Make MojoWaitMany() accept zero handles.

mojo/edk/system/core.cc

 // 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.
 
 #include "mojo/edk/system/core.h"
 
 #include <limits>
 #include <memory>
 #include <utility>
 #include <vector>
@@ skipping 239 matching lines @@
     signals_state.Put(hss);
   return result;
 }
 
 MojoResult Core::WaitMany(UserPointer<const MojoHandle> handles,
                           UserPointer<const MojoHandleSignals> signals,
                           uint32_t num_handles,
                           MojoDeadline deadline,
                           UserPointer<uint32_t> result_index,
                           UserPointer<MojoHandleSignalsState> signals_states) {
-  if (num_handles < 1)
-    return MOJO_RESULT_INVALID_ARGUMENT;
   if (num_handles > GetConfiguration().max_wait_many_num_handles)
     return MOJO_RESULT_RESOURCE_EXHAUSTED;
 
+  uint64_t index = static_cast<uint64_t>(-1);
+  if (num_handles == 0u)
+    return WaitManyInternal(nullptr, nullptr, 0u, deadline, &index, nullptr);
+
   UserPointer<const MojoHandle>::Reader handles_reader(handles, num_handles);
   UserPointer<const MojoHandleSignals>::Reader signals_reader(signals,
                                                               num_handles);
-  uint64_t index = static_cast<uint64_t>(-1);
   MojoResult result;
-  if (signals_states.IsNull()) {
+  if (signals_states.IsNull() || num_handles == 0u) {
     result = WaitManyInternal(handles_reader.GetPointer(),
                               signals_reader.GetPointer(), num_handles,
                               deadline, &index, nullptr);
   } else {
     UserPointer<MojoHandleSignalsState>::Writer signals_states_writer(
         signals_states, num_handles);
     // Note: The |reinterpret_cast| is safe, since |HandleSignalsState| is a
     // subclass of |MojoHandleSignalsState| that doesn't add any data members.
     result = WaitManyInternal(
         handles_reader.GetPointer(), signals_reader.GetPointer(), num_handles,
@@ skipping 554 matching lines @@
 }
 
 // Note: We allow |handles| to repeat the same handle multiple times, since
 // different flags may be specified.
 MojoResult Core::WaitManyInternal(const MojoHandle* handles,
                                   const MojoHandleSignals* signals,
                                   uint32_t num_handles,
                                   MojoDeadline deadline,
                                   uint64_t* result_index,
                                   HandleSignalsState* signals_states) {
-  DCHECK_GT(num_handles, 0u);
   DCHECK_EQ(*result_index, static_cast<uint64_t>(-1));
 
   DispatcherVector dispatchers;
   dispatchers.reserve(num_handles);
 
   {
     MutexLocker locker(&handle_table_mutex_);
     for (uint32_t i = 0; i < num_handles; i++) {
       if (handles[i] == MOJO_HANDLE_INVALID) {
         *result_index = i;
@@ skipping 42 matching lines @@
   if (signals_states) {
     for (; i < num_handles; i++)
       signals_states[i] = dispatchers[i]->GetHandleSignalsState();
   }
 
   return result;
 }
 
 }  // namespace system
 }  // namespace mojo