1.nginx进程模型
nginx采用的是多进程模型，典型的master-worker方式，采用一个master process（监控进程，也叫做主进程）和多个woker process（工作进程）的设计方式，此外，还有1个可选的chache manager和 1 个可选的cache loader进程。
这样设计的好处：
（1）利用多核系统的并发处理能力；
（2）负载均衡；
（3）管理进程会负责监控工作进程的状态，并负责管理其行为。
2. master-worker 启动流程
启动nginx的主进程将充当master进程，而由主进程fork()出来的子进程则充当工作进程。nginx也可以单进程模型执行，在这种进程模型下，主进程就是工作进程，没有监控进程。
Nginx的核心进程模型框图如下：
3.master进程是如何工作的
监控进程充当整个进程组与用户的交互接口，同时对进程进行监护。它不需要处理网络事件，不负责业务的执行，只会通过管理worker进程来实现重启服务、平滑升级、更换日志文件、配置文件实时生效等功能。
其工作流程如下图，它首先fork出worker进程，然后进入for循环，在每一帧循环中调用sigsupend挂起等待信号，如果收到信号，就处理信号，改变响应的标志位，然后根据标志位做出相应的操作。
master进程的标志位有如下7个：
1: sig_atomic_t ngx_reap;
2: sig_atomic_t ngx_terminate;
3: sig_atomic_t ngx_quit;
4: sig_atomic_t ngx_reconfigure;
5: sig_atomic_t ngx_reopen;
6: sig_atomic_t ngx_change_binary;
7: sig_atomic_t ngx_noaccept;每个标志与信号位的及作用的对应关系如下表：
这样，master进程的运行情况如下图：
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下面看一下核心代码：
3.1 master进程住循环函数 ngx_master_process_cycle
1: void
2: ngx_master_process_cycle(ngx_cycle_t *cycle)
3: {
4: char *title;
5: u_char *p;
6: size_t size;
7: ngx_int_t i;
8: ngx_uint_t n, sigio;
9: sigset_t set;
10: struct itimerval itv;
11: ngx_uint_t live;
12: ngx_msec_t delay;
13: ngx_listening_t *ls;
14: ngx_core_conf_t *ccf;
15:
16: //设置屏蔽信号
17: sigemptyset(&set);
18: sigaddset(&set, SIGCHLD);
19: sigaddset(&set, SIGALRM);
20: sigaddset(&set, SIGIO);
21: sigaddset(&set, SIGINT);
22: sigaddset(&set, ngx_signal_value(NGX_RECONFIGURE_SIGNAL));
23: sigaddset(&set, ngx_signal_value(NGX_REOPEN_SIGNAL));
24: sigaddset(&set, ngx_signal_value(NGX_NOACCEPT_SIGNAL));
25: sigaddset(&set, ngx_signal_value(NGX_TERMINATE_SIGNAL));
26: sigaddset(&set, ngx_signal_value(NGX_SHUTDOWN_SIGNAL));
27: sigaddset(&set, ngx_signal_value(NGX_CHANGEBIN_SIGNAL));
28:
29: if (sigprocmask(SIG_BLOCK, &set, NULL) == -1) {
30: ngx_log_error(NGX_LOG_ALERT, cycle->log, ngx_errno,
31: "sigprocmask() failed");
32: }
33:
34: sigemptyset(&set);
35:
36:
37: size = sizeof(master_process);
38:
39: for (i = 0; i < ngx_argc i 40: size 1 41: 42: 43: title='ngx_pnalloc(cycle-'>pool, size);
44:
45: p = ngx_cpymem(title, master_process, sizeof(master_process) - 1);
46: for (i = 0; i < ngx_argc i 47: p 48: p='ngx_cpystrn(p,' u_char ngx_argvi size 49: 50: 51: ngx_setproctitletitle 52: 53: 54: ccf='(ngx_core_conf_t' ngx_get_confcycle->conf_ctx, ngx_core_module);
55:
56: //其中包含了fork产生子进程的内容
57: ngx_start_worker_processes(cycle, ccf->worker_processes,
58: NGX_PROCESS_RESPAWN);
59: //Cache管理进程与cache加载进程的主流程
60: ngx_start_cache_manager_processes(cycle, 0);
61:
62: ngx_new_binary = 0;
63: delay = 0;
64: sigio = 0;
65: live = 1;
66:
67: for ( ;; ) {//循环
68: if (delay) {
69: if (ngx_sigalrm) {
70: sigio = 0;
71: delay *= 2;
72: ngx_sigalrm = 0;
73: }
74:
75: ngx_log_debug1(NGX_LOG_DEBUG_EVENT, cycle->log, 0,
76: "termination cycle: %d", delay);
77:
78: itv.it_interval.tv_sec = 0;
79: itv.it_interval.tv_usec = 0;
80: itv.it_value.tv_sec = delay / 1000;
81: itv.it_value.tv_usec = (delay % 1000 ) * 1000;
82:
83: if (setitimer(ITIMER_REAL, &itv, NULL) == -1) {
84: ngx_log_error(NGX_LOG_ALERT, cycle->log, ngx_errno,
85: "setitimer() failed");
86: }
87: }
88:
89: ngx_log_debug0(NGX_LOG_DEBUG_EVENT, cycle->log, 0, "sigsuspend");
90:
91: sigsuspend(&set);//master进程休眠，等待接受信号被激活
92:
93: ngx_time_update();
94:
95: ngx_log_debug1(NGX_LOG_DEBUG_EVENT, cycle->log, 0,
96: "wake up, sigio %i", sigio);
97:
98: //标志位为1表示需要监控所有子进程
99: if (ngx_reap) {
100: ngx_reap = 0;
101: ngx_log_debug0(NGX_LOG_DEBUG_EVENT, cycle->log, 0, "reap children");
102:
103: live = ngx_reap_children(cycle);//管理子进程
104: }
105:
106: //当live标志位为0（表示所有子进程已经退出）、ngx_terminate标志位为1或者ngx_quit标志位为1表示要退出master进程
107: if (!live && (ngx_terminate || ngx_quit)) {
108: ngx_master_process_exit(cycle);//退出master进程
109: }
110:
111: //ngx_terminate标志位为1，强制关闭服务，发送TERM信号到所有子进程
112: if (ngx_terminate) {
113: if (delay == 0) {
114: delay = 50;
115: }
116:
117: if (sigio) {
118: sigio--;
119: continue;
120: }
121:
122: sigio = ccf->worker_processes + 2 /* cache processes */;
123:
124: if (delay > 1000) {
125: ngx_signal_worker_processes(cycle, SIGKILL);
126: } else {
127: ngx_signal_worker_processes(cycle,
128: ngx_signal_value(NGX_TERMINATE_SIGNAL));
129: }
130:
131: continue;
132: }
133:
134: //ngx_quit标志位为1，优雅的关闭服务
135: if (ngx_quit) {
136: ngx_signal_worker_processes(cycle,
137: ngx_signal_value(NGX_SHUTDOWN_SIGNAL));//向所有子进程发送quit信号
138:
139: ls = cycle->listening.elts;
140: for (n = 0; n < cycle->listening.nelts; n++) {//关闭监听端口
141: if (ngx_close_socket(ls[n].fd) == -1) {
142: ngx_log_error(NGX_LOG_EMERG, cycle->log, ngx_socket_errno,
143: ngx_close_socket_n " %V failed",
144: &ls[n].addr_text);
145: }
146: }
147: cycle->listening.nelts = 0;
148:
149: continue;
150: }
151:
152: //ngx_reconfigure标志位为1，重新读取配置文件
153: //nginx不会让原来的worker子进程再重新读取配置文件，其策略是重新初始化ngx_cycle_t结构体，用它来读取新的额配置文件
154: //再创建新的额worker子进程，销毁旧的worker子进程
155: if (ngx_reconfigure) {
156: ngx_reconfigure = 0;
157:
158: //ngx_new_binary标志位为1，平滑升级Nginx
159: if (ngx_new_binary) {
160: ngx_start_worker_processes(cycle, ccf->worker_processes,
161: NGX_PROCESS_RESPAWN);
162: ngx_start_cache_manager_processes(cycle, 0);
163: ngx_noaccepting = 0;
164:
165: continue;
166: }
167:
168: ngx_log_error(NGX_LOG_NOTICE, cycle->log, 0, "reconfiguring");
169:
170: //初始化ngx_cycle_t结构体
171: cycle = ngx_init_cycle(cycle);
172: if (cycle == NULL) {
173: cycle = (ngx_cycle_t *) ngx_cycle;
174: continue;
175: }
176:
177: ngx_cycle = cycle;
178: ccf = (ngx_core_conf_t *) ngx_get_conf(cycle->conf_ctx,
179: ngx_core_module);
180: //创建新的worker子进程
181: ngx_start_worker_processes(cycle, ccf->worker_processes,
182: NGX_PROCESS_JUST_RESPAWN);
183: ngx_start_cache_manager_processes(cycle, 1);
184:
185: /* allow new processes to start */
186: ngx_msleep(100);
187:
188: live = 1;
189: //向所有子进程发送QUIT信号
190: ngx_signal_worker_processes(cycle,
191: ngx_signal_value(NGX_SHUTDOWN_SIGNAL));
192: }
193: //ngx_restart标志位在ngx_noaccepting（表示正在停止接受新的连接）为1的时候被设置为1.
194: //重启子进程
195: if (ngx_restart) {
196: ngx_restart = 0;
197: ngx_start_worker_processes(cycle, ccf->worker_processes,
198: NGX_PROCESS_RESPAWN);
199: ngx_start_cache_manager_processes(cycle, 0);
200: live = 1;
201: }
202:
203: //ngx_reopen标志位为1，重新打开所有文件
204: if (ngx_reopen) {
205: ngx_reopen = 0;
206: ngx_log_error(NGX_LOG_NOTICE, cycle->log, 0, "reopening logs");
207: ngx_reopen_files(cycle, ccf->user);
208: ngx_signal_worker_processes(cycle,
209: ngx_signal_value(NGX_REOPEN_SIGNAL));
210: }
211:
212: //平滑升级Nginx
213: if (ngx_change_binary) {
214: ngx_change_binary = 0;
215: ngx_log_error(NGX_LOG_NOTICE, cycle->log, 0, "changing binary");
216: ngx_new_binary = ngx_exec_new_binary(cycle, ngx_argv);
217: }
218:
219: //ngx_noaccept为1，表示所有子进程不再处理新的连接
220: if (ngx_noaccept) {
221: ngx_noaccept = 0;
222: ngx_noaccepting = 1;
223: ngx_signal_worker_processes(cycle,
224: ngx_signal_value(NGX_SHUTDOWN_SIGNAL));
225: }
226: }
227: }3.2 master 产生master进程函数
ngx_start_worker_processes
1: static void
2: ngx_start_worker_processes(ngx_cycle_t *cycle, ngx_int_t n, ngx_int_t type)
3: {
4: ngx_int_t i;
5: ngx_channel_t ch;
6:
7: ngx_log_error(NGX_LOG_NOTICE, cycle->log, 0, "start worker processes");
8:
9: ch.command = NGX_CMD_OPEN_CHANNEL;
10:
11: //循环创建n个worker子进程
12: for (i = 0; i < n; i++) {
13: //完成fok新进程的具体工作
14: ngx_spawn_process(cycle, ngx_worker_process_cycle,
15: (void *) (intptr_t) i, "worker process", type);
16:
17: //全局数组ngx_processes就是用来存储每个子进程的相关信息，如：pid，channel，进程做具体事情的接口指针等等，这些信息就是用结构体ngx_process_t来描述的。
18: ch.pid = ngx_processes[ngx_process_slot].pid;
19: ch.slot = ngx_process_slot;
20: ch.fd = ngx_processes[ngx_process_slot].channel[0];
21:
22: /*在ngx_spawn_process创建好一个worker进程返回后，master进程就将worker进程的pid、worker进程在ngx_processes数组中的位置及channel[0]传递给前面已经创建好的worker进程，然后继续循环开始创建下一个worker进程。刚提到一个channel[0]，这里简单说明一下：channel就是一个能够存储2个整型元素的数组而已，这个channel数组就是用于socketpair函数创建一个进程间通道之用的。master和worker进程以及worker进程之间都可以通过这样的一个通道进行通信，这个通道就是在ngx_spawn_process函数中fork之前调用socketpair创建的。*/
23: ngx_pass_open_channel(cycle, &ch);
24: }25: }
3.3 真正的fork函数 ngx_spawn_process
1: //参数解释：
2: //cycle：nginx框架所围绕的核心结构体
3: //proc：子进程中将要执行的工作循环
4: //data：参数
5: //name：子进程名字
6: ngx_pid_t
7: ngx_spawn_process(ngx_cycle_t *cycle, ngx_spawn_proc_pt proc, void *data,
8: char *name, ngx_int_t respawn)
9: {
10: u_long on;
11: ngx_pid_t pid;
12: ngx_int_t s;
13:
14: if (respawn >= 0) {
15: s = respawn;
16:
17: } else {
18: for (s = 0; s < ngx_last_process s 19: if ngx_processess.pid='= -1)' 20: break 21: 22: 23: 24: if s='= NGX_MAX_PROCESSES)' 25: ngx_log_errorngx_log_alert cycle->log, 0,
26: "no more than %d processes can be spawned",
27: NGX_MAX_PROCESSES);
28: return NGX_INVALID_PID;
29: }
30: }
31:
32:
33: if (respawn != NGX_PROCESS_DETACHED) {
34:
35: /* Solaris 9 still has no AF_LOCAL */
36: //创建父子进程间通信的套接字对（基于TCP）
37: if (socketpair(AF_UNIX, SOCK_STREAM, 0, ngx_processes[s].channel) == -1)
38: {
39: ngx_log_error(NGX_LOG_ALERT, cycle->log, ngx_errno,
40: "socketpair() failed while spawning \"%s\"", name);
41: return NGX_INVALID_PID;
42: }
43:
44: ngx_log_debug2(NGX_LOG_DEBUG_CORE, cycle->log, 0,
45: "channel %d:%d",
46: ngx_processes[s].channel[0],
47: ngx_processes[s].channel[1]);
48:
49: //设置为非阻塞模式
50: if (ngx_nonblocking(ngx_processes[s].channel[0]) == -1) {
51: ngx_log_error(NGX_LOG_ALERT, cycle->log, ngx_errno,
52: ngx_nonblocking_n " failed while spawning \"%s\"",
53: name);
54: ngx_close_channel(ngx_processes[s].channel, cycle->log);
55: return NGX_INVALID_PID;
56: }
57:
58: if (ngx_nonblocking(ngx_processes[s].channel[1]) == -1) {
59: ngx_log_error(NGX_LOG_ALERT, cycle->log, ngx_errno,
60: ngx_nonblocking_n " failed while spawning \"%s\"",
61: name);
62: ngx_close_channel(ngx_processes[s].channel, cycle->log);
63: return NGX_INVALID_PID;
64: }
65:
66: on = 1;
67: if (ioctl(ngx_processes[s].channel[0], FIOASYNC, &on) == -1) {
68: ngx_log_error(NGX_LOG_ALERT, cycle->log, ngx_errno,
69: "ioctl(FIOASYNC) failed while spawning \"%s\"", name);
70: ngx_close_channel(ngx_processes[s].channel, cycle->log);
71: return NGX_INVALID_PID;
72: }
73:
74: if (fcntl(ngx_processes[s].channel[0], F_SETOWN, ngx_pid) == -1) {
75: ngx_log_error(NGX_LOG_ALERT, cycle->log, ngx_errno,
76: "fcntl(F_SETOWN) failed while spawning \"%s\"", name);
77: ngx_close_channel(ngx_processes[s].channel, cycle->log);
78: return NGX_INVALID_PID;
79: }
80:
81: if (fcntl(ngx_processes[s].channel[0], F_SETFD, FD_CLOEXEC) == -1) {
82: ngx_log_error(NGX_LOG_ALERT, cycle->log, ngx_errno,
83: "fcntl(FD_CLOEXEC) failed while spawning \"%s\"",
84: name);
85: ngx_close_channel(ngx_processes[s].channel, cycle->log);
86: return NGX_INVALID_PID;
87: }
88:
89: if (fcntl(ngx_processes[s].channel[1], F_SETFD, FD_CLOEXEC) == -1) {
90: ngx_log_error(NGX_LOG_ALERT, cycle->log, ngx_errno,
91: "fcntl(FD_CLOEXEC) failed while spawning \"%s\"",
92: name);
93: ngx_close_channel(ngx_processes[s].channel, cycle->log);
94: return NGX_INVALID_PID;
95: }
96:
97: ngx_channel = ngx_processes[s].channel[1];
98:
99: } else {
100: ngx_processes[s].channel[0] = -1;
101: ngx_processes[s].channel[1] = -1;
102: }
103:
104: ngx_process_slot = s;
105:
106: //创建子进程
107: pid = fork();
108:
109: switch (pid) {
110:
111: case -1:
112: ngx_log_error(NGX_LOG_ALERT, cycle->log, ngx_errno,
113: "fork() failed while spawning \"%s\"", name);
114: ngx_close_channel(ngx_processes[s].channel, cycle->log);
115: return NGX_INVALID_PID;
116:
117: case 0:
118: ngx_pid = ngx_getpid();
119: proc(cycle, data);
120: break;
121:
122: default:
123: break;
124: }
125:
126: ngx_log_error(NGX_LOG_NOTICE, cycle->log, 0, "start %s %P", name, pid);
127:
128: ngx_processes[s].pid = pid;
129: ngx_processes[s].exited = 0;
130:
131: if (respawn >= 0) {
132: return pid;
133: }
134:
135: ngx_processes[s].proc = proc;
136: ngx_processes[s].data = data;
137: ngx_processes[s].name = name;
138: ngx_processes[s].exiting = 0;
139:
140: switch (respawn) {
141:
142: case NGX_PROCESS_NORESPAWN:
143: ngx_processes[s].respawn = 0;
144: ngx_processes[s].just_spawn = 0;
145: ngx_processes[s].detached = 0;
146: break;
147:
148: case NGX_PROCESS_JUST_SPAWN:
149: ngx_processes[s].respawn = 0;
150: ngx_processes[s].just_spawn = 1;
151: ngx_processes[s].detached = 0;
152: break;
153:
154: case NGX_PROCESS_RESPAWN:
155: ngx_processes[s].respawn = 1;
156: ngx_processes[s].just_spawn = 0;
157: ngx_processes[s].detached = 0;
158: break;
159:
160: case NGX_PROCESS_JUST_RESPAWN:
161: ngx_processes[s].respawn = 1;
162: ngx_processes[s].just_spawn = 1;
163: ngx_processes[s].detached = 0;
164: break;
165:
166: case NGX_PROCESS_DETACHED:
167: ngx_processes[s].respawn = 0;
168: ngx_processes[s].just_spawn = 0;
169: ngx_processes[s].detached = 1;
170: break;
171: }
172:
173: if (s == ngx_last_process) {
174: ngx_last_process++;
175: }
176:
177: return pid;
178: }4.worker 进程是如何工作的
worker进程的主要任务是完成具体的任务逻辑。其主要关注点是与客户端或后端真实服务器（此时nginx作为中间代理）之间的数据可读/可写等I/O交互事件，所以工作进程的阻塞点是在像select()、epoll_wait()等这样的I/O多路复用函数调用处，以等待发生数据可读/写事件。当然也可能被新收到的进程信号中断。
master进程是信号来控制worker进程的。当收到信号时，信号处理函数ngx_signal_handler()就会执行。worker进程感兴趣的信号有4个，也是通过4个变量来控制，如下表：
其工作流程如下图所示：
其核心代码如下：
1: static void
2: ngx_worker_process_cycle(ngx_cycle_t *cycle, void *data)
3: {
4: ngx_int_t worker = (intptr_t) data;
5:
6: ngx_uint_t i;
7: ngx_connection_t *c;
8:
9: ngx_process = NGX_PROCESS_WORKER;
10:
11: //子进程初始化
12: ngx_worker_process_init(cycle, worker);
13:
14: ngx_setproctitle("worker process");
15:
16: //这里有一段多线程条件下的代码。由于nginx并不支持多线程，因此删除掉了
17:
18: //循环
19: for ( ;; ) {
20:
21: //ngx_exiting标志位为1，进程退出
22: if (ngx_exiting) {
23: c = cycle->connections;
24: for (i = 0; i < cycle->connection_n; i++) {
25: if (c[i].fd != -1 && c[i].idle) {
26: c[i].close = 1;
27: c[i].read->handler(c[i].read);
28: }
29: }
30:
31: if (ngx_event_timer_rbtree.root == ngx_event_timer_rbtree.sentinel)
32: {
33: ngx_log_error(NGX_LOG_NOTICE, cycle->log, 0, "exiting");
34: ngx_worker_process_exit(cycle);
35: }
36: }
37:
38: ngx_log_debug0(NGX_LOG_DEBUG_EVENT, cycle->log, 0, "worker cycle");
39:
40: ngx_process_events_and_timers(cycle);//处理事件的方法
41:
42: //强制结束进程
43: if (ngx_terminate) {
44: ngx_log_error(NGX_LOG_NOTICE, cycle->log, 0, "exiting");
45: ngx_worker_process_exit(cycle);
46: }
47:
48: //优雅地退出进程
49: if (ngx_quit) {
50: ngx_quit = 0;
51: ngx_log_error(NGX_LOG_NOTICE, cycle->log, 0,
52: "gracefully shutting down");
53: ngx_setproctitle("worker process is shutting down");
54:
55: if (!ngx_exiting) {
56: ngx_close_listening_sockets(cycle);
57: //设置ngx_exiting 标志位
58: ngx_exiting = 1;
59: }
60: }
61:
62: //重新打开所有文件
63: if (ngx_reopen) {
64: ngx_reopen = 0;
65: ngx_log_error(NGX_LOG_NOTICE, cycle->log, 0, "reopening logs");
66: ngx_reopen_files(cycle, -1);
67: }
68: }
69: }————————————————
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