added hook LWIP_HOOK_MEMP_AVAILABLE() to get informed when a memp pool was empty and an item is now available

CHANGELOG

@@ -6,6 +6,10 @@ HISTORY
 
   ++ New features:
 
+  2015-02-13: Simon Goldschmidt
+  * opt.h, memp.c: added hook LWIP_HOOK_MEMP_AVAILABLE() to get informed when
+    a memp pool was empty and an item is now available
+
   2015-02-13: Simon Goldschmidt
   * opt.h, pbuf.h/.c, etharp.c: Added the option PBUF_LINK_ENCAPSULATION_HLEN to
     allocate additional header space for TX on netifs requiring additional headers

src/core/memp.c

@@ -454,6 +454,9 @@ void
 memp_free(memp_t type, void *mem)
 {
   struct memp *memp;
+#ifdef LWIP_HOOK_MEMP_AVAILABLE
+  struct memp *old_first;
+#endif
   SYS_ARCH_DECL_PROTECT(old_level);
 
   if (mem == NULL) {
@@ -474,9 +477,12 @@ memp_free(memp_t type, void *mem)
 #endif /* MEMP_OVERFLOW_CHECK >= 2 */
 #endif /* MEMP_OVERFLOW_CHECK */
 
-  MEMP_STATS_DEC(used, type); 
-  
-  memp->next = memp_tab[type]; 
+  MEMP_STATS_DEC(used, type);
+
+  memp->next = memp_tab[type];
+#ifdef LWIP_HOOK_MEMP_AVAILABLE
+  old_first = memp_tab[type];
+#endif
   memp_tab[type] = memp;
 
 #if MEMP_SANITY_CHECK
@@ -484,6 +490,11 @@ memp_free(memp_t type, void *mem)
 #endif /* MEMP_SANITY_CHECK */
 
   SYS_ARCH_UNPROTECT(old_level);
+#ifdef LWIP_HOOK_MEMP_AVAILABLE
+  if (old_first == NULL) {
+    LWIP_HOOK_MEMP_AVAILABLE(type);
+  }
+#endif
 }
 
 #endif /* MEMP_MEM_MALLOC */

src/include/lwip/opt.h

@@ -2547,6 +2547,11 @@
  * Hook can be used to set prio_vid field of vlan_hdr.
  */
 
+/**
+ * LWIP_HOOK_MEMP_AVAILABLE(memp_t_type):
+ * - called from memp_free() when a memp pool was empty and an item is now available
+ */
+
 /*
    ---------------------------------------
    ---------- Debugging options ----------