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 #include "redis.h"
  32 #include "bio.h"
  33
  34 static pthread_mutex_t bio_mutex[REDIS_BIO_NUM_OPS];
  35 static pthread_cond_t bio_condvar[REDIS_BIO_NUM_OPS];
  36 static list *bio_jobs[REDIS_BIO_NUM_OPS];
  37 /* The following array is used to hold the number of pending jobs for every
  38  * OP type. This allows us to export the bioPendingJobsOfType() API that is
  39  * useful when the main thread wants to perform some operation that may involve
  40  * objects shared with the background thread. The main thread will just wait
  41  * that there are no longer jobs of this type to be executed before performing
  42  * the sensible operation. This data is also useful for reporting. */
  43 static unsigned long long bio_pending[REDIS_BIO_NUM_OPS];
  44
  45 /* This structure represents a background Job. It is only used locally to this
  46  * file as the API deos not expose the internals at all. */
  47 struct bio_job {
  48     time_t time; /* Time at which the job was created. */
  49     /* Job specific arguments pointers. If we need to pass more than three
  50      * arguments we can just pass a pointer to a structure or alike. */
  51     void *arg1, *arg2, *arg3;
  52 };
  53
  54 void *bioProcessBackgroundJobs(void *arg);
  55
  56 /* Make sure we have enough stack to perform all the things we do in the
  57  * main thread. */
  58 #define REDIS_THREAD_STACK_SIZE (1024*1024*4)
  59
  60 /* Initialize the background system, spawning the thread. */
  61 void bioInit(void) {
  62     pthread_attr_t attr;
  63     pthread_t thread;
  64     size_t stacksize;
  65     int j;
  66
  67     /* Initialization of state vars and objects */
  68     for (j = 0; j < REDIS_BIO_NUM_OPS; j++) {
  69         pthread_mutex_init(&bio_mutex[j],NULL);
  70         pthread_cond_init(&bio_condvar[j],NULL);
  71         bio_jobs[j] = listCreate();
  72         bio_pending[j] = 0;
  73     }
  74
  75     /* Set the stack size as by default it may be small in some system */
  76     pthread_attr_init(&attr);
  77     pthread_attr_getstacksize(&attr,&stacksize);
  78     if (!stacksize) stacksize = 1; /* The world is full of Solaris Fixes */
  79     while (stacksize < REDIS_THREAD_STACK_SIZE) stacksize *= 2;
  80     pthread_attr_setstacksize(&attr, stacksize);
  81
  82     /* Ready to spawn our threads. We use the single argument the thread
  83      * function accepts in order to pass the job ID the thread is
  84      * responsible of. */
  85     for (j = 0; j < REDIS_BIO_NUM_OPS; j++) {
  86         void *arg = (void*)(unsigned long) j;
  87         if (pthread_create(&thread,&attr,bioProcessBackgroundJobs,arg) != 0) {
  88             redisLog(REDIS_WARNING,"Fatal: Can't initialize Background Jobs.");
  89             exit(1);
  90         }
  91     }
  92 }
  93
  94 void bioCreateBackgroundJob(int type, void *arg1, void *arg2, void *arg3) {
  95     struct bio_job *job = zmalloc(sizeof(*job));
  96
  97     job->time = time(NULL);
  98     job->arg1 = arg1;
  99     job->arg2 = arg2;
 100     job->arg3 = arg3;
 101     pthread_mutex_lock(&bio_mutex[type]);
 102     listAddNodeTail(bio_jobs[type],job);
 103     bio_pending[type]++;
 104     pthread_cond_signal(&bio_condvar[type]);
 105     pthread_mutex_unlock(&bio_mutex[type]);
 106 }
 107
 108 void *bioProcessBackgroundJobs(void *arg) {
 109     struct bio_job *job;
 110     unsigned long type = (unsigned long) arg;
 111
 112     pthread_detach(pthread_self());
 113     pthread_mutex_lock(&bio_mutex[type]);
 114     while(1) {
 115         listNode *ln;
 116
 117         /* The loop always starts with the lock hold. */
 118         if (listLength(bio_jobs[type]) == 0) {
 119             pthread_cond_wait(&bio_condvar[type],&bio_mutex[type]);
 120             continue;
 121         }
 122         /* Pop the job from the queue. */
 123         ln = listFirst(bio_jobs[type]);
 124         job = ln->value;
 125         /* It is now possible to unlock the background system as we know have
 126          * a stand alone job structure to process.*/
 127         pthread_mutex_unlock(&bio_mutex[type]);
 128
 129         /* Process the job accordingly to its type. */
 130         if (type == REDIS_BIO_CLOSE_FILE) {
 131             close((long)job->arg1);
 132         } else if (type == REDIS_BIO_AOF_FSYNC) {
 133             fsync((long)job->arg1);
 134         } else {
 135             redisPanic("Wrong job type in bioProcessBackgroundJobs().");
 136         }
 137         zfree(job);
 138
 139         /* Lock again before reiterating the loop, if there are no longer
 140          * jobs to process we'll block again in pthread_cond_wait(). */
 141         pthread_mutex_lock(&bio_mutex[type]);
 142         listDelNode(bio_jobs[type],ln);
 143         bio_pending[type]--;
 144     }
 145 }
 146
 147 /* Return the number of pending jobs of the specified type. */
 148 unsigned long long bioPendingJobsOfType(int type) {
 149     unsigned long long val;
 150     pthread_mutex_lock(&bio_mutex[type]);
 151     val = bio_pending[type];
 152     pthread_mutex_unlock(&bio_mutex[type]);
 153     return val;
 154 }
 155
 156 /* Wait until the number of pending jobs of the specified type are
 157  * less or equal to the specified number.
 158  *
 159  * This function may block for long time, it should only be used to perform
 160  * the following tasks:
 161  *
 162  * 1) To avoid that the main thread is pushing jobs of a given time so fast
 163  *    that the background thread can't process them at the same speed.
 164  *    So before creating a new job of a given type the main thread should
 165  *    call something like: bioWaitPendingJobsLE(job_type,10000);
 166  * 2) In order to perform special operations that make it necessary to be sure
 167  *    no one is touching shared resourced in the background.
 168  */
 169 void bioWaitPendingJobsLE(int type, unsigned long long num) {
 170     unsigned long long iteration = 0;
 171
 172     /* We poll the jobs queue aggressively to start, and gradually relax
 173      * the polling speed if it is going to take too much time. */
 174     while(1) {
 175         iteration++;
 176         if (iteration > 1000 && iteration <= 10000) {
 177             usleep(100);
 178         } else if (iteration > 10000) {
 179             usleep(1000);
 180         }
 181         if (bioPendingJobsOfType(type) <= num) break;
 182     }
 183 }
 184
 185 /* Return the older job of the specified type. */
 186 time_t bioOlderJobOfType(int type) {
 187     time_t time;
 188     listNode *ln;
 189     struct bio_job *job;
 190
 191     pthread_mutex_lock(&bio_mutex[type]);
 192     ln = listFirst(bio_jobs[type]);
 193     if (ln == NULL) {
 194         pthread_mutex_unlock(&bio_mutex[type]);
 195         return 0;
 196     }
 197     job = ln->value;
 198     time = job->time;
 199     pthread_mutex_unlock(&bio_mutex[type]);
 200     return time;
 201 }
 202