Gossip about redis source code 78

bio Operation related implementation , For threads , The mutex , Condition variables, , Also need to understand clearly ：

#include "server.h"
#include "bio.h"

static pthread_t bio_threads[BIO_NUM_OPS];
static pthread_mutex_t bio_mutex[BIO_NUM_OPS];
static pthread_cond_t bio_newjob_cond[BIO_NUM_OPS];
static pthread_cond_t bio_step_cond[BIO_NUM_OPS];
static list *bio_jobs[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[BIO_NUM_OPS];

/* This structure represents a background Job. It is only used locally to this
 * file as the API does not expose the internals at all. */
struct bio_job {
    time_t time; /* Time at which the job was created. */
    /* Job specific arguments.*/
    int fd; /* Fd for file based background jobs */
    lazy_free_fn *free_fn; /* Function that will free the provided arguments */
    void *free_args[]; /* List of arguments to be passed to the free function */
};

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 < BIO_NUM_OPS; j++) {
        pthread_mutex_init(&bio_mutex[j],NULL);
        pthread_cond_init(&bio_newjob_cond[j],NULL);
        pthread_cond_init(&bio_step_cond[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 < BIO_NUM_OPS; j++) {
        void *arg = (void*)(unsigned long) j;
        if (pthread_create(&thread,&attr,bioProcessBackgroundJobs,arg) != 0) {
            serverLog(LL_WARNING,"Fatal: Can't initialize Background Jobs.");
            exit(1);
        }
        bio_threads[j] = thread;
    }
}

void bioSubmitJob(int type, struct bio_job *job) {
    job->time = time(NULL);
    pthread_mutex_lock(&bio_mutex[type]);
    listAddNodeTail(bio_jobs[type],job);
    bio_pending[type]++;
    pthread_cond_signal(&bio_newjob_cond[type]);
    pthread_mutex_unlock(&bio_mutex[type]);
}

void bioCreateLazyFreeJob(lazy_free_fn free_fn, int arg_count, ...) {
    va_list valist;
    /* Allocate memory for the job structure and all required
     * arguments */
    struct bio_job *job = zmalloc(sizeof(*job) + sizeof(void *) * (arg_count));
    job->free_fn = free_fn;

    va_start(valist, arg_count);
    for (int i = 0; i < arg_count; i++) {
        job->free_args[i] = va_arg(valist, void *);
    }
    va_end(valist);
    bioSubmitJob(BIO_LAZY_FREE, job);
}

void bioCreateCloseJob(int fd) {
    struct bio_job *job = zmalloc(sizeof(*job));
    job->fd = fd;

    bioSubmitJob(BIO_CLOSE_FILE, job);
}

void bioCreateFsyncJob(int fd) {
    struct bio_job *job = zmalloc(sizeof(*job));
    job->fd = fd;

    bioSubmitJob(BIO_AOF_FSYNC, job);
}

void *bioProcessBackgroundJobs(void *arg) {
    struct bio_job *job;
    unsigned long type = (unsigned long) arg;
    sigset_t sigset;

    /* Check that the type is within the right interval. */
    if (type >= BIO_NUM_OPS) {
        serverLog(LL_WARNING,
            "Warning: bio thread started with wrong type %lu",type);
        return NULL;
    }

    switch (type) {
    case BIO_CLOSE_FILE:
        redis_set_thread_title("bio_close_file");
        break;
    case BIO_AOF_FSYNC:
        redis_set_thread_title("bio_aof_fsync");
        break;
    case BIO_LAZY_FREE:
        redis_set_thread_title("bio_lazy_free");
        break;
    }

    redisSetCpuAffinity(server.bio_cpulist);

    makeThreadKillable();

    pthread_mutex_lock(&bio_mutex[type]);
    /* Block SIGALRM so we are sure that only the main thread will
     * receive the watchdog signal. */
    sigemptyset(&sigset);
    sigaddset(&sigset, SIGALRM);
    if (pthread_sigmask(SIG_BLOCK, &sigset, NULL))
        serverLog(LL_WARNING,
            "Warning: can't mask SIGALRM in bio.c thread: %s", strerror(errno));

    while(1) {
        listNode *ln;

        /* The loop always starts with the lock hold. */
        if (listLength(bio_jobs[type]) == 0) {
            pthread_cond_wait(&bio_newjob_cond[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 == BIO_CLOSE_FILE) {
            close(job->fd);
        } else if (type == BIO_AOF_FSYNC) {
            /* The fd may be closed by main thread and reused for another
             * socket, pipe, or file. We just ignore these errno because
             * aof fsync did not really fail. */
            if (redis_fsync(job->fd) == -1 &&
                errno != EBADF && errno != EINVAL)
            {
                int last_status;
                atomicGet(server.aof_bio_fsync_status,last_status);
                atomicSet(server.aof_bio_fsync_status,C_ERR);
                atomicSet(server.aof_bio_fsync_errno,errno);
                if (last_status == C_OK) {
                    serverLog(LL_WARNING,
                        "Fail to fsync the AOF file: %s",strerror(errno));
                }
            } else {
                atomicSet(server.aof_bio_fsync_status,C_OK);
            }
        } else if (type == BIO_LAZY_FREE) {
            job->free_fn(job->free_args);
        } else {
            serverPanic("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]--;

        /* Unblock threads blocked on bioWaitStepOfType() if any. */
        pthread_cond_broadcast(&bio_step_cond[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;
}

/* If there are pending jobs for the specified type, the function blocks
 * and waits that the next job was processed. Otherwise the function
 * does not block and returns ASAP.
 *
 * The function returns the number of jobs still to process of the
 * requested type.
 *
 * This function is useful when from another thread, we want to wait
 * a bio.c thread to do more work in a blocking way.
 */
unsigned long long bioWaitStepOfType(int type) {
    unsigned long long val;
    pthread_mutex_lock(&bio_mutex[type]);
    val = bio_pending[type];
    if (val != 0) {
        pthread_cond_wait(&bio_step_cond[type],&bio_mutex[type]);
        val = bio_pending[type];
    }
    pthread_mutex_unlock(&bio_mutex[type]);
    return val;
}

/* Kill the running bio threads in an unclean way. This function should be
 * used only when it's critical to stop the threads for some reason.
 * Currently Redis does this only on crash (for instance on SIGSEGV) in order
 * to perform a fast memory check without other threads messing with memory. */
void bioKillThreads(void) {
    int err, j;

    for (j = 0; j < BIO_NUM_OPS; j++) {
        if (bio_threads[j] == pthread_self()) continue;
        if (bio_threads[j] && pthread_cancel(bio_threads[j]) == 0) {
            if ((err = pthread_join(bio_threads[j],NULL)) != 0) {
                serverLog(LL_WARNING,
                    "Bio thread for job type #%d can not be joined: %s",
                        j, strerror(err));
            } else {
                serverLog(LL_WARNING,
                    "Bio thread for job type #%d terminated",j);
            }
        }
    }
}