async-wrap: add event hooks

Call a user-defined callback at specific points in the lifetime of an
asynchronous event. Which are on instantiation, just before/after the
callback has been run.

**If any of these callbacks throws an exception, there is no forgiveness
or recovery. A message will be displayed and a core file dumped.**

Currently these only tie into AsyncWrap, meaning no call to a hook
callback will be made for timers or process.nextTick() events. Though
those will be added in a future commit.

Here are a few notes on how to make the hooks work:

- The "this" of all event hook callbacks is the request object.

- The zero field (kCallInitHook) of the flags object passed to
  setupHooks() must be set != 0 before the init callback will be called.

- kCallInitHook only affects the calling of the init callback. If the
  request object has been run through the create callback it will always
  run the before/after callbacks. Regardless of kCallInitHook.

- In the init callback the property "_asyncQueue" must be attached to
  the request object. e.g.

  function initHook() {
    this._asyncQueue = {};
  }

- DO NOT inspect the properties of the object in the init callback.
  Since the object is in the middle of being instantiated there are some
  cases when a getter is not complete, and doing so will cause Node to
  crash.

PR-URL: https://github.com/joyent/node/pull/8110
Signed-off-by: Trevor Norris <trev.norris@gmail.com>
Reviewed-by: Fedor Indutny <fedor@indutny.com>
Reviewed-by: Alexis Campailla <alexis@janeasystems.com>
Reviewed-by: Julien Gilli <julien.gilli@joyent.com>

1 files changed, 36 insertions, 0 deletions

diff --git a/src/async-wrap-inl.h b/src/async-wrap-inl.h
index 73a177872e..4dbb3a6cfc 100644
--- a/src/async-wrap-inl.h
+++ b/src/async-wrap-inl.h
@@ -27,6 +27,7 @@
 #include "base-object-inl.h"
 #include "env.h"
 #include "env-inl.h"
+#include "node_internals.h"
 #include "util.h"
 #include "util-inl.h"
 #include "v8.h"
@@ -38,7 +39,42 @@ inline AsyncWrap::AsyncWrap(Environment* env,
                             ProviderType provider,
                             AsyncWrap* parent)
     : BaseObject(env, object),
+      has_async_queue_(false),
       provider_type_(provider) {
+  // Check user controlled flag to see if the init callback should run.
+  if (!env->call_async_init_hook())
+    return;
+
+  // TODO(trevnorris): Until it's verified all passed object's are not weak,
+  // add a HandleScope to make sure there's no leak.
+  v8::HandleScope scope(env->isolate());
+
+  v8::Local<v8::Object> parent_obj;
+
+  v8::TryCatch try_catch;
+
+  // If a parent value was sent then call its pre/post functions to let it know
+  // a conceptual "child" is being instantiated (e.g. that a server has
+  // received a connection).
+  if (parent != nullptr) {
+    parent_obj = parent->object();
+    env->async_hooks_pre_function()->Call(parent_obj, 0, nullptr);
+    if (try_catch.HasCaught())
+      FatalError("node::AsyncWrap::AsyncWrap", "parent pre hook threw");
+  }
+
+  env->async_hooks_init_function()->Call(object, 0, nullptr);
+
+  if (try_catch.HasCaught())
+    FatalError("node::AsyncWrap::AsyncWrap", "init hook threw");
+
+  has_async_queue_ = true;
+
+  if (parent != nullptr) {
+    env->async_hooks_post_function()->Call(parent_obj, 0, nullptr);
+    if (try_catch.HasCaught())
+      FatalError("node::AsyncWrap::AsyncWrap", "parent post hook threw");
+  }
 }