Add a memory threshold setting for worker restarts

Introduce `frankenphp_min_memory_mb` option to enforce a minimum memory threshold before handling new requests. This prevents running workers when memory is critically low, enhancing stability. Option is configurable via environment variables or runtime options. Default value is -1 which disables this new functionality.

Author: Karsten Nilsen

src/frankenphp-symfony/README.md

@@ -40,3 +40,17 @@ return function (array $context) {
 ## Options
 
 * `frankenphp_loop_max`: the number of requests after which the worker must restart, to prevent weird memory leaks (default to `500`, set to `-1` to never restart)
+* `frankenphp_min_memory_mb`: the minimum amount of available memory (in MB) required before handling a new request. If available memory falls below this threshold after the first request, the worker will restart (default to `-1` to disable)
+
+These options can also be configured via environment variables:
+
+```
+docker run \
+    -e FRANKENPHP_CONFIG="worker ./public/index.php" \
+    -e APP_RUNTIME=Runtime\\FrankenPhpSymfony\\Runtime \
+    -e FRANKENPHP_LOOP_MAX=500 \
+    -e FRANKENPHP_MIN_MEMORY_MB=64 \
+    -v $PWD:/app \
+    -p 80:80 -p 443:443 \
+    dunglas/frankenphp
+```

src/frankenphp-symfony/src/Runner.php

@@ -19,6 +19,7 @@ class Runner implements RunnerInterface
     public function __construct(
         private HttpKernelInterface $kernel,
         private int $loopMax,
+        private int $minMemoryMb = -1,
     ) {
     }
 
@@ -56,8 +57,40 @@ public function run(): int
             }
 
             gc_collect_cycles();
-        } while ($ret && (-1 === $this->loopMax || ++$loops < $this->loopMax));
+            ++$loops;
+        } while ($ret && (-1 === $this->loopMax || $loops < $this->loopMax) && $this->hasAvailableMemory($loops));
 
         return 0;
     }
+
+    private function hasAvailableMemory(int $loops): bool
+    {
+        if (-1 === $this->minMemoryMb || 1 === $loops) { // Always allow the first cycle
+            return true;
+        }
+
+        $memoryLimit = \ini_get('memory_limit');
+        if (-1 === (int) $memoryLimit || '' === $memoryLimit) {
+            return true;
+        }
+        $memoryLimit = \trim($memoryLimit);
+        if (strlen($memoryLimit) < 2) {
+            return true; // Unexpected value, consider enough mem available
+        }
+        $last = \strtolower($memoryLimit[\strlen($memoryLimit) - 1]);
+        if (!\in_array($last, ['g', 'm', 'k'])) {
+            return true; // Unexpected value, consider enough mem available
+        }
+
+        $value = (int) $memoryLimit; // (int) stops at first non-numeric char
+        $memoryLimitMb = match ($last) {
+            'g' => $value * 1024,
+            'k' => (int) ($value / 1024),
+            default => $value,
+        };
+        $usedMemoryMb = \memory_get_usage(true) / 1024 / 1024;
+        $availableMemoryMb = $memoryLimitMb - $usedMemoryMb;
+
+        return $availableMemoryMb >= $this->minMemoryMb;
+    }
 }

src/frankenphp-symfony/src/Runtime.php

@@ -18,19 +18,21 @@ class Runtime extends SymfonyRuntime
     /**
      * @param array{
      *   frankenphp_loop_max?: int,
+     *   frankenphp_min_memory_mb?: int,
      * } $options
      */
     public function __construct(array $options = [])
     {
         $options['frankenphp_loop_max'] = (int) ($options['frankenphp_loop_max'] ?? $_SERVER['FRANKENPHP_LOOP_MAX'] ?? $_ENV['FRANKENPHP_LOOP_MAX'] ?? 500);
+        $options['frankenphp_min_memory_mb'] = (int) ($options['frankenphp_min_memory_mb'] ?? $_SERVER['FRANKENPHP_MIN_MEMORY_MB'] ?? $_ENV['FRANKENPHP_MIN_MEMORY_MB'] ?? -1);
 
         parent::__construct($options);
     }
 
     public function getRunner(?object $application): RunnerInterface
     {
         if ($application instanceof HttpKernelInterface && ($_SERVER['FRANKENPHP_WORKER'] ?? false)) {
-            return new Runner($application, $this->options['frankenphp_loop_max']);
+            return new Runner($application, $this->options['frankenphp_loop_max'], $this->options['frankenphp_min_memory_mb']);
         }
 
         return parent::getRunner($application);