master和各个worker之间可以使用channel进行通信，主要通过socketpair和文件描述符的传递来完成的；
文件描述传递总体示意图
channel创建
ngx_pid_tngx_spawn_process(ngx_cycle_t *cycle, ngx_spawn_proc_pt proc, void *data,char *name, ngx_int_t respawn){u_longon;ngx_pid_t pid;ngx_int_t s;if (respawn >= 0) {s = respawn;} else {for (s = 0; s < ngx_last_process; s++) {if (ngx_processes[s].pid == -1) {//找到可以记录的索引break;}}if (s == NGX_MAX_PROCESSES) {ngx_log_error(NGX_LOG_ALERT, cycle->log, 0,"no more than %d processes can be spawned",NGX_MAX_PROCESSES);return NGX_INVALID_PID;}}if (respawn != NGX_PROCESS_DETACHED) {/* Solaris 9 still has no AF_LOCAL *///先使用socketpair()创建一对socket描述符，存放在ngx_processes[s]的channel中，，创建一个进程间通信if (socketpair(AF_UNIX, SOCK_STREAM, 0, ngx_processes[s].channel) == -1)//创建socketpair{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]);if (ngx_nonblocking(ngx_processes[s].channel[0]) == -1) {//将文件描述符设置成非阻塞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);//否则关闭return NGX_INVALID_PID;}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;}//打开针对本套节字的异步IO信号接收SIGIOon = 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;}//设置接收SIGIO和SIGURG信号的进程IDif (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;}//exec时关闭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;}ngx_channel = ngx_processes[s].channel[1];} else {ngx_processes[s].channel[0] = -1;ngx_processes[s].channel[1] = -1;}ngx_process_slot = s;//设置好的当前索引pid = fork();//由于子进程继承了父进程的资源，那么父子进程拥有这一对socket描述符switch (pid) {case -1:ngx_log_error(NGX_LOG_ALERT, cycle->log, ngx_errno,"fork() failed while spawning \&;%s\&;", name);ngx_close_channel(ngx_processes[s].channel, cycle->log);return NGX_INVALID_PID;case 0:ngx_pid = ngx_getpid();proc(cycle, data);//传下来的指针不同，比如ngx_cache_manager_process_cycle和ngx_worker_process_cyclebreak;default:break;}ngx_log_error(NGX_LOG_NOTICE, cycle->log, 0, "start %s %P", name, pid);ngx_processes[s].pid = pid;//记录子进程的pidngx_processes[s].exited = 0;if (respawn >= 0) {return pid;}ngx_processes[s].proc = proc;//调用的函数ngx_processes[s].data = data;//参数ngx_processes[s].name = name;//名称ngx_processes[s].exiting = 0;switch (respawn) {case NGX_PROCESS_NORESPAWN:ngx_processes[s].respawn = 0;ngx_processes[s].just_spawn = 0;ngx_processes[s].detached = 0;break;case NGX_PROCESS_JUST_SPAWN:ngx_processes[s].respawn = 0;ngx_processes[s].just_spawn = 1;ngx_processes[s].detached = 0;break;case NGX_PROCESS_RESPAWN:ngx_processes[s].respawn = 1;ngx_processes[s].just_spawn = 0;ngx_processes[s].detached = 0;break;case NGX_PROCESS_JUST_RESPAWN:ngx_processes[s].respawn = 1;ngx_processes[s].just_spawn = 1;ngx_processes[s].detached = 0;break;case NGX_PROCESS_DETACHED:ngx_processes[s].respawn = 0;ngx_processes[s].just_spawn = 0;ngx_processes[s].detached = 1;break;}if (s == ngx_last_process) {ngx_last_process++;//递增}return pid;}
将channel加入监听事件
ngx_worker_process_init函数中
从哪里跌倒就会从哪里爬起来,让我们一起努力吧
