1 files changed, 140 insertions, 0 deletions
diff --git a/base/win/object_watcher.cc b/base/win/object_watcher.cc
new file mode 100644
index 0000000..4f5e7ab
--- /dev/null
+++ b/base/win/object_watcher.cc
@@ -0,0 +1,140 @@
+// Copyright (c) 2011 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 "base/win/object_watcher.h"
+
+#include "base/logging.h"
+
+namespace base {
+namespace win {
+
+//-----------------------------------------------------------------------------
+
+struct ObjectWatcher::Watch : public Task {
+  ObjectWatcher* watcher;    // The associated ObjectWatcher instance
+  HANDLE object;             // The object being watched
+  HANDLE wait_object;        // Returned by RegisterWaitForSingleObject
+  MessageLoop* origin_loop;  // Used to get back to the origin thread
+  Delegate* delegate;        // Delegate to notify when signaled
+  bool did_signal;           // DoneWaiting was called
+
+  virtual void Run() {
+    // The watcher may have already been torn down, in which case we need to
+    // just get out of dodge.
+    if (!watcher)
+      return;
+
+    DCHECK(did_signal);
+    watcher->StopWatching();
+
+    delegate->OnObjectSignaled(object);
+  }
+};
+
+//-----------------------------------------------------------------------------
+
+ObjectWatcher::ObjectWatcher() : watch_(NULL) {
+}
+
+ObjectWatcher::~ObjectWatcher() {
+  StopWatching();
+}
+
+bool ObjectWatcher::StartWatching(HANDLE object, Delegate* delegate) {
+  if (watch_) {
+    NOTREACHED() << "Already watching an object";
+    return false;
+  }
+
+  Watch* watch = new Watch;
+  watch->watcher = this;
+  watch->object = object;
+  watch->origin_loop = MessageLoop::current();
+  watch->delegate = delegate;
+  watch->did_signal = false;
+
+  // Since our job is to just notice when an object is signaled and report the
+  // result back to this thread, we can just run on a Windows wait thread.
+  DWORD wait_flags = WT_EXECUTEINWAITTHREAD | WT_EXECUTEONLYONCE;
+
+  if (!RegisterWaitForSingleObject(&watch->wait_object, object, DoneWaiting,
+                                   watch, INFINITE, wait_flags)) {
+    NOTREACHED() << "RegisterWaitForSingleObject failed: " << GetLastError();
+    delete watch;
+    return false;
+  }
+
+  watch_ = watch;
+
+  // We need to know if the current message loop is going away so we can
+  // prevent the wait thread from trying to access a dead message loop.
+  MessageLoop::current()->AddDestructionObserver(this);
+  return true;
+}
+
+bool ObjectWatcher::StopWatching() {
+  if (!watch_)
+    return false;
+
+  // Make sure ObjectWatcher is used in a single-threaded fashion.
+  DCHECK(watch_->origin_loop == MessageLoop::current());
+
+  // If DoneWaiting is in progress, we wait for it to finish.  We know whether
+  // DoneWaiting happened or not by inspecting the did_signal flag.
+  if (!UnregisterWaitEx(watch_->wait_object, INVALID_HANDLE_VALUE)) {
+    NOTREACHED() << "UnregisterWaitEx failed: " << GetLastError();
+    return false;
+  }
+
+  // Make sure that we see any mutation to did_signal.  This should be a no-op
+  // since we expect that UnregisterWaitEx resulted in a memory barrier, but
+  // just to be sure, we're going to be explicit.
+  MemoryBarrier();
+
+  // If the watch has been posted, then we need to make sure it knows not to do
+  // anything once it is run.
+  watch_->watcher = NULL;
+
+  // If DoneWaiting was called, then the watch would have been posted as a
+  // task, and will therefore be deleted by the MessageLoop.  Otherwise, we
+  // need to take care to delete it here.
+  if (!watch_->did_signal)
+    delete watch_;
+
+  watch_ = NULL;
+
+  MessageLoop::current()->RemoveDestructionObserver(this);
+  return true;
+}
+
+HANDLE ObjectWatcher::GetWatchedObject() {
+  if (!watch_)
+    return NULL;
+
+  return watch_->object;
+}
+
+// static
+void CALLBACK ObjectWatcher::DoneWaiting(void* param, BOOLEAN timed_out) {
+  DCHECK(!timed_out);
+
+  Watch* watch = static_cast<Watch*>(param);
+
+  // Record that we ran this function.
+  watch->did_signal = true;
+
+  // We rely on the locking in PostTask() to ensure that a memory barrier is
+  // provided, which in turn ensures our change to did_signal can be observed
+  // on the target thread.
+  watch->origin_loop->PostTask(FROM_HERE, watch);
+}
+
+void ObjectWatcher::WillDestroyCurrentMessageLoop() {
+  // Need to shutdown the watch so that we don't try to access the MessageLoop
+  // after this point.
+  StopWatching();
+}
+
+}  // namespace win
+}  // namespace base