laravel: improve events watcher registration (#166)

The original code hooks on ServiceProvider::{__construct,boot}. Hooking
on ServiceProvider is a bad idea since it is the parent of all service
providers and thus will hook on all of them. `boot` hook may be run
multiple times, thus the $watcherInstalled check is needed. Even worse,
only a few providers have a `boot` method, making it more unreliable.

This improves it by registering the watchers after application
bootstrap, via Application::booted() Laravel-native hook. The whole
application will be only run once, thus a $watcherInstalled check is not
needed.

To get the Application object, Kernel::__construct is used.

$watcherInstalled in original code is also broken by the fact that it
will be reset on ServiceProvider::__construct, which may happen in the
middle of service providers bootstrapping process, via Laravel
"deferred" provider registration, which is, when booting a provider, it
requests service from another provider that is not registered yet. This
may lead to the watchers being registered multiple times as seen in
open-telemetry/opentelemetry-php#1032.

Fixes: open-telemetry/opentelemetry-php#1032

Co-authored-by: xizhen wang <[email protected]>

Author: xdavidwu

src/LaravelInstrumentation.php

@@ -7,7 +7,6 @@
 use Illuminate\Foundation\Application;
 use Illuminate\Foundation\Http\Kernel;
 use Illuminate\Http\Request;
-use Illuminate\Support\ServiceProvider;
 use OpenTelemetry\API\Common\Instrumentation\CachedInstrumentation;
 use OpenTelemetry\API\Common\Instrumentation\Globals;
 use OpenTelemetry\API\Trace\Span;
@@ -23,8 +22,6 @@
 class LaravelInstrumentation
 {
     public const NAME = 'laravel';
-    private static $watchersInstalled = false;
-    private static $application;
 
     public static function registerWatchers(Application $app, Watcher $watcher)
     {
@@ -96,26 +93,17 @@ public static function register(): void
             }
         );
         hook(
-            ServiceProvider::class,
-            'boot',
-            pre: static function (ServiceProvider $provider, array $params, string $class, string $function, ?string $filename, ?int $lineno) use ($instrumentation) {
-                if (!self::$watchersInstalled) {
-                    self::registerWatchers(self::$application, new ClientRequestWatcher($instrumentation));
-                    self::registerWatchers(self::$application, new ExceptionWatcher());
-                    self::registerWatchers(self::$application, new CacheWatcher());
-                    self::registerWatchers(self::$application, new LogWatcher());
-                    self::registerWatchers(self::$application, new QueryWatcher($instrumentation));
-                    self::$watchersInstalled = true;
-                }
-            },
-            post: null
-        );
-        hook(
-            ServiceProvider::class,
+            Kernel::class,
             '__construct',
-            pre: static function (ServiceProvider $provider, array $params, string $class, string $function, ?string $filename, ?int $lineno) {
-                self::$watchersInstalled = false;
-                self::$application = $params[0];
+            pre: static function (Kernel $kernel, array $params, string $class, string $function, ?string $filename, ?int $lineno) use ($instrumentation) {
+                $app = $params[0];
+                $app->booted(static function (Application $app) use ($instrumentation) {
+                    self::registerWatchers($app, new ClientRequestWatcher($instrumentation));
+                    self::registerWatchers($app, new ExceptionWatcher());
+                    self::registerWatchers($app, new CacheWatcher());
+                    self::registerWatchers($app, new LogWatcher());
+                    self::registerWatchers($app, new QueryWatcher($instrumentation));
+                });
             },
             post: null
         );