Fix threading bug in the brlapi braille controller

chrome/browser/extensions/api/braille_display_private/braille_controller_brlapi.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 "chrome/browser/extensions/api/braille_display_private/braille_controller_brlapi.h"
 
 #include <algorithm>
 #include <cerrno>
 #include <cstring>
 #include <vector>
@@ skipping 116 matching lines @@
   if (function.is_null()) {
     create_brlapi_connection_function_ = base::Bind(
         &BrailleControllerImpl::CreateBrlapiConnection,
         base::Unretained(this));
   } else {
     create_brlapi_connection_function_ = function;
   }
 }
 
 void BrailleControllerImpl::PokeSocketDirForTesting() {
-  OnSocketDirChanged(base::FilePath(), false /*error*/);
+  OnSocketDirChangedOnIOThread();
 }
 
 void BrailleControllerImpl::StartConnecting() {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
   if (started_connecting_)
     return;
   started_connecting_ = true;
   TryLoadLibBrlApi();
   if (!libbrlapi_loader_.loaded()) {
     return;
   }
-  base::FilePath brlapi_dir(BRLAPI_SOCKETPATH);
-  if (!file_path_watcher_.Watch(
-          brlapi_dir, false, base::Bind(
-              &BrailleControllerImpl::OnSocketDirChanged,
-              base::Unretained(this)))) {
-    LOG(WARNING) << "Couldn't watch brlapi directory " << BRLAPI_SOCKETPATH;
-    return;
-  }
+  // One could argue that there is a race condition between starting to
+  // watch the socket asynchonously and trying to connect.  While this is true,
+  // we are actually retrying to connect for a while, so this doesn't matter
+  // in practice.
+  BrowserThread::PostTask(
+      BrowserThread::FILE, FROM_HERE, base::Bind(
+          &BrailleControllerImpl::StartWatchingSocketDirOnFileThread,
+          base::Unretained(this)));
   ResetRetryConnectHorizon();
   TryToConnect();
 }
 
-void BrailleControllerImpl::OnSocketDirChanged(const base::FilePath& path,
-                                               bool error) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
-  DCHECK(libbrlapi_loader_.loaded());
+void BrailleControllerImpl::StartWatchingSocketDirOnFileThread() {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+  base::FilePath brlapi_dir(BRLAPI_SOCKETPATH);
+  if (!file_path_watcher_.Watch(
+          brlapi_dir, false, base::Bind(
+              &BrailleControllerImpl::OnSocketDirChangedOnFileThread,
+              base::Unretained(this)))) {
+    LOG(WARNING) << "Couldn't watch brlapi directory " << BRLAPI_SOCKETPATH;
+  }
+}
+
+void BrailleControllerImpl::OnSocketDirChangedOnFileThread(
+    const base::FilePath& path, bool error) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
   if (error) {
     LOG(ERROR) << "Error watching brlapi directory: " << path.value();
     return;
   }
+  BrowserThread::PostTask(
+      BrowserThread::IO, FROM_HERE, base::Bind(
+          &BrailleControllerImpl::OnSocketDirChangedOnIOThread,
+          base::Unretained(this)));
+}
+
+void BrailleControllerImpl::OnSocketDirChangedOnIOThread() {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
   LOG(INFO) << "BrlAPI directory changed";
   // Every directory change resets the max retry time to the appropriate delay
   // into the future.
   ResetRetryConnectHorizon();
   // Try after an initial delay to give the driver a chance to connect.
   ScheduleTryToConnect();
 }
 
 void BrailleControllerImpl::TryToConnect() {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
@@ skipping 144 matching lines @@
                    base::Passed(&new_state)));
     return;
   }
   FOR_EACH_OBSERVER(BrailleObserver, observers_,
                     OnDisplayStateChanged(*new_state));
 }
 
 }  // namespace braille_display_private
 }  // namespace api
 }  // namespace extensions