SSU: Redesign of the congestion control (tickets #2412, #2649, #2654, #2713),

modelled on TCP Reno (RFCs 5681 and 6298)
- Use a single timer per connection
- Resend up to half the un-acked messages per timer event instead of a single message
- Only send either old or new messages, do not mix
- Cache/avoid several timer calls
- Instead of 3 return values, allocating bandwidth is now a boolean function
- Avoid one of the iterations over all un-acked messages every packet pusher loop
- Remove 100 ms failsafe
- Fix OMF debug log NPE
With the same cpu usage the bandwidth is much higher
Significant speed improvement for lossy connections (e.g. wifi)
Patch by zlatinb

history.txt

@@ -2,7 +2,9 @@
  * NetDB:
    - ECIES router support for encrypted lookups and stores (proposal #156)
    - Reseed after a long downtime
- * SSU: Increase socket buffer size (ticket #2781)
+ * SSU:
+   - Increase socket buffer size (ticket #2781)
+   - Redesign of the congestion control (tickets #2412, #2649, #2654, #2713)
 2020-10-17 zzz
  * i2psnark: Remove references to "maggot" links

router/java/src/net/i2p/router/RouterVersion.java

@@ -18,7 +18,7 @@ public class RouterVersion {
     /** deprecated */
     public final static String ID = "Monotone";
     public final static String VERSION = CoreVersion.VERSION;
-    public final static long BUILD = 8;
+    public final static long BUILD = 9;
 
     /** for example "-test" */
     public final static String EXTRA = "";

router/java/src/net/i2p/router/transport/udp/OutboundMessageFragments.java

@@ -294,17 +294,17 @@ class OutboundMessageFragments {
                             // race with add()
                             _iterator.remove();
                             if (_log.shouldLog(Log.DEBUG))
-                                _log.debug("No more pending messages for " + peer.getRemotePeer());
+                                _log.debug("No more pending messages for " + p.getRemotePeer());
                             continue;
                         }
                         peersProcessed++;
-                        states = p.allocateSend();
+                        states = p.allocateSend(now);
                         if (states != null) {
                             peer = p;
                             // we have something to send and we will be returning it
                             break;
                         } 
-                        int delay = p.getNextDelay();
+                        int delay = p.getNextDelay(now);
                         if (delay < nextSendDelay)
                             nextSendDelay = delay;
                         
@@ -371,6 +371,16 @@ class OutboundMessageFragments {
         return packets;
     }
 
+    /**
+     * Wakes up the packet pusher thread.
+     * @since 0.9.48
+     */
+    void nudge() {
+        synchronized(_activePeers) {
+            _activePeers.notify();
+        }
+    }
+
     /**
      *  @return null if state or peer is null
      */

router/java/src/net/i2p/router/transport/udp/OutboundMessageState.java

@@ -31,7 +31,6 @@ class OutboundMessageState implements CDPQEntry {
     private long _fragmentAcks;
     private final int _numFragments;
     private final long _startedOn;
-    private long _nextSendTime;
     private int _pushCount;
     private int _maxSends;
     // we can't use the ones in _message since it is null for injections
@@ -77,7 +76,6 @@ class OutboundMessageState implements CDPQEntry {
         _i2npMessage = msg;
         _peer = peer;
         _startedOn = _context.clock().now();
-        _nextSendTime = _startedOn;
         _expiration = _startedOn + EXPIRATION;
         //_expiration = msg.getExpiration();
 
@@ -166,9 +164,6 @@ class OutboundMessageState implements CDPQEntry {
         return isComplete();
     }
     
-    public long getNextSendTime() { return _nextSendTime; }
-    public void setNextSendTime(long when) { _nextSendTime = when; }
-
     /**
      *  The max number of sends for any fragment, which is the
      *  same as the push count, at least as it's coded now.

router/java/src/net/i2p/router/transport/udp/UDPTransport.java

@@ -345,6 +345,14 @@ public class UDPTransport extends TransportImpl implements TimedWeightedPriority
 
         _context.simpleTimer2().addPeriodicEvent(new PingIntroducers(), MIN_EXPIRE_TIMEOUT * 3 / 4);
     }
+
+    /**
+     * @returns the instance of OutboundMessageFragments
+     * @since 0.9.48
+     */
+    OutboundMessageFragments getOMF() {
+        return _fragments;
+    }
     
     /**
      *  Pick a port if not previously configured, so that TransportManager may