Release SpdySession socket read buffer

This CL makes the following changes:

(1) Make SpdySession use Socket::ReadIfReady(). This new behavior is
    hidden behind a field trial flag, SocketReadIfReady.
(2) Make SpdySession lazily allocate |read_buffer| on demand.
(3) Make SpdySession release |read_buffer| when Read() completes or
    when ReadIfReady() cannot be completed synchronously.

Re-allocating an 8KiB buffer should be cheap, see more discussion
at https://groups.google.com/a/chromium.org/d/msg/project-trim/QtliUsApxyk/AOSnyuY7CgAJ

BUG=690915

Review-Url: https://codereview.chromium.org/2734933002
Cr-Commit-Position: refs/heads/master@{#455770}

net/spdy/spdy_session.cc

@@ -740,7 +740,6 @@ SpdySession::SpdySession(const SpdySessionKey& spdy_session_key,
       pool_(NULL),
       http_server_properties_(http_server_properties),
       transport_security_state_(transport_security_state),
-      read_buffer_(new IOBuffer(kReadBufferSize)),
       stream_hi_water_mark_(kFirstStreamId),
       last_accepted_push_stream_id_(0),
       unclaimed_pushed_streams_(this),
@@ -1378,8 +1377,9 @@ size_t SpdySession::DumpMemoryStats(StreamSocket::SocketMemoryStats* stats,
   connection_->DumpMemoryStats(stats);
 
   // |connection_| is estimated in stats->total_size. |read_buffer_| is
-  // estimated in kReadBufferSize. TODO(xunjieli): Make them use EMU().
-  return stats->total_size + kReadBufferSize +
+  // estimated in |read_buffer_size|. TODO(xunjieli): Make them use EMU().
+  size_t read_buffer_size = read_buffer_ ? kReadBufferSize : 0;
+  return stats->total_size + read_buffer_size +
          SpdyEstimateMemoryUsage(spdy_session_key_) +
          SpdyEstimateMemoryUsage(pooled_aliases_) +
          SpdyEstimateMemoryUsage(active_streams_) +
@@ -1869,19 +1869,24 @@ int SpdySession::DoReadLoop(ReadState expected_read_state, int result) {
 }
 
 int SpdySession::DoRead() {
+  DCHECK(!read_buffer_);
   CHECK(in_io_loop_);
 
   CHECK(connection_);
   CHECK(connection_->socket());
   read_state_ = READ_STATE_DO_READ_COMPLETE;
   int rv = ERR_READ_IF_READY_NOT_IMPLEMENTED;
+  read_buffer_ = new IOBuffer(kReadBufferSize);
   if (base::FeatureList::IsEnabled(Socket::kReadIfReadyExperiment)) {
     rv = connection_->socket()->ReadIfReady(
         read_buffer_.get(), kReadBufferSize,
         base::Bind(&SpdySession::PumpReadLoop, weak_factory_.GetWeakPtr(),
                    READ_STATE_DO_READ));
-    // TODO(xunjieli): Follow-up CL to release |read_buffer_|.
-    // https://crbug.com/690915.
+    if (rv == ERR_IO_PENDING) {
+      read_buffer_ = nullptr;
+      read_state_ = READ_STATE_DO_READ;
+      return rv;
+    }
   }
   if (rv == ERR_READ_IF_READY_NOT_IMPLEMENTED) {
     // Fallback to regular Read().
@@ -1890,12 +1895,11 @@ int SpdySession::DoRead() {
         base::Bind(&SpdySession::PumpReadLoop, weak_factory_.GetWeakPtr(),
                    READ_STATE_DO_READ_COMPLETE));
   }
-  if (rv == ERR_IO_PENDING)
-    read_state_ = READ_STATE_DO_READ;
   return rv;
 }
 
 int SpdySession::DoReadComplete(int result) {
+  DCHECK(read_buffer_);
   CHECK(in_io_loop_);
 
   // Parse a frame.  For now this code requires that the frame fit into our
@@ -1933,6 +1937,7 @@ int SpdySession::DoReadComplete(int result) {
               SpdyFramer::SPDY_NO_ERROR);
   }
 
+  read_buffer_ = nullptr;
   read_state_ = READ_STATE_DO_READ;
   return OK;
 }

net/spdy/spdy_session.h

@@ -1019,6 +1019,7 @@ class NET_EXPORT SpdySession : public BufferedSpdyFramerVisitorInterface,
   std::unique_ptr<ClientSocketHandle> connection_;
 
   // The read buffer used to read data from the socket.
+  // Non-null if there is a Read() pending.
   scoped_refptr<IOBuffer> read_buffer_;
 
   SpdyStreamId stream_hi_water_mark_;  // The next stream id to use.