[sheepdog] [PATCH] multi-sheep cluster in one zookeeper cluster.

Ruoyu liangry at ucweb.com
Fri Feb 27 04:41:56 CET 2015


On 2015年02月26日 14:50, Yu Yang wrote:
> In order to distinguish different sheep cluster in one zookeeper, one more level
> directory is added in znode as domain. The same domain means the same sheep cluster.
The idea is not bad. But I have some questions. Please think about as below.
>
> Signed-off-by: Yu Yang <yuyang at cmss.chinamobile.com>
>
> 	modified:   sheep/cluster/zookeeper.c
> 	modified:   sheep/sheep.c
> ---
>   sheep/cluster/zookeeper.c |  192 ++++++++++++++++++++++++++++++++-------------
>   sheep/sheep.c             |   10 ++-
>   2 files changed, 143 insertions(+), 59 deletions(-)
>
> diff --git a/sheep/cluster/zookeeper.c b/sheep/cluster/zookeeper.c
> index 3248af2..e492fde 100644
> --- a/sheep/cluster/zookeeper.c
> +++ b/sheep/cluster/zookeeper.c
> @@ -26,15 +26,22 @@
>   #include "rbtree.h"
>   
>   #define SESSION_TIMEOUT 30000		/* millisecond */
> +#define SD_DEFAULT_DOMAIN "sd_domain_default"
Is it the default domain name? Maybe it is too long. I think just 
'default' is enough.
> +
> +static const char base_znode[] = "/sheepdog";
> +static char queue_znode[MAX_NODE_STR_LEN] = "";
> +static const char queue_znode_post[] = "/queue";
> +static char member_znode[MAX_NODE_STR_LEN] = "";
> +static const char member_znode_post[] = "/member";
> +static char master_znode[MAX_NODE_STR_LEN] = "";
> +static const char master_znode_post[] = "/master";
> +static char lock_znode[MAX_NODE_STR_LEN] = "";
> +static const char lock_znode_post[] = "/lock";
>   
> -#define BASE_ZNODE "/sheepdog"
> -#define QUEUE_ZNODE BASE_ZNODE "/queue"
> -#define MEMBER_ZNODE BASE_ZNODE "/member"
> -#define MASTER_ZNODE BASE_ZNODE "/master"
> -#define LOCK_ZNODE BASE_ZNODE "/lock"
>   
>   static int zk_timeout = SESSION_TIMEOUT;
>   static int my_master_seq;
> +static char sd_domain[MAX_NODE_STR_LEN] = SD_DEFAULT_DOMAIN;
>   
>   /* structure for distributed lock */
>   struct cluster_lock {
> @@ -347,7 +354,7 @@ static struct cluster_lock *lock_table_lookup_acquire(uint64_t lock_id)
>   		ret_lock = xzalloc(sizeof(*ret_lock));
>   		ret_lock->id = lock_id;
>   		ret_lock->ref = 1;
> -		snprintf(path, MAX_NODE_STR_LEN, LOCK_ZNODE "/%"PRIu64,
> +		snprintf(path, MAX_NODE_STR_LEN, "%s/%"PRIu64, lock_znode,
>   			 ret_lock->id);
>   		rc = zk_init_node(path);
>   		if (rc)
> @@ -399,8 +406,8 @@ static void lock_table_lookup_release(uint64_t lock_id)
>   			/* free all resource used by this lock */
>   			sd_destroy_mutex(&lock->id_lock);
>   			sem_destroy(&lock->wait_wakeup);
> -			snprintf(path, MAX_NODE_STR_LEN, LOCK_ZNODE "/%"PRIu64,
> -				 lock->id);
> +			snprintf(path, MAX_NODE_STR_LEN, "%s/%"PRIu64,
> +				 lock_znode, lock->id);
>   			/*
>   			 * If deletion of directory 'lock_id' fail, we only get
>   			 * a * empty directory in zookeeper. That's unharmful
> @@ -458,7 +465,7 @@ static int zk_queue_peek(bool *peek)
>   	int rc;
>   	char path[MAX_NODE_STR_LEN];
>   
> -	snprintf(path, sizeof(path), QUEUE_ZNODE "/%010"PRId32, queue_pos);
> +	snprintf(path, sizeof(path), "%s/%010"PRId32, queue_znode, queue_pos);
>   
>   	rc = zk_node_exists(path);
>   	switch (rc) {
> @@ -483,7 +490,8 @@ static int zk_find_seq_node(uint64_t id, char *seq_path, int seq_path_len,
>   	for (int seq = queue_pos; ; seq++) {
>   		struct zk_event ev;
>   
> -		snprintf(seq_path, seq_path_len, QUEUE_ZNODE"/%010"PRId32, seq);
> +		snprintf(seq_path, seq_path_len, "%s/%010"PRId32,
> +				queue_znode, seq);
>   		len = offsetof(typeof(ev), id) + sizeof(ev.id);
>   		rc = zk_get_data(seq_path, &ev, &len);
>   		switch (rc) {
> @@ -513,7 +521,7 @@ static int zk_queue_push(struct zk_event *ev)
>   	bool found;
>   
>   	len = offsetof(typeof(*ev), buf) + ev->buf_len;
> -	snprintf(path, sizeof(path), "%s/", QUEUE_ZNODE);
> +	snprintf(path, sizeof(path), "%s/", queue_znode);
>   again:
>   	rc = zk_create_seq_node(path, (char *)ev, len, buf, sizeof(buf), false);
>   	switch (rc) {
> @@ -537,7 +545,10 @@ again:
>   	if (first_push) {
>   		int32_t seq;
>   
> -		sscanf(buf, QUEUE_ZNODE "/%"PRId32, &seq);
> +		char temp_char_form[MAX_NODE_STR_LEN] = "";
> +		strcpy(temp_char_form, queue_znode);
> +		strcat(temp_char_form, "/%"PRId32);
If temp_char_form is not a pointer, could you please use snprintf 
instead of strcpy and strcat? So do others.
> +		sscanf(buf, temp_char_form, &seq);
>   		queue_pos = seq;
>   		eventfd_xwrite(efd, 1);
>   		first_push = false;
> @@ -568,7 +579,7 @@ static int push_join_response(struct zk_event *ev)
>   	queue_pos--;
>   
>   	len = offsetof(typeof(*ev), buf) + ev->buf_len;
> -	snprintf(path, sizeof(path), QUEUE_ZNODE "/%010"PRId32, queue_pos);
> +	snprintf(path, sizeof(path), "%s/%010"PRId32, queue_znode, queue_pos);
>   
>   	RETURN_IF_ERROR(zk_set_data(path, (char *)ev, len, -1), "");
>   	sd_debug("update path:%s, queue_pos:%010" PRId32 ", len:%d", path,
> @@ -582,7 +593,7 @@ static int zk_queue_pop_advance(struct zk_event *ev)
>   	char path[MAX_NODE_STR_LEN];
>   
>   	len = sizeof(*ev);
> -	snprintf(path, sizeof(path), QUEUE_ZNODE "/%010"PRId32, queue_pos);
> +	snprintf(path, sizeof(path), "%s/%010"PRId32, queue_znode, queue_pos);
>   
>   	RETURN_IF_ERROR(zk_get_data(path, ev, &len), "path %s", path);
>   	sd_debug("%s, type:%d, len:%d, pos:%" PRId32, path, ev->type, len,
> @@ -641,10 +652,16 @@ static inline void build_node_list(void)
>   
>   static int zk_queue_init(void)
>   {
> -	RETURN_IF_ERROR(zk_init_node(BASE_ZNODE), "path %s", BASE_ZNODE);
> -	RETURN_IF_ERROR(zk_init_node(MASTER_ZNODE), "path %s", MASTER_ZNODE);
> -	RETURN_IF_ERROR(zk_init_node(QUEUE_ZNODE), "path %s", QUEUE_ZNODE);
> -	RETURN_IF_ERROR(zk_init_node(MEMBER_ZNODE), "path %s", MEMBER_ZNODE);
> +	char sd_domain_znode[128] = "";
> +	strcpy(sd_domain_znode, base_znode);
> +	strcat(sd_domain_znode, "/");
> +	strcat(sd_domain_znode, sd_domain);
> +	RETURN_IF_ERROR(zk_init_node(base_znode), "path %s", base_znode);
> +	RETURN_IF_ERROR(zk_init_node(sd_domain_znode),
> +					"path %s", sd_domain_znode);
> +	RETURN_IF_ERROR(zk_init_node(master_znode), "path %s", master_znode);
> +	RETURN_IF_ERROR(zk_init_node(queue_znode), "path %s", queue_znode);
> +	RETURN_IF_ERROR(zk_init_node(member_znode), "path %s", member_znode);
>   	return ZOK;
>   }
>   
> @@ -692,6 +709,7 @@ static void zk_watcher(zhandle_t *zh, int type, int state, const char *path,
>   	char str[MAX_NODE_STR_LEN], *p;
>   	uint64_t lock_id;
>   	int ret;
> +	char temp_char_form[MAX_NODE_STR_LEN] = "";
>   
>   	if (type == ZOO_SESSION_EVENT && state == ZOO_EXPIRED_SESSION_STATE) {
>   		/*
> @@ -705,7 +723,9 @@ static void zk_watcher(zhandle_t *zh, int type, int state, const char *path,
>   /* CREATED_EVENT 1, DELETED_EVENT 2, CHANGED_EVENT 3, CHILD_EVENT 4 */
>   	sd_debug("path:%s, type:%d, state:%d", path, type, state);
>   	if (type == ZOO_CREATED_EVENT || type == ZOO_CHANGED_EVENT) {
> -		ret = sscanf(path, MEMBER_ZNODE "/%s", str);
> +		strcpy(temp_char_form, member_znode);
> +		strcat(temp_char_form, "/%s");
> +		ret = sscanf(path, temp_char_form, str);
>   		if (ret == 1)
>   			zk_node_exists(path);
>   		/* kick off the event handler */
> @@ -714,7 +734,9 @@ static void zk_watcher(zhandle_t *zh, int type, int state, const char *path,
>   		struct zk_node *n;
>   
>   		/* process distributed lock */
> -		ret = sscanf(path, LOCK_ZNODE "/%"PRIu64"/%s", &lock_id, str);
> +		strcpy(temp_char_form, lock_znode);
> +		strcat(temp_char_form, "/%"PRIu64"/%s");
> +		ret = sscanf(path, temp_char_form, &lock_id, str);
>   		if (ret == 2) {
>   			ret = lock_table_lookup_wakeup(lock_id);
>   			if (ret)
> @@ -723,13 +745,17 @@ static void zk_watcher(zhandle_t *zh, int type, int state, const char *path,
>   			return;
>   		}
>   
> -		ret = sscanf(path, MASTER_ZNODE "/%s", str);
> +		strcpy(temp_char_form, master_znode);
> +		strcat(temp_char_form, "/%s");
> +		ret = sscanf(path, temp_char_form, str);
>   		if (ret == 1) {
>   			zk_compete_master();
>   			return;
>   		}
>   
> -		ret = sscanf(path, MEMBER_ZNODE "/%s", str);
> +		strcpy(temp_char_form, member_znode);
> +		strcat(temp_char_form, "/%s");
> +		ret = sscanf(path, temp_char_form, str);
>   		if (ret != 1)
>   			return;
>   		p = strrchr(path, '/');
> @@ -815,19 +841,23 @@ static int zk_find_master(int *master_seq, char *master_name)
>   {
>   	int rc, len = MAX_NODE_STR_LEN;
>   	char master_compete_path[MAX_NODE_STR_LEN];
> +	char temp_char_form[MAX_NODE_STR_LEN] = "";
>   
>   	if (*master_seq < 0) {
> -		RETURN_IF_ERROR(zk_get_least_seq(MASTER_ZNODE,
> +		RETURN_IF_ERROR(zk_get_least_seq(master_znode,
>   						 master_compete_path,
>   						 MAX_NODE_STR_LEN, master_name,
>   						 &len), "");
> -		sscanf(master_compete_path, MASTER_ZNODE "/%"PRId32,
> -		       master_seq);
> +		strcpy(temp_char_form, master_znode);
> +		strcat(temp_char_form, "/%"PRId32);
> +		sscanf(master_compete_path, temp_char_form, master_seq);
>   		return ZOK;
>   	} else {
>   		while (true) {
> +			strcpy(temp_char_form, master_znode);
> +			strcat(temp_char_form, "/%010"PRId32);
>   			snprintf(master_compete_path, len,
> -				 MASTER_ZNODE "/%010"PRId32, *master_seq);
> +				 temp_char_form, *master_seq);
>   			rc = zk_get_data(master_compete_path, master_name,
>   					 &len);
>   			switch (rc) {
> @@ -854,10 +884,12 @@ static int zk_verify_last_sheep_join(int seq, int *last_sheep)
>   {
>   	int rc, len = MAX_NODE_STR_LEN;
>   	char path[MAX_NODE_STR_LEN], name[MAX_NODE_STR_LEN];
> +	char temp_char_form[MAX_NODE_STR_LEN] = "";
>   
>   	for (*last_sheep = seq - 1; *last_sheep >= 0; (*last_sheep)--) {
> -		snprintf(path, MAX_NODE_STR_LEN, MASTER_ZNODE "/%010"PRId32,
> -			 *last_sheep);
> +		strcpy(temp_char_form, master_znode);
> +		strcat(temp_char_form, "/%010"PRId32);
> +		snprintf(path, MAX_NODE_STR_LEN, temp_char_form, *last_sheep);
>   		rc = zk_get_data(path, name, &len);
>   		switch (rc) {
>   		case ZNONODE:
> @@ -871,8 +903,9 @@ static int zk_verify_last_sheep_join(int seq, int *last_sheep)
>   
>   		if (!strcmp(name, node_to_str(&this_node.node)))
>   			continue;
> -
> -		snprintf(path, MAX_NODE_STR_LEN, MEMBER_ZNODE "/%s", name);
> +		strcpy(temp_char_form, member_znode);
> +		strcat(temp_char_form, "/%s");
> +		snprintf(path, MAX_NODE_STR_LEN, temp_char_form, name);
>   		rc = zk_node_exists(path);
>   		switch (rc) {
>   		case ZOK:
> @@ -909,23 +942,28 @@ static void zk_compete_master(void)
>   		goto out_unlock;
>   
>   	if (!joined) {
> +		char temp_char_form[MAX_NODE_STR_LEN] = "";
> +		strcpy(temp_char_form, master_znode);
> +		strcat(temp_char_form, "/");
>   		sd_debug("start to compete master for the first time");
>   		do {
>   			if (uatomic_is_true(&stop))
>   				goto out_unlock;
>   			/* duplicate sequential node has no side-effect */
> -			rc = zk_create_seq_node(MASTER_ZNODE "/",
> +			rc = zk_create_seq_node(temp_char_form,
>   						node_to_str(&this_node.node),
>   						MAX_NODE_STR_LEN,
>   						my_compete_path,
>   						MAX_NODE_STR_LEN, true);
>   		} while (rc == ZOPERATIONTIMEOUT || rc == ZCONNECTIONLOSS);
> -		CHECK_ZK_RC(rc, MASTER_ZNODE "/");
> +		CHECK_ZK_RC(rc, temp_char_form);
>   		if (rc != ZOK)
>   			goto out_unlock;
>   
> +		strcpy(temp_char_form, master_znode);
> +		strcat(temp_char_form, "/%"PRId32);
>   		sd_debug("my compete path: %s", my_compete_path);
> -		sscanf(my_compete_path, MASTER_ZNODE "/%"PRId32,
> +		sscanf(my_compete_path, temp_char_form,
>   		       &my_seq);
>   	}
>   
> @@ -964,10 +1002,12 @@ static int zk_join(const struct sd_node *myself,
>   {
>   	int rc;
>   	char path[MAX_NODE_STR_LEN];
> +	char temp_char_form[MAX_NODE_STR_LEN] = "";
>   
>   	this_node.node = *myself;
> -
> -	snprintf(path, sizeof(path), MEMBER_ZNODE "/%s", node_to_str(myself));
> +	strcpy(temp_char_form, member_znode);
> +	strcat(temp_char_form, "/%s");
> +	snprintf(path, sizeof(path), temp_char_form, node_to_str(myself));
>   	rc = zk_node_exists(path);
>   	if (rc == ZOK) {
>   		sd_err("Previous zookeeper session exist, shoot myself. Please "
> @@ -985,17 +1025,21 @@ static int zk_join(const struct sd_node *myself,
>   static int zk_leave(void)
>   {
>   	char path[PATH_MAX];
> +	char temp_char_form[MAX_NODE_STR_LEN] = "";
>   
>   	sd_info("leaving from cluster");
>   	uatomic_set_true(&stop);
>   
>   	if (uatomic_is_true(&is_master)) {
> -		snprintf(path, sizeof(path), MASTER_ZNODE "/%010"PRId32,
> -				my_master_seq);
> +		strcpy(temp_char_form, master_znode);
> +		strcat(temp_char_form, "/%010"PRId32);
> +		snprintf(path, sizeof(path), temp_char_form, my_master_seq);
>   		zk_delete_node(path, -1);
>   	}
>   
> -	snprintf(path, sizeof(path), MEMBER_ZNODE"/%s",
> +	strcpy(temp_char_form, member_znode);
> +	strcat(temp_char_form, "/%s");
> +	snprintf(path, sizeof(path), temp_char_form,
>   		 node_to_str(&this_node.node));
>   	add_event(EVENT_LEAVE, &this_node, NULL, 0);
>   	lock_table_remove_znodes();
> @@ -1038,9 +1082,9 @@ static void watch_all_nodes(void)
>   	struct String_vector strs;
>   	char path[MAX_NODE_STR_LEN];
>   
> -	RETURN_VOID_IF_ERROR(zk_get_children(MEMBER_ZNODE, &strs), "");
> +	RETURN_VOID_IF_ERROR(zk_get_children(member_znode, &strs), "");
>   
> -	FOR_EACH_ZNODE(MEMBER_ZNODE, path, &strs) {
> +	FOR_EACH_ZNODE(member_znode, path, &strs) {
>   		RETURN_VOID_IF_ERROR(zk_node_exists(path), "");
>   	}
>   }
> @@ -1066,6 +1110,7 @@ static void zk_handle_accept(struct zk_event *ev)
>   {
>   	char path[MAX_NODE_STR_LEN];
>   	int rc;
> +	char temp_char_form[MAX_NODE_STR_LEN] = "";
>   
>   	sd_debug("ACCEPT");
>   	if (node_eq(&ev->sender.node, &this_node.node))
> @@ -1074,7 +1119,9 @@ static void zk_handle_accept(struct zk_event *ev)
>   
>   	sd_debug("%s", node_to_str(&ev->sender.node));
>   
> -	snprintf(path, sizeof(path), MEMBER_ZNODE"/%s",
> +	strcpy(temp_char_form, member_znode);
> +	strcat(temp_char_form, "/%s");
> +	snprintf(path, sizeof(path), temp_char_form,
>   		 node_to_str(&ev->sender.node));
>   	if (node_eq(&ev->sender.node, &this_node.node)) {
>   		joined = true;
> @@ -1286,18 +1333,22 @@ static void zk_lock(uint64_t lock_id)
>   	char lowest_seq_path[MAX_NODE_STR_LEN];
>   	char owner_name[MAX_NODE_STR_LEN];
>   	struct cluster_lock *cluster_lock;
> +	char temp_char_form[MAX_NODE_STR_LEN] = "";
>   
>   	cluster_lock = lock_table_lookup_acquire(lock_id);
>   
>   	my_path = cluster_lock->lock_path;
>   
> -	snprintf(parent, MAX_NODE_STR_LEN, LOCK_ZNODE "/%"PRIu64"/",
> +	strcpy(temp_char_form, lock_znode);
> +	strcat(temp_char_form, "/%"PRIu64"/");
> +	snprintf(parent, MAX_NODE_STR_LEN, temp_char_form,
>   		 cluster_lock->id);
>   	/*
>   	 * It need using path without end of '/' to create node of lock_id in
>   	 * zookeeper's API, so we use 'parent_node'.
>   	 */
> -	snprintf(parent_node, MAX_NODE_STR_LEN, LOCK_ZNODE "/%"PRIu64,
> +	temp_char_form[strlen(temp_char_form)-1] = '\0';
> +	snprintf(parent_node, MAX_NODE_STR_LEN, temp_char_form,
>   		 cluster_lock->id);
>   create_seq_node:
>   	/* compete owner of lock is just like zk_compete_master() */
> @@ -1359,7 +1410,8 @@ static void zk_unlock(uint64_t lock_id)
>   
>   static int zk_init(const char *option)
>   {
> -	char *hosts, *to, *p;
> +	char hosts[MAX_NODE_STR_LEN];
> +	const char *pt, *pd;
>   	int ret, interval, retry = 0, max_retry;
>   
>   	if (!option) {
> @@ -1367,17 +1419,29 @@ static int zk_init(const char *option)
>   		return -1;
>   	}
>   
> -	hosts = strtok((char *)option, "=");
> -	if ((to = strtok(NULL, "="))) {
> -		if (sscanf(to, "%u", &zk_timeout) != 1) {
> -			sd_err("Invalid parameter for timeout");
> -			return -1;
> -		}
> -		p = strstr(hosts, "timeout");
> -		*--p = '\0';
> +	pt = strstr(option, "timeout=");
> +	pd = strstr(option, "domain=");
> +	if (pt == NULL && pd == NULL) {
> +		strcpy(hosts, option);
> +	} else if (pt) {
> +		int i = 0;
> +		while (option != pt)
> +			hosts[i++] = *option++;
> +		hosts[i-1] = '\0';
> +		sscanf(pt, "timeout=%d", &zk_timeout);
> +		if (pd)
> +			sscanf(pd, "domain=%s", sd_domain);
> +	} else {
> +		int i = 0;
> +		while (option != pd)
> +			hosts[i++] = *option++;
> +		hosts[i-1] = '\0';
> +		sscanf(pd, "domain=%s", sd_domain);
>   	}
> -	sd_debug("version %d.%d.%d, address %s, timeout %d", ZOO_MAJOR_VERSION,
> -		 ZOO_MINOR_VERSION, ZOO_PATCH_VERSION, hosts, zk_timeout);
> +
> +	sd_debug("version %d.%d.%d, address %s, timeout %d, sheepdog domain %s",
> +			ZOO_MAJOR_VERSION, ZOO_MINOR_VERSION, ZOO_PATCH_VERSION,
> +			hosts, zk_timeout, sd_domain);
>   	zhandle = zookeeper_init(hosts, zk_watcher, zk_timeout, NULL, NULL, 0);
>   	if (!zhandle) {
>   		sd_err("failed to initialize zk server %s", option);
> @@ -1398,6 +1462,18 @@ static int zk_init(const char *option)
>   
>   	uatomic_set_false(&stop);
>   	uatomic_set_false(&is_master);
> +	strcpy(master_znode, base_znode);
> +	strcat(master_znode, "/");
> +	strcat(master_znode, sd_domain);
> +	strcat(master_znode, master_znode_post);
> +	strcpy(queue_znode, base_znode);
> +	strcat(queue_znode, "/");
> +	strcat(queue_znode, sd_domain);
> +	strcat(queue_znode, queue_znode_post);
> +	strcpy(member_znode, base_znode);
> +	strcat(member_znode, "/");
> +	strcat(member_znode, sd_domain);
> +	strcat(member_znode, member_znode_post);
>   	if (zk_queue_init() != ZOK)
>   		return -1;
>   
> @@ -1421,9 +1497,13 @@ static int zk_init(const char *option)
>   		sd_init_mutex(table_locks + i);
>   	}
>   
> -	ret = zk_init_node(LOCK_ZNODE);
> +	strcpy(lock_znode, base_znode);
> +	strcat(lock_znode, "/");
> +	strcat(lock_znode, sd_domain);
> +	strcat(lock_znode, lock_znode_post);
> +	ret = zk_init_node(lock_znode);
>   	if (ret != ZOK) {
> -		sd_err("Failed to create %s %s", LOCK_ZNODE, zerror(ret));
> +		sd_err("Failed to create %s %s", lock_znode, zerror(ret));
>   		free(cluster_locks_table);
>   		return -1;
>   	}
> diff --git a/sheep/sheep.c b/sheep/sheep.c
> index 7d5fa0f..0cbe69b 100644
> --- a/sheep/sheep.c
> +++ b/sheep/sheep.c
> @@ -68,12 +68,16 @@ static const char cluster_help[] =
>   "\tlocal: use local driver\n"
>   "\tcorosync: use corosync driver\n"
>   "\tzookeeper: use zookeeper driver, need extra arguments\n"
> -"\n\tzookeeper arguments: address-list,timeout=value (default as 3000)\n"
> +"\n\tzookeeper arguments: address-list,timeout=value(default as 3000)"
> +",domain=value(default as sd_domain_default)\n"
>   "\nExample:\n\t"
> -"$ sheep -c zookeeper:IP1:PORT1,IP2:PORT2,IP3:PORT3,timeout=1000 ...\n"
> +"$ sheep -c zookeeper:IP1:PORT1,IP2:PORT2,IP3:PORT3,timeout=1000,domain=sheep_01 ...\n"
>   "This tries to use 3 node zookeeper cluster, which can be reached by\n"
>   "IP1:PORT1, IP2:PORT2, IP3:PORT3 to manage membership and broadcast message\n"
> -"and set the timeout of node heartbeat as 1000 milliseconds\n";
> +"and set the timeout of node heartbeat as 1000 milliseconds\n"
> +"and join the domain sheep_01.\n"
> +"Notice that timeout should be followed by domain "
> +"if both are given explicitly.\n";
Why the constraint is needed? Is it possible to parse domain field and 
timeout field in random order?
>   
>   static const char cache_help[] =
>   "Available arguments:\n"





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