(not for commit) Simplified multi-threaded Ganesh with lock on Flush only.

gpu/command_buffer/client/cmd_buffer_helper.cc

Index: gpu/command_buffer/client/cmd_buffer_helper.cc
diff --git a/gpu/command_buffer/client/cmd_buffer_helper.cc b/gpu/command_buffer/client/cmd_buffer_helper.cc
index a99201e4b36164ef01ef218d7651f6fe55e851b9..da458c19c8020486e3498501c3527873c21b9ed8 100644
--- a/gpu/command_buffer/client/cmd_buffer_helper.cc
+++ b/gpu/command_buffer/client/cmd_buffer_helper.cc
@@ -23,6 +23,7 @@ CommandBufferHelper::CommandBufferHelper(CommandBuffer* command_buffer)
       token_(0),
       put_(0),
       last_put_sent_(0),
+      safe_put_point_(0),
 #if defined(CMD_HELPER_PERIODIC_FLUSH_CHECK)
       commands_issued_(0),
 #endif
@@ -64,12 +65,14 @@ void CommandBufferHelper::CalcImmediateEntries(int waiting_count) {
 
   // Limit entry count to force early flushing.
   if (flush_automatically_) {
+    // Cache last_put_sent, as it may change via SafeFlush().
+    int32 last_put_sent = last_put_sent_;
     int32 limit =
         total_entry_count_ /
-        ((curr_get == last_put_sent_) ? kAutoFlushSmall : kAutoFlushBig);
+        ((curr_get == last_put_sent) ? kAutoFlushSmall : kAutoFlushBig);
 
     int32 pending =
-        (put_ + total_entry_count_ - last_put_sent_) % total_entry_count_;
+        (put_ + total_entry_count_ - last_put_sent) % total_entry_count_;
 
     if (pending > 0 && pending >= limit) {
       // Time to force flush.
@@ -146,6 +149,7 @@ bool CommandBufferHelper::WaitForGetOffsetInRange(int32 start, int32 end) {
 }
 
 void CommandBufferHelper::Flush() {
+  base::AutoLock scoped_lock(flush_lock_);
   // Wrap put_ before flush.
   if (put_ == total_entry_count_)
     put_ = 0;
@@ -153,12 +157,30 @@ void CommandBufferHelper::Flush() {
   if (usable() && last_put_sent_ != put_) {
     last_flush_time_ = base::TimeTicks::Now();
     last_put_sent_ = put_;
+    safe_put_point_ = put_;
     command_buffer_->Flush(put_);
     ++flush_generation_;
     CalcImmediateEntries(0);
   }
 }
 
+void CommandBufferHelper::SetSafeFlushPoint() {
+  base::AutoLock scoped_lock(flush_lock_);
+  safe_put_point_ = put_;
+  if (safe_put_point_ == total_entry_count_)
+    safe_put_point_ = 0;
+}
+
+void CommandBufferHelper::SafeFlush() {
+  base::AutoLock scoped_lock(flush_lock_);
+  if (usable() && last_put_sent_ != safe_put_point_) {
+    last_flush_time_ = base::TimeTicks::Now();
+    last_put_sent_ = safe_put_point_;
+    command_buffer_->Flush(safe_put_point_);
+    //++flush_generation_;
+  }
+}
+
 #if defined(CMD_HELPER_PERIODIC_FLUSH_CHECK)
 void CommandBufferHelper::PeriodicFlushCheck() {
   base::TimeTicks current_time = base::TimeTicks::Now();