1 /* $OpenBSD: rthread_file.c,v 1.2 2017/08/15 06:38:41 guenther Exp $ */ 2 /* 3 * Copyright (c) 1995 John Birrell <jb@cimlogic.com.au>. 4 * All rights reserved. 5 * 6 * Redistribution and use in source and binary forms, with or without 7 * modification, are permitted provided that the following conditions 8 * are met: 9 * 1. Redistributions of source code must retain the above copyright 10 * notice, this list of conditions and the following disclaimer. 11 * 2. Redistributions in binary form must reproduce the above copyright 12 * notice, this list of conditions and the following disclaimer in the 13 * documentation and/or other materials provided with the distribution. 14 * 3. All advertising materials mentioning features or use of this software 15 * must display the following acknowledgement: 16 * This product includes software developed by John Birrell. 17 * 4. Neither the name of the author nor the names of any co-contributors 18 * may be used to endorse or promote products derived from this software 19 * without specific prior written permission. 20 * 21 * THIS SOFTWARE IS PROVIDED BY JOHN BIRRELL AND CONTRIBUTORS ``AS IS'' AND 22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 24 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 31 * SUCH DAMAGE. 32 * 33 * $FreeBSD: uthread_file.c,v 1.9 1999/08/28 00:03:32 peter Exp $ 34 * 35 * POSIX stdio FILE locking functions. These assume that the locking 36 * is only required at FILE structure level, not at file descriptor 37 * level too. 38 * 39 */ 40 41 #include <sys/queue.h> 42 #include <pthread.h> 43 #include <stdint.h> 44 #include <stdio.h> 45 #include <stdlib.h> 46 47 #include "rthread.h" 48 #include "rthread_cb.h" 49 50 /* 51 * The FILE lock structure. The FILE *fp is locked if the owner is 52 * not NULL. If not locked, the file lock structure can be 53 * reassigned to a different file by setting fp. 54 */ 55 struct file_lock { 56 LIST_ENTRY(file_lock) entry; /* Entry if file list. */ 57 FILE *fp; /* The target file. */ 58 struct pthread_queue lockers; 59 pthread_t owner; 60 int count; 61 }; 62 63 /* 64 * The number of file lock lists into which the file pointer is 65 * hashed. Ideally, the FILE structure size would have been increased, 66 * but this causes incompatibility, so separate data structures are 67 * required. 68 */ 69 #define NUM_HEADS 128 70 71 /* 72 * This macro casts a file pointer to a long integer and right 73 * shifts this by the number of bytes in a pointer. The shifted 74 * value is then remaindered using the maximum number of hash 75 * entries to produce and index into the array of static lock 76 * structures. If there is a collision, a linear search of the 77 * dynamic list of locks linked to each static lock is perfomed. 78 */ 79 #define file_idx(_p) ((int)((((uintptr_t) _p) >> sizeof(void *)) % NUM_HEADS)) 80 81 /* 82 * Global array of file locks. The first lock for each hash bucket is 83 * allocated statically in the hope that there won't be too many 84 * collisions that require a malloc and an element added to the list. 85 */ 86 static struct static_file_lock { 87 LIST_HEAD(file_list_head, file_lock) head; 88 struct file_lock fl; 89 } flh[NUM_HEADS]; 90 91 /* Lock for accesses to the hash table: */ 92 static _atomic_lock_t hash_lock = _SPINLOCK_UNLOCKED; 93 94 /* 95 * Find a lock structure for a FILE, return NULL if the file is 96 * not locked: 97 */ 98 static 99 struct file_lock * 100 find_lock(int idx, FILE *fp) 101 { 102 struct file_lock *p; 103 104 /* Check if the file is locked using the static structure: */ 105 if (flh[idx].fl.fp == fp && flh[idx].fl.owner != NULL) 106 /* Return a pointer to the static lock: */ 107 p = &flh[idx].fl; 108 else { 109 /* Point to the first dynamic lock: */ 110 p = LIST_FIRST(&flh[idx].head); 111 112 /* 113 * Loop through the dynamic locks looking for the 114 * target file: 115 */ 116 while (p != NULL && (p->fp != fp || p->owner == NULL)) 117 /* Not this file, try the next: */ 118 p = LIST_NEXT(p, entry); 119 } 120 return(p); 121 } 122 123 /* 124 * Lock a file, assuming that there is no lock structure currently 125 * assigned to it. 126 */ 127 static 128 struct file_lock * 129 do_lock(int idx, FILE *fp) 130 { 131 struct file_lock *p; 132 133 /* Check if the static structure is not being used: */ 134 if (flh[idx].fl.owner == NULL) { 135 /* Return a pointer to the static lock: */ 136 p = &flh[idx].fl; 137 } 138 else { 139 /* Point to the first dynamic lock: */ 140 p = LIST_FIRST(&flh[idx].head); 141 142 /* 143 * Loop through the dynamic locks looking for a 144 * lock structure that is not being used: 145 */ 146 while (p != NULL && p->owner != NULL) 147 /* This one is used, try the next: */ 148 p = LIST_NEXT(p, entry); 149 } 150 151 /* 152 * If an existing lock structure has not been found, 153 * allocate memory for a new one: 154 */ 155 if (p == NULL && (p = (struct file_lock *) 156 malloc(sizeof(struct file_lock))) != NULL) { 157 /* Add the new element to the list: */ 158 LIST_INSERT_HEAD(&flh[idx].head, p, entry); 159 } 160 161 /* Check if there is a lock structure to acquire: */ 162 if (p != NULL) { 163 /* Acquire the lock for the running thread: */ 164 p->fp = fp; 165 p->owner = pthread_self(); 166 p->count = 1; 167 TAILQ_INIT(&p->lockers); 168 } 169 return(p); 170 } 171 172 void 173 _thread_flockfile(FILE * fp) 174 { 175 int idx = file_idx(fp); 176 struct file_lock *p; 177 pthread_t self = pthread_self(); 178 179 /* Lock the hash table: */ 180 _spinlock(&hash_lock); 181 182 /* Get a pointer to any existing lock for the file: */ 183 if ((p = find_lock(idx, fp)) == NULL) { 184 /* 185 * The file is not locked, so this thread can 186 * grab the lock: 187 */ 188 do_lock(idx, fp); 189 190 /* 191 * The file is already locked, so check if the 192 * running thread is the owner: 193 */ 194 } else if (p->owner == self) { 195 /* 196 * The running thread is already the 197 * owner, so increment the count of 198 * the number of times it has locked 199 * the file: 200 */ 201 p->count++; 202 } else { 203 /* 204 * The file is locked for another thread. 205 * Append this thread to the queue of 206 * threads waiting on the lock. 207 */ 208 TAILQ_INSERT_TAIL(&p->lockers,self,waiting); 209 while (p->owner != self) { 210 __thrsleep(self, 0, NULL, &hash_lock, NULL); 211 _spinlock(&hash_lock); 212 } 213 } 214 215 /* Unlock the hash table: */ 216 _spinunlock(&hash_lock); 217 } 218 219 int 220 _thread_ftrylockfile(FILE * fp) 221 { 222 int ret = -1; 223 int idx = file_idx(fp); 224 struct file_lock *p; 225 226 /* Lock the hash table: */ 227 _spinlock(&hash_lock); 228 229 /* Get a pointer to any existing lock for the file: */ 230 if ((p = find_lock(idx, fp)) == NULL) { 231 /* 232 * The file is not locked, so this thread can 233 * grab the lock: 234 */ 235 p = do_lock(idx, fp); 236 237 /* 238 * The file is already locked, so check if the 239 * running thread is the owner: 240 */ 241 } else if (p->owner == pthread_self()) { 242 /* 243 * The running thread is already the 244 * owner, so increment the count of 245 * the number of times it has locked 246 * the file: 247 */ 248 p->count++; 249 } else { 250 /* 251 * The file is locked for another thread, 252 * so this try fails. 253 */ 254 p = NULL; 255 } 256 257 /* Unlock the hash table: */ 258 _spinunlock(&hash_lock); 259 260 /* Check if the lock was obtained: */ 261 if (p != NULL) 262 /* Return success: */ 263 ret = 0; 264 265 return (ret); 266 } 267 268 void 269 _thread_funlockfile(FILE * fp) 270 { 271 int idx = file_idx(fp); 272 struct file_lock *p; 273 274 /* Lock the hash table: */ 275 _spinlock(&hash_lock); 276 277 /* 278 * Get a pointer to the lock for the file and check that 279 * the running thread is the one with the lock: 280 */ 281 if ((p = find_lock(idx, fp)) != NULL && p->owner == pthread_self()) { 282 /* 283 * Check if this thread has locked the FILE 284 * more than once: 285 */ 286 if (--p->count == 0) { 287 /* Get the new owner of the lock: */ 288 if ((p->owner = TAILQ_FIRST(&p->lockers)) != NULL) { 289 /* Pop the thread off the queue: */ 290 TAILQ_REMOVE(&p->lockers,p->owner,waiting); 291 292 /* 293 * This is the first lock for the new 294 * owner: 295 */ 296 p->count = 1; 297 298 __thrwakeup(p->owner, 1); 299 } 300 } 301 } 302 303 /* Unlock the hash table: */ 304 _spinunlock(&hash_lock); 305 } 306