From 5aff42b0aadff5ff5ba3a9c3ab2264eae4982d57 Mon Sep 17 00:00:00 2001
From: Keith Winstein <keithw@mit.edu>
Date: Fri, 30 Sep 2011 13:51:36 -0400
Subject: [PATCH] Further improvements to smooth shutdown (and fix bug re:
 shutdown acceleration)

---
 stm-server.cpp      |  2 +-
 transportsender.cpp | 22 +++++++++-------------
 transportsender.hpp |  5 +++--
 3 files changed, 13 insertions(+), 16 deletions(-)

diff --git a/stm-server.cpp b/stm-server.cpp
index 6053857..81f3c27 100644
--- a/stm-server.cpp
+++ b/stm-server.cpp
@@ -256,7 +256,7 @@ void serve( int host_fd )
       if ( (pollfds[ 1 ].revents)
 	   & (POLLERR | POLLHUP | POLLNVAL) ) {
 	/* host problem */
-	if ( network.attached() && (!network.shutdown_in_progress()) ) {
+	if ( network.attached() ) {
 	  network.start_shutdown();
 	} else {
 	  break;
diff --git a/transportsender.cpp b/transportsender.cpp
index cc19f5a..1d52e5d 100644
--- a/transportsender.cpp
+++ b/transportsender.cpp
@@ -14,7 +14,7 @@ TransportSender<MyState>::TransportSender( Connection *s_connection, MyState &in
     next_send_time( timestamp() ),
     verbose( false ),
     shutdown_in_progress( false ),
-    shutdown_timestamp( -1 ),
+    shutdown_tries( 0 ),
     ack_num( 0 ),
     pending_data_ack( false )
 {
@@ -42,8 +42,6 @@ int TransportSender<MyState>::wait_time( void )
     next_ack_time = timestamp() + ACK_DELAY;
   }
 
-  uint64_t next_wakeup = next_ack_time;
-
   if ( !(current_state == sent_states.back().state) ) { /* pending data to send */
     if ( next_send_time > timestamp() + SEND_MINDELAY ) {
       next_send_time = timestamp() + SEND_MINDELAY;
@@ -59,6 +57,8 @@ int TransportSender<MyState>::wait_time( void )
     next_ack_time = sent_states.back().timestamp + send_interval();
   }
 
+  uint64_t next_wakeup = next_ack_time;
+
   if ( next_send_time < next_wakeup ) {
     next_wakeup = next_send_time;
   }
@@ -244,6 +244,10 @@ void TransportSender<MyState>::send_in_fragments( string diff, uint64_t new_num
   for ( auto i = fragments.begin(); i != fragments.end(); i++ ) {
     connection->send( i->tostring() );
 
+    if ( new_num == uint64_t(-1) ) {
+      shutdown_tries++;
+    }
+
     if ( verbose ) {
       fprintf( stderr, "[%d] Sent [%d=>%d] id %d, frag %d ack=%d, throwaway=%d, len=%d, frame rate=%.2f, timeout=%d\n",
 	       (int)(timestamp() % 100000), (int)inst.old_num(), (int)inst.new_num(), (int)i->id, (int)i->fragment_num,
@@ -280,17 +284,9 @@ void TransportSender<MyState>::process_acknowledgment_through( uint64_t ack_num
   assert( !sent_states.empty() );
 }
 
-/* give up on getting acknowledgement for shutdown after 5 RTTs */
+/* give up on getting acknowledgement for shutdown */
 template <class MyState>
 bool TransportSender<MyState>::shutdown_ack_timed_out( void )
 {
-  if ( !shutdown_in_progress ) {
-    return false;
-  }
-
-  if ( timestamp() - shutdown_timestamp > 5 * connection->get_SRTT() ) {
-    return true;
-  }
-
-  return false;
+  return shutdown_tries >= SHUTDOWN_RETRIES;
 }
diff --git a/transportsender.hpp b/transportsender.hpp
index 940bd9d..6850a55 100644
--- a/transportsender.hpp
+++ b/transportsender.hpp
@@ -24,6 +24,7 @@ namespace Network {
     static const int ACK_INTERVAL = 1000; /* ms between empty acks */
     static const int ACK_DELAY = 10; /* ms before delayed ack */
     static const int SEND_MINDELAY = 20; /* ms to collect all input */
+    static const int SHUTDOWN_RETRIES = 3; /* number of shutdown packets to send before giving up */
 
     /* helper methods for tick() */
     unsigned int send_interval( void );
@@ -55,7 +56,7 @@ namespace Network {
 
     bool verbose;
     bool shutdown_in_progress;
-    uint64_t shutdown_timestamp;
+    int shutdown_tries;
 
     /* information about receiver state */
     uint64_t ack_num;
@@ -81,7 +82,7 @@ namespace Network {
     void set_data_ack( void ) { pending_data_ack = true; }
 
     /* Starts shutdown sequence */
-    void start_shutdown( void ) { shutdown_in_progress = true; shutdown_timestamp = timestamp(); }
+    void start_shutdown( void ) { shutdown_in_progress = true; }
 
     /* Misc. getters and setters */
     /* Cannot modify current_state while shutdown in progress */