forwarder2: Make the Forwarder instances operate on a single thread.

tools/android/forwarder2/pipe_notifier.cc

 // Copyright (c) 2012 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 "tools/android/forwarder2/pipe_notifier.h"
 
 #include <fcntl.h>
 #include <unistd.h>
 #include <sys/socket.h>
 #include <sys/types.h>
@@ skipping 16 matching lines @@
 PipeNotifier::~PipeNotifier() {
   close(receiver_fd_);
   close(sender_fd_);
 }
 
 bool PipeNotifier::Notify() {
   CHECK_NE(-1, sender_fd_);
   errno = 0;
   int ret = HANDLE_EINTR(write(sender_fd_, "1", 1));
   if (ret < 0) {
-    LOG(WARNING) << "Error while notifying pipe. " << safe_strerror(errno);
+    PLOG(ERROR) << "write";
     return false;
   }
   return true;
 }
 
+void PipeNotifier::Reset() {
+  char c;
+  int ret = HANDLE_EINTR(read(receiver_fd_, &c, 1));
+  if (ret < 0) {
+    PLOG(ERROR) << "read";
+    return;
+  }
+  DCHECK_EQ(1, ret);
+  DCHECK_EQ('1', c);
+}
+
 }  // namespace forwarder