Zookeeper distributed locks in Spring Boot
Distributed lock is a synchronization tool commonly used in distributed systems. It can coordinate access to shared resources among multiple processes to avoid data inconsistency or repeated processing. In a distributed environment, due to network communication delays and node failures, traditional lock mechanisms cannot meet the requirements. Therefore, distributed locks have become one of the common solutions to achieve distributed synchronization.
Zookeeper is a distributed coordination service that provides a highly available, high-performance, and scalable distributed lock mechanism. Spring Boot is a development framework based on the Spring framework, which provides integrated support for Zookeeper distributed locks. This article will introduce the principle and usage of Zookeeper distributed locks in Spring Boot.
principle
The principle of Zookeeper distributed lock is based on Zookeeper's node synchronization mechanism. In Zookeeper, each node has a version number, and the status changes of the nodes will be recorded. When a process wants to acquire a lock, it creates a temporary node in Zookeeper and tries to acquire the lock. If the node is successfully created, the lock is acquired successfully; otherwise, the process needs to wait until the lock is released.
The implementation of Zookeeper distributed locks needs to consider the following issues:
- How to ensure the mutual exclusion of locks: only one process can acquire the lock, and other processes need to wait.
- How to ensure lock reentrancy: the same process can acquire locks repeatedly without deadlock.
- How to avoid eternal waiting for locks: If a process crashes after acquiring a lock, how to ensure that the lock can be released.
In order to solve these problems, Zookeeper distributed lock adopts the following mechanism:
- Take advantage of the mutual exclusion of Zookeeper nodes: each node can only be created by one process at a time.
- Take advantage of the ephemeral nature of Zookeeper nodes: when a process crashes or disconnects, the nodes it created are automatically deleted.
- Take advantage of the order of Zookeeper nodes: the nodes in Zookeeper are arranged in an orderly manner, and each node has a unique number. When a process acquires a lock, it will create a node with a serial number, and then judge whether it is the smallest node. If it is the smallest node, the lock is acquired successfully; otherwise, the process needs to wait.
Instructions
Spring Boot's support for Zookeeper distributed locks is spring-integration-zookeeperimplemented through modules. Below is a simple example that demonstrates how to use Zookeeper distributed locks in Spring Boot.
First, we need to pom.xmladd the following dependencies to :
<dependency>
<groupId>org.springframework.integration</groupId>
<artifactId>spring-integration-zookeeper</artifactId>
<version>5.5.0</version>
</dependency>
We can then use the class in Spring Boot ZookeeperLockRegistryto create a distributed lock. Here's an ZookeeperLockRegistryexample using the class:
@Configuration
public class ZookeeperLockConfiguration {
@Bean
public ZookeeperLockRegistry zookeeperLockRegistry(CuratorFramework curatorFramework) {
return new ZookeeperLockRegistry(curatorFramework, "/locks");
}
@Bean
public CuratorFramework curatorFramework() throws Exception {
return CuratorFrameworkFactory.newClient("127.0.0.1:2181", new RetryUntilElapsed(1000, 4));
}
}
In the above example, we created a zookeeperLockRegistrybean named to manage distributed locks. We also created a curatorFrameworkbean called to create the Zookeeper client.
ZookeeperLockRegistryNow, we can use the class to create a lock object where we need to use distributed locks , and call lock()the method to acquire the lock. Here is an example:
@Autowired
private ZookeeperLockRegistry zookeeperLockRegistry;
public void doSomething() {
Lock lock = zookeeperLockRegistry.obtain("my-lock");
if (lock.tryLock()) {
try {
// TODO: 执行业务逻辑
} finally {
lock.unlock();
}
} else {
// TODO: 获取锁失败的处理逻辑
}
}
In the above example, we first zookeeperLockRegistry.obtain("my-lock")obtained a my-locklock object named through the method. Then, we call tryLock()the method to try to acquire the lock. If the lock is acquired successfully, we can execute the business logic; otherwise, we need to handle the failure to acquire the lock.
It should be noted that when using distributed locks, we need to follow the following principles:
- The scope of the lock should be as small as possible: the smaller the scope of the lock, the weaker the mutual exclusion of the lock, and the higher the throughput of the system.
- The timeout of the lock should be set reasonably: if the lock holder crashes or the network has problems, other processes need to wait for a period of time before acquiring the lock, and this time should not be set too long or too short.
- The release of the lock should be performed in the finally block: no matter whether the business logic is abnormal or not, it should be guaranteed that the lock can be released.
code example
Below is a complete Spring Boot project that demonstrates how to use Zookeeper distributed locks. In this project, we simulated a simple counter. Multiple processes can add one to the counter at the same time, but only one process can successfully acquire the lock and perform the operation, while other processes need to wait.
@SpringBootApplication
public class ZookeeperLockDemoApplication {
public static void main(String[] args) {
SpringApplication.run(ZookeeperLockDemoApplication.class, args);
}
@Bean
public ZookeeperLockRegistry zookeeperLockRegistry(CuratorFramework curatorFramework) {
return new ZookeeperLockRegistry(curatorFramework, "/locks");
}
@Bean
public CuratorFramework curatorFramework() throws Exception {
return CuratorFrameworkFactory.newClient("127.0.0.1:2181", new RetryUntilElapsed(1000, 4));
}
}
@RestController
public class CounterController {
private AtomicInteger counter = new AtomicInteger(0);
@Autowired
private ZookeeperLockRegistry zookeeperLockRegistry;
@GetMapping("/counter")
public int getCounter() {
return counter.get();
}
@PostMapping("/counter")
public int increaseCounter() {
Lock lock = zookeeperLockRegistry.obtain("/counter-lock");
try {
if (lock.tryLock(10, TimeUnit.SECONDS)) {
try {
counter.incrementAndGet();
} finally {
lock.unlock();
}
} else {
throw new RuntimeException("Failed to acquire lock for counter!");
}
} catch (InterruptedException e) {
throw new RuntimeException("Failed to acquire lock for counter!", e);
}
return counter.get();
}
}
In the above code, we have created a CounterControllerRESTful interface called that provides read and write operations on the counter. In the write operation, we use zookeeperLockRegistry.obtain("/counter-lock")the method to acquire a /counter-locklock object named , and call tryLock(10, TimeUnit.SECONDS)the method to try to acquire the lock with a timeout of 10 seconds. If the lock is acquired successfully, we can increment the counter; otherwise, we throw a runtime exception.
in conclusion
Zookeeper distributed lock is one of the common solutions for distributed synchronization. It implements a highly available, high-performance, and scalable distributed lock mechanism based on Zookeeper's node synchronization mechanism. In Spring Boot, we can spring-integration-zookeeperintegrate the support of Zookeeper distributed locks through the module, which is very convenient to use.
When using Zookeeper distributed locks, we need to follow some principles, such as the scope of the lock should be as small as possible, the timeout of the lock should be set reasonably, the release of the lock should be performed in the finally block, and so on. In addition, it should be noted that although distributed locks can solve the problem of distributed synchronization,