Plumb the handle signals state out of Waiter::Wait().

mojo/edk/system/waiter.h

Index: mojo/edk/system/waiter.h
diff --git a/mojo/edk/system/waiter.h b/mojo/edk/system/waiter.h
index 229214a80f5d8d1374b352787dce77a606a8d223..afe5b89ae587f4aab6704e1e86ff3f25e446efcd 100644
--- a/mojo/edk/system/waiter.h
+++ b/mojo/edk/system/waiter.h
@@ -34,28 +34,19 @@ class Waiter final : public Awakable {
   // Waits until a suitable |Awake()| is called. (|context| may be null, in
   // which case, obviously no context is ever returned.)
   // Returns:
-  //   - The result given to the first call to |Awake()| (possibly before this
-  //     call to |Wait()|); in this case, |*context| is set to the value passed
-  //     to that call to |Awake()|.
-  //   - |MOJO_RESULT_DEADLINE_EXCEEDED| if the deadline was exceeded; in this
-  //     case |*context| is not modified.
+  //   - |MOJO_RESULT_OK| if |Awake()| was called with |AwakeReason::SATISFIED|;
+  //   - |MOJO_RESULT_CANCELLED| if |Awake()| was called with
+  //     |AwakeReason::CANCELLED|;
+  //   - |MOJO_RESULT_FAILED_PRECONDITION| if |Awake()| was called with
+  //     |AwakeReason::UNSATISFIABLE|; or
+  //   - |MOJO_RESULT_DEADLINE_EXCEEDED| if the deadline was exceeded.
   //
-  // Usually, the context passed to |Awake()| will be the value passed to
-  // |Dispatcher::AddAwakable()|, which is usually the index to the array of
-  // handles passed to |MojoWaitMany()| (or 0 for |MojoWait()|).
-  //
-  // Typical |Awake()| results are:
-  //   - |MOJO_RESULT_OK| if one of the flags passed to
-  //     |MojoWait()|/|MojoWaitMany()| (hence |Dispatcher::AddAwakable()|) was
-  //     satisfied;
-  //   - |MOJO_RESULT_CANCELLED| if a handle (on which
-  //     |MojoWait()|/|MojoWaitMany()| was called) was closed (hence the
-  //     dispatcher closed); and
-  //   - |MOJO_RESULT_FAILED_PRECONDITION| if one of the set of flags passed to
-  //     |MojoWait()|/|MojoWaitMany()| cannot or can no longer be satisfied by
-  //     the corresponding handle (e.g., if the other end of a message or data
-  //     pipe is closed).
-  MojoResult Wait(MojoDeadline deadline, uint64_t* context);
+  // In all the cases except |MOJO_RESULT_DEADLINE_EXCEEDED|, the context and
+  // signals state passed to |Awake()| be made available via |*context| and
+  // |*signals_state|, respectively (unless the respective pointer is null).
+  MojoResult Wait(MojoDeadline deadline,
+                  uint64_t* context,
+                  HandleSignalsState* signals_state);
 
   // |Awakable| implementation:
   bool Awake(uint64_t context,
@@ -69,7 +60,8 @@ class Waiter final : public Awakable {
   bool initialized_ MOJO_GUARDED_BY(mutex_);
 #endif
   bool awoken_ MOJO_GUARDED_BY(mutex_);
-  MojoResult awake_result_ MOJO_GUARDED_BY(mutex_);
+  AwakeReason awake_reason_ MOJO_GUARDED_BY(mutex_);
+  HandleSignalsState signals_state_ MOJO_GUARDED_BY(mutex_);
   uint64_t awake_context_ MOJO_GUARDED_BY(mutex_);
 
   MOJO_DISALLOW_COPY_AND_ASSIGN(Waiter);