_ELISION_NP:
  72     elision:
  73       if (lll_trylock_elision (mutex->__data.__lock,
  74                                mutex->__data.__elision) != 0)
  75         break;
  76       /* Don't record the ownership.  */
  77       return 0;
  78
  79     case PTHREAD_MUTEX_TIMED_NP:
  80       if (DO_ELISION (mutex))
  81         goto elision;
  82       /*FALL THROUGH*/
  83     case PTHREAD_MUTEX_ADAPTIVE_NP:
  84     case PTHREAD_MUTEX_ERRORCHECK_NP:
  85       if (lll_trylock (mutex->__data.__lock) != 0)
  86         break;
  87
  88       /* Record the ownership.  */
  89       mutex->__data.__owner = id;
  90       ++mutex->__data.__nusers;
  91
  92       return 0;
  93
  94     case PTHREAD_MUTEX_ROBUST_RECURSIVE_NP:
  95     case PTHREAD_MUTEX_ROBUST_ERRORCHECK_NP:
  96     case PTHREAD_MUTEX_ROBUST_NORMAL_NP:
  97     case PTHREAD_MUTEX_ROBUST_ADAPTIVE_NP:
  98       THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending,
  99                      &mutex->__data.__list.__next);
 100
 101       oldval = mutex->__data.__lock;
 102       do
 103         {
 104         again:
 105           if ((oldval & FUTEX_OWNER_DIED) != 0)
 106             {
 107               /* The previous owner died.  Try locking the mutex.  */
 108               int newval = id | (oldval & FUTEX_WAITERS);
 109
 110               newval
 111                 = atomic_compare_and_exchange_val_acq (&mutex->__data.__lock,
 112                                                        newval, oldval);
 113
 114               if (newval != oldval)
 115                 {
 116                   oldval = newval;
 117                   goto again;
 118                 }
 119
 120               /* We got the mutex.  */
 121               mutex->__data.__count = 1;
 122               /* But it is inconsistent unless marked otherwise.  */
 123               mutex->__data.__owner = PTHREAD_MUTEX_INCONSISTENT;
 124
 125               ENQUEUE_MUTEX (mutex);
 126               THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
 127
 128               /* Note that we deliberately exist here.  If we fall
 129                  through to the end of the function __nusers would be
 130                  incremented which is not correct because the old
 131                  owner has to be discounted.  */
 132               return EOWNERDEAD;
 133             }
 134
 135           /* Check whether we already hold the mutex.  */
 136           if (__glibc_unlikely ((oldval & FUTEX_TID_MASK) == id))
 137             {
 138               int kind = PTHREAD_MUTEX_TYPE (mutex);
 139               if (kind == PTHREAD_MUTEX_ROBUST_ERRORCHECK_NP)
 140                 {
 141                   THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending,
 142                                  NULL);
 143                   return EDEADLK;
 144                 }
 145
 146               if (kind == PTHREAD_MUTEX_ROBUST_RECURSIVE_NP)
 147                 {
 148                   THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending,
 149                                  NULL);
 150
 151                   /* Just bump the counter.  */
 152                   if (__glibc_unlikely (mutex->__data.__count + 1 == 0))
 153                     /* Overflow of the counter.  */
 154                     return EAGAIN;
 155
 156                   ++mutex->__data.__count;
 157
 158                   return 0;
 159                 }
 160             }
 161
 162           oldval = atomic_compare_and_exchange_val_acq (&mutex->__data.__lock,
 163                                                         id, 0);
 164           if (oldval != 0 && (oldval & FUTEX_OWNER_DIED) == 0)
 165             {
 166               THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
 167
 168               return EBUSY;
 169             }
 170
 171           if (__builtin_expect (mutex->__data.__owner
 172                                 == PTHREAD_MUTEX_NOTRECOVERABLE, 0))
 173             {
 174               /* This mutex is now not recoverable.  */
 175               mutex->__data.__count = 0;
 176               if (oldval == id)
 177                 lll_unlock (mutex->__data.__lock,
 178                             PTHREAD_ROBUST_MUTEX_PSHARED (mutex));
 179               THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
 180               return ENOTRECOVERABLE;
 181             }
 182         }
 183       while ((oldval & FUTEX_OWNER_DIED) != 0);
 184
 185       ENQUEUE_MUTEX (mutex);
 186       THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
 187
 188       mutex->__data.__owner = id;
 189       ++mutex->__data.__nusers;
 190       mutex->__data.__count = 1;
 191
 192       return 0;
 193
 194     /* The PI support requires the Linux futex system call.  If that's not
 195        available, pthread_mutex_init should never have allowed the type to
 196        be set.  So it will get the default case for an invalid type.  */
 197 #ifdef __NR_futex
 198     case PTHREAD_MUTEX_PI_RECURSIVE_NP:
 199     case PTHREAD_MUTEX_PI_ERRORCHECK_NP:
 200     case PTHREAD_MUTEX_PI_NORMAL_NP:
 201     case PTHREAD_MUTEX_PI_ADAPTIVE_NP:
 202     case PTHREAD_MUTEX_PI_ROBUST_RECURSIVE_NP:
 203     case PTHREAD_MUTEX_PI_ROBUST_ERRORCHECK_NP:
 204     case PTHREAD_MUTEX_PI_ROBUST_NORMAL_NP:
 205     case PTHREAD_MUTEX_PI_ROBUST_ADAPTIVE_NP:
 206       {
 207         int kind = mutex->__data.__kind & PTHREAD_MUTEX_KIND_MASK_NP;
 208         int robust = mutex->__data.__kind & PTHREAD_MUTEX_ROBUST_NORMAL_NP;
 209
 210         if (robust)
 211           /* Note: robust PI futexes are signaled by setting bit 0.  */
 212           THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending,
 213                          (void *) (((uintptr_t) &mutex->__data.__list.__next)
 214                                    | 1));
 215
 216         oldval = mutex->__data.__lock;
 217
 218         /* Check whether we already hold the mutex.  */
 219         if (__glibc_unlikely ((oldval & FUTEX_TID_MASK) == id))
 220           {
 221             if (kind == PTHREAD_MUTEX_ERRORCHECK_NP)
 222               {
 223                 THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
 224                 return EDEADLK;
 225               }
 226
 227             if (kind == PTHREAD_MUTEX_RECURSIVE_NP)
 228               {
 229                 THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
 230
 231                 /* Just bump the counter.  */
 232                 if (__glibc_unlikely (mutex->__data.__count + 1 == 0))
 233                   /* Overflow of the counter.  */
 234                   return EAGAIN;
 235
 236                 ++mutex->__data.__count;
 237
 238                 return 0;
 239               }
 240           }
 241
 242         oldval
 243           = atomic_compare_and_exchange_val_acq (&mutex->__data.__lock,
 244                                                  id, 0);
 245
 246         if (oldval != 0)
 247           {
 248             if ((oldval & FUTEX_OWNER_DIED) == 0)
 249               {
 250                 THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
 251
 252                 return EBUSY;
 253               }
 254
 255             assert (robust);
 256
 257             /* The mutex owner died.  The kernel will now take care of
 258                everything.  */
 259             int private = (robust
 260                            ? PTHREAD_ROBUST_MUTEX_PSHARED (mutex)
 261                            : PTHREAD_MUTEX_PSHARED (mutex));
 262             INTERNAL_SYSCALL_DECL (__err);
 263             int e = INTERNAL_SYSCALL (futex, __err, 4, &mutex->__data.__lock,
 264                                       __lll_private_flag (FUTEX_TRYLOCK_PI,
 265                                                           private), 0, 0);
 266
 267             if (INTERNAL_SYSCALL_ERROR_P (e, __err)
 268                 && INTERNAL_SYSCALL_ERRNO (e, __err) == EWOULDBLOCK)
 269               {
 270                 THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
 271
 272                 return EBUSY;
 273               }
 274
 275             oldval = mutex->__data.__lock;
 276           }
 277
 278         if (__glibc_unlikely (oldval & FUTEX_OWNER_DIED))
 279           {
 280             atomic_and (&mutex->__data.__lock, ~FUTEX_OWNER_DIED);
 281
 282             /* We got the mutex.  */
 283             mutex->__data.__count = 1;
 284             /* But it is inconsistent unless marked otherwise.  */
 285             mutex->__data.__owner = PTHREAD_MUTEX_INCONSISTENT;
 286
 287             ENQUEUE_MUTEX (mutex);
 288             THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
 289
 290             /* Note that we deliberately exit here.  If we fall
 291                through to the end of the function __nusers would be
 292                incremented which is not correct because the old owner
 293                has to be discounted.  */
 294             return EOWNERDEAD;
 295           }
 296
 297         if (robust
 298             && __builtin_expect (mutex->__data.__owner
 299                                  == PTHREAD_MUTEX_NOTRECOVERABLE, 0))
 300           {
 301             /* This mutex is now not recoverable.  */
 302             mutex->__data.__count = 0;
 303
 304             INTERNAL_SYSCALL_DECL (__err);
 305             INTERNAL_SYSCALL (futex, __err, 4, &mutex->__data.__lock,
 306                               __lll_private_flag (FUTEX_UNLOCK_PI,
 307                                                   PTHREAD_ROBUST_MUTEX_PSHARED (mutex)),
 308                               0, 0);
 309
 310             THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
 311             return ENOTRECOVERABLE;
 312           }
 313
 314         if (robust)
 315           {
 316             ENQUEUE_MUTEX_PI (mutex);
 317             THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
 318           }
 319
 320         mutex->__data.__owner = id;
 321         ++mutex->__data.__nusers;
 322         mutex->__data.__count = 1;
 323
 324         return 0;
 325       }
 326 #endif  /* __NR_futex.  */
 327
 328     case PTHREAD_MUTEX_PP_RECURSIVE_NP:
 329     case PTHREAD_MUTEX_PP_ERRORCHECK_NP:
 330     case PTHREAD_MUTEX_PP_NORMAL_NP:
 331     case PTHREAD_MUTEX_PP_ADAPTIVE_NP:
 332       {
 333         int kind = mutex->__data.__kind & PTHREAD_MUTEX_KIND_MASK_NP;
 334
 335         oldval = mutex->__data.__lock;
 336
 337         /* Check whether we already hold the mutex.  */
 338         if (mutex->__data.__owner == id)
 339           {
 340             if (kind == PTHREAD_MUTEX_ERRORCHECK_NP)
 341               return EDEADLK;
 342
 343             if (kind == PTHREAD_MUTEX_RECURSIVE_NP)
 344               {
 345                 /* Just bump the counter.  */
 346                 if (__glibc_unlikely (mutex->__data.__count + 1 == 0))
 347                   /* Overflow of the counter.  */
 348                   return EAGAIN;
 349
 350                 ++mutex->__data.__count;
 351
 352                 return 0;
 353               }
 354           }
 355
 356         int oldprio = -1, ceilval;
 357         do
 358           {
 359             int ceiling = (oldval & PTHREAD_MUTEX_PRIO_CEILING_MASK)
 360                           >> PTHREAD_MUTEX_PRIO_CEILING_SHIFT;
 361
 362             if (__pthread_current_priority () > ceiling)
 363               {
 364                 if (oldprio != -1)
 365                   __pthread_tpp_change_priority (oldprio, -1);
 366                 return EINVAL;
 367               }
 368
 369             int retval = __pthread_tpp_change_priority (oldprio, ceiling);
 370             if (retval)
 371               return retval;
 372
 373             ceilval = ceiling << PTHREAD_MUTEX_PRIO_CEILING_SHIFT;
 374             oldprio = ceiling;
 375
 376             oldval
 377               = atomic_compare_and_exchange_val_acq (&mutex->__data.__lock,
 378                                                      ceilval | 1, ceilval);
 379
 380             if (oldval == ceilval)
 381               break;
 382           }
 383         while ((oldval & PTHREAD_MUTEX_PRIO_CEILING_MASK) != ceilval);
 384
 385         if (oldval != ceilval)
 386           {
 387             __pthread_tpp_change_priority (oldprio, -1);
 388             break;
 389           }
 390
 391         assert (mutex->__data.__owner == 0);
 392         /* Record the ownership.  */
 393         mutex->__data.__owner = id;
 394         ++mutex->__data.__nusers;
 395         mutex->__data.__count = 1;
 396
 397         return 0;
 398       }
 399       break;
 400
 401     default:
 402       /* Correct code cannot set any other type.  */
 403       return EINVAL;
 404     }
 405
 406   return EBUSY;
 407 }
 408
 409 #ifndef __pthread_mutex_trylock
 410 #ifndef pthread_mutex_trylock
 411 strong_alias (__pthread_mutex_trylock, pthread_mutex_trylock)
 412 #endif
 413 #endif