mojo: Add async waiter for python bindings

mojo/public/python/src/python_system_helper.cc

Index: mojo/public/python/src/python_system_helper.cc
diff --git a/mojo/public/python/src/python_system_helper.cc b/mojo/public/python/src/python_system_helper.cc
index 91032053bff05d706deb63771da6bef7f32739fd..f4555f5f9f52d3fcca63342856f5e24b3a283efe 100644
--- a/mojo/public/python/src/python_system_helper.cc
+++ b/mojo/public/python/src/python_system_helper.cc
@@ -6,6 +6,7 @@
 
 #include "Python.h"
 
+#include "mojo/public/cpp/environment/environment.h"
 #include "mojo/public/cpp/environment/logging.h"
 #include "mojo/public/cpp/system/macros.h"
 #include "mojo/public/cpp/utility/run_loop.h"
@@ -14,13 +15,9 @@ namespace {
 
 class ScopedGIL {
  public:
-  ScopedGIL() {
-    state_ = PyGILState_Ensure();
-  }
+  ScopedGIL() { state_ = PyGILState_Ensure(); }
 
-  ~ScopedGIL() {
-    PyGILState_Release(state_);
-  }
+  ~ScopedGIL() { PyGILState_Release(state_); }
 
  private:
   PyGILState_STATE state_;
@@ -31,7 +28,7 @@ class ScopedGIL {
 class PythonClosure : public mojo::Closure::Runnable {
  public:
   PythonClosure(PyObject* callable) : callable_(callable) {
-    MOJO_CHECK(callable);
+    MOJO_DCHECK(callable);
     Py_XINCREF(callable);
   }
 
@@ -64,9 +61,68 @@ class PythonClosure : public mojo::Closure::Runnable {
   MOJO_DISALLOW_COPY_AND_ASSIGN(PythonClosure);
 };
 
+void AsyncCallbackForwarder(void* closure, MojoResult result) {
+  mojo::Callback<void(MojoResult)>* callback =
+      static_cast<mojo::Callback<void(MojoResult)>*>(closure);
+  // callback will be deleted when it is run.
+  callback->Run(result);
+}
+
 }  // namespace
 
 namespace mojo {
+namespace python {
+
+class PythonAsyncWaiter::AsyncWaiterRunnable
+    : public mojo::Callback<void(MojoResult)>::Runnable {
+ public:
+  AsyncWaiterRunnable(PyObject* callable, CallbackMap* callbacks)
+      : wait_id_(0), callable_(callable), callbacks_(callbacks) {
+    MOJO_DCHECK(callable);
+    MOJO_DCHECK(callbacks_);
+    Py_XINCREF(callable);
+  }
+
+  virtual ~AsyncWaiterRunnable() {
+    ScopedGIL acquire_gil;
+    Py_DECREF(callable_);
+  }
+
+  void set_wait_id(int wait_id) { wait_id_ = wait_id; }
+
+  virtual void Run(MojoResult mojo_result) const MOJO_OVERRIDE {
+    MOJO_DCHECK(wait_id_);
+
+    // Remove to reference to this object from PythonAsyncWaiter and ensure this
+    // object will be destroyed when this method exits.
+    internal::SharedPtr<mojo::Callback<void(MojoResult)> > self =

[sdefresne, 2014/09/18 08:37:01]

Why don't you DCHECK that wait_id_ is in callbacks_?

[qsr, 2014/09/18 08:56:10]

Done.

+        (*callbacks_)[wait_id_];
+    callbacks_->erase(wait_id_);
+
+    ScopedGIL acquire_gil;
+    PyObject* empty_tuple = Py_BuildValue("(i)", mojo_result);

[sdefresne, 2014/09/18 08:37:00]

nit: empty_tuple is not empty, maybe rename to args_tuple?

[qsr, 2014/09/18 08:56:10]

Done.

+    if (!empty_tuple) {
+      mojo::RunLoop::current()->Quit();
+      return;
+    }
+
+    PyObject* result = PyObject_CallObject(callable_, empty_tuple);
+    Py_DECREF(empty_tuple);
+    if (result) {
+      Py_DECREF(result);
+    } else {
+      mojo::RunLoop::current()->Quit();
+      return;
+    }
+  }
+
+ private:
+  MojoAsyncWaitID wait_id_;
+  PyObject* callable_;
+  CallbackMap* callbacks_;
+
+  MOJO_DISALLOW_COPY_AND_ASSIGN(AsyncWaiterRunnable);
+};
 
 Closure BuildClosure(PyObject* callable) {
   if (!PyCallable_Check(callable))
@@ -76,4 +132,39 @@ Closure BuildClosure(PyObject* callable) {
       static_cast<mojo::Closure::Runnable*>(new PythonClosure(callable)));
 }
 
+PythonAsyncWaiter::PythonAsyncWaiter() {
+  async_waiter_ = Environment::GetDefaultAsyncWaiter();
+}
+
+PythonAsyncWaiter::~PythonAsyncWaiter() {
+  for (CallbackMap::const_iterator it = callbacks_.begin();
+       it != callbacks_.end();
+       ++it) {
+    async_waiter_->CancelWait(it->first);
+  }
+}
+
+MojoAsyncWaitID PythonAsyncWaiter::AsyncWait(MojoHandle handle,
+                                             MojoHandleSignals signals,
+                                             MojoDeadline deadline,
+                                             PyObject* callable) {
+  AsyncWaiterRunnable* runner = new AsyncWaiterRunnable(callable, &callbacks_);
+  internal::SharedPtr<mojo::Callback<void(MojoResult)> > callback(
+      new mojo::Callback<void(MojoResult)>(
+          static_cast<mojo::Callback<void(MojoResult)>::Runnable*>(runner)));
+  MojoAsyncWaitID wait_id = async_waiter_->AsyncWait(
+      handle, signals, deadline, &AsyncCallbackForwarder, callback.get());
+  callbacks_[wait_id] = callback;
+  runner->set_wait_id(wait_id);
+  return wait_id;
+}
+
+void PythonAsyncWaiter::CancelWait(MojoAsyncWaitID wait_id) {
+  if (callbacks_.find(wait_id) != callbacks_.end()) {
+    async_waiter_->CancelWait(wait_id);
+    callbacks_.erase(wait_id);
+  }
+}
+
+}  // namespace python
 }  // namespace mojo