仅在更新变量时同步变量

Question

用例：数据存储的凭据轮换

我想要什么：

调用 updateCredentials 时，它将等到所有线程完成获取凭据（通过同步）以将凭据更新为新凭据。
我不想调用 doSomeQuery 让彼此等待获取凭据。这个对象可以在多线程中使用，等待很浪费。

是否有实现此目的的方法/模式？下面的代码示例实现了第 1 项但未实现第 2 项。

private Object credentialUpdate = new Object();

public void updateCredentials(String user, String pass) {
    synchronize(credentialUpdate) {
      this.user = user;
      this.pass = pass;
    }
}

public void doSomeQuery(String query) {
    String curUser;
    String curPass; 
    synchronize(credentialUpdate) {
        curUser = this.user;
        curPass;
    }
    // execute query
}

Answer 1

使用 java.util.concurrent.locks.ReadWriteLock 及其实现 ReentrantReadWriteLock。来自 Javadoc:

A ReadWriteLock maintains a pair of associated locks, one for read-only operations and one for writing. The read lock may be held simultaneously by multiple reader threads, so long as there are no writers. The write lock is exclusive.

仅在更新变量时同步变量

Synchronize on variable only when it is being updated

java

locking

synchronized