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 single thread performing all the I/O operations in the queue.
  20  * Currently there is no way for the creator of the job to be notified about
  21  * the completion of the operation, this will only be added when/if needed.
  22  */
  23
  24 #include "redis.h"
  25 #include "bio.h"
  26
  27 static pthread_mutex_t bio_mutex;
  28 static pthread_cond_t bio_condvar;
  29 list *bio_jobs;
  30
  31 /* This structure represents a background Job. It is only used locally to this
  32  * file as the API deos not expose the internals at all. */
  33 struct bio_job {
  34     int type;       /* Job type, for instance BIO_JOB_CLOSE */
  35     void *data;     /* Job specific arguments pointer. */
  36 }
  37
  38 void *bioProcessBackgroundJobs(void *arg);
  39
  40 /* Initialize the background system, spawning the thread. */
  41 void bioInit(void) {
  42     pthread_attr_t attr;
  43     pthread_t thread;
  44     size_t stacksize;
  45
  46     pthread_mutex_init(bio_mutex,NULL);
  47     pthread_cond_init(bio_condvar,NULL);
  48     bio_jobs = listCreate();
  49
  50     /* Set the stack size as by default it may be small in some system */
  51     pthread_attr_init(&attr);
  52     pthread_attr_getstacksize(&attr);
  53     if (!stacksize) stacksize = 1; /* The world is full of Solaris Fixes */
  54     while (stacksize < REDIS_THREAD_STACK_SIZE) stacksize *= 2;
  55     pthread_attr_setstacksize(&attr, stacksize);
  56
  57     /* Ready to spawn our thread */
  58     if (pthread_create(&thread,&attr,bioProcessBackgroundJobs,NULL) != 0) {
  59         redisLog(REDIS_WARNING,"Fatal: Can't initialize Background Jobs.");
  60         exit(1);
  61     }
  62 }
  63
  64 void bioCreateBackgroundJob(int type, void *data) {
  65     struct bio_job *job = zmalloc(sizeof(*job));
  66
  67     job->type = type;
  68     job->data = data;
  69     pthread_mutex_lock(&bio_mutex);
  70     listAddNodeTail(bio_jobs,job);
  71     pthread_mutex_unlock(&bio_mutex);
  72 }
  73
  74 void *bioProcessBackgroundJobs(void *arg) {
  75     struct bio_job *job;
  76
  77     pthread_detach(pthread_self());
  78     pthread_mutex_lock(&bio_mutex);
  79     while(1) {
  80         listNode *ln;
  81
  82         /* The loop always starts with the lock hold. */
  83         if (listLength(server.io_newjobs) == 0) {
  84             pthread_cond_wait(&bio_condvar,&bio_mutex);
  85             continue;
  86         }
  87         /* Pop the job from the queue. */
  88         ln = listFirst(bio_jobs);
  89         job = ln->value;
  90         listDelNode(bio_jobs,ln);
  91         /* It is now possible to unlock the background system as we know have
  92          * a stand alone job structure to process.*/
  93         pthread_mutex_unlock(&bio_mutex);
  94
  95         /* Process the job accordingly to its type. */
  96         if (job->type == REDIS_BIO_CLOSE_FILE) {
  97             close((long)job->data);
  98         } else {
  99             redisPanic("Wrong job type in bioProcessBackgroundJobs().");
 100         }
 101         zfree(job);
 102
 103         /* Lock again before reiterating the loop, if there are no longer
 104          * jobs to process we'll block again in pthread_cond_wait(). */
 105         pthread_mutex_lock(&bio_mutex);
 106     }
 107 }