int main(int argc, char *argv[])
{
    zend_signal_startup();
    // 將全局變量sapi_module設(shè)置為cgi_sapi_module
    sapi_startup(&cgi_sapi_module);
    fcgi_init();
    // 獲取命令行參數(shù)，其中php-fpm -D、-i等參數(shù)都是在這里被解析出來的
    // ...
    cgi_sapi_module.startup(&cgi_sapi_module);
    fpm_init(argc, argv, fpm_config ? fpm_config : CGIG(fpm_config), fpm_prefix, fpm_pid, test_conf, php_allow_to_run_as_root, force_daemon, force_stderr);
    // master進程會在這一步死循環(huán),后面的流程都是子進程在執(zhí)行。
    fcgi_fd = fpm_run(&max_requests);
    fcgi_fd = fpm_run(&max_requests);
    request = fpm_init_request(fcgi_fd);
    // accept請求
    // ....
}

// fpm中的事件結(jié)構(gòu)體
struct fpm_event_s {
    // 事件的句柄
    int fd;
    // 下一次觸發(fā)的事件
    struct timeval timeout;
    // 頻率:多久執(zhí)行一次
    struct timeval frequency;
    // 事件觸發(fā)時調(diào)用的函數(shù)
    void (*callback)(struct fpm_event_s *, short, void *);
    void *arg;                // 調(diào)用callback時的參數(shù)
    // FPM_EV_READ:讀;FPM_EV_TIMEOUT:;FPM_EV_PERSIST:;FPM_EV_EDGE:;
    int flags;
    int index;                // 在fd句柄數(shù)組中的索引
    // 事件的類型 FPM_EV_READ:讀;FPM_EV_TIMEOUT:計時器;FPM_EV_PERSIST:;FPM_EV_EDGE:;
    short which;
};
// 事件隊列
typedef struct fpm_event_queue_s {
    struct fpm_event_queue_s *prev;
    struct fpm_event_queue_s *next;
    struct fpm_event_s *ev;
} fpm_event_queue;

void fpm_event_loop(int err)
{
    static struct fpm_event_s signal_fd_event;
    // 創(chuàng)建一個事件:管道sp[0]可讀時觸發(fā)
    fpm_event_set(&signal_fd_event, fpm_signals_get_fd(), FPM_EV_READ, &fpm_got_signal, NULL);
    // 將事件添加進queue
    fpm_event_add(&signal_fd_event, 0);
    // 處理定時器等邏輯
    // 以阻塞的方式獲取事件
    // module->wait()是一個接口定義的方法簽名，下面展示kqueue的實現(xiàn)
    ret = module->wait(fpm_event_queue_fd, timeout);
}
int fpm_event_add(struct fpm_event_s *ev, unsigned long int frequency)
{
    // ...
    // 如果事件是觸發(fā)事件則之間添加進queue中
    // 對于定時器事件先根據(jù)事件的frequency設(shè)置事件的觸發(fā)頻率和下一次觸發(fā)的事件
    if (fpm_event_queue_add(&fpm_event_queue_timer, ev) != 0) {
        return -1;
    }
    return 0;
}
static int fpm_event_queue_add(struct fpm_event_queue_s **queue, struct fpm_event_s *ev)
{
    // ...
    // 構(gòu)建并將當(dāng)前事件插入事件隊列queue中
    if (*queue == fpm_event_queue_fd && module->add) {
        // module->add(ev)是一個接口定義的方法簽名，下面展示kqueue的實現(xiàn)
        module->add(ev);
    }
    return 0;
}
// kqueue關(guān)于添加事件到kqueue的實現(xiàn)
static int fpm_event_kqueue_add(struct fpm_event_s *ev) /* {{{ */
{
    struct kevent k;
    int flags = EV_ADD;
    if (ev->flags & FPM_EV_EDGE) {
            flags = flags | EV_CLEAR;
    }
    EV_SET(&k, ev->fd, EVFILT_READ, flags, 0, 0, (void *)ev);
    if (kevent(kfd, &k, 1, NULL, 0, NULL) < 0) {
        zlog(ZLOG_ERROR, "kevent: unable to add event");
        return -1;
    }
    /* mark the event as registered */
    ev->index = ev->fd;
    return 0;
}

// kqueue關(guān)于從kqueue中監(jiān)聽事件的實現(xiàn)
static int fpm_event_kqueue_wait(struct fpm_event_queue_s *queue, unsigned long int timeout) /* {{{ */
{
    struct timespec t;
    int ret, i;
    /* ensure we have a clean kevents before calling kevent() */
    memset(kevents, 0, sizeof(struct kevent) * nkevents);
    /* convert ms to timespec struct */
    t.tv_sec = timeout / 1000;
    t.tv_nsec = (timeout % 1000) * 1000 * 1000;
    /* wait for incoming event or timeout */
    ret = kevent(kfd, NULL, 0, kevents, nkevents, &t);
    if (ret == -1) {
        /* trigger error unless signal interrupt */
        if (errno != EINTR) {
            zlog(ZLOG_WARNING, "epoll_wait() returns %d", errno);
            return -1;
        }
    }
    /* fire triggered events */
    for (i = 0; i < ret; i++) {
        if (kevents[i].udata) {
            struct fpm_event_s *ev = (struct fpm_event_s *)kevents[i].udata;
            fpm_event_fire(ev);
            /* sanity check */
            if (fpm_globals.parent_pid != getpid()) {
                return -2;
            }
        }
    }
    return ret;
}

// fpm_scoreboard_s 結(jié)構(gòu)
struct fpm_scoreboard_s {
    union {
        atomic_t lock;
        char dummy[16];
    };
    char pool[32];
    int pm;                    // 進程的管理方式 static、dynamic、ondemand
    time_t start_epoch;
    int idle;                // 空閑的worker進程數(shù)
    int active;                // 繁忙的worker進程數(shù)
    int active_max;            // 最大繁忙進程數(shù)
    unsigned long int requests;
    unsigned int max_children_reached;
    int lq;
    int lq_max;
    unsigned int lq_len;
    unsigned int nprocs;
    int free_proc;
    unsigned long int slow_rq;
    struct fpm_scoreboard_proc_s *procs[];
};

int fpm_signals_init_main() /* {{{ */
{
    struct sigaction act;
    // 創(chuàng)建一個全雙工套接字
    // 全雙工的套接字是一個可以讀、寫的socket通道[0]和[1]，每個進程固定一個管道。
    // 寫數(shù)據(jù)時：管道不滿不會被阻塞；讀數(shù)據(jù)時：管道里沒有數(shù)據(jù)會阻塞(可設(shè)置)
    // 向sp[0]寫入數(shù)據(jù)時，sp[0]的讀取將會被阻塞,sp[1]的寫管道會被阻塞，sp[1]中此時讀取sp[0]的數(shù)據(jù)
    if (0 > socketpair(AF_UNIX, SOCK_STREAM, 0, sp)) {
        zlog(ZLOG_SYSERROR, "failed to init signals: socketpair()");
        return -1;
    }
    if (0 > fd_set_blocked(sp[0], 0) || 0 > fd_set_blocked(sp[1], 0)) {
        zlog(ZLOG_SYSERROR, "failed to init signals: fd_set_blocked()");
        return -1;
    }
    if (0 > fcntl(sp[0], F_SETFD, FD_CLOEXEC) || 0 > fcntl(sp[1], F_SETFD, FD_CLOEXEC)) {
        zlog(ZLOG_SYSERROR, "falied to init signals: fcntl(F_SETFD, FD_CLOEXEC)");
        return -1;
    }
    memset(&act, 0, sizeof(act));
    act.sa_handler = sig_handler;       // 監(jiān)聽到信號調(diào)用這個函數(shù)
    sigfillset(&act.sa_mask);
    if (0 > sigaction(SIGTERM,  &act, 0) ||
        0 > sigaction(SIGINT,   &act, 0) ||
        0 > sigaction(SIGUSR1,  &act, 0) ||
        0 > sigaction(SIGUSR2,  &act, 0) ||
        0 > sigaction(SIGCHLD,  &act, 0) ||
        0 > sigaction(SIGQUIT,  &act, 0)) {
        zlog(ZLOG_SYSERROR, "failed to init signals: sigaction()");
        return -1;
    }
    return 0;
}
// 所有信號共用同一個處理函數(shù)
static void sig_handler(int signo) /* {{{ */
{
    static const char sig_chars[NSIG + 1] = {
        [SIGTERM] = 'T',
        [SIGINT]  = 'I',
        [SIGUSR1] = '1',
        [SIGUSR2] = '2',
        [SIGQUIT] = 'Q',
        [SIGCHLD] = 'C'
    };
    char s;
    int saved_errno;
    if (fpm_globals.parent_pid != getpid()) {
        return;
    }
    saved_errno = errno;
    s = sig_chars[signo];
    zend_quiet_write(sp[1], &s, sizeof(s)); // 將信息對應(yīng)的字節(jié)寫進管道sp[1]端，此時sp[1]端的讀數(shù)據(jù)會阻塞;數(shù)據(jù)可以從sp[0]端讀取
    errno = saved_errno;
}

int fpm_event_init_main()
{
    // ...
    if (module->init(max) < 0) {
        zlog(ZLOG_ERROR, "Unable to initialize the event module %s", module->name);
        return -1;
    }
    // ...
}
// max用于指定kqueue事件數(shù)組的大小
static int fpm_event_kqueue_init(int max) /* {{{ */
{
    if (max < 1) {
        return 0;
    }
    kfd = kqueue();
    if (kfd < 0) {
        zlog(ZLOG_ERROR, "kqueue: unable to initialize");
        return -1;
    }
    kevents = malloc(sizeof(struct kevent) * max);
    if (!kevents) {
        zlog(ZLOG_ERROR, "epoll: unable to allocate %d events", max);
        return -1;
    }
    memset(kevents, 0, sizeof(struct kevent) * max);
    nkevents = max;
    return 0;
}

int fpm_run(int *max_requests) /* {{{ */
{
    struct fpm_worker_pool_s *wp;
    /* create initial children in all pools */
    for (wp = fpm_worker_all_pools; wp; wp = wp->next) {
        int is_parent;
        is_parent = fpm_children_create_initial(wp);
        if (!is_parent) {
            goto run_child;
        }
    }
    /* run event loop forever */
    fpm_event_loop(0);
run_child: /* only workers reach this point */
    fpm_cleanups_run(FPM_CLEANUP_CHILD);
    *max_requests = fpm_globals.max_requests;
    return fpm_globals.listening_socket;
}

...
// 初始化request
request = fpm_init_request(fcgi_fd);
zend_first_try {
    // accept接收請求
    while (EXPECTED(fcgi_accept_request(request) >= 0)) {
        init_request_info();
        fpm_request_info();
        if (UNEXPECTED(php_request_startup() == FAILURE)) {
            // ...
        }
        if (UNEXPECTED(fpm_status_handle_request())) {
            goto fastcgi_request_done;
        }
        ...
        // 打開配置文件中DOCUMENT_ROOT設(shè)置的腳本
        if (UNEXPECTED(php_fopen_primary_script(&file_handle) == FAILURE)) {
            ...
        }
        fpm_request_executing();
        // 執(zhí)行腳本
        php_execute_script(&file_handle);
        ...
    }
    // 銷毀請求request
    fcgi_destroy_request(request);
    // fcgi退出
    fcgi_shutdown();
    if (cgi_sapi_module.php_ini_path_override) {
        free(cgi_sapi_module.php_ini_path_override);
    }
    if (cgi_sapi_module.ini_entries) {
        free(cgi_sapi_module.ini_entries);
    }
} zend_catch {
    ...
} zend_end_try();