lazy allocation and early release memory in QuicStreamSequencerBuffer. Protected by --quic_reduce_s…

net/quic/core/quic_stream_sequencer_buffer.cc

Index: net/quic/core/quic_stream_sequencer_buffer.cc
diff --git a/net/quic/core/quic_stream_sequencer_buffer.cc b/net/quic/core/quic_stream_sequencer_buffer.cc
index 011a016d100b582b731563c0b0eba849b5dcf530..c839e0795720cb4dadc9f183a187a2a5b33b8bdd 100644
--- a/net/quic/core/quic_stream_sequencer_buffer.cc
+++ b/net/quic/core/quic_stream_sequencer_buffer.cc
@@ -47,7 +47,11 @@ QuicStreamSequencerBuffer::QuicStreamSequencerBuffer(size_t max_capacity_bytes)
       blocks_count_(
           ceil(static_cast<double>(max_capacity_bytes) / kBlockSizeBytes)),
       total_bytes_read_(0),
-      blocks_(blocks_count_) {
+      reduce_sequencer_buffer_memory_life_time_(
+          FLAGS_quic_reduce_sequencer_buffer_memory_life_time),  // NOLINT
+      blocks_(reduce_sequencer_buffer_memory_life_time_
+                  ? nullptr
+                  : new BufferBlock*[blocks_count_]()) {
   Clear();
 }
 
@@ -56,9 +60,11 @@ QuicStreamSequencerBuffer::~QuicStreamSequencerBuffer() {
 }
 
 void QuicStreamSequencerBuffer::Clear() {
-  for (size_t i = 0; i < blocks_count_; ++i) {
-    if (blocks_[i] != nullptr) {
-      RetireBlock(i);
+  if (!reduce_sequencer_buffer_memory_life_time_ || blocks_ != nullptr) {
+    for (size_t i = 0; i < blocks_count_; ++i) {
+      if (blocks_[i] != nullptr) {
+        RetireBlock(i);
+      }
     }
   }
   num_bytes_buffered_ = 0;
@@ -169,6 +175,13 @@ QuicErrorCode QuicStreamSequencerBuffer::OnStreamData(
       bytes_avail = total_bytes_read_ + max_buffer_capacity_bytes_ - offset;
     }
 
+    if (reduce_sequencer_buffer_memory_life_time_ && blocks_ == nullptr) {
+      blocks_.reset(new BufferBlock*[blocks_count_]());
+      for (size_t i = 0; i < blocks_count_; ++i) {
+        blocks_[i] = nullptr;
+      }
+    }
+
     if (blocks_[write_block_num] == nullptr) {
       // TODO(danzh): Investigate if using a freelist would improve performance.
       // Same as RetireBlock().
@@ -393,6 +406,15 @@ size_t QuicStreamSequencerBuffer::FlushBufferedFrames() {
   return total_bytes_read_ - prev_total_bytes_read;
 }
 
+void QuicStreamSequencerBuffer::ReleaseWholeBuffer() {
+  if (!reduce_sequencer_buffer_memory_life_time_) {
+    // Don't release buffer if flag is off.
+    return;
+  }
+  Clear();
+  blocks_.reset(nullptr);
+}
+
 size_t QuicStreamSequencerBuffer::ReadableBytes() const {
   return gaps_.front().begin_offset - total_bytes_read_;
 }