Upstream: the "zone" directive.

Upstreams with the "zone" directive are kept in shared memory,
with a consistent view of all worker processes.

src/core/ngx_cycle.c

@@ -441,7 +441,8 @@ ngx_init_cycle(ngx_cycle_t *old_cycle)
             }
 
             if (shm_zone[i].tag == oshm_zone[n].tag
-                && shm_zone[i].shm.size == oshm_zone[n].shm.size)
+                && shm_zone[i].shm.size == oshm_zone[n].shm.size
+                && !shm_zone[i].noreuse)
             {
                 shm_zone[i].shm.addr = oshm_zone[n].shm.addr;
 
@@ -1234,6 +1235,7 @@ ngx_shared_memory_add(ngx_conf_t *cf, ngx_str_t *name, size_t size, void *tag)
     shm_zone->shm.exists = 0;
     shm_zone->init = NULL;
     shm_zone->tag = tag;
+    shm_zone->noreuse = 0;
 
     return shm_zone;
 }

src/core/ngx_cycle.h

@@ -31,6 +31,7 @@ struct ngx_shm_zone_s {
     ngx_shm_t                 shm;
     ngx_shm_zone_init_pt      init;
     void                     *tag;
+    ngx_uint_t                noreuse;  /* unsigned  noreuse:1; */
 };
 
 

src/core/ngx_rwlock.c

@@ -109,4 +109,12 @@ ngx_rwlock_unlock(ngx_atomic_t *lock)
 }
 
 
+#else
+
+#if (NGX_HTTP_UPSTREAM_ZONE)
+
+#error ngx_atomic_cmp_set() is not defined!
+
+#endif
+
 #endif