timers: do not retain a reference to the async store after firing

Signed-off-by: Matteo Collina <hello@matteocollina.com>

Author: mcollina

lib/async_hooks.js

@@ -381,4 +381,7 @@ module.exports = {
   asyncWrapProviders: ObjectFreeze({ __proto__: null, ...asyncWrap.Providers }),
   // Embedder API
   AsyncResource,
+  getActiveStores () {
+    return [...storageList];
+  }
 };

lib/internal/timers.js

@@ -121,6 +121,8 @@ let debug = require('internal/util/debuglog').debuglog('timer', (fn) => {
   debug = fn;
 });
 
+let asyncHooks = null;
+
 // *Must* match Environment::ImmediateInfo::Fields in src/env.h.
 const kCount = 0;
 const kRefCount = 1;
@@ -164,6 +166,7 @@ function initAsyncResource(resource, type) {
   if (initHooksExist())
     emitInit(asyncId, type, triggerAsyncId, resource);
 }
+
 class Timeout {
   // Timer constructor function.
   // The entire prototype is defined in lib/timers.js
@@ -429,6 +432,20 @@ function setPosition(node, pos) {
   node.priorityQueuePosition = pos;
 }
 
+function removeAllStores (timer) {
+  // TODO(mcollina): move the list of stores to private
+  asyncHooks ??= require('async_hooks');
+
+  // TODO(mcollina): this does a copy for safety, we
+  // should be fast and unsafe.
+  const activeStores = asyncHooks.getActiveStores();
+
+  // Use for loop for speed
+  for (let i = 0; i < activeStores.length; i++) {
+    timer[activeStores[i].kResourceStore] = undefined;
+  }
+}
+
 function getTimerCallbacks(runNextTicks) {
   // If an uncaught exception was thrown during execution of immediateQueue,
   // this queue will store all remaining Immediates that need to run upon
@@ -594,6 +611,9 @@ function getTimerCallbacks(runNextTicks) {
           if (timer[kRefed])
             timeoutInfo[0]--;
 
+          removeAllStores(timer);
+          timer._onTimeout = undefined;
+
           if (destroyHooksExist())
             emitDestroy(asyncId);
         }

test/parallel/timeout-async-store-leak.js

@@ -0,0 +1,15 @@
+'use strict';
+
+const common = require('../common');
+const { AsyncLocalStorage } = require('async_hooks');
+const assert = require('assert');
+
+const asyncLocalStorage = new AsyncLocalStorage();
+asyncLocalStorage.run({}, common.mustCall(() => {
+  const timeout = setTimeout(common.mustCall(() => {
+    setImmediate(common.mustCall(() => {
+      assert.strictEqual(timeout[asyncLocalStorage.kResourceStore], undefined);
+      assert.strictEqual(timeout._onTimeout, undefined);
+    }))
+  }));
+}));