Nginx Source Analysis--nginx interprocess communication

There are many IPC under Linux, the Nginx process is the process of affinity, for their communication we choose TCP socket to communicate. The advantage of TCP sockets for process communication is that 1.socket is a file descriptor and simple to operate. 2. Two-way flow. 3. There is another important benefit: The record can be reproduced, we can use tcpdump to crawl information, easy to debug.

Of course, for the sharing of large amounts of data between processes, we use shared memory naturally.

Use the Socketpair () function to create an anonymous socket for communication between the master process (parent) and the work process (child processes) and the work process.

Socketpair () see here.

First look at the definition of nginx process

Ngx_process.h

typedef struct {  ngx_pid_t   pid;  int status;  ngx_socket_tchannel[2];//here is the two descriptors used to store Socketpair  ngx_spawn_proc_pt   proc;  void   *data;

In the NGINX_PROCESS.C

Ngx_pid_tngx_spawn_process (ngx_cycle_t *cycle, ngx_spawn_proc_pt proc, void *data,  char *name, ngx_int_t respawn) {  u_long on;  ngx_pid_t  pid;  ngx_int_t  S;  .. if (Socketpair (Af_unix, Sock_stream, 0, ngx_processes[s].channel) = =-1)  //note before fork Oh    {      ngx_log_error ( Ngx_log_alert, Cycle->log, Ngx_errno,              "Socketpair () failed while spawning \"%s\ "," name ";      return ngx_invalid_pid;    } ...  Pid=fork ();..

Before executing the fork, call Socketpair () to create a pair of socket descriptors in the variable ngx_process[s].channel, after fork (), the child process inherits the pair of the socket descriptor of the parent process, and Nginx will now Use Channel[0] to the parent process, and channel[1] to the child process. You can then implement communication for the parent-child process.

if (Ngx_add_channel_event (cycle, Ngx_channel, ngx_read_event,                              Ngx_channel_handler)   //Sub-process joins the channel to the Listener event , Ngx_channel_handler is the callback function for the event response        = = Ngx_error)    {

So how does the child process and the child process communicate directly?

In fact, the subprocess work_process directly communicates through this socket: The master parent process will tell the new process to the child process that was generated before each fork of a new process.

In the NGX_PROCESS_CYCLE.C

Ngx_pass_open_channel (ngx_cycle_t *cycle, ngx_channel_t *ch) {  ngx_int_t  i;  for (i = 0; i < ngx_last_process; i++) {    if (i = = Ngx_process_slot      | | ngx_processes[i].pid = = 1      | | ngx_pro Cesses[i].channel[0] = =-1)    {      continue;    }

The parameter ch contains the new subprocess PID, process information, and channel descriptors that were just created in the global array.

This way the process directly has its own information including the socket descriptor. This allows communication to be done with each other through this.

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• This article from: Hobby Linux Technology Network
• This article link: http://www.ahlinux.com/nginx/9112.html

Nginx Source Analysis--nginx interprocess communication