假设我有一个进程，它只生成一个子进程。现在，当父进程由于某种原因(正常或不正常，通过kill， ^C，断言失败或其他任何原因)退出时，我希望子进程死亡。如何正确地做到这一点?
关于stackoverflow的一些类似问题:
(前面问过)当父进程退出的时候，我怎么能让子进程退出呢? (稍后问)用fork()创建的子进程会在父进程被杀死时自动被杀死吗?
关于Windows的stackoverflow也有类似的问题:
如何在Windows中自动销毁子进程? 当父进程被杀死时，杀死子进程
当前回答
我找到了两个解，都不完美。
1.当收到SIGTERM信号时，通过Kill (-pid)杀死所有子结点。 显然，这个解决方案不能处理“kill -9”，但它确实适用于大多数情况，而且非常简单，因为它不需要记住所有的子进程。
var childProc = require('child_process').spawn('tail', ['-f', '/dev/null'], {stdio:'ignore'});
var counter=0;
setInterval(function(){
console.log('c '+(++counter));
},1000);
if (process.platform.slice(0,3) != 'win') {
function killMeAndChildren() {
/*
* On Linux/Unix(Include Mac OS X), kill (-pid) will kill process group, usually
* the process itself and children.
* On Windows, an JOB object has been applied to current process and children,
* so all children will be terminated if current process dies by anyway.
*/
console.log('kill process group');
process.kill(-process.pid, 'SIGKILL');
}
/*
* When you use "kill pid_of_this_process", this callback will be called
*/
process.on('SIGTERM', function(err){
console.log('SIGTERM');
killMeAndChildren();
});
}
通过同样的方式，如果你调用process，你可以像上面那样安装'exit'处理程序。退出的地方。 注意:Ctrl+C和突然崩溃已经被操作系统自动处理来杀死进程组，这里不再赘述。
2.使用chjj/pty.js生成附加控制终端的进程。 当你以任何方式甚至kill -9终止当前进程时，所有的子进程也会被自动终止(由操作系统?)我猜是因为当前进程占用终端的另一侧，所以如果当前进程死亡，子进程将获得SIGPIPE，因此死亡。
var pty = require('pty.js');
//var term =
pty.spawn('any_child_process', [/*any arguments*/], {
name: 'xterm-color',
cols: 80,
rows: 30,
cwd: process.cwd(),
env: process.env
});
/*optionally you can install data handler
term.on('data', function(data) {
process.stdout.write(data);
});
term.write(.....);
*/
其他回答
我认为一种快速而又不那么简单的方法是在子节点和父节点之间创建一个管道。当父节点退出时，子节点将收到一个SIGPIPE。
Historically, from UNIX v7, the process system has detected orphanity of processes by checking a process' parent id. As I say, historically, the init(8) system process is a special process by only one reason: It cannot die. It cannot die because the kernel algorithm to deal with assigning a new parent process id, depends on this fact. when a process executes its exit(2) call (by means of a process system call or by external task as sending it a signal or the like) the kernel reassigns all children of this process the id of the init process as their parent process id. This leads to the most easy test, and most portable way of knowing if a process has got orphan. Just check the result of the getppid(2) system call and if it is the process id of the init(2) process then the process got orphan before the system call.
这种方法会产生两个问题:
first, we have the possibility of changing the init process to any user process, so How can we assure that the init process will always be parent of all orphan processes? Well, in the exit system call code there's a explicit check to see if the process executing the call is the init process (the process with pid equal to 1) and if that's the case, the kernel panics (It should not be able anymore to maintain the process hierarchy) so it is not permitted for the init process to do an exit(2) call. second, there's a race condition in the basic test exposed above. Init process' id is assumed historically to be 1, but that's not warranted by the POSIX approach, that states (as exposed in other response) that only a system's process id is reserved for that purpose. Almost no posix implementation does this, and you can assume in original unix derived systems that having 1 as response of getppid(2) system call is enough to assume the process is orphan. Another way to check is to make a getppid(2) just after the fork and compare that value with the result of a new call. This simply doesn't work in all cases, as both call are not atomic together, and the parent process can die after the fork(2) and before the first getppid(2) system call. The processparent id only changes once, when its parent does anexit(2)call, so this should be enough to check if thegetppid(2)result changed between calls to see that parent process has exit. This test is not valid for the actual children of the init process, because they are always children ofinit(8)`, but you can assume safely these processes as having no parent either (except when you substitute in a system the init process)
我找到了两个解，都不完美。
1.当收到SIGTERM信号时，通过Kill (-pid)杀死所有子结点。 显然，这个解决方案不能处理“kill -9”，但它确实适用于大多数情况，而且非常简单，因为它不需要记住所有的子进程。
var childProc = require('child_process').spawn('tail', ['-f', '/dev/null'], {stdio:'ignore'});
var counter=0;
setInterval(function(){
console.log('c '+(++counter));
},1000);
if (process.platform.slice(0,3) != 'win') {
function killMeAndChildren() {
/*
* On Linux/Unix(Include Mac OS X), kill (-pid) will kill process group, usually
* the process itself and children.
* On Windows, an JOB object has been applied to current process and children,
* so all children will be terminated if current process dies by anyway.
*/
console.log('kill process group');
process.kill(-process.pid, 'SIGKILL');
}
/*
* When you use "kill pid_of_this_process", this callback will be called
*/
process.on('SIGTERM', function(err){
console.log('SIGTERM');
killMeAndChildren();
});
}
通过同样的方式，如果你调用process，你可以像上面那样安装'exit'处理程序。退出的地方。 注意:Ctrl+C和突然崩溃已经被操作系统自动处理来杀死进程组，这里不再赘述。
2.使用chjj/pty.js生成附加控制终端的进程。 当你以任何方式甚至kill -9终止当前进程时，所有的子进程也会被自动终止(由操作系统?)我猜是因为当前进程占用终端的另一侧，所以如果当前进程死亡，子进程将获得SIGPIPE，因此死亡。
var pty = require('pty.js');
//var term =
pty.spawn('any_child_process', [/*any arguments*/], {
name: 'xterm-color',
cols: 80,
rows: 30,
cwd: process.cwd(),
env: process.env
});
/*optionally you can install data handler
term.on('data', function(data) {
process.stdout.write(data);
});
term.write(.....);
*/
正如其他人指出的那样，当父进程退出时，依赖父进程pid变成1是不可移植的。不需要等待特定的父进程ID，只需要等待ID发生变化:
pit_t pid = getpid();
switch (fork())
{
case -1:
{
abort(); /* or whatever... */
}
default:
{
/* parent */
exit(0);
}
case 0:
{
/* child */
/* ... */
}
}
/* Wait for parent to exit */
while (getppid() != pid)
;
如果不想以全速轮询，可以根据需要添加微睡眠。
在我看来，这个选项比使用管道或依赖于信号更简单。
在Linux下，你可以在子进程中安装父进程死亡信号，例如:
#include <sys/prctl.h> // prctl(), PR_SET_PDEATHSIG
#include <signal.h> // signals
#include <unistd.h> // fork()
#include <stdio.h> // perror()
// ...
pid_t ppid_before_fork = getpid();
pid_t pid = fork();
if (pid == -1) { perror(0); exit(1); }
if (pid) {
; // continue parent execution
} else {
int r = prctl(PR_SET_PDEATHSIG, SIGTERM);
if (r == -1) { perror(0); exit(1); }
// test in case the original parent exited just
// before the prctl() call
if (getppid() != ppid_before_fork)
exit(1);
// continue child execution ...
请注意，在fork之前存储父进程id，并在prctl()之后在子进程中测试它，消除了prctl()和调用子进程的退出之间的竞争条件。
还要注意，子进程的父进程死亡信号在新创建的子进程中被清除。它不受execve()的影响。
如果我们确定负责收养所有孤儿的系统进程PID为1，这个测试就可以简化:
pid_t pid = fork();
if (pid == -1) { perror(0); exit(1); }
if (pid) {
; // continue parent execution
} else {
int r = prctl(PR_SET_PDEATHSIG, SIGTERM);
if (r == -1) { perror(0); exit(1); }
// test in case the original parent exited just
// before the prctl() call
if (getppid() == 1)
exit(1);
// continue child execution ...
但是，依赖于系统进程的初始化和PID 1是不可移植的。posix . 1的授权- 2008指定:
调用进程的所有现有子进程和僵尸进程的父进程ID应设置为实现定义的系统进程的进程ID。也就是说，这些进程应该由一个特殊的系统进程继承。
传统上，采用所有孤儿进程的系统进程是PID 1，即init -它是所有进程的祖先。
在像Linux或FreeBSD这样的现代系统上，另一个进程可能具有这个角色。例如，在Linux上，一个进程可以调用prctl(PR_SET_CHILD_SUBREAPER, 1)来将自己建立为继承其任何后代的所有孤儿的系统进程(参见Fedora 25上的一个例子)。
