pthread_lock.c revision 1.1.2.9
1 /* $NetBSD: pthread_lock.c,v 1.1.2.9 2002/10/16 18:34:40 nathanw Exp $ */ 2 3 /*- 4 * Copyright (c) 2001 The NetBSD Foundation, Inc. 5 * All rights reserved. 6 * 7 * This code is derived from software contributed to The NetBSD Foundation 8 * by Nathan J. Williams. 9 * 10 * Redistribution and use in source and binary forms, with or without 11 * modification, are permitted provided that the following conditions 12 * are met: 13 * 1. Redistributions of source code must retain the above copyright 14 * notice, this list of conditions and the following disclaimer. 15 * 2. Redistributions in binary form must reproduce the above copyright 16 * notice, this list of conditions and the following disclaimer in the 17 * documentation and/or other materials provided with the distribution. 18 * 3. All advertising materials mentioning features or use of this software 19 * must display the following acknowledgement: 20 * This product includes software developed by the NetBSD 21 * Foundation, Inc. and its contributors. 22 * 4. Neither the name of The NetBSD Foundation nor the names of its 23 * contributors may be used to endorse or promote products derived 24 * from this software without specific prior written permission. 25 * 26 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 27 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 28 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 29 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 30 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 31 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 32 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 33 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 34 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 35 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 36 * POSSIBILITY OF SUCH DAMAGE. 37 */ 38 39 #include <assert.h> 40 #include <errno.h> 41 42 #include "pthread.h" 43 #include "pthread_int.h" 44 45 #undef PTHREAD_SA_DEBUG 46 47 #ifdef PTHREAD_SA_DEBUG 48 #define SDPRINTF(x) DPRINTF(x) 49 #else 50 #define SDPRINTF(x) 51 #endif 52 53 /* How many times to try before checking whether we've been continued. */ 54 #define NSPINS 20 /* XXX arbitrary */ 55 56 static int nspins = NSPINS; 57 58 void 59 pthread_lockinit(pthread_spin_t *lock) 60 { 61 62 __cpu_simple_lock_init(lock); 63 } 64 65 void 66 pthread_spinlock(pthread_t thread, pthread_spin_t *lock) 67 { 68 int count, ret; 69 70 count = nspins; 71 SDPRINTF(("(pthread_spinlock %p) incrementing spinlock from %d\n", 72 thread, thread->pt_spinlocks)); 73 ++thread->pt_spinlocks; 74 75 do { 76 while (((ret = __cpu_simple_lock_try(lock)) == 0) && --count) 77 ; 78 79 if (ret == 1) 80 break; 81 82 /* 83 * As long as this is uniprocessor, encountering a 84 * locked spinlock is a bug. 85 */ 86 assert (ret == 1); 87 88 SDPRINTF(("(pthread_spinlock %p) decrementing spinlock from %d\n", 89 thread, thread->pt_spinlocks)); 90 --thread->pt_spinlocks; 91 92 /* 93 * We may be preempted while spinning. If so, we will 94 * be restarted here if thread->pt_spinlocks is 95 * nonzero, which can happen if: 96 * a) we just got the lock 97 * b) we haven't yet decremented the lock count. 98 * If we're at this point, (b) applies. Therefore, 99 * check if we're being continued, and if so, bail. 100 * (in case (a), we should let the code finish and 101 * we will bail out in pthread_spinunlock()). 102 */ 103 if ((thread->pt_next != NULL) && 104 (thread->pt_type != PT_THREAD_UPCALL)) { 105 PTHREADD_ADD(PTHREADD_SPINPREEMPT); 106 pthread__switch(thread, thread->pt_next); 107 } 108 /* try again */ 109 count = nspins; 110 SDPRINTF(("(pthread_spinlock %p) incrementing spinlock from %d\n", 111 thread, thread->pt_spinlocks)); 112 ++thread->pt_spinlocks; 113 } while (/*CONSTCOND*/1); 114 115 PTHREADD_ADD(PTHREADD_SPINLOCKS); 116 /* Got it! We're out of here. */ 117 } 118 119 120 int 121 pthread_spintrylock(pthread_t thread, pthread_spin_t *lock) 122 { 123 int ret; 124 125 SDPRINTF(("(pthread_spinlock %p) incrementing spinlock from %d\n", 126 thread, thread->pt_spinlocks)); 127 ++thread->pt_spinlocks; 128 129 ret = __cpu_simple_lock_try(lock); 130 131 if (ret == 0) { 132 SDPRINTF(("(pthread_spintrylock %p) decrementing spinlock from %d\n", 133 thread, thread->pt_spinlocks)); 134 --thread->pt_spinlocks; 135 /* See above. */ 136 if ((thread->pt_next != NULL) && 137 (thread->pt_type != PT_THREAD_UPCALL)) { 138 PTHREADD_ADD(PTHREADD_SPINPREEMPT); 139 pthread__switch(thread, thread->pt_next); 140 } 141 } 142 143 return ret; 144 } 145 146 147 void 148 pthread_spinunlock(pthread_t thread, pthread_spin_t *lock) 149 { 150 151 __cpu_simple_unlock(lock); 152 SDPRINTF(("(pthread_spinunlock %p) decrementing spinlock from %d\n", 153 thread, thread->pt_spinlocks)); 154 --thread->pt_spinlocks; 155 156 PTHREADD_ADD(PTHREADD_SPINUNLOCKS); 157 158 /* 159 * If we were preempted while holding a spinlock, the 160 * scheduler will notice this and continue us. To be good 161 * citzens, we must now get out of here if that was our 162 * last spinlock. 163 * XXX when will we ever have more than one? 164 */ 165 166 if ((thread->pt_spinlocks == 0) && (thread->pt_next != NULL) 167 && (thread->pt_type != PT_THREAD_UPCALL)) { 168 PTHREADD_ADD(PTHREADD_SPINPREEMPT); 169 pthread__switch(thread, thread->pt_next); 170 } 171 } 172 173 174 /* 175 * Public (POSIX-specified) spinlocks. 176 * These don't interact with the spin-preemption code, nor do they 177 * perform any adaptive sleeping. 178 */ 179 180 int 181 pthread_spin_init(pthread_spinlock_t *lock, int pshared) 182 { 183 184 #ifdef ERRORCHECK 185 if ((lock == NULL) || 186 ((pshared != PTHREAD_PROCESS_PRIVATE) && 187 (pshared != PTHREAD_PROCESS_SHARED))) 188 return EINVAL; 189 #endif 190 lock->pts_magic = _PT_SPINLOCK_MAGIC; 191 /* 192 * We don't actually use the pshared flag for anything; 193 * cpu simple locks have all the process-shared properties 194 * that we want anyway. 195 */ 196 lock->pts_flags = pshared; 197 pthread_lockinit(&lock->pts_spin); 198 199 return 0; 200 } 201 202 int 203 pthread_spin_destroy(pthread_spinlock_t *lock) 204 { 205 206 #ifdef ERRORCHECK 207 if ((lock == NULL) || (lock->pts_magic != _PT_SPINLOCK_MAGIC)) 208 return EINVAL; 209 210 if (lock->pts_spin != __SIMPLELOCK_UNLOCKED) 211 return EBUSY; 212 #endif 213 214 lock->pts_magic = _PT_SPINLOCK_DEAD; 215 216 return 0; 217 } 218 219 int 220 pthread_spin_lock(pthread_spinlock_t *lock) 221 { 222 223 #ifdef ERRORCHECK 224 if ((lock == NULL) || (lock->pts_magic != _PT_SPINLOCK_MAGIC)) 225 return EINVAL; 226 #endif 227 228 __cpu_simple_lock(&lock->pts_spin); 229 230 return 0; 231 } 232 233 int 234 pthread_spin_trylock(pthread_spinlock_t *lock) 235 { 236 237 #ifdef ERRORCHECK 238 if ((lock == NULL) || (lock->pts_magic != _PT_SPINLOCK_MAGIC)) 239 return EINVAL; 240 #endif 241 242 if (__cpu_simple_lock_try(&lock->pts_spin) == 0) 243 return EBUSY; 244 245 return 0; 246 } 247 248 int 249 pthread_spin_unlock(pthread_spinlock_t *lock) 250 { 251 252 #ifdef ERRORCHECK 253 if ((lock == NULL) || (lock->pts_magic != _PT_SPINLOCK_MAGIC)) 254 return EINVAL; 255 #endif 256 257 __cpu_simple_unlock(&lock->pts_spin); 258 259 return 0; 260 } 261 262
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