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The Process Component
The Process Component¶
The Process component executes commands in sub-processes.
Installation¶
You can install the component in 2 different ways:
- Install it via Composer (
symfony/process
on Packagist); - Use the official Git repository (https://github.com/symfony/process).
Then, require the vendor/autoload.php
file to enable the autoloading mechanism
provided by Composer. Otherwise, your application won’t be able to find the classes
of this Symfony component.
Usage¶
The Symfony\Component\Process\Process
class allows you to execute
a command in a sub-process:
use Symfony\Component\Process\Process;
use Symfony\Component\Process\Exception\ProcessFailedException;
$process = new Process('ls -lsa');
$process->run();
// executes after the command finishes
if (!$process->isSuccessful()) {
throw new ProcessFailedException($process);
}
echo $process->getOutput();
The component takes care of the subtle differences between the different platforms when executing the command.
The getOutput()
method always returns the whole content of the standard
output of the command and getErrorOutput()
the content of the error
output. Alternatively, the getIncrementalOutput()
and getIncrementalErrorOutput()
methods return the new output since the last call.
The clearOutput()
method clears
the contents of the output and
clearErrorOutput()
clears
the contents of the error output.
New in version 3.1: Support for streaming the output of a process was introduced in Symfony 3.1.
You can also use the Symfony\Component\Process\Process
class with the
foreach construct to get the output while it is generated. By default, the loop waits
for new output before going to the next iteration:
$process = new Process('ls -lsa');
$process->start();
foreach ($process as $type => $data) {
if ($process::OUT === $type) {
echo "\nRead from stdout: ".$data;
} else { // $process::ERR === $type
echo "\nRead from stderr: ".$data;
}
}
Tip
The Process component internally uses a PHP iterator to get the output while
it is generated. That iterator is exposed via the getIterator()
method
to allow customizing its behavior:
$process = new Process('ls -lsa');
$process->start();
$iterator = $process->getIterator($process::ITER_SKIP_ERR | $process::ITER_KEEP_OUTPUT);
foreach ($iterator as $data) {
echo $data."\n";
}
New in version 3.2: The getIterator()
method was introduced in Symfony 3.2.
The mustRun()
method is identical to run()
, except that it will throw
a Symfony\Component\Process\Exception\ProcessFailedException
if the process couldn’t be executed successfully (i.e. the process exited
with a non-zero code):
use Symfony\Component\Process\Exception\ProcessFailedException;
use Symfony\Component\Process\Process;
$process = new Process('ls -lsa');
try {
$process->mustRun();
echo $process->getOutput();
} catch (ProcessFailedException $e) {
echo $e->getMessage();
}
Getting real-time Process Output¶
When executing a long running command (like rsync-ing files to a remote
server), you can give feedback to the end user in real-time by passing an
anonymous function to the
run()
method:
use Symfony\Component\Process\Process;
$process = new Process('ls -lsa');
$process->run(function ($type, $buffer) {
if (Process::ERR === $type) {
echo 'ERR > '.$buffer;
} else {
echo 'OUT > '.$buffer;
}
});
Running Processes Asynchronously¶
You can also start the subprocess and then let it run asynchronously, retrieving
output and the status in your main process whenever you need it. Use the
start()
method to start an asynchronous
process, the isRunning()
method
to check if the process is done and the
getOutput()
method to get the output:
$process = new Process('ls -lsa');
$process->start();
while ($process->isRunning()) {
// waiting for process to finish
}
echo $process->getOutput();
You can also wait for a process to end if you started it asynchronously and are done doing other stuff:
$process = new Process('ls -lsa');
$process->start();
// ... do other things
$process->wait();
// ... do things after the process has finished
Note
The wait()
method is blocking,
which means that your code will halt at this line until the external
process is completed.
Note
If a Response
is sent before a child process had a chance to complete,
the server process will be killed (depending on your OS). It means that
your task will be stopped right away. Running an asynchronous process
is not the same as running a process that survives its parent process.
If you want your process to survive the request/response cycle, you can
take advantage of the kernel.terminate
event, and run your command
synchronously inside this event. Be aware that kernel.terminate
is called only if you use PHP-FPM.
Caution
Beware also that if you do that, the said PHP-FPM process will not be available to serve any new request until the subprocess is finished. This means you can quickly block your FPM pool if you’re not careful enough. That is why it’s generally way better not to do any fancy things even after the request is sent, but to use a job queue instead.
wait()
takes one optional argument:
a callback that is called repeatedly whilst the process is still running, passing
in the output and its type:
$process = new Process('ls -lsa');
$process->start();
$process->wait(function ($type, $buffer) {
if (Process::ERR === $type) {
echo 'ERR > '.$buffer;
} else {
echo 'OUT > '.$buffer;
}
});
Streaming to the Standard Input of a Process¶
New in version 3.1: Support for streaming the input of a process was introduced in Symfony 3.1.
Before a process is started, you can specify its standard input using either the
setInput()
method or the 4th argument
of the constructor. The provided input can be a string, a stream resource or a
Traversable object:
$process = new Process('cat');
$process->setInput('foobar');
$process->run();
When this input is fully written to the subprocess standard input, the corresponding pipe is closed.
In order to write to a subprocess standard input while it is running, the component
provides the Symfony\Component\Process\InputStream
class:
$input = new InputStream();
$input->write('foo');
$process = new Process('cat');
$process->setInput($input);
$process->start();
// ... read process output or do other things
$input->write('bar');
$input->close();
$process->wait();
// will echo: foobar
echo $process->getOutput();
The write()
method accepts scalars,
stream resources or Traversable objects as argument. As shown in the above example,
you need to explicitly call the close()
method when you are done writing to the standard input of the subprocess.
Stopping a Process¶
Any asynchronous process can be stopped at any time with the
stop()
method. This method takes
two arguments: a timeout and a signal. Once the timeout is reached, the signal
is sent to the running process. The default signal sent to a process is SIGKILL
.
Please read the signal documentation below
to find out more about signal handling in the Process component:
$process = new Process('ls -lsa');
$process->start();
// ... do other things
$process->stop(3, SIGINT);
Executing PHP Code in Isolation¶
If you want to execute some PHP code in isolation, use the PhpProcess
instead:
use Symfony\Component\Process\PhpProcess;
$process = new PhpProcess(<<<EOF
<?php echo 'Hello World'; ?>
EOF
);
$process->run();
To make your code work better on all platforms, you might want to use the
Symfony\Component\Process\ProcessBuilder
class instead:
use Symfony\Component\Process\ProcessBuilder;
$builder = new ProcessBuilder(array('ls', '-lsa'));
$builder->getProcess()->run();
In case you are building a binary driver, you can use the
setPrefix()
method to prefix all
the generated process commands.
The following example will generate two process commands for a tar binary adapter:
use Symfony\Component\Process\ProcessBuilder;
$builder = new ProcessBuilder();
$builder->setPrefix('/usr/bin/tar');
// '/usr/bin/tar' '--list' '--file=archive.tar.gz'
echo $builder
->setArguments(array('--list', '--file=archive.tar.gz'))
->getProcess()
->getCommandLine();
// '/usr/bin/tar' '-xzf' 'archive.tar.gz'
echo $builder
->setArguments(array('-xzf', 'archive.tar.gz'))
->getProcess()
->getCommandLine();
Process Timeout¶
You can limit the amount of time a process takes to complete by setting a timeout (in seconds):
use Symfony\Component\Process\Process;
$process = new Process('ls -lsa');
$process->setTimeout(3600);
$process->run();
If the timeout is reached, a
Symfony\Component\Process\Exception\RuntimeException
is thrown.
For long running commands, it is your responsibility to perform the timeout check regularly:
$process->setTimeout(3600);
$process->start();
while ($condition) {
// ...
// check if the timeout is reached
$process->checkTimeout();
usleep(200000);
}
Process Idle Timeout¶
In contrast to the timeout of the previous paragraph, the idle timeout only considers the time since the last output was produced by the process:
use Symfony\Component\Process\Process;
$process = new Process('something-with-variable-runtime');
$process->setTimeout(3600);
$process->setIdleTimeout(60);
$process->run();
In the case above, a process is considered timed out, when either the total runtime exceeds 3600 seconds, or the process does not produce any output for 60 seconds.
Process Signals¶
When running a program asynchronously, you can send it POSIX signals with the
signal()
method:
use Symfony\Component\Process\Process;
$process = new Process('find / -name "rabbit"');
$process->start();
// will send a SIGKILL to the process
$process->signal(SIGKILL);
Caution
Due to some limitations in PHP, if you’re using signals with the Process component, you may have to prefix your commands with exec. Please read Symfony Issue#5759 and PHP Bug#39992 to understand why this is happening.
POSIX signals are not available on Windows platforms, please refer to the PHP documentation for available signals.
Process Pid¶
You can access the pid of a running process with the
getPid()
method.
1 2 3 4 5 6 | use Symfony\Component\Process\Process;
$process = new Process('/usr/bin/php worker.php');
$process->start();
$pid = $process->getPid();
|
Caution
Due to some limitations in PHP, if you want to get the pid of a symfony Process, you may have to prefix your commands with exec. Please read Symfony Issue#5759 to understand why this is happening.
Disabling Output¶
As standard output and error output are always fetched from the underlying process,
it might be convenient to disable output in some cases to save memory.
Use disableOutput()
and
enableOutput()
to toggle this feature:
use Symfony\Component\Process\Process;
$process = new Process('/usr/bin/php worker.php');
$process->disableOutput();
$process->run();
Caution
You cannot enable or disable the output while the process is running.
If you disable the output, you cannot access getOutput()
,
getIncrementalOutput()
, getErrorOutput()
, getIncrementalErrorOutput()
or
setIdleTimeout()
.
However, it is possible to pass a callback to the start
, run
or mustRun
methods to handle process output in a streaming fashion.
New in version 3.1: The ability to pass a callback to these methods when output is disabled was added in Symfony 3.1.
This work, including the code samples, is licensed under a Creative Commons BY-SA 3.0 license.