`child_process` module.
It is possible to stream data through a child's `stdin`, `stdout`, and
-`stderr` in a fully non-blocking way.
+`stderr` in a fully non-blocking way. (Note that some programs use
+line-buffered I/O internally. That doesn't affect node.js but it means
+data you send to the child process is not immediately consumed.)
To create a child process use `require('child_process').spawn()` or
`require('child_process').fork()`. The semantics of each are slightly
The ChildProcess class is not intended to be used directly. Use the
`spawn()` or `fork()` methods to create a Child Process instance.
+### Event: 'error'
+
+* `err` {Error Object} the error.
+
+Emitted when:
+
+1. The process could not be spawned, or
+2. The process could not be killed, or
+3. Sending a message to the child process failed for whatever reason.
+
+Note that the `exit`-event may or may not fire after an error has occured. If
+you are listening on both events to fire a function, remember to guard against
+calling your function twice.
+
+See also [`ChildProcess#kill()`](#child_process_child_kill_signal) and
+[`ChildProcess#send()`](#child_process_child_send_message_sendhandle).
+
### Event: 'exit'
* `code` {Number} the exit code, if it exited normally.
Note that the child process stdio streams might still be open.
+Also, note that node establishes signal handlers for `'SIGINT'` and `'SIGTERM`',
+so it will not terminate due to receipt of those signals, it will exit.
+
See `waitpid(2)`.
### Event: 'close'
+* `code` {Number} the exit code, if it exited normally.
+* `signal` {String} the signal passed to kill the child process, if it
+ was killed by the parent.
+
This event is emitted when the stdio streams of a child process have all
terminated. This is distinct from 'exit', since multiple processes
might share the same stdio streams.
### Event: 'disconnect'
-This event is emitted after using the `.disconnect()` method in the parent or
-in the child. After disconnecting it is no longer possible to send messages.
-An alternative way to check if you can send messages is to see if the
-`child.connected` property is `true`.
+This event is emitted after calling the `.disconnect()` method in the parent
+or in the child. After disconnecting it is no longer possible to send messages,
+and the `.connected` property is false.
### Event: 'message'
console.log('Spawned child pid: ' + grep.pid);
grep.stdin.end();
+### child.connected
+
+* {Boolean} Set to false after `.disconnect' is called
+
+If `.connected` is false, it is no longer possible to send messages.
+
### child.kill([signal])
* `signal` {String}
var spawn = require('child_process').spawn,
grep = spawn('grep', ['ssh']);
- grep.on('exit', function (code, signal) {
+ grep.on('close', function (code, signal) {
console.log('child process terminated due to receipt of signal '+signal);
});
// send SIGHUP to process
grep.kill('SIGHUP');
-Note that while the function is called `kill`, the signal delivered to the child
-process may not actually kill it. `kill` really just sends a signal to a process.
+May emit an `'error'` event when the signal cannot be delivered. Sending a
+signal to a child process that has already exited is not an error but may
+have unforeseen consequences: if the PID (the process ID) has been reassigned
+to another process, the signal will be delivered to that process instead.
+What happens next is anyone's guess.
+
+Note that while the function is called `kill`, the signal delivered to the
+child process may not actually kill it. `kill` really just sends a signal
+to a process.
See `kill(2)`
In the child the `process` object will have a `send()` method, and `process`
will emit objects each time it receives a message on its channel.
+Please note that the `send()` method on both the parent and child are
+synchronous - sending large chunks of data is not advised (pipes can be used
+instead, see
+[`child_process.spawn`](#child_process_child_process_spawn_command_args_options)).
+
There is a special case when sending a `{cmd: 'NODE_foo'}` message. All messages
containing a `NODE_` prefix in its `cmd` property will not be emitted in
the `message` event, since they are internal messages used by node core.
socket object to another process. The child will receive the object as its
second argument to the `message` event.
+Emits an `'error'` event if the message cannot be sent, for example because
+the child process has already exited.
+
#### Example: sending server object
Here is an example of sending a server:
Note that the server is now shared between the parent and child, this means
that some connections will be handled by the parent and some by the child.
+For `dgram` servers the workflow is exactly the same. Here you listen on
+a `message` event instead of `connection` and use `server.bind` instead of
+`server.listen`. (Currently only supported on UNIX platforms.)
+
#### Example: sending socket object
Here is an example of sending a socket. It will spawn two children and handle
### child.disconnect()
-To close the IPC connection between parent and child use the
-`child.disconnect()` method. This allows the child to exit gracefully since
-there is no IPC channel keeping it alive. When calling this method the
-`disconnect` event will be emitted in both parent and child, and the
-`connected` flag will be set to `false`. Please note that you can also call
-`process.disconnect()` in the child process.
+Close the IPC channel between parent and child, allowing the child to exit
+gracefully once there are no other connections keeping it alive. After calling
+this method the `.connected` flag will be set to `false` in both the parent and
+child, and it is no longer possible to send messages.
+
+The 'disconnect' event will be emitted when there are no messages in the process
+of being received, most likely immediately.
+
+Note that you can also call `process.disconnect()` in the child process.
## child_process.spawn(command, [args], [options])
console.log('stderr: ' + data);
});
- ls.on('exit', function (code) {
+ ls.on('close', function (code) {
console.log('child process exited with code ' + code);
});
console.log('ps stderr: ' + data);
});
- ps.on('exit', function (code) {
+ ps.on('close', function (code) {
if (code !== 0) {
console.log('ps process exited with code ' + code);
}
console.log('grep stderr: ' + data);
});
- grep.on('exit', function (code) {
+ grep.on('close', function (code) {
if (code !== 0) {
console.log('grep process exited with code ' + code);
}
stderr]` to existing streams; `-1` meant that a new stream should be created.
Use at your own risk.
-There are several internal options. In particular `stdinStream`,
-`stdoutStream`, `stderrStream`. They are for INTERNAL USE ONLY. As with all
-undocumented APIs in Node, they should not be used.
-
See also: `child_process.exec()` and `child_process.fork()`
## child_process.exec(command, [options], callback)
* `command` {String} The command to run, with space-separated arguments
* `options` {Object}
* `cwd` {String} Current working directory of the child process
- * `stdio` {Array|String} Child's stdio configuration. (See above)
- * `customFds` {Array} **Deprecated** File descriptors for the child to use
- for stdio. (See above)
* `env` {Object} Environment key-value pairs
* `encoding` {String} (Default: 'utf8')
+ * `shell` {String} Shell to execute the command with
+ (Default: '/bin/sh' on UNIX, 'cmd.exe' on Windows, The shell should
+ understand the `-c` switch on UNIX or `/s /c` on Windows. On Windows,
+ command line parsing should be compatible with `cmd.exe`.)
* `timeout` {Number} (Default: 0)
- * `maxBuffer` {Number} (Default: 200*1024)
+ * `maxBuffer` {Number} (Default: `200*1024`)
* `killSignal` {String} (Default: 'SIGTERM')
* `callback` {Function} called with the output when process terminates
* `error` {Error}
* `args` {Array} List of string arguments
* `options` {Object}
* `cwd` {String} Current working directory of the child process
- * `stdio` {Array|String} Child's stdio configuration. (See above)
- * `customFds` {Array} **Deprecated** File descriptors for the child to use
- for stdio. (See above)
* `env` {Object} Environment key-value pairs
* `encoding` {String} (Default: 'utf8')
* `timeout` {Number} (Default: 0)
leaner than `child_process.exec`. It has the same options.
-## child\_process.fork(modulePath, [args], [options])
+## child_process.fork(modulePath, [args], [options])
* `modulePath` {String} The module to run in the child
* `args` {Array} List of string arguments
* `env` {Object} Environment key-value pairs
* `encoding` {String} (Default: 'utf8')
* `execPath` {String} Executable used to create the child process
+ * `execArgv` {Array} List of string arguments passed to the executable
+ (Default: `process.execArgv`)
+ * `silent` {Boolean} If true, prevent stdout and stderr in the spawned node
+ process from being associated with the parent's (default is false)
* Return: ChildProcess object
This is a special case of the `spawn()` functionality for spawning Node
instance, the returned object has a communication channel built-in. See
`child.send(message, [sendHandle])` for details.
-By default the spawned Node process will have the stdout, stderr associated
-with the parent's. To change this behavior set the `silent` property in the
-`options` object to `true`.
-
-The child process does not automatically exit once it's done, you need to call
-`process.exit()` explicitly. This limitation may be lifted in the future.
-
These child Nodes are still whole new instances of V8. Assume at least 30ms
startup and 10mb memory for each new Node. That is, you cannot create many
thousands of them.
projects / platform / upstream / nodejs.git / blobdiff