mem-pool: minor fix and clarification

A comment has been added to pool_destructor() function to explain why
locks are not needed there. Also, the initialization of 'poison' field
has been moved inside a locked region for further safety and clarity.

Change-Id: Idbf23bda7f9228d60c644a1bea4b6c2cfc582090
updates: bz#1193929
Signed-off-by: Xavi Hernandez <xhernandez@redhat.com>

1 files changed, 10 insertions, 3 deletions

diff --git a/libglusterfs/src/mem-pool.c b/libglusterfs/src/mem-pool.c
index ec8e40d2bc0..4ef62b8da48 100644
--- a/libglusterfs/src/mem-pool.c
+++ b/libglusterfs/src/mem-pool.c
@@ -527,7 +527,15 @@ pool_destructor(void *arg)
 {
     per_thread_pool_list_t *pool_list = arg;
 
-    /* The pool-sweeper thread will take it from here. */
+    /* The pool-sweeper thread will take it from here.
+     *
+     * We can change 'poison' here without taking locks because the change
+     * itself doesn't interact with other parts of the code and a simple write
+     * is already atomic from the point of view of the processor.
+     *
+     * This change can modify what mem_put() does, but both possibilities are
+     * fine until the sweeper thread kicks in. The real synchronization must be
+     * between mem_put() and the sweeper thread. */
     pool_list->poison = 1;
 }
 
@@ -789,9 +797,8 @@ mem_get_pool_list(void)
         }
     }
 
-    pool_list->poison = 0;
-
     (void)pthread_mutex_lock(&pool_lock);
+    pool_list->poison = 0;
     list_add(&pool_list->thr_list, &pool_threads);
     (void)pthread_mutex_unlock(&pool_lock);