From e926a93568535083c60e0a3d1a7424f76913cca9 Mon Sep 17 00:00:00 2001
From: goldsimon <goldsimon@gmx.de>
Date: Tue, 20 Jan 2015 12:45:26 +0100
Subject: [PATCH] tcp_kill_prio(): prefer nearly-closed connections (waiting
 for the last ACK only) over established connections when out of tcp pcbs

---
 CHANGELOG      |  4 ++++
 src/core/tcp.c | 43 ++++++++++++++++++++++++++++++-------------
 2 files changed, 34 insertions(+), 13 deletions(-)

diff --git a/CHANGELOG b/CHANGELOG
index 3bf40441..a4d9b378 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -6,6 +6,10 @@ HISTORY
 
   ++ New features:
 
+  2015-01-02: Simon Goldschmidt
+  * tcp.c: tcp_kill_prio(): prefer nearly-closed connections (waiting for the
+    last ACK only) over established connections when out of tcp pcbs
+
   2015-01-17: Simon Goldschmidt
   * api: allow enabling socket API without (public) netconn API - netconn API is
     still used by sockets, but keeping it private (static) should allow better
diff --git a/src/core/tcp.c b/src/core/tcp.c
index 4051579a..5edc73cd 100644
--- a/src/core/tcp.c
+++ b/src/core/tcp.c
@@ -1287,26 +1287,43 @@ tcp_recv_null(void *arg, struct tcp_pcb *pcb, struct pbuf *p, err_t err)
 static void
 tcp_kill_prio(u8_t prio)
 {
-  struct tcp_pcb *pcb, *inactive;
-  u32_t inactivity;
-  u8_t mprio;
+  struct tcp_pcb *pcb, *inactive, *lastack;
+  u32_t inactivity, inactivity_lastack;
+  u8_t minprio, minprio_lastack;
 
+  minprio = prio;
+  minprio_lastack = prio;
 
-  mprio = TCP_PRIO_MAX;
-  
-  /* We kill the oldest active connection that has lower priority than prio. */
+  /* We kill the oldest active connection that has lower priority than prio.
+     However, already closed connections waiting for the last ack are closed first
+     since they don't lose data. */
   inactivity = 0;
   inactive = NULL;
+  inactivity_lastack = 0;
+  lastack = NULL;
   for(pcb = tcp_active_pcbs; pcb != NULL; pcb = pcb->next) {
-    if (pcb->prio <= prio &&
-       pcb->prio <= mprio &&
-       (u32_t)(tcp_ticks - pcb->tmr) >= inactivity) {
-      inactivity = tcp_ticks - pcb->tmr;
-      inactive = pcb;
-      mprio = pcb->prio;
+    if ((lastack != NULL) || (pcb->state == LAST_ACK) || (pcb->state == CLOSING)) {
+      /* found at least one pcb in last ack phase */
+      if ((pcb->prio < minprio_lastack) ||
+          (u32_t)(tcp_ticks - pcb->tmr) >= inactivity_lastack) {
+        inactivity_lastack = tcp_ticks - pcb->tmr;
+        lastack = pcb;
+        minprio_lastack = pcb->prio;
+      }
+    } else if (pcb->prio <= minprio) {
+      if ((pcb->prio < minprio) ||
+          (u32_t)(tcp_ticks - pcb->tmr) >= inactivity) {
+        inactivity = tcp_ticks - pcb->tmr;
+        inactive = pcb;
+        minprio = pcb->prio;
+      }
     }
   }
-  if (inactive != NULL) {
+  if (lastack != NULL) {
+    LWIP_DEBUGF(TCP_DEBUG, ("tcp_kill_prio: killing oldest PCB in LAST_ACK or CLOSING %p (%"S32_F")\n",
+           (void *)lastack, inactivity_lastack));
+    tcp_abort(lastack);
+  } else if (inactive != NULL) {
     LWIP_DEBUGF(TCP_DEBUG, ("tcp_kill_prio: killing oldest PCB %p (%"S32_F")\n",
            (void *)inactive, inactivity));
     tcp_abort(inactive);