マルチスレッドなmemcachedのincrが想定通り動かない時がある件についてです。
A：memcached 1.4.4に以下のパッチを適用
*** memcached.c_org 2009-11-27 14:45:13.000000000 +0900
--- memcached.c 2010-03-30 21:03:08.000000000 +0900
***************
*** 54,59 ****
--- 54,60 ----
#endif
#endif
+ pthread_mutex_t test_lock = PTHREAD_MUTEX_INITIALIZER;
/*
* forward declarations
*/
***************
*** 1017,1022 ****
--- 1018,1024 ----
req->message.body.expiration);
}
+ pthread_mutex_lock(&test_lock);
it = item_get(key, nkey);
if (it && (c->binary_header.request.cas == 0 ||
c->binary_header.request.cas == ITEM_get_cas(it))) {
***************
*** 1082,1087 ****
--- 1084,1090 ----
write_bin_error(c, PROTOCOL_BINARY_RESPONSE_KEY_ENOENT, 0);
}
+ pthread_mutex_unlock(&test_lock);
}
static void complete_update_bin(conn *c) {B：frsyukiさんの検証プログラムに以下のパッチを適用
*** test.c_org 2010-03-30 21:08:36.000000000 +0900 --- test.c 2010-03-30 21:08:56.000000000 +0900 *************** *** 8,14 **** const char* g_host = "127.0.0.1"; unsigned short g_port = 11211; ! bool g_binary = false; const char* g_key = "test"; size_t g_key_len = 4; --- 8,14 ---- const char* g_host = "127.0.0.1"; unsigned short g_port = 11211; ! bool g_binary = true; const char* g_key = "test"; size_t g_key_len = 4;
AなしBなし
$ while true; do ./test_ascii; done expected: 100000 result: 100000 expected: 100000 result: 99960 expected: 100000 result: 100000 expected: 100000 result: 99998
AありBなし
$ while true; do ./test_ascii; done expected: 100000 result: 99976 expected: 100000 result: 100000 expected: 100000 result: 100000 expected: 100000 result: 99997
AなしBあり
$ while true; do ./test_binary; done expected: 100000 result: 99998 expected: 100000 result: 100000 expected: 100000 result: 99985 expected: 100000 result: 100000
AありBあり
$ while true; do ./test_binary; done expected: 100000 result: 100000 expected: 100000 result: 100000 expected: 100000 result: 100000 expected: 100000 result: 100000 expected: 100000 result: 100000 expected: 100000 result: 100000 expected: 100000 result: 100000 expected: 100000 result: 100000 expected: 100000 result: 100000 expected: 100000 result: 100000 expected: 100000 result: 100000 expected: 100000 result: 100000 expected: 100000 result: 100000 expected: 100000 result: 100000 expected: 100000 result: 100000 expected: 100000 result: 100000 expected: 100000 result: 100000 expected: 100000 result: 100000 expected: 100000 result: 100000 expected: 100000 result: 100000 expected: 100000 result: 100000 expected: 100000 result: 100000 expected: 100000 result: 100000 expected: 100000 result: 100000 expected: 100000 result: 100000 expected: 100000 result: 100000 expected: 100000 result: 100000 expected: 100000 result: 100000 expected: 100000 result: 100000
いかがでしょう？
2010/03/31追記
ASCIIプロトコルについても修正しました。手元の環境ではAありBなしでも正しく動いています。
*** memcached.c_org 2009-11-27 14:45:13.000000000 +0900
--- memcached.c 2010-03-31 01:29:22.000000000 +0900
***************
*** 54,59 ****
--- 54,60 ----
#endif
#endif
+ pthread_mutex_t incr_lock = PTHREAD_MUTEX_INITIALIZER;
/*
* forward declarations
*/
***************
*** 1017,1022 ****
--- 1018,1024 ----
req->message.body.expiration);
}
+ pthread_mutex_lock(&incr_lock);
it = item_get(key, nkey);
if (it && (c->binary_header.request.cas == 0 ||
c->binary_header.request.cas == ITEM_get_cas(it))) {
***************
*** 1082,1087 ****
--- 1084,1090 ----
write_bin_error(c, PROTOCOL_BINARY_RESPONSE_KEY_ENOENT, 0);
}
+ pthread_mutex_unlock(&incr_lock);
}
static void complete_update_bin(conn *c) {
***************
*** 2780,2785 ****
--- 2783,2789 ----
return;
}
+ pthread_mutex_lock(&incr_lock);
it = item_get(key, nkey);
if (!it) {
pthread_mutex_lock(&c->thread->stats.mutex);
***************
*** 2791,2796 ****
--- 2795,2801 ----
pthread_mutex_unlock(&c->thread->stats.mutex);
out_string(c, "NOT_FOUND");
+ pthread_mutex_unlock(&incr_lock);
return;
}
***************
*** 2806,2811 ****
--- 2811,2817 ----
break;
}
item_remove(it); /* release our reference */
+ pthread_mutex_unlock(&incr_lock);
}
/*ここまでの内容をまとめてコミュニティに報告しました。
Issue 127 - memcached - incr/decr operations are not thread safe. - Project Hosting on Google Code