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This article mainly introduces "how to realize zookeeper distributed lock". In daily operation, I believe many people have doubts about how to implement zookeeper distributed lock. The editor consulted all kinds of data and sorted out simple and easy-to-use operation methods. I hope it will be helpful to answer the doubt of "how to realize zookeeper distributed lock". Next, please follow the editor to study!

Architecture introduction

Before introducing the implementation of distributed locks using Zookeeper, take a look at the current system architecture diagram

Explanation: the entire area on the left represents a Zookeeper cluster, locker is a persistent node of Zookeeper, and node_1, node_2, and node_3 are temporary sequential nodes under the persistent node locker. Client_1, client_2, and client_n represent multiple clients, and Service represents shared resources that require mutually exclusive access.

The idea of distributed Lock acquisition

1. The general idea of obtaining a distributed lock, create a temporary sequential node under the locker node when acquiring the distributed lock, and delete the temporary node when the lock is released.

B. The client calls the createNode method to create a temporary sequential node under locker, and then calls getChildren ("locker") to get all the child nodes under the locker. Note that no Watcher is set at this time.

C. After the client acquires all the child nodes path, if it finds that the child node it has created has the lowest sequence number, it is considered that the client has acquired the lock.

D. If you find that the node you created is not the smallest of all the child nodes of locker, it means that you have not acquired the lock. In this case, the client needs to find the node that is smaller than you, then call the exist () method on it, and register the event listener on it.

E. After that, if the concerned node is deleted, the Watcher of the client will receive the corresponding notification and determine again whether the created node has the lowest sequence number among the locker child nodes. If so, the lock is acquired. If not, repeat the above steps to continue to obtain a node smaller than yourself and register the listener.

2. The core algorithm for obtaining distributed locks is analyzed in the same flowchart below, as shown below:

Explanation: when client A wants to acquire distributed locks, it first creates a temporary sequential node (node_n) under locker, and then immediately acquires all (first-level) child nodes under locker.

At this point, because there will be multiple clients fighting for locks at the same time, the number of child nodes under the locker will be greater than 1. For sequential nodes, the characteristic is that the node name is automatically followed by a numerical number, and the node number created first is smaller than that created later, so the child nodes can be sorted from small to large according to the numerical order of the suffix of the node name. in this way, the first is the first created sequential node, at this time it represents the first client to win the lock!

At this point, it is determined whether the smallest node is the node_n created before client A, if so, client A has acquired the lock, and if not, it means that the lock has been acquired by other clients, so client A has to wait for it to release the lock, that is, client B, which is waiting for the lock to be acquired, will delete the node it created. At this point, we can know whether client B has released the lock by listening to the delete event of the sequential node that is smaller than node_n. If so, client An acquires all the child nodes under locker again and compares it with the node_n node created by itself again until the node_n created by client A has the lowest sequence number of all the child nodes of locker, which means that client A has acquired the lock!

At this point, the study on "how to implement zookeeper distributed locks" is over. I hope to be able to solve your doubts. The collocation of theory and practice can better help you learn, go and try it! If you want to continue to learn more related knowledge, please continue to follow the website, the editor will continue to work hard to bring you more practical articles!

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