Flapper field trial to use workerpool for sync file operations.

Flash private file operations are synchronous, and were being
scheduled on the browser's FILE thread.  This thread can have lots of
relatively long-running stuff on it.  Add a 50% field trial to
schedule on a blocking worker-pool thread, and histogram hung-plugin
instances to see if it helps.

BUG=153383


Review URL: https://chromiumcodereview.appspot.com/11016016

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@160026 0039d316-1c4b-4281-b951-d872f2087c98

3 files changed, 69 insertions, 1 deletions

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 5de7fbf..e07bb99 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"
@@ -60,20 +62,67 @@ IPC::PlatformFileForTransit PlatformFileToPlatformFileForTransit(
   return file;
 }
 
+// Run a field trial comparing the effect of the FILE thread versus
+// blocking worker pool on hung-plugin reports.
+// TODO(shess): Remove once the workpool is proven superior.
+// http://crbug.com/153383
+const char* const kIOFieldTrialName = "FlapperIOThread";
+const char* const kPoolGroupName = "PoolThread";
+const char* const kFileGroupName = "FileThread";
+
+bool g_use_file_thread = true;
+
+void ActivateThreadFieldTrial() {
+  static bool activated = false;
+  if (activated)
+    return;
+
+  activated = true;
+
+  // The field trial will expire on Jan 1st, 2014.
+  scoped_refptr<base::FieldTrial> trial(
+      base::FieldTrialList::FactoryGetFieldTrial(
+          kIOFieldTrialName, 1000, kPoolGroupName, 2014, 1, 1, NULL));
+
+  // 50% goes into the FILE thread group.
+  trial->AppendGroup(kFileGroupName, 500);
+
+  g_use_file_thread = (trial->group_name() == kFileGroupName);
+}
+
 }  // namespace
 
 PepperFileMessageFilter::PepperFileMessageFilter(int child_id)
         : child_id_(child_id),
           channel_(NULL) {
+  ActivateThreadFieldTrial();
 }
 
 void PepperFileMessageFilter::OverrideThreadForMessage(
     const IPC::Message& message,
     BrowserThread::ID* thread) {
-  if (IPC_MESSAGE_CLASS(message) == PepperFileMsgStart)
+  if (IPC_MESSAGE_CLASS(message) == PepperFileMsgStart && g_use_file_thread)
     *thread = BrowserThread::FILE;
 }
 
+base::TaskRunner* PepperFileMessageFilter::OverrideTaskRunnerForMessage(
+    const IPC::Message& message) {
+  // The blocking pool provides a pool of threads to run file
+  // operations, instead of a single thread which might require
+  // queuing time.  Since these messages are synchronous as sent from
+  // the plugin, the sending thread cannot send a new message until
+  // this one returns, so there is no need to sequence tasks here.  If
+  // the plugin has multiple threads, it cannot make assumptions about
+  // ordering of IPC message sends, so it cannot make assumptions
+  // about ordering of operations caused by those IPC messages.
+  if (IPC_MESSAGE_CLASS(message) == PepperFileMsgStart) {
+    // Should never get here if using the FILE thread.
+    DCHECK(!g_use_file_thread);
+    return BrowserThread::GetBlockingPool();
+  }
+  return NULL;
+}
+
 bool PepperFileMessageFilter::OnMessageReceived(const IPC::Message& message,
                                                 bool* message_was_ok) {
   bool handled = true;
diff --git a/content/browser/renderer_host/pepper/pepper_file_message_filter.h b/content/browser/renderer_host/pepper/pepper_file_message_filter.h
index c5065f1..074d655 100644
--- a/content/browser/renderer_host/pepper/pepper_file_message_filter.h
+++ b/content/browser/renderer_host/pepper/pepper_file_message_filter.h
@@ -36,6 +36,8 @@ class PepperFileMessageFilter : public content::BrowserMessageFilter {
   virtual void OverrideThreadForMessage(
       const IPC::Message& message,
       content::BrowserThread::ID* thread) OVERRIDE;
+  virtual base::TaskRunner* OverrideTaskRunnerForMessage(
+      const IPC::Message& message) OVERRIDE;
   virtual bool OnMessageReceived(const IPC::Message& message,
                                  bool* message_was_ok) OVERRIDE;
   virtual void OnDestruct() const OVERRIDE;
diff --git a/content/browser/web_contents/web_contents_impl.cc b/content/browser/web_contents/web_contents_impl.cc
index 4e94230..089d1f9 100644
--- a/content/browser/web_contents/web_contents_impl.cc
+++ b/content/browser/web_contents/web_contents_impl.cc
@@ -7,6 +7,7 @@
 #include <utility>
 
 #include "base/command_line.h"
+#include "base/metrics/field_trial.h"
 #include "base/metrics/histogram.h"
 #include "base/metrics/stats_counters.h"
 #include "base/string16.h"
@@ -2339,6 +2340,22 @@ void WebContentsImpl::OnSetSelectedColorInColorChooser(int color_chooser_id,
 void WebContentsImpl::OnPepperPluginHung(int plugin_child_id,
                                          const FilePath& path,
                                          bool is_hung) {
+  HISTOGRAM_COUNTS("Pepper.PluginHung", 1);
+
+  // Determine how often hangs happen when using worker pool versus
+  // FILE thread.  kFieldTrialName needs to match the value in
+  // pepper_file_message_filter.cc, but plumbing that through would be
+  // disruptive for temporary code.
+  // TODO(shess): Remove once the workpool is proven superior.
+  // http://crbug.com/153383
+  static const char* const kFieldTrialName = "FlapperIOThread";
+  static const bool hung_trial_exists =
+      base::FieldTrialList::TrialExists(kFieldTrialName);
+  if (hung_trial_exists) {
+    HISTOGRAM_COUNTS(base::FieldTrial::MakeName("Pepper.PluginHung",
+                                                kFieldTrialName), 1);
+  }
+
   FOR_EACH_OBSERVER(WebContentsObserver, observers_,
                     PluginHungStatusChanged(plugin_child_id, path, is_hung));
 }