Mojo: Armed Watchers

third_party/WebKit/Source/core/mojo/MojoWatcher.h

Index: third_party/WebKit/Source/core/mojo/MojoWatcher.h
diff --git a/third_party/WebKit/Source/core/mojo/MojoWatcher.h b/third_party/WebKit/Source/core/mojo/MojoWatcher.h
index fe6e193d1a500872e08a14d49aeb186f3813b5a2..ece74d5ccac5c23632123e719a2e2402566d24c4 100644
--- a/third_party/WebKit/Source/core/mojo/MojoWatcher.h
+++ b/third_party/WebKit/Source/core/mojo/MojoWatcher.h
@@ -10,6 +10,7 @@
 #include "bindings/core/v8/TraceWrapperMember.h"
 #include "core/dom/ContextLifecycleObserver.h"
 #include "mojo/public/cpp/system/handle.h"
+#include "mojo/public/cpp/system/watcher.h"
 
 namespace blink {
 
@@ -47,16 +48,21 @@ class MojoWatcher final : public GarbageCollectedFinalized<MojoWatcher>,
 
   MojoWatcher(ExecutionContext*, MojoWatchCallback*);
   MojoResult watch(mojo::Handle, const MojoHandleSignals&);
+  MojoResult arm(MojoResult* readyResult);
 
   static void onHandleReady(uintptr_t context,
                             MojoResult,
                             MojoHandleSignalsState,
-                            MojoWatchNotificationFlags);
+                            MojoWatcherNotificationFlags);
   void runReadyCallback(MojoResult);
 
   RefPtr<WebTaskRunner> m_taskRunner;
   TraceWrapperMember<MojoWatchCallback> m_callback;
+  mojo::ScopedWatcherHandle m_watcherHandle;
   mojo::Handle m_handle;
+
+  // Cross-thread reference to self, used as the watch context.
+  std::unique_ptr<CrossThreadPersistent<MojoWatcher>> m_context;

[haraken, 2017/03/14 09:51:01]

This looks strange in a coupe of ways.

The only thing we need to make sure is that MojoWatcher's wrapper does not get
collected while the watcher is running. If MojoWatcher's wrapper is alive, the
MojoWatcher is kept alive as well.

To achieve that, you just need to return true from hasPendingActivity() while
the watcher is running. i.e., one boolean flag would be sufficient, I guess.

[Ken Rockot(use gerrit already), 2017/03/14 14:17:40]

I see, thanks for the clarification. Actually we don't even need a bool, we can
use the validity of m_handle as a signal still. I've made it so that explicit
cancel() does not reset this value, but instead only resets the watcher handle
itself. This achieves the desired behavior.

 };
 
 }  // namespace blink