node: implement unhandled rejection tracking

Implement unhandled rejection tracking for promises as
specified in https://gist.github.com/benjamingr/0237932cee84712951a2

Fixes #256
PR-URL: #758
Reviewed-By: Trevor Norris <trev.norris@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Domenic Denicola <domenic@domenicdenicola.com>

src/env.h

@@ -235,6 +235,7 @@ namespace node {
   V(module_load_list_array, v8::Array)                                        \
   V(pipe_constructor_template, v8::FunctionTemplate)                          \
   V(process_object, v8::Object)                                               \
+  V(promise_reject_function, v8::Function)                                    \
   V(script_context_constructor_template, v8::FunctionTemplate)                \
   V(script_data_constructor_function, v8::Function)                           \
   V(secure_context_constructor_template, v8::FunctionTemplate)                \

src/node.cc

@@ -98,6 +98,8 @@ using v8::Message;
 using v8::Number;
 using v8::Object;
 using v8::ObjectTemplate;
+using v8::Promise;
+using v8::PromiseRejectMessage;
 using v8::PropertyCallbackInfo;
 using v8::String;
 using v8::TryCatch;
@@ -982,6 +984,37 @@ void SetupNextTick(const FunctionCallbackInfo<Value>& args) {
       FIXED_ONE_BYTE_STRING(args.GetIsolate(), "_setupNextTick"));
 }
 
+void PromiseRejectCallback(PromiseRejectMessage message) {
+  Local<Promise> promise = message.GetPromise();
+  Isolate* isolate = promise->GetIsolate();
+  Local<Value> value = message.GetValue();
+  Local<Integer> event = Integer::New(isolate, message.GetEvent());
+
+  Environment* env = Environment::GetCurrent(isolate);
+  Local<Function> callback = env->promise_reject_function();
+
+  if (value.IsEmpty())
+    value = Undefined(isolate);
+
+  Local<Value> args[] = { event, promise, value };
+  Local<Object> process = env->process_object();
+
+  callback->Call(process, ARRAY_SIZE(args), args);
+}
+
+void SetupPromises(const FunctionCallbackInfo<Value>& args) {
+  Environment* env = Environment::GetCurrent(args);
+  Isolate* isolate = env->isolate();
+
+  CHECK(args[0]->IsFunction());
+
+  isolate->SetPromiseRejectCallback(PromiseRejectCallback);
+  env->set_promise_reject_function(args[0].As<Function>());
+
+  env->process_object()->Delete(
+      FIXED_ONE_BYTE_STRING(args.GetIsolate(), "_setupPromises"));
+}
+
 
 Handle<Value> MakeCallback(Environment* env,
                            Handle<Value> recv,
@@ -2572,6 +2605,14 @@ void StopProfilerIdleNotifier(const FunctionCallbackInfo<Value>& args) {
     obj->ForceSet(OneByteString(env->isolate(), str), var, v8::ReadOnly);     \
   } while (0)
 
+#define READONLY_DONT_ENUM_PROPERTY(obj, str, var)                            \
+  do {                                                                        \
+    obj->ForceSet(OneByteString(env->isolate(), str),                         \
+                  var,                                                        \
+                  static_cast<v8::PropertyAttribute>(v8::ReadOnly |           \
+                                                     v8::DontEnum));          \
+  } while (0)
+
 
 void SetupProcessObject(Environment* env,
                         int argc,
@@ -2632,6 +2673,20 @@ void SetupProcessObject(Environment* env,
       "modules",
       FIXED_ONE_BYTE_STRING(env->isolate(), node_modules_version));
 
+  // process._promiseRejectEvent
+  Local<Object> promiseRejectEvent = Object::New(env->isolate());
+  READONLY_DONT_ENUM_PROPERTY(process,
+                              "_promiseRejectEvent",
+                              promiseRejectEvent);
+  READONLY_PROPERTY(promiseRejectEvent,
+                    "unhandled",
+                    Integer::New(env->isolate(),
+                                 v8::kPromiseRejectWithNoHandler));
+  READONLY_PROPERTY(promiseRejectEvent,
+                    "handled",
+                    Integer::New(env->isolate(),
+                                 v8::kPromiseHandlerAddedAfterReject));
+
 #if HAVE_OPENSSL
   // Stupid code to slice out the version string.
   {  // NOLINT(whitespace/braces)
@@ -2790,6 +2845,7 @@ void SetupProcessObject(Environment* env,
   env->SetMethod(process, "_linkedBinding", LinkedBinding);
 
   env->SetMethod(process, "_setupNextTick", SetupNextTick);
+  env->SetMethod(process, "_setupPromises", SetupPromises);
   env->SetMethod(process, "_setupDomainUse", SetupDomainUse);
 
   // pre-set _events object for faster emit checks

src/node.js

@@ -31,6 +31,7 @@
     startup.processAssert();
     startup.processConfig();
     startup.processNextTick();
+    startup.processPromises();
     startup.processStdio();
     startup.processKillAndExit();
     startup.processSignalHandlers();
@@ -264,8 +265,11 @@
     });
   };
 
+  var addPendingUnhandledRejection;
+  var hasBeenNotifiedProperty = new WeakMap();
   startup.processNextTick = function() {
     var nextTickQueue = [];
+    var pendingUnhandledRejections = [];
     var microtasksScheduled = false;
 
     // Used to run V8's micro task queue.
@@ -318,7 +322,8 @@
       microtasksScheduled = false;
       _runMicrotasks();
 
-      if (tickInfo[kIndex] < tickInfo[kLength])
+      if (tickInfo[kIndex] < tickInfo[kLength] ||
+          emitPendingUnhandledRejections())
         scheduleMicrotasks();
     }
 
@@ -388,6 +393,57 @@
       nextTickQueue.push(obj);
       tickInfo[kLength]++;
     }
+
+    function emitPendingUnhandledRejections() {
+      var hadListeners = false;
+      while (pendingUnhandledRejections.length > 0) {
+        var promise = pendingUnhandledRejections.shift();
+        var reason = pendingUnhandledRejections.shift();
+        if (hasBeenNotifiedProperty.get(promise) === false) {
+          hasBeenNotifiedProperty.set(promise, true);
+          if (!process.emit('unhandledRejection', reason, promise)) {
+            // Nobody is listening.
+            // TODO(petkaantonov) Take some default action, see #830
+          } else
+            hadListeners = true;
+        }
+      }
+      return hadListeners;
+    }
+
+    addPendingUnhandledRejection = function(promise, reason) {
+      pendingUnhandledRejections.push(promise, reason);
+      scheduleMicrotasks();
+    };
+  };
+
+  startup.processPromises = function() {
+    var promiseRejectEvent = process._promiseRejectEvent;
+
+    function unhandledRejection(promise, reason) {
+      hasBeenNotifiedProperty.set(promise, false);
+      addPendingUnhandledRejection(promise, reason);
+    }
+
+    function rejectionHandled(promise) {
+      var hasBeenNotified = hasBeenNotifiedProperty.get(promise);
+      if (hasBeenNotified !== undefined) {
+        hasBeenNotifiedProperty.delete(promise);
+        if (hasBeenNotified === true)
+          process.emit('rejectionHandled', promise);
+      }
+    }
+
+    process._setupPromises(function(event, promise, reason) {
+      if (event === promiseRejectEvent.unhandled)
+        unhandledRejection(promise, reason);
+      else if (event === promiseRejectEvent.handled)
+        process.nextTick(function() {
+          rejectionHandled(promise);
+        });
+      else
+        NativeModule.require('assert').fail('unexpected PromiseRejectEvent');
+    });
   };
 
   function evalScript(name) {