mojo: Add a runloop utility in python

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
new file mode 100644
index 0000000000000000000000000000000000000000..91032053bff05d706deb63771da6bef7f32739fd
--- /dev/null
+++ b/mojo/public/python/src/python_system_helper.cc
@@ -0,0 +1,79 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "mojo/public/python/src/python_system_helper.h"
+
+#include "Python.h"
+
+#include "mojo/public/cpp/environment/logging.h"
+#include "mojo/public/cpp/system/macros.h"
+#include "mojo/public/cpp/utility/run_loop.h"
+
+namespace {
+
+class ScopedGIL {
+ public:
+  ScopedGIL() {
+    state_ = PyGILState_Ensure();
+  }
+
+  ~ScopedGIL() {
+    PyGILState_Release(state_);
+  }
+
+ private:
+  PyGILState_STATE state_;
+
+  MOJO_DISALLOW_COPY_AND_ASSIGN(ScopedGIL);
+};
+
+class PythonClosure : public mojo::Closure::Runnable {
+ public:
+  PythonClosure(PyObject* callable) : callable_(callable) {
+    MOJO_CHECK(callable);
+    Py_XINCREF(callable);
+  }
+
+  virtual ~PythonClosure() {
+    ScopedGIL acquire_gil;
+    Py_DECREF(callable_);
+  }
+
+  virtual void Run() const MOJO_OVERRIDE {
+    ScopedGIL acquire_gil;
+    PyObject* empty_tuple = PyTuple_New(0);
+    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:
+  PyObject* callable_;
+
+  MOJO_DISALLOW_COPY_AND_ASSIGN(PythonClosure);
+};
+
+}  // namespace
+
+namespace mojo {
+
+Closure BuildClosure(PyObject* callable) {
+  if (!PyCallable_Check(callable))
+    return Closure();
+
+  return Closure(
+      static_cast<mojo::Closure::Runnable*>(new PythonClosure(callable)));
+}
+
+}  // namespace mojo