Support already registered signal handlers

[d-s-codappix]

We have the situation that we have a long running command line task which has its own signal handlers registered.
Within this task we use the fork package, which overwrites the registered handlers, ignoring any pre registered handlers.

It would be cool if the handlers would be respected.
Our current patch looks like this:

diff --git a/src/Fork.php b/src/Fork.php
index f4f322e..fa7ec89 100644
--- a/src/Fork.php
+++ b/src/Fork.php
@@ -150,22 +150,39 @@ class Fork
     {
         pcntl_async_signals(true);
 
-        pcntl_signal(SIGQUIT, fn () => $this->exit());
-        pcntl_signal(SIGTERM, fn () => $this->exit());
-        pcntl_signal(SIGINT, fn () => $this->exit());
+        $this->registerExitFor(SIGQUIT);
+        $this->registerExitFor(SIGTERM);
+        $this->registerExitFor(SIGINT);
+    }
+
+    protected function registerExitFor(int $signalNumber): void
+    {
+        $previousHandler = pcntl_signal_get_handler($signalNumber);
+        pcntl_signal($signalNumber, function (int $signo, mixed $siginfo) use ($previousHandler) {
+            $this->exit();
+
+            if (is_callable($previousHandler)) {
+                $previousHandler($signo, $siginfo);
+            }
+
+            $this->killPid(getmypid());
+        });
     }
 
     protected function exit(): void
+    {
+        foreach ($this->runningTasks as $task) {
+            $this->killPid($task->pid());
+        }
+    }
+
+    private function killPid(int $pid): void
     {
         if (! extension_loaded('posix')) {
             exit;
         }
 
-        foreach ($this->runningTasks as $task) {
-            posix_kill($task->pid(), SIGKILL);
-        }
-
-        posix_kill(getmypid(), SIGKILL);
+        posix_kill($pid, SIGKILL);
     }
 
     protected function currentlyInChildTask(int $pid): bool

It includes a small refactoring to not duplicate code for the new logic.

FYI: I wasn't able to create this as an issue/bug report. There is an endless loop to the template selection when choosing "Report a bug".