src/lwp/lock.c

   1 /*
   2  * Copyright 2000, International Business Machines Corporation and others.
   3  * All Rights Reserved.
   4  *
   5  * This software has been released under the terms of the IBM Public
   6  * License.  For details, see the LICENSE file in the top-level source
   7  * directory or online at http://www.openafs.org/dl/license10.html
   8  */
   9
  10 /*******************************************************************\
  11 *                                                                   *
  12 *       Information Technology Center                               *
  13 *       Carnegie-Mellon University                                  *
  14 *                                                                   *
  15 *                                                                   *
  16 *                                                                   *
  17 \*******************************************************************/
  18
  19
  20 /*
  21         Locking routines for Vice.
  22
  23 */
  24
  25 #include <afsconfig.h>
  26 #include <afs/param.h>
  27
  28
  29 #ifdef AFS_PTHREAD_ENV
  30 #include <afs/assert.h>
  31 #else /* AFS_PTHREAD_ENV */
  32 #include <assert.h>
  33 #endif /* AFS_PTHRED_ENV */
  34 #include "lwp.h"
  35 #include "lock.h"
  36 #include <stdio.h>
  37
  38 #define FALSE   0
  39 #define TRUE    1
  40
  41 void
  42 Lock_Init(struct Lock *lock)
  43 {
  44     lock->readers_reading = 0;
  45     lock->excl_locked = 0;
  46     lock->wait_states = 0;
  47     lock->num_waiting = 0;
  48 #ifdef AFS_PTHREAD_ENV
  49     assert(pthread_mutex_init(&lock->mutex, (const pthread_mutexattr_t *)0) ==
  50            0);
  51     assert(pthread_cond_init(&lock->read_cv, (const pthread_condattr_t *)0) ==
  52            0);
  53     assert(pthread_cond_init(&lock->write_cv, (const pthread_condattr_t *)0)
  54            == 0);
  55 #endif /* AFS_PTHRED_ENV */
  56 }
  57
  58 void
  59 Lock_Destroy(struct Lock *lock)
  60 {
  61 #ifdef AFS_PTHREAD_ENV
  62     assert(pthread_mutex_destroy(&lock->mutex) == 0);
  63     assert(pthread_cond_destroy(&lock->read_cv) == 0);
  64     assert(pthread_cond_destroy(&lock->write_cv) == 0);
  65 #endif /* AFS_PTHRED_ENV */
  66 }
  67 \f
  68 void
  69 Afs_Lock_Obtain(struct Lock *lock, int how)
  70 {
  71     switch (how) {
  72
  73     case READ_LOCK:
  74         lock->num_waiting++;
  75         do {
  76             lock->wait_states |= READ_LOCK;
  77 #ifdef AFS_PTHREAD_ENV
  78             assert(pthread_cond_wait(&lock->read_cv, &lock->mutex) == 0);
  79 #else /* AFS_PTHREAD_ENV */
  80             LWP_WaitProcess(&lock->readers_reading);
  81 #endif /* AFS_PTHREAD_ENV */
  82         } while (lock->excl_locked & WRITE_LOCK);
  83         lock->num_waiting--;
  84         lock->readers_reading++;
  85         break;
  86
  87     case WRITE_LOCK:
  88         lock->num_waiting++;
  89         do {
  90             lock->wait_states |= WRITE_LOCK;
  91 #ifdef AFS_PTHREAD_ENV
  92             assert(pthread_cond_wait(&lock->write_cv, &lock->mutex) == 0);
  93 #else /* AFS_PTHREAD_ENV */
  94             LWP_WaitProcess(&lock->excl_locked);
  95 #endif /* AFS_PTHREAD_ENV */
  96         } while (lock->excl_locked || lock->readers_reading);
  97         lock->num_waiting--;
  98         lock->excl_locked = WRITE_LOCK;
  99         break;
 100
 101     case SHARED_LOCK:
 102         lock->num_waiting++;
 103         do {
 104             lock->wait_states |= SHARED_LOCK;
 105 #ifdef AFS_PTHREAD_ENV
 106             assert(pthread_cond_wait(&lock->write_cv, &lock->mutex) == 0);
 107 #else /* AFS_PTHREAD_ENV */
 108             LWP_WaitProcess(&lock->excl_locked);
 109 #endif /* AFS_PTHREAD_ENV */
 110         } while (lock->excl_locked);
 111         lock->num_waiting--;
 112         lock->excl_locked = SHARED_LOCK;
 113         break;
 114
 115     case BOOSTED_LOCK:
 116         lock->num_waiting++;
 117         do {
 118             lock->wait_states |= WRITE_LOCK;
 119 #ifdef AFS_PTHREAD_ENV
 120             assert(pthread_cond_wait(&lock->write_cv, &lock->mutex) == 0);
 121 #else /* AFS_PTHREAD_ENV */
 122             LWP_WaitProcess(&lock->excl_locked);
 123 #endif /* AFS_PTHREAD_ENV */
 124         } while (lock->readers_reading);
 125         lock->num_waiting--;
 126         lock->excl_locked = WRITE_LOCK;
 127         break;
 128
 129     default:
 130         printf("Can't happen, bad LOCK type: %d\n", how);
 131         assert(0);
 132     }
 133 }
 134
 135 /* wake up readers waiting for this lock */
 136 void
 137 Afs_Lock_WakeupR(struct Lock *lock)
 138 {
 139     if (lock->wait_states & READ_LOCK) {
 140         lock->wait_states &= ~READ_LOCK;
 141 #ifdef AFS_PTHREAD_ENV
 142         assert(pthread_cond_broadcast(&lock->read_cv) == 0);
 143 #else /* AFS_PTHREAD_ENV */
 144         LWP_NoYieldSignal(&lock->readers_reading);
 145 #endif /* AFS_PTHREAD_ENV */
 146     }
 147 }
 148
 149 /* release a lock, giving preference to new readers */
 150 void
 151 Afs_Lock_ReleaseR(struct Lock *lock)
 152 {
 153     if (lock->wait_states & READ_LOCK) {
 154         lock->wait_states &= ~READ_LOCK;
 155 #ifdef AFS_PTHREAD_ENV
 156         assert(pthread_cond_broadcast(&lock->read_cv) == 0);
 157 #else /* AFS_PTHREAD_ENV */
 158         LWP_NoYieldSignal(&lock->readers_reading);
 159 #endif /* AFS_PTHREAD_ENV */
 160     } else {
 161         lock->wait_states &= ~EXCL_LOCKS;
 162 #ifdef AFS_PTHREAD_ENV
 163         assert(pthread_cond_broadcast(&lock->write_cv) == 0);
 164 #else /* AFS_PTHREAD_ENV */
 165         LWP_NoYieldSignal(&lock->excl_locked);
 166 #endif /* AFS_PTHREAD_ENV */
 167     }
 168 }
 169
 170 /* release a lock, giving preference to new writers */
 171 void
 172 Afs_Lock_ReleaseW(struct Lock *lock)
 173 {
 174     if (lock->wait_states & EXCL_LOCKS) {
 175         lock->wait_states &= ~EXCL_LOCKS;
 176 #ifdef AFS_PTHREAD_ENV
 177         assert(pthread_cond_broadcast(&lock->write_cv) == 0);
 178 #else /* AFS_PTHREAD_ENV */
 179         LWP_NoYieldSignal(&lock->excl_locked);
 180 #endif /* AFS_PTHREAD_ENV */
 181     } else {
 182         lock->wait_states &= ~READ_LOCK;
 183 #ifdef AFS_PTHREAD_ENV
 184         assert(pthread_cond_broadcast(&lock->read_cv) == 0);
 185 #else /* AFS_PTHREAD_ENV */
 186         LWP_NoYieldSignal(&lock->readers_reading);
 187 #endif /* AFS_PTHREAD_ENV */
 188     }
 189 }
 190
 191 #ifndef AFS_PTHREAD_ENV
 192 /* These next guys exist to provide an interface to drop a lock atomically with
 193  * blocking.  They're trivial to do in a non-preemptive LWP environment.
 194  */
 195
 196 /* release a write lock and sleep on an address, atomically */
 197 void
 198 LWP_WaitProcessR(void *addr, struct Lock *alock)
 199 {
 200     ReleaseReadLock(alock);
 201     LWP_WaitProcess(addr);
 202 }
 203
 204 /* release a write lock and sleep on an address, atomically */
 205 void
 206 LWP_WaitProcessW(void *addr, struct Lock *alock)
 207 {
 208     ReleaseWriteLock(alock);
 209     LWP_WaitProcess(addr);
 210 }
 211
 212 /* release a write lock and sleep on an address, atomically */
 213 void
 214 LWP_WaitProcessS(void *addr, struct Lock *alock)
 215 {
 216     ReleaseSharedLock(alock);
 217     LWP_WaitProcess(addr);
 218 }
 219 #endif /* AFS_PTHREAD_ENV */