Keith Winstein
290 lines
9.0 KiB
C++
290 lines
9.0 KiB
C++
#include <assert.h>
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#include <iostream>
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#include "networktransport.hpp"
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using namespace Network;
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using namespace std;
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template <class MyState, class RemoteState>
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uint64_t Transport<MyState, RemoteState>::timestamp( void )
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{
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struct timespec tp;
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if ( clock_gettime( CLOCK_MONOTONIC, &tp ) < 0 ) {
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throw NetworkException( "clock_gettime", errno );
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}
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uint64_t millis = tp.tv_nsec / 1000000;
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millis += uint64_t( tp.tv_sec ) * 1000000;
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return millis;
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}
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template <class MyState, class RemoteState>
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Transport<MyState, RemoteState>::Transport( MyState &initial_state, RemoteState &initial_remote )
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: connection(),
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server( true ),
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current_state( initial_state ),
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sent_states( 1, TimestampedState<MyState>( timestamp(), 0, initial_state ) ),
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assumed_receiver_state( sent_states.begin() ),
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timeout( INITIAL_TIMEOUT ),
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received_states( 1, TimestampedState<RemoteState>( timestamp(), 0, initial_remote ) )
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{
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/* server */
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}
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template <class MyState, class RemoteState>
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Transport<MyState, RemoteState>::Transport( MyState &initial_state, RemoteState &initial_remote,
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const char *key_str, const char *ip, int port )
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: connection( key_str, ip, port ),
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server( false ),
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current_state( initial_state ),
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sent_states( 1, TimestampedState<MyState>( timestamp(), 0, initial_state ) ),
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assumed_receiver_state( sent_states.begin() ),
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timeout( INITIAL_TIMEOUT ),
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received_states( 1, TimestampedState<RemoteState>( timestamp(), 0, initial_remote ) )
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{
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/* client */
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}
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template <class MyState, class RemoteState>
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void Transport<MyState, RemoteState>::tick( void )
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{
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/* Update assumed receiver state */
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update_assumed_receiver_state();
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/* Cut out common prefix of all states */
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rationalize_states();
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/* Determine if a new diff or empty ack needs to be sent */
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if ( timestamp() - sent_states.back().timestamp >= int64_t( SEND_INTERVAL ) ) {
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/* Send diffs or ack */
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send_to_receiver();
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}
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}
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template <class MyState, class RemoteState>
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void Transport<MyState, RemoteState>::send_to_receiver( void )
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{
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/* We don't want to assume that this sequence of diffs will
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necessarily bring the receiver to the _actual_ current
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state. That requires perfect round-trip stability of the diff
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mechanism -- stronger than we need (and probably too fragile).
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Instead, we produce the full diff, unlimited by MTU, between
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the assumed receiver state and current state, and apply that
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diff to produce a target receiver state. Then we produce a
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sequence of diffs (this time limited by MTU) that bring us to
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that state. */
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if ( !connection.get_attached() ) {
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return;
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}
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MyState target_receiver_state( assumed_receiver_state->state );
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target_receiver_state.apply_string( current_state.diff_from( target_receiver_state, -1 ) );
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if ( assumed_receiver_state->state == target_receiver_state ) {
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/* send empty ack */
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if ( timestamp() - sent_states.back().timestamp < int64_t( ACK_INTERVAL ) ) {
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return;
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}
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Instruction inst( assumed_receiver_state->num,
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assumed_receiver_state->num,
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received_states.back().num,
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sent_states.front().num,
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"" );
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string s = inst.tostring();
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connection.send( s );
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assumed_receiver_state->timestamp = timestamp();
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return;
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}
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int tries = 0;
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while ( !(assumed_receiver_state->state == target_receiver_state) ) {
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if ( tries++ > 1024 ) {
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fprintf( stderr, "BUG: Convergence limit exceeded.\n" );
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exit( 1 );
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}
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Instruction inst( assumed_receiver_state->num,
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-1,
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received_states.back().num,
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sent_states.front().num,
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current_state.diff_from( assumed_receiver_state->state,
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connection.get_MTU() - HEADER_LEN ) );
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MyState new_state = assumed_receiver_state->state;
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new_state.apply_string( inst.diff );
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/* Find the right "new_num" for this instruction. */
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/* Has this state previously been sent? */
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/* should replace with hash table if this becomes demanding */
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typename list< TimestampedState<MyState> >::iterator previously_sent = sent_states.begin();
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while ( ( previously_sent != sent_states.end() )
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&& ( !(previously_sent->state == new_state) ) ) {
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previously_sent++;
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}
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/* Reusing state numbers is only for intermediate states */
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/* If this is the final diff in a sequence, make sure it does get the highest
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state number (even if we've retread to previously-seen ground ) */
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/* This will force the client to update to this state */
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typename list< TimestampedState<MyState> >::iterator last = sent_states.end();
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last--;
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if ( (previously_sent != last)
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&& (new_state == target_receiver_state) ) {
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previously_sent = sent_states.end();
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}
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if ( previously_sent == sent_states.end() ) { /* not previously sent */
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inst.new_num = sent_states.back().num + 1;
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sent_states.push_back( TimestampedState<MyState>( timestamp(), inst.new_num, new_state ) );
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previously_sent = sent_states.end();
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previously_sent--;
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} else {
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inst.new_num = previously_sent->num;
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previously_sent->timestamp = timestamp();
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}
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/* send instruction */
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/* XXX what about MTU problem? */
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string s = inst.tostring();
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try {
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connection.send( s );
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} catch ( MTUException m ) {
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continue;
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}
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/* successfully sent, probably */
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/* ("probably" because the FIRST size-exceeded datagram doesn't get an error) */
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assumed_receiver_state = previously_sent;
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}
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}
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template <class MyState, class RemoteState>
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void Transport<MyState, RemoteState>::update_assumed_receiver_state( void )
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{
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uint64_t now = timestamp();
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/* start from what is known and give benefit of the doubt to unacknowledged states
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transmitted recently enough ago */
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assumed_receiver_state = sent_states.begin();
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for ( typename list< TimestampedState<MyState> >::iterator i = sent_states.begin();
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i != sent_states.end();
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i++ ) {
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assert( now >= i->timestamp );
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if ( now - i->timestamp < int64_t(timeout) ) {
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assumed_receiver_state = i;
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}
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}
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}
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template <class MyState, class RemoteState>
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void Transport<MyState, RemoteState>::rationalize_states( void )
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{
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MyState * const known_receiver_state = &sent_states.front().state;
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current_state.subtract( known_receiver_state );
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for ( typename list< TimestampedState<MyState> >::reverse_iterator i = sent_states.rbegin();
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i != sent_states.rend();
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i++ ) {
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i->state.subtract( known_receiver_state );
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}
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}
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template <class MyState, class RemoteState>
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void Transport<MyState, RemoteState>::recv( void )
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{
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string s( connection.recv() );
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Instruction inst( s );
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process_acknowledgment_through( inst.ack_num );
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// process_throwaway_until( inst.throwaway.num );
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/* first, make sure we don't already have the new state */
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for ( typename list< TimestampedState<RemoteState> >::iterator i = received_states.begin();
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i != received_states.end();
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i++ ) {
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if ( inst.new_num == i->num ) {
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i->timestamp = timestamp();
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return;
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}
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}
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/* now, make sure we do have the old state */
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bool found = 0;
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typename list< TimestampedState<RemoteState> >::iterator reference_state = received_states.begin();
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while ( reference_state != received_states.end() ) {
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if ( inst.old_num == reference_state->num ) {
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found = true;
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break;
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}
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reference_state++;
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}
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if ( !found ) {
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// fprintf( stderr, "Ignoring out-of-order packet. Reference state %d has been discarded or hasn't yet been received.\n", int(inst.old_num) );
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return;
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}
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/* apply diff to reference state */
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TimestampedState<RemoteState> new_state = *reference_state;
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new_state.timestamp = timestamp();
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new_state.num = inst.new_num;
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new_state.state.apply_string( inst.diff );
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if ( new_state.num > received_states.back().num ) {
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process_throwaway_until( inst.throwaway_num );
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}
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/* Insert new state in sorted place */
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for ( typename list< TimestampedState<RemoteState> >::iterator i = received_states.begin();
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i != received_states.end();
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i++ ) {
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if ( i->num > new_state.num ) {
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received_states.insert( i, new_state );
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return;
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}
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}
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received_states.push_back( new_state );
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}
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template <class MyState, class RemoteState>
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void Transport<MyState, RemoteState>::process_acknowledgment_through( uint64_t ack_num )
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{
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typename list< TimestampedState<MyState> >::iterator i = sent_states.begin();
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while ( i != sent_states.end() ) {
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typename list< TimestampedState<MyState> >::iterator inext = i;
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inext++;
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if ( i->num < ack_num ) {
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sent_states.erase( i );
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}
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i = inext;
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}
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assert( sent_states.size() > 0 );
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assert( sent_states.front().num == ack_num );
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}
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template <class MyState, class RemoteState>
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void Transport<MyState, RemoteState>::process_throwaway_until( uint64_t throwaway_num )
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{
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typename list< TimestampedState<MyState> >::iterator i = received_states.begin();
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while ( i != received_states.end() ) {
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typename list< TimestampedState<MyState> >::iterator inext = i;
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inext++;
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if ( i->num < throwaway_num ) {
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sent_states.erase( i );
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}
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i = inext;
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}
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assert( received_states.size() > 0 );
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}
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