[sheepdog] [PATCH v2 1/2] cluster: add the distributed lock implemented by zookeeper for object-storage
Robin Dong
robin.k.dong at gmail.com
Fri Nov 29 10:10:31 CET 2013
Implement the distributed lock by zookeeper (refer: http://zookeeper.apache.org/doc/trunk/recipes.html)
The routine is:
1. create a seq-ephemeral znode in lock directory (use lock-id as dir name)
2. get smallest file path as owner of the lock; the other thread wait on a pthread_mutex_t
3. if owner of the lock release it (or the owner is killed by accident), zookeeper will
trigger zk_watch() which will wake up all waiting threads to compete new owner of the lock
We add ->local_lock for dist_mutex to avoid many threads in one sheepdog daemon to create too many files
in a lock directory.
Signed-off-by: Robin Dong <sanbai at taobao.com>
---
sheep/cluster.h | 15 +++++
sheep/cluster/zookeeper.c | 140 ++++++++++++++++++++++++++++++++++++++++++++-
2 files changed, 154 insertions(+), 1 deletions(-)
diff --git a/sheep/cluster.h b/sheep/cluster.h
index 81b5ae4..0aa058c 100644
--- a/sheep/cluster.h
+++ b/sheep/cluster.h
@@ -23,6 +23,13 @@
#include "sheep.h"
#include "config.h"
+struct dist_mutex {
+ uint32_t id; /* id of this mutex */
+ pthread_mutex_t wait;
+ pthread_mutex_t local_lock;
+ char ephemeral_path[MAX_NODE_STR_LEN];
+};
+
/*
* maximum payload size sent in ->notify and ->unblock, it should be large
* enough to support COROSYNC_MAX_NODES * struct sd_node
@@ -109,6 +116,14 @@ struct cluster_driver {
int (*unblock)(void *msg, size_t msg_len);
/*
+ * A distributed mutex lock to avoid race condition when using swift
+ * interface to add/delete/list object.
+ */
+ int (*init_mutex)(struct dist_mutex *mutex, uint32_t id);
+ void (*lock_mutex)(struct dist_mutex *mutex);
+ void (*unlock_mutex)(struct dist_mutex *mutex);
+
+ /*
* Update the specific node in the driver's private copy of nodes
*
* Returns SD_RES_XXX
diff --git a/sheep/cluster/zookeeper.c b/sheep/cluster/zookeeper.c
index fa89c46..ddf6a22 100644
--- a/sheep/cluster/zookeeper.c
+++ b/sheep/cluster/zookeeper.c
@@ -30,6 +30,21 @@
#define QUEUE_ZNODE BASE_ZNODE "/queue"
#define MEMBER_ZNODE BASE_ZNODE "/member"
#define MASTER_ZNONE BASE_ZNODE "/master"
+#define LOCK_ZNODE BASE_ZNODE "/lock"
+
+#define MAX_MUTEX_NR 4096
+#define WAIT_TIME 1 /* second */
+
+static struct dist_mutex **mutex_array;
+
+/*
+ * Wait a while when create, delete or get_children fail on
+ * zookeeper lock so it will not print too much loop log
+ */
+static void zk_wait(void)
+{
+ sleep(WAIT_TIME);
+}
/* iterate child znodes */
#define FOR_EACH_ZNODE(parent, path, strs) \
@@ -506,6 +521,7 @@ static void zk_watcher(zhandle_t *zh, int type, int state, const char *path,
{
struct zk_node znode;
char str[MAX_NODE_STR_LEN], *p;
+ uint32_t lock_id;
int ret;
if (type == ZOO_SESSION_EVENT && state == ZOO_EXPIRED_SESSION_STATE) {
@@ -528,6 +544,14 @@ static void zk_watcher(zhandle_t *zh, int type, int state, const char *path,
} else if (type == ZOO_DELETED_EVENT) {
struct zk_node *n;
+ /* process distributed lock */
+ ret = sscanf(path, LOCK_ZNODE "/%u/%s", &lock_id, str);
+ if (ret == 2 && lock_id < MAX_MUTEX_NR &&
+ mutex_array && mutex_array[lock_id]) {
+ pthread_mutex_unlock(&(mutex_array[lock_id]->wait));
+ sd_debug("release lock %u %s", lock_id, str);
+ }
+
ret = sscanf(path, MASTER_ZNONE "/%s", str);
if (ret == 1) {
zk_compete_master();
@@ -1058,6 +1082,108 @@ kick_block_event:
kick_block_event();
}
+static int zk_init_mutex(struct dist_mutex *mutex, uint32_t id)
+{
+ int rc;
+ char path[MAX_NODE_STR_LEN];
+
+ if (id > MAX_MUTEX_NR) {
+ sd_err("lock-id is too large!");
+ rc = -1;
+ goto err;
+ }
+
+ mutex_array[id] = mutex;
+ mutex->id = id;
+ snprintf(path, MAX_NODE_STR_LEN, LOCK_ZNODE "/%u", mutex->id);
+ rc = zk_init_node(path);
+ if (rc)
+ goto err;
+
+ rc = pthread_mutex_init(&mutex->wait, NULL);
+ if (rc) {
+ sd_err("failed to init mutex->wait");
+ goto err;
+ }
+
+ rc = pthread_mutex_init(&mutex->local_lock, NULL);
+ if (rc) {
+ sd_err("failed to init mutex->local_lock");
+ goto err;
+ }
+
+ return 0;
+err:
+ mutex_array[id] = NULL;
+ return rc;
+}
+
+static void zk_lock_mutex(struct dist_mutex *mutex)
+{
+ int flags = ZOO_SEQUENCE | ZOO_EPHEMERAL;
+ int rc, len = MAX_NODE_STR_LEN;
+ char *my_path;
+ char parent[MAX_NODE_STR_LEN];
+ char lowest_seq_path[MAX_NODE_STR_LEN];
+ char owner_name[MAX_NODE_STR_LEN];
+
+ /*
+ * if many threads use locks with same id, we should use
+ * ->local_lock to avoid the only zookeeper handler to
+ * create many seq-ephemeral files.
+ */
+ pthread_mutex_lock(&mutex->local_lock);
+
+ my_path = mutex->ephemeral_path;
+
+ /* compete owner of lock is just like zk_compete_master() */
+ snprintf(parent, MAX_NODE_STR_LEN, LOCK_ZNODE "/%u/", mutex->id);
+ while (true) {
+ rc = zoo_create(zhandle, parent, "", 0, &ZOO_OPEN_ACL_UNSAFE,
+ flags, my_path, MAX_NODE_STR_LEN);
+ if (rc == ZOK)
+ break;
+ sd_err("failed to create path:%s, %s", my_path, zerror(rc));
+ zk_wait();
+ }
+ sd_debug("create path %s success", my_path);
+
+ /* create node ok now */
+ snprintf(parent, MAX_NODE_STR_LEN, LOCK_ZNODE "/%u", mutex->id);
+ while (true) {
+ zk_get_least_seq(parent, lowest_seq_path, MAX_NODE_STR_LEN,
+ owner_name, &len);
+
+ /* I got the lock */
+ if (!strncmp(lowest_seq_path, my_path, strlen(my_path))) {
+ sd_debug("I am master now. %s", lowest_seq_path);
+ return;
+ }
+
+ /* I failed to get the lock */
+ rc = zoo_exists(zhandle, lowest_seq_path, 1, NULL);
+ if (rc == ZOK) {
+ sd_debug("call zoo_exits success %s", lowest_seq_path);
+ pthread_mutex_lock(&mutex->wait);
+ } else {
+ sd_err("failed to call zoo_exists %s", zerror(rc));
+ if (rc != ZNONODE)
+ zk_wait();
+ }
+ }
+}
+
+static void zk_unlock_mutex(struct dist_mutex *mutex)
+{
+ int rc;
+ rc = zk_delete_node(mutex->ephemeral_path, -1);
+ if (rc != ZOK)
+ sd_err("Failed to delete path: %s %s", mutex->ephemeral_path,
+ zerror(rc));
+ pthread_mutex_unlock(&mutex->local_lock);
+}
+
+
static int zk_init(const char *option)
{
char *hosts, *to, *p;
@@ -1102,6 +1228,15 @@ static int zk_init(const char *option)
return -1;
}
+ /* init distributed mutex lock */
+ mutex_array = xzalloc(sizeof(struct zk_mutex *) * MAX_MUTEX_NR);
+
+ ret = zk_init_node(LOCK_ZNODE);
+ if (ret != ZOK) {
+ sd_err("Failed to create %s %s", LOCK_ZNODE, zerror(ret));
+ free(mutex_array);
+ return -1;
+ }
return 0;
}
@@ -1122,7 +1257,10 @@ static struct cluster_driver cdrv_zookeeper = {
.notify = zk_notify,
.block = zk_block,
.unblock = zk_unblock,
- .update_node = zk_update_node,
+ .init_mutex = zk_init_mutex,
+ .lock_mutex = zk_lock_mutex,
+ .unlock_mutex = zk_unlock_mutex,
+ .update_node = zk_update_node,
.get_local_addr = get_local_addr,
};
--
1.7.1
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