Mojo: Armed Watchers

mojo/edk/system/watcher.cc

Index: mojo/edk/system/watcher.cc
diff --git a/mojo/edk/system/watcher.cc b/mojo/edk/system/watcher.cc
index 25c227641efafc4f09081efbad8c037e15f99c1d..7853bd2183ca4cf3fa449b45e833bb8a18a7bd15 100644
--- a/mojo/edk/system/watcher.cc
+++ b/mojo/edk/system/watcher.cc
@@ -17,19 +17,21 @@ Watcher::Watcher(MojoHandleSignals signals, const WatchCallback& callback)
 void Watcher::MaybeInvokeCallback(MojoResult result,
                                   const HandleSignalsState& state,
                                   MojoWatchNotificationFlags flags) {
-  base::AutoLock lock(lock_);
+  base::AutoLock lock(notification_lock_);
   if (is_cancelled_)
     return;
 
   callback_.Run(result, state, flags);
 }
 
-void Watcher::NotifyForStateChange(const HandleSignalsState& signals_state) {
+void Watcher::NotifyState(const HandleSignalsState& signals_state) {
   RequestContext* request_context = RequestContext::current();
-  if (signals_state.satisfies(signals_)) {
+  if (signals_state.satisfies(signals_) && is_armed_.Get()) {
+    is_armed_.Set(false);
     request_context->AddWatchNotifyFinalizer(
         make_scoped_refptr(this), MOJO_RESULT_OK, signals_state);
-  } else if (!signals_state.can_satisfy(signals_)) {
+  } else if (!signals_state.can_satisfy(signals_) && is_armed_.Get()) {
+    is_armed_.Set(false);
     request_context->AddWatchNotifyFinalizer(
         make_scoped_refptr(this), MOJO_RESULT_FAILED_PRECONDITION,
         signals_state);
@@ -42,8 +44,21 @@ void Watcher::NotifyClosed() {
       make_scoped_refptr(this), MOJO_RESULT_CANCELLED, closed_state);
 }
 
+MojoResult Watcher::Arm(const HandleSignalsState& current_state) {
+  if (is_armed_.Get())
+    return MOJO_RESULT_OK;
+
+  if (current_state.satisfies(signals_))
+    return MOJO_RESULT_ALREADY_EXISTS;
+  else if (!current_state.can_satisfy(signals_))
+    return MOJO_RESULT_FAILED_PRECONDITION;
+
+  is_armed_.Set(true);
+  return MOJO_RESULT_OK;
+}
+
 void Watcher::Cancel() {
-  base::AutoLock lock(lock_);
+  base::AutoLock lock(notification_lock_);
   is_cancelled_ = true;
 }