Make a fairer combined message loop

base/message_loop/message_loop.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 "base/message_loop/message_loop.h"
 
 #include <algorithm>
 
 #include "base/bind.h"
 #include "base/compiler_specific.h"
@@ skipping 79 matching lines @@
 MessageLoop::MessagePumpFactory* message_pump_for_ui_factory_ = NULL;
 
 // Create a process-wide unique ID to represent this task in trace events. This
 // will be mangled with a Process ID hash to reduce the likelyhood of colliding
 // with MessageLoop pointers on other processes.
 uint64 GetTaskTraceID(const PendingTask& task, MessageLoop* loop) {
   return (static_cast<uint64>(task.sequence_num) << 32) |
          static_cast<uint64>(reinterpret_cast<intptr_t>(loop));
 }
 
+// Returns true if MessagePump::ScheduleWork() must be called one
+// time for every task that is added to the MessageLoop incoming queue.
+bool AlwaysNotifyPump(MessageLoop::Type type) {
+#if defined(OS_ANDROID)
+  return type == MessageLoop::TYPE_UI;
+#else
+  return false;
+#endif
+}
+
 }  // namespace
 
 //------------------------------------------------------------------------------
 
 #if defined(OS_WIN)
 
 // Upon a SEH exception in this thread, it restores the original unhandled
 // exception filter.
 static int SEHFilter(LPTOP_LEVEL_EXCEPTION_FILTER old_filter) {
   ::SetUnhandledExceptionFilter(old_filter);
@@ skipping 507 matching lines @@
     // tasks (to faciliate FIFO sorting when two tasks have the same
     // delayed_run_time value) and for identifying the task in about:tracing.
     pending_task->sequence_num = next_sequence_num_++;
 
     TRACE_EVENT_FLOW_BEGIN0("task", "MessageLoop::PostTask",
         TRACE_ID_MANGLE(GetTaskTraceID(*pending_task, this)));
 
     bool was_empty = incoming_queue_.empty();
     incoming_queue_.push(*pending_task);
     pending_task->task.Reset();
-    if (!was_empty)
+    // The Android UI message loop needs to get notified each time
+    // a task is added to the incoming queue.
+    if (!was_empty && !AlwaysNotifyPump(type_))
       return true;  // Someone else should have started the sub-pump.
 
     pump = pump_;
   }
   // Since the incoming_queue_ may contain a task that destroys this message
   // loop, we cannot exit incoming_queue_lock_ until we are done with |this|.
   // We use a stack-based reference to the message pump so that we can call
   // ScheduleWork outside of incoming_queue_lock_.
 
   pump->ScheduleWork();
@@ skipping 187 matching lines @@
       fd,
       persistent,
       mode,
       controller,
       delegate);
 }
 
 #endif
 
 }  // namespace base