nginx 父子进程通信 channel

        nginx 中利用socketpair()函数，创建一对相互连接的socket，实现父子进程的通信。 下面分析下整个过程：

 

一  创建

       在子进程创建之前，需要创建这样一对连接：  ngx_spawn_process函数(ngx_process.c中)

//创建一对匿名的已经连接的套接字 if (socketpair(AF_UNIX, SOCK_STREAM, 0, ngx_processes[s].channel) == -1) { ngx_log_error(NGX_LOG_ALERT, cycle->log, ngx_errno, "socketpair() failed while spawning /"%s/"", name); return NGX_INVALID_PID; } ngx_log_debug2(NGX_LOG_DEBUG_CORE, cycle->log, 0, "channel %d:%d", ngx_processes[s].channel[0], ngx_processes[s].channel[1]); //设置成非阻塞模式 if (ngx_nonblocking(ngx_processes[s].channel[0]) == -1) { ngx_log_error(NGX_LOG_ALERT, cycle->log, ngx_errno, ngx_nonblocking_n " failed while spawning /"%s/"", name); ngx_close_channel(ngx_processes[s].channel, cycle->log); return NGX_INVALID_PID; } //设置成非阻塞模式 if (ngx_nonblocking(ngx_processes[s].channel[1]) == -1) { ngx_log_error(NGX_LOG_ALERT, cycle->log, ngx_errno, ngx_nonblocking_n " failed while spawning /"%s/"", name); ngx_close_channel(ngx_processes[s].channel, cycle->log); return NGX_INVALID_PID; } //打开异步模式 on = 1; if (ioctl(ngx_processes[s].channel[0], FIOASYNC, &on) == -1) { ngx_log_error(NGX_LOG_ALERT, cycle->log, ngx_errno, "ioctl(FIOASYNC) failed while spawning /"%s/"", name); ngx_close_channel(ngx_processes[s].channel, cycle->log); return NGX_INVALID_PID; } if (fcntl(ngx_processes[s].channel[0], F_SETOWN, ngx_pid) == -1) { ngx_log_error(NGX_LOG_ALERT, cycle->log, ngx_errno, "fcntl(F_SETOWN) failed while spawning /"%s/"", name); ngx_close_channel(ngx_processes[s].channel, cycle->log); return NGX_INVALID_PID; } if (fcntl(ngx_processes[s].channel[0], F_SETFD, FD_CLOEXEC) == -1) { ngx_log_error(NGX_LOG_ALERT, cycle->log, ngx_errno, "fcntl(FD_CLOEXEC) failed while spawning /"%s/"", name); ngx_close_channel(ngx_processes[s].channel, cycle->log); return NGX_INVALID_PID; } if (fcntl(ngx_processes[s].channel[1], F_SETFD, FD_CLOEXEC) == -1) { ngx_log_error(NGX_LOG_ALERT, cycle->log, ngx_errno, "fcntl(FD_CLOEXEC) failed while spawning /"%s/"", name); ngx_close_channel(ngx_processes[s].channel, cycle->log); return NGX_INVALID_PID; } //设置即将创建子进程的channel ，这个在后面会用到 ngx_channel = ngx_processes[s].channel[1];

 

二 创建子进程

     接着会通过fork创建子进程，在子进程中，会调用ngx_worker_process_init 函数(ngx_process_cycle.c)

//关闭所有其它进程对应的 channel[1] 和 自己的 channel[0] for (n = 0; n < ngx_last_process; n++) { if (ngx_processes[n].pid == -1) { continue; } if (n == ngx_process_slot) { continue; } if (ngx_processes[n].channel[1] == -1) { continue; } if (close(ngx_processes[n].channel[1]) == -1) { ngx_log_error(NGX_LOG_ALERT, cycle->log, ngx_errno, "close() channel failed"); } } if (close(ngx_processes[ngx_process_slot].channel[0]) == -1) { ngx_log_error(NGX_LOG_ALERT, cycle->log, ngx_errno, "close() channel failed"); }#if 0 ngx_last_process = 0;#endif //调用epoll add 把ngx_chanel 加入epoll 中 if (ngx_add_channel_event(cycle, ngx_channel, NGX_READ_EVENT, ngx_channel_handler) == NGX_ERROR) { /* fatal */ exit(2); }

 

channel[0] 是用来发送信息的，channel[1]是用来接收信息的。那么对自己而言，它需要向其他进程发送信息，需要保留其它进程的channel[0], 关闭channel[1]; 对自己而言，则需要关闭channel[0]。 最后把ngx_channel放到epoll中，从第一部分中的介绍我们可以知道，这个ngx_channel实际就是自己的 channel[1]。这样有信息进来的时候就可以通知到了。

 

三 实现子进程自己的通信

       子进程创建的时候，父进程的东西都会被子进程继承，所以后面创建的进程能够得到前面进程的channel信息，直接可以和他们通信，那么前面创建的进程如何知道后面的进程信息呢？ 很简单，既然前面创建的进程能够接受消息，那么我就发个信息告诉他后面的进程的channel,并把信息保存在channel[0]中，这样就可以相互通信了。

  ngx_pass_open_channel函数中实现(ngx_process_cycle.c)

 

static voidngx_pass_open_channel(ngx_cycle_t *cycle, ngx_channel_t *ch){ ngx_int_t i; //遍历所有的进程 for (i = 0; i < ngx_last_process; i++) { //不能是当前channel if (i == ngx_process_slot || ngx_processes[i].pid == -1 || ngx_processes[i].channel[0] == -1) { continue; } ngx_log_debug6(NGX_LOG_DEBUG_CORE, cycle->log, 0, "pass channel s:%d pid:%P fd:%d to s:%i pid:%P fd:%d", ch->slot, ch->pid, ch->fd, i, ngx_processes[i].pid, ngx_processes[i].channel[0]); /* TODO: NGX_AGAIN */ //向 每个进程 channel[0]发送信息 ngx_write_channel(ngx_processes[i].channel[0], ch, sizeof(ngx_channel_t), cycle->log); }}

 

我们来看看 ngx_write_channel

 

ngx_int_tngx_write_channel(ngx_socket_t s, ngx_channel_t *ch, size_t size, ngx_log_t *log){ ssize_t n; ngx_err_t err; struct iovec iov[1]; struct msghdr msg;#if (NGX_HAVE_MSGHDR_MSG_CONTROL) union { struct cmsghdr cm; char space[CMSG_SPACE(sizeof(int))]; } cmsg; if (ch->fd == -1) { msg.msg_control = NULL; msg.msg_controllen = 0; } else { msg.msg_control = (caddr_t) &cmsg; msg.msg_controllen = sizeof(cmsg); cmsg.cm.cmsg_len = CMSG_LEN(sizeof(int)); cmsg.cm.cmsg_level = SOL_SOCKET; cmsg.cm.cmsg_type = SCM_RIGHTS; /* * We have to use ngx_memcpy() instead of simple * *(int *) CMSG_DATA(&cmsg.cm) = ch->fd; * because some gcc 4.4 with -O2/3/s optimization issues the warning: * dereferencing type-punned pointer will break strict-aliasing rules * * Fortunately, gcc with -O1 compiles this ngx_memcpy() * in the same simple assigment as in the code above */ //赋值信息到 cmsg.cm ngx_memcpy(CMSG_DATA(&cmsg.cm), &ch->fd, sizeof(int)); } msg.msg_flags = 0;#else if (ch->fd == -1) { msg.msg_accrights = NULL; msg.msg_accrightslen = 0; } else { msg.msg_accrights = (caddr_t) &ch->fd; msg.msg_accrightslen = sizeof(int); }#endif iov[0].iov_base = (char *) ch; iov[0].iov_len = size; msg.msg_name = NULL; msg.msg_namelen = 0; msg.msg_iov = iov; msg.msg_iovlen = 1; n = sendmsg(s, &msg, 0); if (n == -1) { err = ngx_errno; if (err == NGX_EAGAIN) { return NGX_AGAIN; } ngx_log_error(NGX_LOG_ALERT, log, err, "sendmsg() failed"); return NGX_ERROR; } return NGX_OK;}

 

其实就是复制信息，在发送。我们再看看接受到信息的那段如何处理：ngx_chanel_read 函数

ngx_int_tngx_read_channel(ngx_socket_t s, ngx_channel_t *ch, size_t size, ngx_log_t *log){ ssize_t n; ngx_err_t err; struct iovec iov[1]; struct msghdr msg;#if (NGX_HAVE_MSGHDR_MSG_CONTROL) union { struct cmsghdr cm; char space[CMSG_SPACE(sizeof(int))]; } cmsg;#else int fd;#endif iov[0].iov_base = (char *) ch; iov[0].iov_len = size; msg.msg_name = NULL; msg.msg_namelen = 0; msg.msg_iov = iov; msg.msg_iovlen = 1;#if (NGX_HAVE_MSGHDR_MSG_CONTROL) msg.msg_control = (caddr_t) &cmsg; msg.msg_controllen = sizeof(cmsg);#else msg.msg_accrights = (caddr_t) &fd; msg.msg_accrightslen = sizeof(int);#endif //接收消息 n = recvmsg(s, &msg, 0); if (n == -1) { err = ngx_errno; if (err == NGX_EAGAIN) { return NGX_AGAIN; } ngx_log_error(NGX_LOG_ALERT, log, err, "recvmsg() failed"); return NGX_ERROR; } if (n == 0) { ngx_log_debug0(NGX_LOG_DEBUG_CORE, log, 0, "recvmsg() returned zero"); return NGX_ERROR; } if ((size_t) n < sizeof(ngx_channel_t)) { ngx_log_error(NGX_LOG_ALERT, log, 0, "recvmsg() returned not enough data: %uz", n); return NGX_ERROR; }#if (NGX_HAVE_MSGHDR_MSG_CONTROL) // if (ch->command == NGX_CMD_OPEN_CHANNEL) { if (cmsg.cm.cmsg_len < (socklen_t) CMSG_LEN(sizeof(int))) { ngx_log_error(NGX_LOG_ALERT, log, 0, "recvmsg() returned too small ancillary data"); return NGX_ERROR; } if (cmsg.cm.cmsg_level != SOL_SOCKET || cmsg.cm.cmsg_type != SCM_RIGHTS) { ngx_log_error(NGX_LOG_ALERT, log, 0, "recvmsg() returned invalid ancillary data " "level %d or type %d", cmsg.cm.cmsg_level, cmsg.cm.cmsg_type); return NGX_ERROR; } /* ch->fd = *(int *) CMSG_DATA(&cmsg.cm); */ //复制 fd ngx_memcpy(&ch->fd, CMSG_DATA(&cmsg.cm), sizeof(int)); } if (msg.msg_flags & (MSG_TRUNC|MSG_CTRUNC)) { ngx_log_error(NGX_LOG_ALERT, log, 0, "recvmsg() truncated data"); }#else if (ch->command == NGX_CMD_OPEN_CHANNEL) { if (msg.msg_accrightslen != sizeof(int)) { ngx_log_error(NGX_LOG_ALERT, log, 0, "recvmsg() returned no ancillary data"); return NGX_ERROR; } ch->fd = fd; }#endif return n;}

先接受信息，再复制信息，下面就是真正的处理了 ngx_channel_handler函数中(ngx_process_cycle.c)

 

            ngx_processes[ch.slot].pid = ch.pid;
            ngx_processes[ch.slot].channel[0] = ch.fd;

就是在对应的位置上复制pid和fd,下次向往哪个进程发信息的时候，直接发到 ngx_process[目标进程].channel[0]

 

 

四 父进程

     对于父进程而言，他知道所有进程的channel[0]， 直接可以向子进程发送命令。

 

 

疑问： 父进程的channel[1]没有关闭，那么是不是子进程A向B发送信息的时候，父进程也能收到？知道了高手指导下，谢谢