Remove call to IsRunningSequenceOnCurrentThread() in media_file_system_backend.cc

chrome/browser/media_galleries/fileapi/media_file_system_backend.cc

 // Copyright (c) 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/media_galleries/fileapi/media_file_system_backend.h"
 
 #include <string>
 #include <utility>
 #include <vector>
 
 #include "base/bind.h"
 #include "base/files/file_path.h"
+#include "base/lazy_instance.h"
 #include "base/logging.h"
 #include "base/sequenced_task_runner.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_util.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/threading/sequenced_worker_pool.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "build/build_config.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/extensions/extension_service.h"
@@ skipping 27 matching lines @@
 #include "chrome/browser/media_galleries/fileapi/picasa_file_util.h"
 #endif  // defined(OS_WIN) || defined(OS_MACOSX)
 
 using storage::FileSystemContext;
 using storage::FileSystemURL;
 
 namespace {
 
 const char kMediaGalleryMountPrefix[] = "media_galleries-";
 
+#if DCHECK_IS_ON()
+base::LazyInstance<base::SequenceChecker>::Leaky g_media_sequence_checker =
+    LAZY_INSTANCE_INITIALIZER;
+#endif
+
 void OnPreferencesInit(
     const content::ResourceRequestInfo::WebContentsGetter& web_contents_getter,
     const extensions::Extension* extension,
     MediaGalleryPrefId pref_id,
     const base::Callback<void(base::File::Error result)>& callback) {
   content::WebContents* contents = web_contents_getter.Run();
   if (!contents) {
     content::BrowserThread::PostTask(
         content::BrowserThread::IO, FROM_HERE,
         base::Bind(callback, base::File::FILE_ERROR_FAILED));
@@ skipping 73 matching lines @@
       picasa_file_util_used_(false),
       itunes_file_util_used_(false)
 #endif  // defined(OS_WIN) || defined(OS_MACOSX)
 {
 }
 
 MediaFileSystemBackend::~MediaFileSystemBackend() {
 }
 
 // static
-bool MediaFileSystemBackend::CurrentlyOnMediaTaskRunnerThread() {
-  base::SequencedWorkerPool* pool = content::BrowserThread::GetBlockingPool();
-  base::SequencedWorkerPool::SequenceToken media_sequence_token =
-      pool->GetNamedSequenceToken(kMediaTaskRunnerName);
-  return pool->IsRunningSequenceOnCurrentThread(media_sequence_token);
+void MediaFileSystemBackend::AssertCurrentlyOnMediaSequence() {
+#if DCHECK_IS_ON()
+  DCHECK(g_media_sequence_checker.Get().CalledOnValidSequence());

[Reilly Grant (use Gerrit), 2016/09/07 18:07:05]

I don't like consolidating the DCHECK into a single place because it means the
line number reported is not as useful.

[fdoray, 2016/09/07 19:21:51]

I don't want a public CurrentlyOnMediaTaskRunnerThread() method that relies on
SequenceChecker because people could be tempted to use it outside of DCHECKs.
e.g.:
  if (MediaFileSystemBackend::CurrentlyOnMediaTaskRunnerThread())
    ThisIsAlwaysCalledInANonDCHECKBuild();

Since DCHECK prints a stack trace, does this CL really makes it harder to
understand reported errors?

Potential solutions:
1. Keep this CL as-is.
2. Have a CurrentlyOnMediaSequence() method based on SequenceChecker - with a
comment that says that it shouldn't be used outside of DCHECKs since it always
returns true in non-DCHECK builds.
3. Have a GetMediaSequenceChecker() method that returns a SequenceChecker. I
believe that people are familiar with the fact that SequenceChecker is a no-op
in non-DCHECK builds and won't try to do if
(MediaFileSystemBackend::GetMediaSequenceChecker().CalledOnValidSequence()) {
... }

[Reilly Grant (use Gerrit), 2016/09/07 20:58:55]

I prefer option 2. Stack traces often do not include line numbers.

+#endif
 }
 
 // static
 scoped_refptr<base::SequencedTaskRunner>
 MediaFileSystemBackend::MediaTaskRunner() {
   base::SequencedWorkerPool* pool = content::BrowserThread::GetBlockingPool();
   base::SequencedWorkerPool::SequenceToken media_sequence_token =
       pool->GetNamedSequenceToken(kMediaTaskRunnerName);
   return pool->GetSequencedTaskRunner(media_sequence_token);
 }
@@ skipping 211 matching lines @@
 
 const storage::ChangeObserverList* MediaFileSystemBackend::GetChangeObservers(
     storage::FileSystemType type) const {
   return NULL;
 }
 
 const storage::AccessObserverList* MediaFileSystemBackend::GetAccessObservers(
     storage::FileSystemType type) const {
   return NULL;
 }