Function redisFork

src/server.cpp:6958–7014

purpose is one of CHILD_TYPE_ types */

/* purpose is one of CHILD_TYPE_ types */
int redisFork(int purpose) {
    int childpid;
    long long start = ustime();
    
    if (isMutuallyExclusiveChildType(purpose)) {
        if (hasActiveChildProcess())
            return -1;

        openChildInfoPipe();
    }
    long long startWriteLock = ustime();
    aeAcquireForkLock();
    latencyAddSampleIfNeeded("fork-lock",(ustime()-startWriteLock)/1000);
    if ((childpid = fork()) == 0) {
        /* Child */
        aeForkLockInChild();
        aeReleaseForkLock();
        g_pserver->in_fork_child = purpose;
        setOOMScoreAdj(CONFIG_OOM_BGCHILD);
        setupChildSignalHandlers();
        closeChildUnusedResourceAfterFork();
    } else {
        /* Parent */
        aeReleaseForkLock();
        g_pserver->stat_total_forks++;
        g_pserver->stat_fork_time = ustime()-start;
        g_pserver->stat_fork_rate = (double) zmalloc_used_memory() * 1000000 / g_pserver->stat_fork_time / (1024*1024*1024); /* GB per second. */
        latencyAddSampleIfNeeded("fork",g_pserver->stat_fork_time/1000);
        if (childpid == -1) {
            if (isMutuallyExclusiveChildType(purpose)) closeChildInfoPipe();
            return -1;
        }

        /* The child_pid and child_type are only for mutual exclusive children.
         * other child types should handle and store their pid's in dedicated variables.
         *
         * Today, we allows CHILD_TYPE_LDB to run in parallel with the other fork types:
         * - it isn't used for production, so it will not make the server be less efficient
         * - used for debugging, and we don't want to block it from running while other
         *   forks are running (like RDB and AOF) */
        if (isMutuallyExclusiveChildType(purpose)) {
            g_pserver->child_pid = childpid;
            g_pserver->child_type = purpose;
            g_pserver->stat_current_cow_bytes = 0;
            g_pserver->stat_current_cow_updated = 0;
            g_pserver->stat_current_save_keys_processed = 0;
            g_pserver->stat_module_progress = 0;
            g_pserver->stat_current_save_keys_total = dbTotalServerKeyCount();
        }

        updateDictResizePolicy();
        moduleFireServerEvent(REDISMODULE_EVENT_FORK_CHILD,
                              REDISMODULE_SUBEVENT_FORK_CHILD_BORN,
                              NULL);
    }
    return childpid;
}