Mojo EDK: Introduce MojoQueryHandleSignalsState API

mojo/public/c/system/functions.h

 // Copyright 2014 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.
 
 // This file contains basic functions common to different Mojo system APIs.
 //
 // Note: This header should be compilable as C.
 
 #ifndef MOJO_PUBLIC_C_SYSTEM_FUNCTIONS_H_
 #define MOJO_PUBLIC_C_SYSTEM_FUNCTIONS_H_
@@ skipping 28 matching lines @@
 // Returns:
 //   |MOJO_RESULT_OK| on success.
 //   |MOJO_RESULT_INVALID_ARGUMENT| if |handle| is not a valid handle.
 //
 // Concurrent operations on |handle| may succeed (or fail as usual) if they
 // happen before the close, be cancelled with result |MOJO_RESULT_CANCELLED| if
 // they properly overlap (this is likely the case with |MojoWait()|, etc.), or
 // fail with |MOJO_RESULT_INVALID_ARGUMENT| if they happen after.
 MOJO_SYSTEM_EXPORT MojoResult MojoClose(MojoHandle handle);
 
+// Queries the last known signals state of a handle.
+//
+// Note that no guarantees can be made about the accuracy of the returned
+// signals state by the time this returns, as other threads in the system may
+// change the handle's state at any time. Use with appropriate discretion.
+//
+// Returns:
+//   |MOJO_RESULT_OK| on success. |*signals_state| is populated with the
+//       last known signals state of |handle|.
+//   |MOJO_RESULT_INVALID_ARGUMENT| if |handle| is not a valid handle or
+//       |signals_state| is null.
+MOJO_SYSTEM_EXPORT MojoResult
+MojoQueryHandleSignalsState(MojoHandle handle,
+                            struct MojoHandleSignalsState* signals_state);
+
 // Waits on the given handle until one of the following happens:
 //   - A signal indicated by |signals| is satisfied.
 //   - It becomes known that no signal indicated by |signals| will ever be
 //     satisfied. (See the description of the |MOJO_RESULT_CANCELLED| and
 //     |MOJO_RESULT_FAILED_PRECONDITION| return values below.)
 //   - Until |deadline| has passed.
 //
 // If |deadline| is |MOJO_DEADLINE_INDEFINITE|, this will wait "forever" (until
 // one of the other wait termination conditions is satisfied). If |deadline| is
 // 0, this will return |MOJO_RESULT_DEADLINE_EXCEEDED| only if one of the other
@@ skipping 79 matching lines @@
 //     |MOJO_RESULT_INVALID_ARGUMENT| if |type| is not recognized. In this case,
 //         |value| is untouched.
 MOJO_SYSTEM_EXPORT MojoResult MojoGetProperty(MojoPropertyType type,
                                               void* value);
 
 #ifdef __cplusplus
 }  // extern "C"
 #endif
 
 #endif  // MOJO_PUBLIC_C_SYSTEM_FUNCTIONS_H_