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 (__builtin_expect (mutex->__data.__count + 1 == 0, 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 (__builtin_expect ((oldval & FUTEX_TID_MASK) == id, 0))
 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 (__builtin_expect (mutex->__data.__count + 1 == 0, 0))
 153                     /* Overflow of the counter.  */
 154                     return EAGAIN;
 155
 156                   ++mutex->__data.__count;
 157
 158                   return 0;
 159                 }
 160             }
 161
 162           oldval = lll_robust_trylock (mutex->__data.__lock, id);
 163           if (oldval != 0 && (oldval & FUTEX_OWNER_DIED) == 0)
 164             {
 165               THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
 166
 167               return EBUSY;
 168             }
 169
 170           if (__builtin_expect (mutex->__data.__owner
 171                                 == PTHREAD_MUTEX_NOTRECOVERABLE, 0))
 172             {
 173               /* This mutex is now not recoverable.  */
 174               mutex->__data.__count = 0;
 175               if (oldval == id)
 176                 lll_unlock (mutex->__data.__lock,
 177                             PTHREAD_ROBUST_MUTEX_PSHARED (mutex));
 178               THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
 179               return ENOTRECOVERABLE;
 180             }
 181         }
 182       while ((oldval & FUTEX_OWNER_DIED) != 0);
 183
 184       ENQUEUE_MUTEX (mutex);
 185       THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
 186
 187       mutex->__data.__owner = id;
 188       ++mutex->__data.__nusers;
 189       mutex->__data.__count = 1;
 190
 191       return 0;
 192
 193     case PTHREAD_MUTEX_PI_RECURSIVE_NP:
 194     case PTHREAD_MUTEX_PI_ERRORCHECK_NP:
 195     case PTHREAD_MUTEX_PI_NORMAL_NP:
 196     case PTHREAD_MUTEX_PI_ADAPTIVE_NP:
 197     case PTHREAD_MUTEX_PI_ROBUST_RECURSIVE_NP:
 198     case PTHREAD_MUTEX_PI_ROBUST_ERRORCHECK_NP:
 199     case PTHREAD_MUTEX_PI_ROBUST_NORMAL_NP:
 200     case PTHREAD_MUTEX_PI_ROBUST_ADAPTIVE_NP:
 201       {
 202         int kind = mutex->__data.__kind & PTHREAD_MUTEX_KIND_MASK_NP;
 203         int robust = mutex->__data.__kind & PTHREAD_MUTEX_ROBUST_NORMAL_NP;
 204
 205         if (robust)
 206           /* Note: robust PI futexes are signaled by setting bit 0.  */
 207           THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending,
 208                          (void *) (((uintptr_t) &mutex->__data.__list.__next)
 209                                    | 1));
 210
 211         oldval = mutex->__data.__lock;
 212
 213         /* Check whether we already hold the mutex.  */
 214         if (__builtin_expect ((oldval & FUTEX_TID_MASK) == id, 0))
 215           {
 216             if (kind == PTHREAD_MUTEX_ERRORCHECK_NP)
 217               {
 218                 THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
 219                 return EDEADLK;
 220               }
 221
 222             if (kind == PTHREAD_MUTEX_RECURSIVE_NP)
 223               {
 224                 THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
 225
 226                 /* Just bump the counter.  */
 227                 if (__builtin_expect (mutex->__data.__count + 1 == 0, 0))
 228                   /* Overflow of the counter.  */
 229                   return EAGAIN;
 230
 231                 ++mutex->__data.__count;
 232
 233                 return 0;
 234               }
 235           }
 236
 237         oldval
 238           = atomic_compare_and_exchange_val_acq (&mutex->__data.__lock,
 239                                                  id, 0);
 240
 241         if (oldval != 0)
 242           {
 243             if ((oldval & FUTEX_OWNER_DIED) == 0)
 244               {
 245                 THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
 246
 247                 return EBUSY;
 248               }
 249
 250             assert (robust);
 251
 252             /* The mutex owner died.  The kernel will now take care of
 253                everything.  */
 254             int private = (robust
 255                            ? PTHREAD_ROBUST_MUTEX_PSHARED (mutex)
 256                            : PTHREAD_MUTEX_PSHARED (mutex));
 257             INTERNAL_SYSCALL_DECL (__err);
 258             int e = INTERNAL_SYSCALL (futex, __err, 4, &mutex->__data.__lock,
 259                                       __lll_private_flag (FUTEX_TRYLOCK_PI,
 260                                                           private), 0, 0);
 261
 262             if (INTERNAL_SYSCALL_ERROR_P (e, __err)
 263                 && INTERNAL_SYSCALL_ERRNO (e, __err) == EWOULDBLOCK)
 264               {
 265                 THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
 266
 267                 return EBUSY;
 268               }
 269
 270             oldval = mutex->__data.__lock;
 271           }
 272
 273         if (__builtin_expect (oldval & FUTEX_OWNER_DIED, 0))
 274           {
 275             atomic_and (&mutex->__data.__lock, ~FUTEX_OWNER_DIED);
 276
 277             /* We got the mutex.  */
 278             mutex->__data.__count = 1;
 279             /* But it is inconsistent unless marked otherwise.  */
 280             mutex->__data.__owner = PTHREAD_MUTEX_INCONSISTENT;
 281
 282             ENQUEUE_MUTEX (mutex);
 283             THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
 284
 285             /* Note that we deliberately exit here.  If we fall
 286                through to the end of the function __nusers would be
 287                incremented which is not correct because the old owner
 288                has to be discounted.  */
 289             return EOWNERDEAD;
 290           }
 291
 292         if (robust
 293             && __builtin_expect (mutex->__data.__owner
 294                                  == PTHREAD_MUTEX_NOTRECOVERABLE, 0))
 295           {
 296             /* This mutex is now not recoverable.  */
 297             mutex->__data.__count = 0;
 298
 299             INTERNAL_SYSCALL_DECL (__err);
 300             INTERNAL_SYSCALL (futex, __err, 4, &mutex->__data.__lock,
 301                               __lll_private_flag (FUTEX_UNLOCK_PI,
 302                                                   PTHREAD_ROBUST_MUTEX_PSHARED (mutex)),
 303                               0, 0);
 304
 305             THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
 306             return ENOTRECOVERABLE;
 307           }
 308
 309         if (robust)
 310           {
 311             ENQUEUE_MUTEX_PI (mutex);
 312             THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
 313           }
 314
 315         mutex->__data.__owner = id;
 316         ++mutex->__data.__nusers;
 317         mutex->__data.__count = 1;
 318
 319         return 0;
 320       }
 321
 322     case PTHREAD_MUTEX_PP_RECURSIVE_NP:
 323     case PTHREAD_MUTEX_PP_ERRORCHECK_NP:
 324     case PTHREAD_MUTEX_PP_NORMAL_NP:
 325     case PTHREAD_MUTEX_PP_ADAPTIVE_NP:
 326       {
 327         int kind = mutex->__data.__kind & PTHREAD_MUTEX_KIND_MASK_NP;
 328
 329         oldval = mutex->__data.__lock;
 330
 331         /* Check whether we already hold the mutex.  */
 332         if (mutex->__data.__owner == id)
 333           {
 334             if (kind == PTHREAD_MUTEX_ERRORCHECK_NP)
 335               return EDEADLK;
 336
 337             if (kind == PTHREAD_MUTEX_RECURSIVE_NP)
 338               {
 339                 /* Just bump the counter.  */
 340                 if (__builtin_expect (mutex->__data.__count + 1 == 0, 0))
 341                   /* Overflow of the counter.  */
 342                   return EAGAIN;
 343
 344                 ++mutex->__data.__count;
 345
 346                 return 0;
 347               }
 348           }
 349
 350         int oldprio = -1, ceilval;
 351         do
 352           {
 353             int ceiling = (oldval & PTHREAD_MUTEX_PRIO_CEILING_MASK)
 354                           >> PTHREAD_MUTEX_PRIO_CEILING_SHIFT;
 355
 356             if (__pthread_current_priority () > ceiling)
 357               {
 358                 if (oldprio != -1)
 359                   __pthread_tpp_change_priority (oldprio, -1);
 360                 return EINVAL;
 361               }
 362
 363             int retval = __pthread_tpp_change_priority (oldprio, ceiling);
 364             if (retval)
 365               return retval;
 366
 367             ceilval = ceiling << PTHREAD_MUTEX_PRIO_CEILING_SHIFT;
 368             oldprio = ceiling;
 369
 370             oldval
 371               = atomic_compare_and_exchange_val_acq (&mutex->__data.__lock,
 372                                                      ceilval | 1, ceilval);
 373
 374             if (oldval == ceilval)
 375               break;
 376           }
 377         while ((oldval & PTHREAD_MUTEX_PRIO_CEILING_MASK) != ceilval);
 378
 379         if (oldval != ceilval)
 380           {
 381             __pthread_tpp_change_priority (oldprio, -1);
 382             break;
 383           }
 384
 385         assert (mutex->__data.__owner == 0);
 386         /* Record the ownership.  */
 387         mutex->__data.__owner = id;
 388         ++mutex->__data.__nusers;
 389         mutex->__data.__count = 1;
 390
 391         return 0;
 392       }
 393       break;
 394
 395     default:
 396       /* Correct code cannot set any other type.  */
 397       return EINVAL;
 398     }
 399
 400   return EBUSY;
 401 }
 402
 403 #ifndef __pthread_mutex_trylock
 404 #ifndef pthread_mutex_trylock
 405 strong_alias (__pthread_mutex_trylock, pthread_mutex_trylock)
 406 #endif
 407 #endif