Fix --trace-shutdown with thread-local tracing.

With thread-local tracing (r221766), TraceLog::Flush() is async and
needs to be called from a thread having a message loop. It also requires
that tracing has been stopped.

BrowserShutdownProfileDumper is a special caller that TraceLog::Flush()
was originally called from a thread without message loop.

Now start another thread for flushing, and call TraceLog::SetDisabled()
before TraceLog::Flush().

The calling thread needs to wait for the completion of the flush,
otherwise the browser may shutdown before all trace events written.
Temporarily allow the thread to wait in ThreadRestrictions.

BUG=none
TEST=manual run chrome with --trace-shutdown. Should not assert. Should generate correct trace file.

Review URL: https://chromiumcodereview.appspot.com/24047007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@223819 0039d316-1c4b-4281-b951-d872f2087c98

base/debug/trace_event_impl.cc

@@ -1334,6 +1334,7 @@ void TraceLog::Flush(const TraceLog::OutputCallback& cb) {
     scoped_refptr<RefCountedString> empty_result = new RefCountedString;
     if (!cb.is_null())
       cb.Run(empty_result, false);
+    LOG(WARNING) << "Ignored TraceLog::Flush called when tracing is enabled";
     return;
   }
 

base/threading/thread_restrictions.h

@@ -42,6 +42,7 @@ class Predictor;
 }
 namespace content {
 class BrowserGpuChannelHostFactory;
+class BrowserShutdownProfileDumper;
 class BrowserTestBase;
 class GLHelper;
 class GpuChannelHost;
@@ -176,6 +177,7 @@ class BASE_EXPORT ThreadRestrictions {
  private:
   // DO NOT ADD ANY OTHER FRIEND STATEMENTS, talk to jam or brettw first.
   // BEGIN ALLOWED USAGE.
+  friend class content::BrowserShutdownProfileDumper;
   friend class content::BrowserTestBase;
   friend class content::NestedMessagePumpAndroid;
   friend class content::RenderWidgetHelper;

content/browser/browser_shutdown_profile_dumper.cc

@@ -11,6 +11,9 @@
 #include "base/file_util.h"
 #include "base/files/file_path.h"
 #include "base/logging.h"
+#include "base/synchronization/waitable_event.h"
+#include "base/threading/thread.h"
+#include "base/threading/thread_restrictions.h"
 #include "content/public/common/content_switches.h"
 
 namespace content {
@@ -43,9 +46,31 @@ void BrowserShutdownProfileDumper::WriteTracesToDisc(
   WriteString("{\"traceEvents\":");
   WriteString("[");
 
+  // TraceLog::Flush() requires the calling thread to have a message loop.
+  // As the message loop of the current thread may have quit, start another
+  // thread for flushing the trace.
+  base::WaitableEvent flush_complete_event(false, false);
+  base::Thread flush_thread("browser_shutdown_trace_event_flush");
+  flush_thread.Start();
+  flush_thread.message_loop()->PostTask(
+      FROM_HERE,
+      base::Bind(&BrowserShutdownProfileDumper::EndTraceAndFlush,
+                 base::Unretained(this),
+                 base::Unretained(&flush_complete_event)));
+
+  bool original_wait_allowed = base::ThreadRestrictions::SetWaitAllowed(true);
+  flush_complete_event.Wait();
+  base::ThreadRestrictions::SetWaitAllowed(original_wait_allowed);
+}
+
+void BrowserShutdownProfileDumper::EndTraceAndFlush(
+    base::WaitableEvent* flush_complete_event) {
+  while (base::debug::TraceLog::GetInstance()->IsEnabled())
+    base::debug::TraceLog::GetInstance()->SetDisabled();
   base::debug::TraceLog::GetInstance()->Flush(
       base::Bind(&BrowserShutdownProfileDumper::WriteTraceDataCollected,
-      base::Unretained(this)));
+                 base::Unretained(this),
+                 base::Unretained(flush_complete_event)));
 }
 
 base::FilePath BrowserShutdownProfileDumper::GetFileName() {
@@ -61,10 +86,13 @@ base::FilePath BrowserShutdownProfileDumper::GetFileName() {
 }
 
 void BrowserShutdownProfileDumper::WriteTraceDataCollected(
+    base::WaitableEvent* flush_complete_event,
     const scoped_refptr<base::RefCountedString>& events_str,
     bool has_more_events) {
-  if (!IsFileValid())
+  if (!IsFileValid()) {
+    flush_complete_event->Signal();
     return;
+  }
   if (blocks_) {
     // Blocks are not comma separated. Beginning with the second block we
     // start therefore to add one in front of the previous block.
@@ -77,6 +105,7 @@ void BrowserShutdownProfileDumper::WriteTraceDataCollected(
     WriteString("]");
     WriteString("}");
     CloseFile();
+    flush_complete_event->Signal();
   }
 }
 

content/browser/browser_shutdown_profile_dumper.h

@@ -14,6 +14,7 @@
 
 namespace base {
 class FilePath;
+class WaitableEvent;
 }
 
 namespace content {
@@ -36,12 +37,15 @@ class BrowserShutdownProfileDumper {
   // Writes all traces which happened to disk.
   void WriteTracesToDisc(const base::FilePath& file_name);
 
+  void EndTraceAndFlush(base::WaitableEvent* flush_complete_event);
+
   // Returns the file name where we should save the trace dump to.
   base::FilePath GetFileName();
 
   // The callback for the |TraceLog::Flush| function. It saves all traces to
   // disc.
   void WriteTraceDataCollected(
+      base::WaitableEvent* flush_complete_event,
       const scoped_refptr<base::RefCountedString>& events_str,
       bool has_more_events);