feature symfony#53968 [Process] allow to ignore signals when executing a process (joelwurtz)

This PR was merged into the 7.1 branch.

Discussion
----------

[Process] allow to ignore signals when executing a process

| Q             | A
| ------------- | ---
| Branch?       | 7.1
| Bug fix?      | no
| New feature?  | yes
| Deprecations? | no
| Issues        |
| License       | MIT

This PR allow to a process to ignore signals dispatched by PHP

This can be useful when using symfony messenger where the handler would execute a Process and receives a SIGTERM, actually the handler would fail with a `ProcessSignaledException` instead of waiting for the handler to terminate and gracefully shutdown.

Please note that ignoring a signal will also disallow to send this signal with the `posix_kill` function

Commits
-------

7bb6ecf feat(process): allow to ignore signals when executing a process

Author: fabpot

src/Symfony/Component/Process/CHANGELOG.md

@@ -1,6 +1,11 @@
 CHANGELOG
 =========
 
+7.1
+---
+
+ * Add `Process::setIgnoredSignals()` to disable signal propagation to the child process
+
 6.4
 ---
 

src/Symfony/Component/Process/Process.php

@@ -77,6 +77,7 @@ class Process implements \IteratorAggregate
     private bool $tty = false;
     private bool $pty;
     private array $options = ['suppress_errors' => true, 'bypass_shell' => true];
+    private array $ignoredSignals = [];
 
     private WindowsPipes|UnixPipes $processPipes;
 
@@ -346,9 +347,23 @@ public function start(?callable $callback = null, array $env = []): void
 
             return true;
         });
+
+        $oldMask = [];
+
+        if (\function_exists('pcntl_sigprocmask')) {
+            // we block signals we want to ignore, as proc_open will use fork / posix_spawn which will copy the signal mask this allow to block
+            // signals in the child process
+            pcntl_sigprocmask(\SIG_BLOCK, $this->ignoredSignals, $oldMask);
+        }
+
         try {
             $process = @proc_open($commandline, $descriptors, $this->processPipes->pipes, $this->cwd, $envPairs, $this->options);
         } finally {
+            if (\function_exists('pcntl_sigprocmask')) {
+                // we restore the signal mask here to avoid any side effects
+                pcntl_sigprocmask(\SIG_SETMASK, $oldMask);
+            }
+
             restore_error_handler();
         }
 
@@ -1206,6 +1221,20 @@ public function setOptions(array $options): void
         }
     }
 
+    /**
+     * Defines a list of posix signals that will not be propagated to the process.
+     *
+     * @param list<\SIG*> $signals
+     */
+    public function setIgnoredSignals(array $signals): void
+    {
+        if ($this->isRunning()) {
+            throw new RuntimeException('Setting ignored signals while the process is running is not possible.');
+        }
+
+        $this->ignoredSignals = $signals;
+    }
+
     /**
      * Returns whether TTY is supported on the current operating system.
      */
@@ -1455,6 +1484,11 @@ private function resetProcessData(): void
      */
     private function doSignal(int $signal, bool $throwException): bool
     {
+        // Signal seems to be send when sigchild is enable, this allow blocking the signal correctly in this case
+        if ($this->isSigchildEnabled() && \in_array($signal, $this->ignoredSignals)) {
+            return false;
+        }
+
         if (null === $pid = $this->getPid()) {
             if ($throwException) {
                 throw new LogicException('Cannot send signal on a non running process.');

src/Symfony/Component/Process/Tests/ProcessTest.php

@@ -1663,6 +1663,36 @@ public function testNotTerminableInputPipe()
         $this->assertFalse($process->isRunning());
     }
 
+    public function testIgnoringSignal()
+    {
+        if (!\function_exists('pcntl_signal')) {
+            $this->markTestSkipped('pnctl extension is required.');
+        }
+
+        $process = $this->getProcess('sleep 10');
+        $process->setIgnoredSignals([\SIGTERM]);
+
+        $process->start();
+        $process->stop(timeout: 0.2);
+
+        $this->assertNotSame(\SIGTERM, $process->getTermSignal());
+    }
+
+    // This test ensure that the previous test is reliable, in case of the sleep command ignoring the SIGTERM signal
+    public function testNotIgnoringSignal()
+    {
+        if (!\function_exists('pcntl_signal')) {
+            $this->markTestSkipped('pnctl extension is required.');
+        }
+
+        $process = $this->getProcess('sleep 10');
+
+        $process->start();
+        $process->stop(timeout: 0.2);
+
+        $this->assertSame(\SIGTERM, $process->getTermSignal());
+    }
+
     private function getProcess(string|array $commandline, ?string $cwd = null, ?array $env = null, mixed $input = null, ?int $timeout = 60): Process
     {
         if (\is_string($commandline)) {