[sheepdog] [PATCH v5] sheep/cluster: add the distributed lock implemented by zookeeper for object-storage
Liu Yuan
namei.unix at gmail.com
Mon Dec 2 07:42:07 CET 2013
On Mon, Dec 02, 2013 at 12:53:54PM +0800, Robin Dong wrote:
> 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 (cluster_lock->wait)
> 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 use dlock_array to store pointers of cluster_locks in this sheep daemon so when receiving the event of ZOO_DELETED_EVENT
> the program will wake up all waiters (in this sheep daemon) who is sleeping on the lock id and let them compete for new
> owner.
> dlock_array is just a normal array using lock-id as index, so imaging a scenario: two threads (A and B) in one sheep daemon
> call zk_lock() for same lock-id, they will create two znodes in zookeeper but set dlock_array[lock_id] to only one of
> them (for example, set to B). After that, when ZOO_DELETED_EVENT comes, the zk_waiter() will only wake up thread B and thread A
> will sleep on '->wait' forever becuase no one could wakeup him.
> We have two method to solve this problem:
> A. using more complicated structure instead of dlock_array to store both A and B 's lock handle.
> B. adding a lock to avoid A and B call zk_lock() in the same time.
> We prefer method B because it also avoid creating too many files in a directory of zookeeper which will take too much pressure
> on zookeeper server if the number of sheep deamons are huge. Therefore we add 'local_lock' in 'struct cluster_lock'.
The commit log should be 80-width.
>
> v4 --> v5:
> 1. rename 'dlock' to 'cluster_lock'
> 2. change dlock_array to hash table
>
> v3 --> v4:
> 1. change some comment
> 2. change type of 'lock_id' from uint32_t to uint64_t
>
> v2 --> v3:
> 1. change cluster interface to init_lock()/lock()/unlock()
> 2. change 'struct zk_mutex' to 'struct cluster_lock'
> 3. add empty implementation to local/corosync
>
> v1 --> v2:
> move code from sheep/http/lock.c into sheep/cluster/zookeeper.c using cluster framework
>
> Signed-off-by: Robin Dong <sanbai at taobao.com>
> ---
> include/sheep.h | 9 ++
> sheep/cluster.h | 29 +++++++
> sheep/cluster/corosync.c | 16 ++++
> sheep/cluster/local.c | 16 ++++
> sheep/cluster/zookeeper.c | 187 ++++++++++++++++++++++++++++++++++++++++++++-
> 5 files changed, 256 insertions(+), 1 deletions(-)
>
> diff --git a/include/sheep.h b/include/sheep.h
> index 293e057..aab69ef 100644
> --- a/include/sheep.h
> +++ b/include/sheep.h
> @@ -255,6 +255,15 @@ static inline void nodes_to_buffer(struct rb_root *nroot, void *buffer)
>
> #define MAX_NODE_STR_LEN 256
>
> +/* structure for distributed lock */
> +struct cluster_lock {
> + struct hlist_node hnode;
> + uint64_t id; /* id of this mutex */
This comment is meangless, how about 'id is passed by users to represent a
lock handle'?
> + pthread_mutex_t wait;
how about pthread_mutex_t wait_release; /* wait for the release of id by other lock owner */
> + pthread_mutex_t local_lock;
how about pthread_mutex_t id_lock; /* lock for different threads of the same node on the same id */
> + char ephemeral_path[MAX_NODE_STR_LEN];
how about char lock_path[] ?
> +};
> +
> static inline const char *node_to_str(const struct sd_node *id)
> {
> static __thread char str[MAX_NODE_STR_LEN];
> diff --git a/sheep/cluster.h b/sheep/cluster.h
> index 81b5ae4..08df91c 100644
> --- a/sheep/cluster.h
> +++ b/sheep/cluster.h
> @@ -109,6 +109,35 @@ struct cluster_driver {
> int (*unblock)(void *msg, size_t msg_len);
>
> /*
> + * Init a distributed mutually exclusive lock to avoid race condition
> + * when the whole sheepdog cluster process one exclusive resource.
> + *
> + * This function use 'lock_id' as the id of this distributed lock.
> + * A thread can create many locks in one sheep daemon.
> + *
> + * Returns SD_RES_XXX
> + */
> + int (*init_lock)(struct cluster_lock *lock, uint64_t lock_id);
> +
> + /*
> + * Acquire the distributed lock.
> + *
> + * The cluster_lock referenced by 'lock' shall be locked by calling
> + * cluster->lock(). If the cluster_lock is already locked, the calling
> + * thread shall block until the cluster_lock becomes available.
> + */
> + void (*lock)(struct cluster_lock *lock);
> +
> + /*
> + * Release the distributed lock.
> + *
> + * If the owner of the cluster_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
> + */
> + void (*unlock)(struct cluster_lock *lock);
> +
> + /*
> * Update the specific node in the driver's private copy of nodes
> *
> * Returns SD_RES_XXX
> diff --git a/sheep/cluster/corosync.c b/sheep/cluster/corosync.c
> index ea4421b..7382d9a 100644
> --- a/sheep/cluster/corosync.c
> +++ b/sheep/cluster/corosync.c
> @@ -774,6 +774,19 @@ again:
> return 0;
> }
>
> +static int corosync_init_lock(struct cluster_lock *cluster_lock, uint32_t id)
> +{
> + return -1;
> +}
> +
> +static void corosync_lock(struct cluster_lock *cluster_lock)
> +{
> +}
> +
> +static void corosync_unlock(struct cluster_lock *cluster_lock)
> +{
> +}
> +
> static int corosync_update_node(struct sd_node *node)
> {
> struct cpg_node cnode = this_node;
> @@ -794,6 +807,9 @@ static struct cluster_driver cdrv_corosync = {
> .notify = corosync_notify,
> .block = corosync_block,
> .unblock = corosync_unblock,
> + .init_lock = corosync_init_lock,
> + .lock = corosync_lock,
> + .unlock = corosync_unlock,
> .update_node = corosync_update_node,
> };
>
> diff --git a/sheep/cluster/local.c b/sheep/cluster/local.c
> index b8cbb5c..4c4d83b 100644
> --- a/sheep/cluster/local.c
> +++ b/sheep/cluster/local.c
> @@ -547,6 +547,19 @@ static int local_init(const char *option)
> return 0;
> }
>
> +static int local_init_lock(struct cluster_lock *cluster_lock, uint64_t id)
> +{
> + return -1;
> +}
> +
> +static void local_lock(struct cluster_lock *cluster_lock)
> +{
> +}
> +
> +static void local_unlock(struct cluster_lock *cluster_lock)
> +{
> +}
> +
> static int local_update_node(struct sd_node *node)
> {
> struct local_node lnode = this_node;
> @@ -566,6 +579,9 @@ static struct cluster_driver cdrv_local = {
> .notify = local_notify,
> .block = local_block,
> .unblock = local_unblock,
> + .init_lock = local_init_lock,
> + .lock = local_lock,
> + .unlock = local_unlock,
> .update_node = local_update_node,
> };
>
> diff --git a/sheep/cluster/zookeeper.c b/sheep/cluster/zookeeper.c
> index fa89c46..fab31f4 100644
> --- a/sheep/cluster/zookeeper.c
> +++ b/sheep/cluster/zookeeper.c
> @@ -30,6 +30,60 @@
> #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 WAIT_TIME 1 /* second */
> +
> +#define HASH_BUCKET_NR 4097
why not 4096 instead of 4097, an odd number?
> +static struct hlist_head *cluster_locks_table;
> +
> +/*
> + * All the operations of the lock table is protected by
> + * cluster_lock->local_lock so we don't need to add lock here
> + */
> +
> +static void del_lock_in_table(uint64_t lock_id)
> +{
> + uint64_t hval = lock_id % HASH_BUCKET_NR;
> + struct hlist_node *iter;
> + struct cluster_lock *lock;
> +
> + hlist_for_each_entry(lock, iter, cluster_locks_table + hval, hnode) {
> + if (lock->id == lock_id) {
> + hlist_del(iter);
> + break;
> + }
> + }
> +}
> +
> +static void set_lock_in_table(uint64_t lock_id,
> + struct cluster_lock *cluster_lock)
> +{
> + uint64_t hval = lock_id % HASH_BUCKET_NR;
> + hlist_add_head(&(cluster_lock->hnode), cluster_locks_table + hval);
> +}
> +
> +static struct cluster_lock *get_lock_in_table(uint64_t lock_id)
> +{
> + uint64_t hval = lock_id % HASH_BUCKET_NR;
> + struct hlist_node *iter;
> + struct cluster_lock *lock;
> +
> + hlist_for_each_entry(lock, iter, cluster_locks_table + hval, hnode)
> + if (lock->id == lock_id)
> + return lock;
> +
> + return NULL;
> +}
How about name them as lock_table_{add,del,lookup}? And this table should be
protected by a dedicated lock.
> +
> +/*
> + * 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) \
> @@ -505,7 +559,9 @@ static void zk_watcher(zhandle_t *zh, int type, int state, const char *path,
> void *ctx)
> {
> struct zk_node znode;
> + struct cluster_lock *cluster_lock;
> char str[MAX_NODE_STR_LEN], *p;
> + uint64_t lock_id;
> int ret;
>
> if (type == ZOO_SESSION_EVENT && state == ZOO_EXPIRED_SESSION_STATE) {
> @@ -528,6 +584,16 @@ 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 "/%lu/%s", &lock_id, str);
> + if (ret == 2) {
> + cluster_lock = get_lock_in_table(lock_id);
> + if (cluster_lock) {
> + pthread_mutex_unlock(&(cluster_lock->wait));
> + sd_debug("release lock %lu %s", lock_id, str);
> + }
> + }
> +
Here we should return after processing?
Thanks
Yuan
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