DevTools: Parallelize trace messages serialization.

base/debug/trace_event_impl.cc

Index: base/debug/trace_event_impl.cc
diff --git a/base/debug/trace_event_impl.cc b/base/debug/trace_event_impl.cc
index 1a64eb0f6edc25fd315343636c1af42638334961..18351a540666be9d30282000c0a0982cd23aac46 100644
--- a/base/debug/trace_event_impl.cc
+++ b/base/debug/trace_event_impl.cc
@@ -32,6 +32,7 @@
 #include "base/third_party/dynamic_annotations/dynamic_annotations.h"
 #include "base/threading/platform_thread.h"
 #include "base/threading/thread_id_name_manager.h"
+#include "base/threading/worker_pool.h"
 #include "base/time/time.h"
 
 #if defined(OS_WIN)
@@ -73,7 +74,7 @@ const size_t kTraceEventVectorBigBufferChunks =
     512000000 / kTraceBufferChunkSize;
 const size_t kTraceEventVectorBufferChunks = 256000 / kTraceBufferChunkSize;
 const size_t kTraceEventRingBufferChunks = kTraceEventVectorBufferChunks / 4;
-const size_t kTraceEventBatchChunks = 1000 / kTraceBufferChunkSize;
+const size_t kTraceEventBufferSize = 10 * 1024 * 1024;
 // Can store results for 30 seconds with 1 ms sampling interval.
 const size_t kMonitorTraceEventBufferChunks = 30000 / kTraceBufferChunkSize;
 // ECHO_TO_CONSOLE needs a small buffer to hold the unfinished COMPLETE events.
@@ -1752,19 +1753,17 @@ void TraceLog::ConvertTraceEventsToTraceFormat(
     scoped_refptr<RefCountedString> json_events_str_ptr =
         new RefCountedString();
 
-    for (size_t i = 0; i < kTraceEventBatchChunks; ++i) {
+    while (json_events_str_ptr->size() < kTraceEventBufferSize) {
       const TraceBufferChunk* chunk = logged_events->NextChunk();
-      if (!chunk) {
-        has_more_events = false;
+      has_more_events = chunk;
+      if (!chunk)
         break;
-      }
       for (size_t j = 0; j < chunk->size(); ++j) {
-        if (i > 0 || j > 0)
+        if (json_events_str_ptr->size())
           json_events_str_ptr->data().append(",");
         chunk->GetEventAt(j)->AppendAsJSON(&(json_events_str_ptr->data()));
       }
     }
-
     flush_output_callback.Run(json_events_str_ptr, has_more_events);
   } while (has_more_events);
 }
@@ -1788,8 +1787,16 @@ void TraceLog::FinishFlush(int generation) {
     flush_output_callback_.Reset();
   }
 
-  ConvertTraceEventsToTraceFormat(previous_logged_events.Pass(),
-                                  flush_output_callback);
+  if (!WorkerPool::PostTask(
+          FROM_HERE,
+          Bind(&TraceLog::ConvertTraceEventsToTraceFormat,

[Sami, 2014/12/10 14:56:01]

Could you turn ConvertTraceEventsToTraceFormat into a static function to make it
clearer that it doesn't need to access member variables and hence can be run on
a different thread? Please also add a comment there mentioning that it can be on
a different thread.

[loislo, 2014/12/10 15:31:38]

Done.

+               Unretained(this),
+               Passed(&previous_logged_events),
+               flush_output_callback),
+          true)) {
+    ConvertTraceEventsToTraceFormat(previous_logged_events.Pass(),
+                                    flush_output_callback);
+  }
 }
 
 // Run in each thread holding a local event buffer.