Only install handler when first listener is registered

CHANGELOG.md

@@ -1,5 +1,11 @@
 # Changelog
 
+## [Unreleased]
+
+### Changed
+
+- `Innmind\Signals\Handler` will install its handler function only when first registering a user listener
+
 ## 4.0.0 - 2025-08-20
 
 ### Added

README.md

@@ -21,7 +21,7 @@ use Innmind\Signals\{
     Info,
 };
 
-$handler = Handler::main(); // automatically enable async signal at instanciation
+$handler = Handler::main(); // automatically enable async signal on first `->listen()` call
 
 $handler->listen(Signal::interrupt, function(Signal $signal, Info $info): void {
     echo 'foo';

src/Handler/Main.php

@@ -18,28 +18,36 @@
  */
 final class Main
 {
-    /** @var Map<Signal, Sequence<callable(Signal, Info): void>> */
-    private Map $handlers;
-    private bool $wasAsync;
-
-    private function __construct()
-    {
-        /** @var Map<Signal, Sequence<callable(Signal, Info): void>> */
-        $this->handlers = Map::of();
-        $this->wasAsync = \pcntl_async_signals();
-        \pcntl_async_signals(true);
+    /**
+     * @param Map<Signal, Sequence<callable(Signal, Info): void>> $handlers
+     */
+    private function __construct(
+        private Map $handlers,
+        private bool $installed,
+        private bool $wasAsync,
+    ) {
     }
 
     public static function install(): self
     {
-        return new self;
+        return new self(
+            Map::of(),
+            false,
+            false,
+        );
     }
 
     /**
      * @param callable(Signal, Info): void $listener
      */
     public function listen(Signal $signal, callable $listener): void
     {
+        if (!$this->installed) {
+            $this->wasAsync = \pcntl_async_signals();
+            \pcntl_async_signals(true);
+            $this->installed = true;
+        }
+
         $handlers = $this->installSignal($signal);
         $this->handlers = ($this->handlers)(
             $signal,
@@ -67,6 +75,7 @@ public function remove(callable $listener): void
         );
 
         if ($this->handlers->empty()) {
+            $this->installed = false;
             \pcntl_async_signals($this->wasAsync);
         }
     }

tests/HandlerTest.php

@@ -20,11 +20,12 @@ class HandlerTest extends TestCase
 
     public function testNothingHappensByDefaultWhenReceivingSignal()
     {
+        $async = \pcntl_async_signals();
         $handler = Handler::main();
 
         $this->fork();
 
-        $this->assertTrue(\pcntl_async_signals());
+        $this->assertSame($async, \pcntl_async_signals());
     }
 
     public function testAllListenersAreCalledInOrderOnSignal()