Ensure TimelineEventRingRecorder outputs blocks in increasing time order

runtime/vm/timeline.cc

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include <cstdlib>
 
 #include "vm/isolate.h"
 #include "vm/json_stream.h"
 #include "vm/lockers.h"
 #include "vm/object.h"
@@ skipping 402 matching lines @@
   for (intptr_t i = 0; i < num_blocks_; i++) {
     TimelineEventBlock* block = blocks_[i];
     delete block;
   }
   free(blocks_);
   event_objects_ = Array::null();
 }
 
 
 void TimelineEventRingRecorder::PrintJSONEvents(JSONArray* events) const {
-  // TODO(johnmccutchan): This output needs to start with the oldest block
-  // first.
+  intptr_t block_offset = FindOldestBlockIndex();
+  if (block_offset == -1) {
+    // All blocks are empty.
+    return;
+  }
   for (intptr_t block_idx = 0; block_idx < num_blocks_; block_idx++) {
-    TimelineEventBlock* block = blocks_[block_idx];
+    TimelineEventBlock* block =
+        blocks_[(block_idx + block_offset) % num_blocks_];
     if (block->IsEmpty()) {
       // Skip empty blocks.
       continue;
     }
     for (intptr_t event_idx = 0; event_idx < block->length(); event_idx++) {
       TimelineEvent* event = block->At(event_idx);
       if (event->IsValid()) {
         events->AddValue(event);
       }
     }
@@ skipping 27 matching lines @@
 TimelineEventBlock* TimelineEventRingRecorder::GetNewBlockLocked() {
   if (block_cursor_ == num_blocks_) {
     block_cursor_ = 0;
   }
   TimelineEventBlock* block = blocks_[block_cursor_++];
   block->Reset();
   return block;
 }
 
 
+intptr_t TimelineEventRingRecorder::FindOldestBlockIndex() const {
+  int64_t earliest_time = kMaxInt64;
+  intptr_t earliest_index = -1;
+  for (intptr_t block_idx = 0; block_idx < num_blocks_; block_idx++) {
+    TimelineEventBlock* block = blocks_[block_idx];
+    if (block->IsEmpty()) {
+      // Skip empty blocks.
+      continue;
+    }
+    if (block->LowerTimeBound() < earliest_time) {
+      earliest_time = block->LowerTimeBound();
+      earliest_index = block_idx;
+    }
+  }
+  return earliest_index;
+}
+
+
 void TimelineEventRingRecorder::VisitObjectPointers(
     ObjectPointerVisitor* visitor) {
   visitor->VisitPointer(reinterpret_cast<RawObject**>(&event_objects_));
 }
 
 
 TimelineEvent* TimelineEventRingRecorder::StartEvent(const Object& obj) {
   TimelineEvent* event = StartEvent();
   if (event == NULL) {
     return NULL;
@@ skipping 235 matching lines @@
   }
   if (current_ == NULL) {
     current_ = recorder_->GetHeadBlock();
   } else {
     current_ = current_->next();
   }
   return current_ != NULL;
 }
 
 }  // namespace dart