Mojo: Implement plumbing to support passing handles over MessagePipes.

mojo/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_SYSTEM_DISPATCHER_H_
 #define MOJO_SYSTEM_DISPATCHER_H_
 
+#include <vector>
+
 #include "base/basictypes.h"
 #include "base/memory/ref_counted.h"
 #include "base/synchronization/lock.h"
 #include "mojo/public/system/core.h"
 #include "mojo/public/system/system_export.h"
 
 namespace mojo {
 namespace system {
 
+class CoreImpl;
 class Waiter;
 
 // A |Dispatcher| implements Mojo primitives that are "attached" to a particular
 // handle. This includes most (all?) primitives except for |MojoWait...()|. This
 // object is thread-safe, with its state being protected by a single lock
 // |lock_|, which is also made available to implementation subclasses (via the
 // |lock()| method).
 class MOJO_SYSTEM_EXPORT Dispatcher :
     public base::RefCountedThreadSafe<Dispatcher> {
  public:
   // These methods implement the various primitives named |Mojo...()|. These
   // take |lock_| and handle races with |Close()|. Then they call out to
   // subclasses' |...ImplNoLock()| methods (still under |lock_|), which actually
   // implement the primitives.
   // NOTE(vtl): This puts a big lock around each dispatcher (i.e., handle), and
   // prevents the various |...ImplNoLock()|s from releasing the lock as soon as
   // possible. If this becomes an issue, we can rethink this.
   MojoResult Close();
-  MojoResult WriteMessage(const void* bytes,
-                          uint32_t num_bytes,
-                          const MojoHandle* handles,
-                          uint32_t num_handles,
+  // |dispatchers| may be non-null if and only if there are handles to be
+  // written, in which case this will be called with all the dispatchers' locks
+  // held. On success, all the dispatchers must have been moved to a closed
+  // state; on failure, they should remain in their original state.
+  MojoResult WriteMessage(const void* bytes, uint32_t num_bytes,
+                          const std::vector<Dispatcher*>* dispatchers,
                           MojoWriteMessageFlags flags);
-  MojoResult ReadMessage(void* bytes,
-                         uint32_t* num_bytes,
-                         MojoHandle* handles,
-                         uint32_t* num_handles,
-                         MojoReadMessageFlags flags);
+  // |dispatchers| must be non-null if |max_num_dispatchers| is nonzero. On
+  // success, it will be set to the dispatchers to be received (and assigned
+  // handles) as part of the message.
+  MojoResult ReadMessage(
+      void* bytes, uint32_t* num_bytes,
+      uint32_t max_num_dispatchers,
+      std::vector<scoped_refptr<Dispatcher> >* dispatchers,
+      MojoReadMessageFlags flags);
 
   // Adds a waiter to this dispatcher. The waiter will be woken up when this
   // object changes state to satisfy |flags| with result |wake_result| (which
   // must be >= 0, i.e., a success status). It will also be woken up when it
   // becomes impossible for the object to ever satisfy |flags| with a suitable
   // error status.
   //
   // Returns:
   //  - |MOJO_RESULT_OK| if the waiter was added;
   //  - |MOJO_RESULT_ALREADY_EXISTS| if |flags| is already satisfied;
@@ skipping 12 matching lines @@
   virtual ~Dispatcher();
 
   // These are to be overridden by subclasses (if necessary). They are called
   // exactly once -- first |CancelAllWaitersNoLock()|, then |CloseImplNoLock()|,
   // when the dispatcher is being closed. They are called under |lock_|.
   virtual void CancelAllWaitersNoLock();
   virtual MojoResult CloseImplNoLock();
 
   // These are to be overridden by subclasses (if necessary). They are never
   // called after the dispatcher has been closed. They are called under |lock_|.
-  virtual MojoResult WriteMessageImplNoLock(const void* bytes,
-                                            uint32_t num_bytes,
-                                            const MojoHandle* handles,
-                                            uint32_t num_handles,
-                                            MojoWriteMessageFlags flags);
-  virtual MojoResult ReadMessageImplNoLock(void* bytes,
-                                           uint32_t* num_bytes,
-                                           MojoHandle* handles,
-                                           uint32_t* num_handles,
-                                           MojoReadMessageFlags flags);
+  // See the descriptions of the methods without the "ImplNoLock" for more
+  // information.
+  virtual MojoResult WriteMessageImplNoLock(
+      const void* bytes, uint32_t num_bytes,
+      const std::vector<Dispatcher*>* dispatchers,
+      MojoWriteMessageFlags flags);
+  virtual MojoResult ReadMessageImplNoLock(
+      void* bytes, uint32_t* num_bytes,
+      uint32_t max_num_dispatchers,
+      std::vector<scoped_refptr<Dispatcher> >* dispatchers,
+      MojoReadMessageFlags flags);
   virtual MojoResult AddWaiterImplNoLock(Waiter* waiter,
                                          MojoWaitFlags flags,
                                          MojoResult wake_result);
   virtual void RemoveWaiterImplNoLock(Waiter* waiter);
 
   // Available to subclasses. (Note: Returns a non-const reference, just like
   // |base::AutoLock|'s constructor takes a non-const reference.
   base::Lock& lock() const { return lock_; }
 
  private:
+  // For |WriteMessage()|, |CoreImpl| needs access to |lock()|.
+  friend class CoreImpl;
+
   // This protects the following members as well as any state added by
   // subclasses.
   mutable base::Lock lock_;
   bool is_closed_;
 
   DISALLOW_COPY_AND_ASSIGN(Dispatcher);
 };
 
 }  // namespace system
 }  // namespace mojo
 
 #endif  // MOJO_SYSTEM_DISPATCHER_H_