1 /* Background I/O service for Redis. 2 * 3 * This file implements operations that we need to perform in the background. 4 * Currently there is only a single operation, that is a background close(2) 5 * system call. This is needed as when the process is the last owner of a 6 * reference to a file closing it means unlinking it, and the deletion of the 7 * file is slow, blocking the server. 8 * 9 * In the future we'll either continue implementing new things we need or 10 * we'll switch to libeio. However there are probably long term uses for this 11 * file as we may want to put here Redis specific background tasks (for instance 12 * it is not impossible that we'll need a non blocking FLUSHDB/FLUSHALL 13 * implementation). 14 * 15 * DESIGN 16 * ------ 17 * 18 * The design is trivial, we have a structure representing a job to perform 19 * and a different thread and job queue for every job type. 20 * Every thread wait for new jobs in its queue, and process every job 21 * sequentially. 22 * 23 * Jobs of the same type are guaranteed to be processed from the least 24 * recently inserted to the most recently inserted (older jobs processed 25 * first). 26 * 27 * Currently there is no way for the creator of the job to be notified about 28 * the completion of the operation, this will only be added when/if needed. 29 * 30 * ---------------------------------------------------------------------------- 31 * 32 * Copyright (c) 2009-2012, Salvatore Sanfilippo <antirez at gmail dot com> 33 * All rights reserved. 34 * 35 * Redistribution and use in source and binary forms, with or without 36 * modification, are permitted provided that the following conditions are met: 37 * 38 * * Redistributions of source code must retain the above copyright notice, 39 * this list of conditions and the following disclaimer. 40 * * Redistributions in binary form must reproduce the above copyright 41 * notice, this list of conditions and the following disclaimer in the 42 * documentation and/or other materials provided with the distribution. 43 * * Neither the name of Redis nor the names of its contributors may be used 44 * to endorse or promote products derived from this software without 45 * specific prior written permission. 46 * 47 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" 48 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 49 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 50 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE 51 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 52 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 53 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 54 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 55 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 56 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 57 * POSSIBILITY OF SUCH DAMAGE. 58 */ 59 60 61 #include "server.h" 62 #include "bio.h" 63 64 static pthread_t bio_threads[BIO_NUM_OPS]; 65 static pthread_mutex_t bio_mutex[BIO_NUM_OPS]; 66 static pthread_cond_t bio_condvar[BIO_NUM_OPS]; 67 static list *bio_jobs[BIO_NUM_OPS]; 68 /* The following array is used to hold the number of pending jobs for every 69 * OP type. This allows us to export the bioPendingJobsOfType() API that is 70 * useful when the main thread wants to perform some operation that may involve 71 * objects shared with the background thread. The main thread will just wait 72 * that there are no longer jobs of this type to be executed before performing 73 * the sensible operation. This data is also useful for reporting. */ 74 static unsigned long long bio_pending[BIO_NUM_OPS]; 75 76 /* This structure represents a background Job. It is only used locally to this 77 * file as the API does not expose the internals at all. */ 78 struct bio_job { 79 time_t time; /* Time at which the job was created. */ 80 /* Job specific arguments pointers. If we need to pass more than three 81 * arguments we can just pass a pointer to a structure or alike. */ 82 void *arg1, *arg2, *arg3; 83 }; 84 85 void *bioProcessBackgroundJobs(void *arg); 86 87 /* Make sure we have enough stack to perform all the things we do in the 88 * main thread. */ 89 #define REDIS_THREAD_STACK_SIZE (1024*1024*4) 90 91 /* Initialize the background system, spawning the thread. */ 92 void bioInit(void) { 93 pthread_attr_t attr; 94 pthread_t thread; 95 size_t stacksize; 96 int j; 97 98 /* Initialization of state vars and objects */ 99 for (j = 0; j < BIO_NUM_OPS; j++) { 100 pthread_mutex_init(&bio_mutex[j],NULL); 101 pthread_cond_init(&bio_condvar[j],NULL); 102 bio_jobs[j] = listCreate(); 103 bio_pending[j] = 0; 104 } 105 106 /* Set the stack size as by default it may be small in some system */ 107 pthread_attr_init(&attr); 108 pthread_attr_getstacksize(&attr,&stacksize); 109 if (!stacksize) stacksize = 1; /* The world is full of Solaris Fixes */ 110 while (stacksize < REDIS_THREAD_STACK_SIZE) stacksize *= 2; 111 pthread_attr_setstacksize(&attr, stacksize); 112 113 /* Ready to spawn our threads. We use the single argument the thread 114 * function accepts in order to pass the job ID the thread is 115 * responsible of. */ 116 for (j = 0; j < BIO_NUM_OPS; j++) { 117 void *arg = (void*)(unsigned long) j; 118 if (pthread_create(&thread,&attr,bioProcessBackgroundJobs,arg) != 0) { 119 serverLog(LL_WARNING,"Fatal: Can't initialize Background Jobs."); 120 exit(1); 121 } 122 bio_threads[j] = thread; 123 } 124 } 125 126 void bioCreateBackgroundJob(int type, void *arg1, void *arg2, void *arg3) { 127 struct bio_job *job = zmalloc(sizeof(*job)); 128 129 job->time = time(NULL); 130 job->arg1 = arg1; 131 job->arg2 = arg2; 132 job->arg3 = arg3; 133 pthread_mutex_lock(&bio_mutex[type]); 134 listAddNodeTail(bio_jobs[type],job); 135 bio_pending[type]++; 136 pthread_cond_signal(&bio_condvar[type]); 137 pthread_mutex_unlock(&bio_mutex[type]); 138 } 139 140 void *bioProcessBackgroundJobs(void *arg) { 141 struct bio_job *job; 142 unsigned long type = (unsigned long) arg; 143 sigset_t sigset; 144 145 /* Check that the type is within the right interval. */ 146 if (type >= BIO_NUM_OPS) { 147 serverLog(LL_WARNING, 148 "Warning: bio thread started with wrong type %lu",type); 149 return NULL; 150 } 151 152 /* Make the thread killable at any time, so that bioKillThreads() 153 * can work reliably. */ 154 pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, NULL); 155 pthread_setcanceltype(PTHREAD_CANCEL_ASYNCHRONOUS, NULL); 156 157 pthread_mutex_lock(&bio_mutex[type]); 158 /* Block SIGALRM so we are sure that only the main thread will 159 * receive the watchdog signal. */ 160 sigemptyset(&sigset); 161 sigaddset(&sigset, SIGALRM); 162 if (pthread_sigmask(SIG_BLOCK, &sigset, NULL)) 163 serverLog(LL_WARNING, 164 "Warning: can't mask SIGALRM in bio.c thread: %s", strerror(errno)); 165 166 while(1) { 167 listNode *ln; 168 169 /* The loop always starts with the lock hold. */ 170 if (listLength(bio_jobs[type]) == 0) { 171 pthread_cond_wait(&bio_condvar[type],&bio_mutex[type]); 172 continue; 173 } 174 /* Pop the job from the queue. */ 175 ln = listFirst(bio_jobs[type]); 176 job = ln->value; 177 /* It is now possible to unlock the background system as we know have 178 * a stand alone job structure to process.*/ 179 pthread_mutex_unlock(&bio_mutex[type]); 180 181 /* Process the job accordingly to its type. */ 182 if (type == BIO_CLOSE_FILE) { 183 close((long)job->arg1); 184 } else if (type == BIO_AOF_FSYNC) { 185 aof_fsync((long)job->arg1); 186 } else { 187 serverPanic("Wrong job type in bioProcessBackgroundJobs()."); 188 } 189 zfree(job); 190 191 /* Lock again before reiterating the loop, if there are no longer 192 * jobs to process we'll block again in pthread_cond_wait(). */ 193 pthread_mutex_lock(&bio_mutex[type]); 194 listDelNode(bio_jobs[type],ln); 195 bio_pending[type]--; 196 } 197 } 198 199 /* Return the number of pending jobs of the specified type. */ 200 unsigned long long bioPendingJobsOfType(int type) { 201 unsigned long long val; 202 pthread_mutex_lock(&bio_mutex[type]); 203 val = bio_pending[type]; 204 pthread_mutex_unlock(&bio_mutex[type]); 205 return val; 206 } 207 208 /* Kill the running bio threads in an unclean way. This function should be 209 * used only when it's critical to stop the threads for some reason. 210 * Currently Redis does this only on crash (for instance on SIGSEGV) in order 211 * to perform a fast memory check without other threads messing with memory. */ 212 void bioKillThreads(void) { 213 int err, j; 214 215 for (j = 0; j < BIO_NUM_OPS; j++) { 216 if (pthread_cancel(bio_threads[j]) == 0) { 217 if ((err = pthread_join(bio_threads[j],NULL)) != 0) { 218 serverLog(LL_WARNING, 219 "Bio thread for job type #%d can be joined: %s", 220 j, strerror(err)); 221 } else { 222 serverLog(LL_WARNING, 223 "Bio thread for job type #%d terminated",j); 224 } 225 } 226 } 227 } 228