How to use locking mechanism to ensure thread safety of Java functions?

Answer: The Java lock mechanism ensures thread safety by limiting the number of threads that access shared resources at the same time. Practical case: The locking method uses the synchronized keyword to lock the method. Practical case: Locking code blocks uses synchronized blocks to lock code blocks. Practical case: ReentrantLock uses ReentrantLock instance locking to provide more fine-grained control. The choice of lock depends on the code block size and call frequency, synchronized is suitable for small code blocks, and ReentrantLock is suitable for complex scenarios. Note: Avoid nested locks, release locks promptly, and consider using fair locks to prevent starvation problems.

How to use the lock mechanism to ensure the thread safety of Java functions?

Preface

In multi-threaded programming, thread safety is crucial. When multiple threads access shared data at the same time, data inconsistency or program crash may result. The locking mechanism is a commonly used solution in Java to ensure that functions can be executed safely in a concurrent environment.

What is a lock?

A lock is a synchronization mechanism that allows only one thread to access a protected code block or data structure at a time. When a thread acquires a lock, other threads are blocked from executing that block of code until the lock is released.

Locks in Java

There are two built-in locks in Java:

• synchronized Keywords: Used to lock methods or code blocks.
• ReentrantLock Class: Provides more fine-grained lock control.

Practical case: locking method

The following code demonstrates how to use the synchronized keyword to lock a method:

class SharedResource {
    public synchronized void update() {
        // 被保护的代码块
    }
}

Practical case: Locking code block

The following code demonstrates how to use the synchronized block to lock a code block:

class SharedResource {
    public void update() {
        synchronized (this) {
            // 被保护的代码块
        }
    }
}

Practical case: ReentrantLock

The following code demonstrates how to use ReentrantLock to lock:

class SharedResource {
    private final ReentrantLock lock = new ReentrantLock();
    public void update() {
        lock.lock();
        try {
            // 被保护的代码块
        } finally {
            lock.unlock();
        }
    }
}

Choose the correct lock

Which type of lock to choose depends on the specific scenario. Generally speaking, the synchronized keyword is an easy-to-use choice if the locking code block is small and not called often. If you need more fine-grained control or deadlock handling, ReentrantLock is more suitable.

Other notes

• Avoid nested locks: When the same thread holds a lock, do not try to acquire the same lock again.
• Release the lock promptly: When the lock is no longer needed, it must be released immediately to avoid thread deadlock.
• Consider fair locks: ReentrantLock supports fair locks, which means that threads waiting to acquire locks will acquire locks in FIFO (first in, first out) order. This prevents hunger problems.

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