Thread protection and deadlock detection technology in Java

Thread protection and deadlock detection technology in Java

As an object-oriented programming language widely used in enterprise-level applications, Java has powerful multi-threaded programming capabilities. In actual application process, thread protection and deadlock detection technology are crucial, they can effectively ensure thread safety and application reliability. This article will discuss this.

1. Thread protection technology

Thread protection refers to restricting and controlling shared resources to ensure that multi-threaded programs can ensure the correctness and integrity of data when accessing the same shared resource at the same time. sex. Java provides three thread protection technologies: mutex locks, semaphores, and condition variables.

1. Mutex lock

Mutex lock is the most basic thread protection technology. Under the protection of a mutex lock, only one thread can access shared resources, and other threads must wait for the mutex lock to be released before they can access it. In Java, mutex locks are mainly implemented through the synchronized keyword.

The following is a simple mutex lock example:

class Counter {
    private int count = 0;
    //使用 synchronized 实现互斥锁
    public synchronized void increment(){
        count += 1;
        //模拟执行某些操作
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println(count);
    }
}
public class MutexExample {
    public static void main(String[] args) throws InterruptedException {
        Counter counter = new Counter();
        //创建两个线程并行执行
        Thread t1 = new Thread(() -> {
            for (int i = 0; i < 3; i++) {
                counter.increment();
            }
        });
        Thread t2 = new Thread(() -> {
            for (int i = 0; i < 3; i++) {
                counter.increment();
            }
        });
        t1.start();
        t2.start();
        //等待两个线程执行完毕
        t1.join();
        t2.join();
    }
}

2. Semaphore

The semaphore is a thread protection technology that can be accessed by multiple threads. It maintains the number of threads that can access shared resources through a counter. When a thread wants to access shared resources, it needs to apply for a semaphore first. If the semaphore counter is greater than 0, the thread can access the shared resources, otherwise the thread must wait for the semaphore. The counter can only be accessed if it is greater than 0.

In Java, semaphore is mainly implemented through the Semaphore class. The example is as follows:

import java.util.concurrent.Semaphore;
class Counter {
    private int count = 0;
    private Semaphore sem = new Semaphore(1);
    //使用 Semaphore 实现线程保护
    public void increment(){
        try {
            sem.acquire();
            count += 1;
            //模拟执行某些操作
            Thread.sleep(1000);
            System.out.println(count);
            sem.release();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}
public class SemaphoreExample {
    public static void main(String[] args) throws InterruptedException {
        Counter counter = new Counter();
        //创建两个线程并行执行
        Thread t1 = new Thread(() -> {
            for (int i = 0; i < 3; i++) {
                counter.increment();
            }
        });
        Thread t2 = new Thread(() -> {
            for (int i = 0; i < 3; i++) {
                counter.increment();
            }
        });
        t1.start();
        t2.start();
        //等待两个线程执行完毕
        t1.join();
        t2.join();
    }
}

3. Condition variable

A condition variable is a type that allows a thread to wait for certain conditions to be met. Thread protection technology that continues execution later, which can be used in conjunction with a mutex lock. In Java, condition variables are mainly implemented through the Condition interface and the ReentrantLock class. Examples are as follows:

import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;
class Counter {
    private int count = 0;
    private ReentrantLock lock = new ReentrantLock();
    private Condition cond = lock.newCondition();
    public void increment() {
        lock.lock();
        try {
            count += 1;
            //模拟执行某些操作
            Thread.sleep(1000);
            System.out.println(count);
            cond.signalAll();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }
    public void waitUntil(int target) {
        lock.lock();
        try {
            while (count < target) {
                cond.await();
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }
}
public class ConditionVariableExample {
    public static void main(String[] args) throws InterruptedException {
        Counter counter = new Counter();
        //创建两个线程并行执行
        Thread t1 = new Thread(() -> {
            for (int i = 0; i < 3; i++) {
                counter.increment();
            }
        });
        Thread t2 = new Thread(() -> {
            counter.waitUntil(3);
            System.out.println("Target reached");
        });
        t1.start();
        t2.start();
        //等待两个线程执行完毕
        t1.join();
        t2.join();
    }
}

2. Deadlock detection technology

Deadlock refers to multiple threads waiting for each other to release what they hold. resources, causing the program to be unable to continue execution. Java provides tools and techniques to detect and avoid deadlocks.

1.jstack

jstack is a tool provided by the Java runtime environment. It can be used to view the status of the CPU occupied by each thread in the Java virtual machine and the locks held by the threads. and waiting locks. jstack outputs the stack trace of the thread to view the resources occupied by the thread to determine whether there is a deadlock.

2.jvisualvm

jvisualvm is a graphical tool that comes with JDK, which can be used to monitor the usage of resources such as threads, CPU, memory and stack. Through jvisualvm, we can easily check the resources occupied by threads, detect and diagnose deadlocks in time, and take corresponding measures in a timely manner.

3.ThreadMXBean

ThreadMXBean is one of the Java management interfaces. It provides some tools and methods that can be used to monitor and manage threads in the JVM, including thread status and thread CPU usage. situation, thread occupation lock, thread deadlock and other information. By using ThreadMXBean, we can easily locate deadlock problems in the program and make timely adjustments and optimizations.

Summary

This article provides a brief introduction and example demonstration of thread protection and deadlock detection technology in Java. In actual development, we must carefully understand and master these technologies to ensure the correctness and reliability of multi-threaded programs, thereby improving the performance and stability of applications.

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