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/* Background I/O service for Redis.
*
* This file implements operations that we need to perform in the background.
* Currently there is only a single operation, that is a background close(2)
* system call. This is needed as when the process is the last owner of a
* reference to a file closing it means unlinking it, and the deletion of the
* file is slow, blocking the server.
*
* In the future we'll either continue implementing new things we need or
* we'll switch to libeio. However there are probably long term uses for this
* file as we may want to put here Redis specific background tasks (for instance
* it is not impossible that we'll need a non blocking FLUSHDB/FLUSHALL
* implementation).
*
* DESIGN
* ------
*
* The design is trivial, we have a structure representing a job to perform
* and a different thread and job queue for every job type.
* Every thread wait for new jobs in its queue, and process every job
* sequentially.
*
* Currently there is no way for the creator of the job to be notified about
* the completion of the operation, this will only be added when/if needed.
*/
#include "redis.h"
#include "bio.h"
static pthread_mutex_t bio_mutex[REDIS_BIO_NUM_OPS];
static pthread_cond_t bio_condvar[REDIS_BIO_NUM_OPS];
static list *bio_jobs[REDIS_BIO_NUM_OPS];
/* The following array is used to hold the number of pending jobs for every
* OP type. This allows us to export the bioPendingJobsOfType() API that is
* useful when the main thread wants to perform some operation that may involve
* objects shared with the background thread. The main thread will just wait
* that there are no longer jobs of this type to be executed before performing
* the sensible operation. This data is also useful for reporting. */
static unsigned long long bio_pending[REDIS_BIO_NUM_OPS];
/* This structure represents a background Job. It is only used locally to this
* file as the API deos not expose the internals at all. */
struct bio_job {
time_t time; /* Time at which the job was created. */
/* Job specific arguments pointers. If we need to pass more than three
* arguments we can just pass a pointer to a structure or alike. */
void *arg1, *arg2, *arg3;
};
void *bioProcessBackgroundJobs(void *arg);
/* Make sure we have enough stack to perform all the things we do in the
* main thread. */
#define REDIS_THREAD_STACK_SIZE (1024*1024*4)
/* Initialize the background system, spawning the thread. */
void bioInit(void) {
pthread_attr_t attr;
pthread_t thread;
size_t stacksize;
int j;
/* Initialization of state vars and objects */
for (j = 0; j < REDIS_BIO_NUM_OPS; j++) {
pthread_mutex_init(&bio_mutex[j],NULL);
pthread_cond_init(&bio_condvar[j],NULL);
bio_jobs[j] = listCreate();
bio_pending[j] = 0;
}
/* Set the stack size as by default it may be small in some system */
pthread_attr_init(&attr);
pthread_attr_getstacksize(&attr,&stacksize);
if (!stacksize) stacksize = 1; /* The world is full of Solaris Fixes */
while (stacksize < REDIS_THREAD_STACK_SIZE) stacksize *= 2;
pthread_attr_setstacksize(&attr, stacksize);
/* Ready to spawn our threads. We use the single argument the thread
* function accepts in order to pass the job ID the thread is
* responsible of. */
for (j = 0; j < REDIS_BIO_NUM_OPS; j++) {
void *arg = (void*)(unsigned long) j;
if (pthread_create(&thread,&attr,bioProcessBackgroundJobs,arg) != 0) {
redisLog(REDIS_WARNING,"Fatal: Can't initialize Background Jobs.");
exit(1);
}
}
}
void bioCreateBackgroundJob(int type, void *arg1, void *arg2, void *arg3) {
struct bio_job *job = zmalloc(sizeof(*job));
job->time = time(NULL);
job->arg1 = arg1;
job->arg2 = arg2;
job->arg3 = arg3;
pthread_mutex_lock(&bio_mutex[type]);
listAddNodeTail(bio_jobs[type],job);
bio_pending[type]++;
pthread_cond_signal(&bio_condvar[type]);
pthread_mutex_unlock(&bio_mutex[type]);
}
void *bioProcessBackgroundJobs(void *arg) {
struct bio_job *job;
unsigned long type = (unsigned long) arg;
pthread_detach(pthread_self());
pthread_mutex_lock(&bio_mutex[type]);
while(1) {
listNode *ln;
/* The loop always starts with the lock hold. */
if (listLength(bio_jobs[type]) == 0) {
pthread_cond_wait(&bio_condvar[type],&bio_mutex[type]);
continue;
}
/* Pop the job from the queue. */
ln = listFirst(bio_jobs[type]);
job = ln->value;
/* It is now possible to unlock the background system as we know have
* a stand alone job structure to process.*/
pthread_mutex_unlock(&bio_mutex[type]);
/* Process the job accordingly to its type. */
if (type == REDIS_BIO_CLOSE_FILE) {
close((long)job->arg1);
} else {
redisPanic("Wrong job type in bioProcessBackgroundJobs().");
}
zfree(job);
/* Lock again before reiterating the loop, if there are no longer
* jobs to process we'll block again in pthread_cond_wait(). */
pthread_mutex_lock(&bio_mutex[type]);
listDelNode(bio_jobs[type],ln);
bio_pending[type]--;
}
}
/* Return the number of pending jobs of the specified type. */
unsigned long long bioPendingJobsOfType(int type) {
unsigned long long val;
pthread_mutex_lock(&bio_mutex[type]);
val = bio_pending[type];
pthread_mutex_unlock(&bio_mutex[type]);
return val;
}
/* Wait until the number of pending jobs of the specified type are
* less or equal to the specified number.
*
* This function may block for long time, it should only be used to perform
* the following tasks:
*
* 1) To avoid that the main thread is pushing jobs of a given time so fast
* that the background thread can't process them at the same speed.
* So before creating a new job of a given type the main thread should
* call something like: bioWaitPendingJobsLE(job_type,10000);
* 2) In order to perform special operations that make it necessary to be sure
* no one is touching shared resourced in the background.
*/
void bioWaitPendingJobsLE(int type, unsigned long long num) {
unsigned long long iteration = 0;
/* We poll the jobs queue aggressively to start, and gradually relax
* the polling speed if it is going to take too much time. */
while(1) {
iteration++;
if (iteration > 1000 && iteration <= 10000) {
usleep(100);
} else if (iteration > 10000) {
usleep(1000);
}
if (bioPendingJobsOfType(type) <= num) break;
}
}
/* Return the older job of the specified type. */
time_t bioOlderJobOfType(int type) {
time_t time;
listNode *ln;
struct bio_job *job;
pthread_mutex_lock(&bio_mutex[type]);
ln = listFirst(bio_jobs[type]);
job = ln->value;
time = job->time;
pthread_mutex_unlock(&bio_mutex[type]);
return time;
}
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