Flapper field trial to use workerpool for sync file operations.

content/browser/renderer_host/pepper/pepper_file_message_filter.cc

Index: content/browser/renderer_host/pepper/pepper_file_message_filter.cc
diff --git a/content/browser/renderer_host/pepper/pepper_file_message_filter.cc b/content/browser/renderer_host/pepper/pepper_file_message_filter.cc
index 5de7fbf19fcda606694d66f38d7f78e7f1cf80e5..9a431dcd86f94782592aac490dcef1225e3d7359 100644
--- a/content/browser/renderer_host/pepper/pepper_file_message_filter.cc
+++ b/content/browser/renderer_host/pepper/pepper_file_message_filter.cc
@@ -8,8 +8,10 @@
 #include "base/file_path.h"
 #include "base/file_util.h"
 #include "base/logging.h"
+#include "base/metrics/field_trial.h"
 #include "base/platform_file.h"
 #include "base/process_util.h"
+#include "base/threading/sequenced_worker_pool.h"
 #include "content/browser/child_process_security_policy_impl.h"
 #include "content/browser/renderer_host/render_process_host_impl.h"
 #include "content/public/browser/browser_thread.h"
@@ -60,6 +62,29 @@ IPC::PlatformFileForTransit PlatformFileToPlatformFileForTransit(
   return file;
 }
 
+// TODO(shess): http://crbug.com/153383 debugging.  This is only
+// necessary while determining if (and how much) worker pool mitigates
+// the problem.
+bool UseFileThread() {
+  static bool use_file_thread = true;
+
+  static bool activated = false;
+  if (!activated) {
+    // NOTE(shess): These need to match the values in pepper_flash.cc.
+    // Since this code is only temporary, it is not worth plumbing
+    // shared access through.
+    const char* const kFieldTrialName = "FlapperIOThread";
+    const char* const kFileGroupName = "FileThread";
+
+    std::string active = base::FieldTrialList::FindFullName(kFieldTrialName);
+    use_file_thread = (active == kFileGroupName);
+
+    activated = true;
+  }
+
+  return use_file_thread;
+}
+
 }  // namespace
 
 PepperFileMessageFilter::PepperFileMessageFilter(int child_id)
@@ -70,10 +95,20 @@ PepperFileMessageFilter::PepperFileMessageFilter(int child_id)
 void PepperFileMessageFilter::OverrideThreadForMessage(
     const IPC::Message& message,
     BrowserThread::ID* thread) {
-  if (IPC_MESSAGE_CLASS(message) == PepperFileMsgStart)
+  if (IPC_MESSAGE_CLASS(message) == PepperFileMsgStart && UseFileThread())
     *thread = BrowserThread::FILE;
 }
 
+base::TaskRunner* PepperFileMessageFilter::OverrideTaskRunnerForMessage(
+    const IPC::Message& message) {
+  if (IPC_MESSAGE_CLASS(message) == PepperFileMsgStart) {
+    // Should never get here if using the FILE thread.
+    DCHECK(!UseFileThread());
+    return BrowserThread::GetBlockingPool();

[yzshen1, 2012/10/02 23:33:44]

According to the comments of GetBlockingPool(), this is also used for "random
blocking operations". Is it guaranteed that it is less busy than the FILE thread
and to what extent?

Because blocking these file tasks is very bad (will block flapper && any
renderer that sends sync messages to flapper), we need to use a very responsive
task runner here.

[Scott Hess - ex-Googler, 2012/10/02 23:42:31]

I'll talk to Brett.

[yzshen1, 2012/10/02 23:52:10]

I am very curious about the result. Please let me know. :)
On 2012/10/02 23:42:31, shess wrote:

+  }
+  return NULL;
+}
+
 bool PepperFileMessageFilter::OnMessageReceived(const IPC::Message& message,
                                                 bool* message_was_ok) {
   bool handled = true;