src/bio.c

   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 "redis.h"
  62 #include "bio.h"
  63
  64 static pthread_t bio_threads[REDIS_BIO_NUM_OPS];
  65 static pthread_mutex_t bio_mutex[REDIS_BIO_NUM_OPS];
  66 static pthread_cond_t bio_condvar[REDIS_BIO_NUM_OPS];
  67 static list *bio_jobs[REDIS_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[REDIS_BIO_NUM_OPS];
  75
  76 /* This structure represents a background Job. It is only used locally to this
  77  * file as the API deos 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 < REDIS_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 < REDIS_BIO_NUM_OPS; j++) {
 117         void *arg = (void*)(unsigned long) j;
 118         if (pthread_create(&thread,&attr,bioProcessBackgroundJobs,arg) != 0) {
 119             redisLog(REDIS_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     /* Make the thread killable at any time, so that bioKillThreads()
 146      * can work reliably. */
 147     pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, NULL);
 148     pthread_setcanceltype(PTHREAD_CANCEL_ASYNCHRONOUS, NULL);
 149
 150     pthread_mutex_lock(&bio_mutex[type]);
 151     /* Block SIGALRM so we are sure that only the main thread will
 152      * receive the watchdog signal. */
 153     sigemptyset(&sigset);
 154     sigaddset(&sigset, SIGALRM);
 155     if (pthread_sigmask(SIG_BLOCK, &sigset, NULL))
 156         redisLog(REDIS_WARNING,
 157             "Warning: can't mask SIGALRM in bio.c thread: %s", strerror(errno));
 158
 159     while(1) {
 160         listNode *ln;
 161
 162         /* The loop always starts with the lock hold. */
 163         if (listLength(bio_jobs[type]) == 0) {
 164             pthread_cond_wait(&bio_condvar[type],&bio_mutex[type]);
 165             continue;
 166         }
 167         /* Pop the job from the queue. */
 168         ln = listFirst(bio_jobs[type]);
 169         job = ln->value;
 170         /* It is now possible to unlock the background system as we know have
 171          * a stand alone job structure to process.*/
 172         pthread_mutex_unlock(&bio_mutex[type]);
 173
 174         /* Process the job accordingly to its type. */
 175         if (type == REDIS_BIO_CLOSE_FILE) {
 176             close((long)job->arg1);
 177         } else if (type == REDIS_BIO_AOF_FSYNC) {
 178             aof_fsync((long)job->arg1);
 179         } else {
 180             redisPanic("Wrong job type in bioProcessBackgroundJobs().");
 181         }
 182         zfree(job);
 183
 184         /* Lock again before reiterating the loop, if there are no longer
 185          * jobs to process we'll block again in pthread_cond_wait(). */
 186         pthread_mutex_lock(&bio_mutex[type]);
 187         listDelNode(bio_jobs[type],ln);
 188         bio_pending[type]--;
 189     }
 190 }
 191
 192 /* Return the number of pending jobs of the specified type. */
 193 unsigned long long bioPendingJobsOfType(int type) {
 194     unsigned long long val;
 195     pthread_mutex_lock(&bio_mutex[type]);
 196     val = bio_pending[type];
 197     pthread_mutex_unlock(&bio_mutex[type]);
 198     return val;
 199 }
 200
 201 /* Kill the running bio threads in an unclean way. This function should be
 202  * used only when it's critical to stop the threads for some reason.
 203  * Currently Redis does this only on crash (for instance on SIGSEGV) in order
 204  * to perform a fast memory check without other threads messing with memory. */
 205 void bioKillThreads(void) {
 206     int err, j;
 207
 208     for (j = 0; j < REDIS_BIO_NUM_OPS; j++) {
 209         if (pthread_cancel(bio_threads[j]) == 0) {
 210             if ((err = pthread_join(bio_threads[j],NULL)) != 0) {
 211                 redisLog(REDIS_WARNING,
 212                     "Bio thread for job type #%d can be joined: %s",
 213                         j, strerror(err));
 214             } else {
 215                 redisLog(REDIS_WARNING,
 216                     "Bio thread for job type #%d terminated",j);
 217             }
 218         }
 219     }
 220 }