Add documentation and a unit test for ObjectWatcher.

This documentation clarifies the expected behaviour when a watched PROCESS finishes before observation using ObjectWatcher begins. A unit-test confirms that the behaviour is as expected.

BUG=None
TEST=base_unittests --gtest_filter=ObjectWatcherTest.*


Review URL: https://chromiumcodereview.appspot.com/10979071

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@161735 0039d316-1c4b-4281-b951-d872f2087c98

2 files changed, 27 insertions, 2 deletions

diff --git a/base/win/object_watcher.h b/base/win/object_watcher.h
index 6a570b2..742f2b0 100644
--- a/base/win/object_watcher.h
+++ b/base/win/object_watcher.h
@@ -42,6 +42,8 @@ namespace win {
 // signaled.  ObjectWatcher makes this task easy.  When MyClass goes out of
 // scope, the watcher_ will be destroyed, and there is no need to worry about
 // OnObjectSignaled being called on a deleted MyClass pointer.  Easy!
+// If the object is already signaled before being watched, OnObjectSignaled is
+// still called after (but not necessarily immediately after) watch is started.
 //
 class BASE_EXPORT ObjectWatcher : public MessageLoop::DestructionObserver {
  public:
diff --git a/base/win/object_watcher_unittest.cc b/base/win/object_watcher_unittest.cc
index fe151d9..b4e0255 100644..100755
--- a/base/win/object_watcher_unittest.cc
+++ b/base/win/object_watcher_unittest.cc
@@ -70,7 +70,6 @@ void RunTest_BasicCancel(MessageLoop::Type message_loop_type) {
   CloseHandle(event);
 }
 
-
 void RunTest_CancelAfterSet(MessageLoop::Type message_loop_type) {
   MessageLoop message_loop(message_loop_type);
 
@@ -79,7 +78,7 @@ void RunTest_CancelAfterSet(MessageLoop::Type message_loop_type) {
   int counter = 1;
   DecrementCountDelegate delegate(&counter);
 
-    // A manual-reset event that is not yet signaled.
+  // A manual-reset event that is not yet signaled.
   HANDLE event = CreateEvent(NULL, TRUE, FALSE, NULL);
 
   bool ok = watcher.StartWatching(event, &delegate);
@@ -100,6 +99,24 @@ void RunTest_CancelAfterSet(MessageLoop::Type message_loop_type) {
   CloseHandle(event);
 }
 
+void RunTest_SignalBeforeWatch(MessageLoop::Type message_loop_type) {
+  MessageLoop message_loop(message_loop_type);
+
+  ObjectWatcher watcher;
+
+  // A manual-reset event that is signaled before we begin watching.
+  HANDLE event = CreateEvent(NULL, TRUE, TRUE, NULL);
+
+  QuitDelegate delegate;
+  bool ok = watcher.StartWatching(event, &delegate);
+  EXPECT_TRUE(ok);
+
+  MessageLoop::current()->Run();
+
+  EXPECT_EQ(NULL, watcher.GetWatchedObject());
+  CloseHandle(event);
+}
+
 void RunTest_OutlivesMessageLoop(MessageLoop::Type message_loop_type) {
   // Simulate a MessageLoop that dies before an ObjectWatcher.  This ordinarily
   // doesn't happen when people use the Thread class, but it can happen when
@@ -139,6 +156,12 @@ TEST(ObjectWatcherTest, CancelAfterSet) {
   RunTest_CancelAfterSet(MessageLoop::TYPE_UI);
 }
 
+TEST(ObjectWatcherTest, SignalBeforeWatch) {
+  RunTest_SignalBeforeWatch(MessageLoop::TYPE_DEFAULT);
+  RunTest_SignalBeforeWatch(MessageLoop::TYPE_IO);
+  RunTest_SignalBeforeWatch(MessageLoop::TYPE_UI);
+}
+
 TEST(ObjectWatcherTest, OutlivesMessageLoop) {
   RunTest_OutlivesMessageLoop(MessageLoop::TYPE_DEFAULT);
   RunTest_OutlivesMessageLoop(MessageLoop::TYPE_IO);