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_mutex_t bio_mutex[REDIS_BIO_NUM_OPS];
  65 static pthread_cond_t bio_condvar[REDIS_BIO_NUM_OPS];
  66 static list *bio_jobs[REDIS_BIO_NUM_OPS];
  67 /* The following array is used to hold the number of pending jobs for every
  68  * OP type. This allows us to export the bioPendingJobsOfType() API that is
  69  * useful when the main thread wants to perform some operation that may involve
  70  * objects shared with the background thread. The main thread will just wait
  71  * that there are no longer jobs of this type to be executed before performing
  72  * the sensible operation. This data is also useful for reporting. */
  73 static unsigned long long bio_pending[REDIS_BIO_NUM_OPS];
  74
  75 /* This structure represents a background Job. It is only used locally to this
  76  * file as the API deos not expose the internals at all. */
  77 struct bio_job {
  78     time_t time; /* Time at which the job was created. */
  79     /* Job specific arguments pointers. If we need to pass more than three
  80      * arguments we can just pass a pointer to a structure or alike. */
  81     void *arg1, *arg2, *arg3;
  82 };
  83
  84 void *bioProcessBackgroundJobs(void *arg);
  85
  86 /* Make sure we have enough stack to perform all the things we do in the
  87  * main thread. */
  88 #define REDIS_THREAD_STACK_SIZE (1024*1024*4)
  89
  90 /* Initialize the background system, spawning the thread. */
  91 void bioInit(void) {
  92     pthread_attr_t attr;
  93     pthread_t thread;
  94     size_t stacksize;
  95     int j;
  96
  97     /* Initialization of state vars and objects */
  98     for (j = 0; j < REDIS_BIO_NUM_OPS; j++) {
  99         pthread_mutex_init(&bio_mutex[j],NULL);
 100         pthread_cond_init(&bio_condvar[j],NULL);
 101         bio_jobs[j] = listCreate();
 102         bio_pending[j] = 0;
 103     }
 104
 105     /* Set the stack size as by default it may be small in some system */
 106     pthread_attr_init(&attr);
 107     pthread_attr_getstacksize(&attr,&stacksize);
 108     if (!stacksize) stacksize = 1; /* The world is full of Solaris Fixes */
 109     while (stacksize < REDIS_THREAD_STACK_SIZE) stacksize *= 2;
 110     pthread_attr_setstacksize(&attr, stacksize);
 111
 112     /* Ready to spawn our threads. We use the single argument the thread
 113      * function accepts in order to pass the job ID the thread is
 114      * responsible of. */
 115     for (j = 0; j < REDIS_BIO_NUM_OPS; j++) {
 116         void *arg = (void*)(unsigned long) j;
 117         if (pthread_create(&thread,&attr,bioProcessBackgroundJobs,arg) != 0) {
 118             redisLog(REDIS_WARNING,"Fatal: Can't initialize Background Jobs.");
 119             exit(1);
 120         }
 121     }
 122 }
 123
 124 void bioCreateBackgroundJob(int type, void *arg1, void *arg2, void *arg3) {
 125     struct bio_job *job = zmalloc(sizeof(*job));
 126
 127     job->time = time(NULL);
 128     job->arg1 = arg1;
 129     job->arg2 = arg2;
 130     job->arg3 = arg3;
 131     pthread_mutex_lock(&bio_mutex[type]);
 132     listAddNodeTail(bio_jobs[type],job);
 133     bio_pending[type]++;
 134     pthread_cond_signal(&bio_condvar[type]);
 135     pthread_mutex_unlock(&bio_mutex[type]);
 136 }
 137
 138 void *bioProcessBackgroundJobs(void *arg) {
 139     struct bio_job *job;
 140     unsigned long type = (unsigned long) arg;
 141     sigset_t sigset;
 142
 143     pthread_detach(pthread_self());
 144     pthread_mutex_lock(&bio_mutex[type]);
 145     /* Block SIGALRM so we are sure that only the main thread will
 146      * receive the watchdog signal. */
 147     sigemptyset(&sigset);
 148     sigaddset(&sigset, SIGALRM);
 149     if (pthread_sigmask(SIG_BLOCK, &sigset, NULL))
 150         redisLog(REDIS_WARNING,
 151             "Warning: can't mask SIGALRM in bio.c thread: %s", strerror(errno));
 152
 153     while(1) {
 154         listNode *ln;
 155
 156         /* The loop always starts with the lock hold. */
 157         if (listLength(bio_jobs[type]) == 0) {
 158             pthread_cond_wait(&bio_condvar[type],&bio_mutex[type]);
 159             continue;
 160         }
 161         /* Pop the job from the queue. */
 162         ln = listFirst(bio_jobs[type]);
 163         job = ln->value;
 164         /* It is now possible to unlock the background system as we know have
 165          * a stand alone job structure to process.*/
 166         pthread_mutex_unlock(&bio_mutex[type]);
 167
 168         /* Process the job accordingly to its type. */
 169         if (type == REDIS_BIO_CLOSE_FILE) {
 170             close((long)job->arg1);
 171         } else if (type == REDIS_BIO_AOF_FSYNC) {
 172             aof_fsync((long)job->arg1);
 173         } else {
 174             redisPanic("Wrong job type in bioProcessBackgroundJobs().");
 175         }
 176         zfree(job);
 177
 178         /* Lock again before reiterating the loop, if there are no longer
 179          * jobs to process we'll block again in pthread_cond_wait(). */
 180         pthread_mutex_lock(&bio_mutex[type]);
 181         listDelNode(bio_jobs[type],ln);
 182         bio_pending[type]--;
 183     }
 184 }
 185
 186 /* Return the number of pending jobs of the specified type. */
 187 unsigned long long bioPendingJobsOfType(int type) {
 188     unsigned long long val;
 189     pthread_mutex_lock(&bio_mutex[type]);
 190     val = bio_pending[type];
 191     pthread_mutex_unlock(&bio_mutex[type]);
 192     return val;
 193 }
 194
 195 #if 0 /* We don't use the following code for now, and bioWaitPendingJobsLE
 196          probably needs a rewrite using conditional variables instead of the
 197          current implementation. */
 198
 199
 200 /* Wait until the number of pending jobs of the specified type are
 201  * less or equal to the specified number.
 202  *
 203  * This function may block for long time, it should only be used to perform
 204  * the following tasks:
 205  *
 206  * 1) To avoid that the main thread is pushing jobs of a given time so fast
 207  *    that the background thread can't process them at the same speed.
 208  *    So before creating a new job of a given type the main thread should
 209  *    call something like: bioWaitPendingJobsLE(job_type,10000);
 210  * 2) In order to perform special operations that make it necessary to be sure
 211  *    no one is touching shared resourced in the background.
 212  */
 213 void bioWaitPendingJobsLE(int type, unsigned long long num) {
 214     unsigned long long iteration = 0;
 215
 216     /* We poll the jobs queue aggressively to start, and gradually relax
 217      * the polling speed if it is going to take too much time. */
 218     while(1) {
 219         iteration++;
 220         if (iteration > 1000 && iteration <= 10000) {
 221             usleep(100);
 222         } else if (iteration > 10000) {
 223             usleep(1000);
 224         }
 225         if (bioPendingJobsOfType(type) <= num) break;
 226     }
 227 }
 228
 229 /* Return the older job of the specified type. */
 230 time_t bioOlderJobOfType(int type) {
 231     time_t time;
 232     listNode *ln;
 233     struct bio_job *job;
 234
 235     pthread_mutex_lock(&bio_mutex[type]);
 236     ln = listFirst(bio_jobs[type]);
 237     if (ln == NULL) {
 238         pthread_mutex_unlock(&bio_mutex[type]);
 239         return 0;
 240     }
 241     job = ln->value;
 242     time = job->time;
 243     pthread_mutex_unlock(&bio_mutex[type]);
 244     return time;
 245 }
 246
 247 #endif