test: add gc tracking to common API

PR-URL: #21794 Reviewed-By: Rich Trott <[email protected]> Reviewed-By: James M Snell <[email protected]>
nodejs · Jul 16, 2018 · b338ff5 · b338ff5
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diff --git a/test/common/README.md b/test/common/README.md
@@ -322,6 +322,21 @@ otherwise.
 ### noWarnCode
 See `common.expectWarning()` for usage.
 
+### onGC(target, listener)
+* `target` [&lt;Object>]
+* `listener` [&lt;Object>]
+  * `ongc` [&lt;Function>]
+
+Installs a GC listener for the collection of `target`.
+
+This uses `async_hooks` for GC tracking. This means that it enables
+`async_hooks` tracking, which may affect the test functionality. It also
+means that between a `global.gc()` call and the listener being invoked
+a full `setImmediate()` invocation passes.
+
+`listener` is an object to make it easier to use a closure; the target object
+should not be in scope when `listener.ongc()` is created.
+
 ### opensslCli
 * [&lt;boolean>]
 

diff --git a/test/common/index.js b/test/common/index.js
@@ -883,3 +883,30 @@ exports.isCPPSymbolsNotMapped = exports.isWindows ||
                                 exports.isAIX ||
                                 exports.isLinuxPPCBE ||
                                 exports.isFreeBSD;
+
+const gcTrackerMap = new WeakMap();
+const gcTrackerTag = 'NODE_TEST_COMMON_GC_TRACKER';
+
+exports.onGC = function(obj, gcListener) {
+  const async_hooks = require('async_hooks');
+
+  const onGcAsyncHook = async_hooks.createHook({
+    init: exports.mustCallAtLeast(function(id, type, trigger, resource) {
+      if (this.trackedId === undefined) {
+        assert.strictEqual(type, gcTrackerTag);
+        this.trackedId = id;
+      }
+    }),
+    destroy(id) {
+      assert.notStrictEqual(this.trackedId, -1);
+      if (id === this.trackedId) {
+        this.gcListener.ongc();
+        onGcAsyncHook.disable();
+      }
+    }
+  }).enable();
+  onGcAsyncHook.gcListener = gcListener;
+
+  gcTrackerMap.set(obj, new async_hooks.AsyncResource(gcTrackerTag));
+  obj = null;
+};
diff --git a/test/parallel/test-common-gc.js b/test/parallel/test-common-gc.js
@@ -0,0 +1,15 @@
+'use strict';
+// Flags: --expose-gc
+const common = require('../common');
+
+{
+  const gcListener = { ongc: common.mustCall() };
+  common.onGC({}, gcListener);
+  global.gc();
+}
+
+{
+  const gcListener = { ongc: common.mustNotCall() };
+  common.onGC(process, gcListener);
+  global.gc();
+}