Make it possible to remove an Awakable with a specific "context" from a Dispatcher.

mojo/edk/system/dispatcher.h

 // Copyright 2013 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.
 
 #ifndef MOJO_EDK_SYSTEM_DISPATCHER_H_
 #define MOJO_EDK_SYSTEM_DISPATCHER_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 178 matching lines @@
   HandleSignalsState GetHandleSignalsState() const;
 
   // Adds an awakable to this dispatcher, which will be woken up when this
   // object changes state to satisfy |signals| with context |context|. It will
   // also be woken up when it becomes impossible for the object to ever satisfy
   // |signals| with a suitable error status.
   //
   // If |signals_state| is non-null, on *failure* |*signals_state| will be set
   // to the current handle signals state (on success, it is left untouched).
   //
+  // Any awakable that's added must either eventually be removed (using
+  // |RemoveAwakable()| or |RemoveAwakableWithContext()|, below). If an
+  // awakable's |Awake()| is called (by this dispatcher) and it returns false,
+  // that is equivalent to |RemoveAwakableWithContext()| being called for that
+  // awakable and the context passed to |Awake()|.
+  //
   // Returns:
   //  - |MOJO_RESULT_OK| if the awakable was added;
   //  - |MOJO_RESULT_ALREADY_EXISTS| if |signals| is already satisfied (if
   //    |force| is true, the awakable will still be added);
   //  - |MOJO_RESULT_INVALID_ARGUMENT| if the dispatcher has been closed; and
   //  - |MOJO_RESULT_FAILED_PRECONDITION| if it is not (or no longer) possible
   //    that |signals| will ever be satisfied.
   MojoResult AddAwakable(Awakable* awakable,
                          MojoHandleSignals signals,
                          uint64_t context,
                          HandleSignalsState* signals_state);
   // Like |AddAwakable()|, but in the |MOJO_RESULT_ALREADY_EXISTS| case still
   // adds the awakable (|MOJO_RESULT_ALREADY_EXISTS| will still be returned and
   // |*signals_state| will still be set if |signals_state| is non-null).
   MojoResult AddAwakableUnconditional(Awakable* awakable,
                                       MojoHandleSignals signals,
                                       uint64_t context,
                                       HandleSignalsState* signals_state);
-  // Removes an awakable from this dispatcher. (It is valid to call this
-  // multiple times for the same |awakable| on the same object, so long as
-  // |AddAwakable()| was called at most once.) If |signals_state| is non-null,
-  // |*signals_state| will be set to the current handle signals state.
+  // Removes an awakable from this dispatcher. This will remove all instances of
+  // |awakable|, regardless of context. (It is valid to call this multiple times
+  // for the same |awakable| on the same object.) If |signals_state| is
+  // non-null, |*signals_state| will be set to the current handle signals state.
   void RemoveAwakable(Awakable* awakable, HandleSignalsState* signals_state);
+  // Like |RemoveAwakable()|, but only removes "instances" with the given
+  // context. (This may also be called multiple times, and there may be multiple
+  // instances with the same context.)
+  void RemoveAwakableWithContext(Awakable* awakable,
+                                 uint64_t context,
+                                 HandleSignalsState* signals_state);
 
   // A dispatcher must be put into a special state in order to be sent across a
   // message pipe. Outside of tests, only |HandleTableAccess| is allowed to do
   // this, since there are requirements on the handle table (see below).
   //
   // In this special state, only a restricted set of operations is allowed.
   // These are the ones available as |HandleTransport| methods. Other
   // |Dispatcher| methods must not be called until |HandleTransport::End()| has
   // been called.
   class HandleTableAccess {
@@ skipping 158 matching lines @@
       MOJO_SHARED_LOCKS_REQUIRED(mutex_);
   virtual MojoResult AddAwakableImplNoLock(Awakable* awakable,
                                            MojoHandleSignals signals,
                                            bool force,
                                            uint64_t context,
                                            HandleSignalsState* signals_state)
       MOJO_EXCLUSIVE_LOCKS_REQUIRED(mutex_);
   virtual void RemoveAwakableImplNoLock(Awakable* awakable,
                                         HandleSignalsState* signals_state)
       MOJO_EXCLUSIVE_LOCKS_REQUIRED(mutex_);
+  virtual void RemoveAwakableWithContextImplNoLock(
+      Awakable* awakable,
+      uint64_t context,
+      HandleSignalsState* signals_state) MOJO_EXCLUSIVE_LOCKS_REQUIRED(mutex_);
 
   // These implement the API used to serialize dispatchers to a |Channel|
   // (described below). They will only be called on a dispatcher that's attached
   // to and "owned" by a |MessageInTransit|. See the non-"impl" versions for
   // more information.
   //
   // Note: |StartSerializeImplNoLock()| is actually called with |mutex_| NOT
   // held, since the dispatcher should only be accessible to the calling thread.
   // On Debug builds, |EndSerializeAndCloseImplNoLock()| is called with |mutex_|
   // held, to satisfy any |mutex_.AssertHeld()| (e.g., in |CloseImplNoLock()| --
@@ skipping 92 matching lines @@
 
 // So logging macros and |DCHECK_EQ()|, etc. work.
 inline std::ostream& operator<<(std::ostream& out, Dispatcher::Type type) {
   return out << static_cast<int>(type);
 }
 
 }  // namespace system
 }  // namespace mojo
 
 #endif  // MOJO_EDK_SYSTEM_DISPATCHER_H_