How to solve inter-thread communication issues in Java

How to solve the inter-thread communication problem in Java?

In Java multi-threaded programming, inter-thread communication is an important concept. In practical applications, different threads may need to cooperate with each other, share data, or interact. However, since threads execute concurrently, we need appropriate mechanisms to ensure correct communication between threads. In Java, we can solve the problem of inter-thread communication in the following ways.

1. Use shared variables for communication

Shared variables are the simplest and most direct way of communication. Multiple threads can communicate by reading and writing shared variables. In Java, shared variables should be modified using the volatile keyword to ensure visibility. At the same time, we also need to use the synchronized keyword to ensure atomicity and prevent multiple threads from reading and writing shared variables at the same time.

The following is a simple sample code:

public class SharedVariableCommunication {
    private volatile boolean flag = false;

    public void setFlag(boolean value) {
        flag = value;
    }

    public boolean getFlag() {
        return flag;
    }

    public static void main(String[] args) throws InterruptedException {
        SharedVariableCommunication communication = new SharedVariableCommunication();

        Thread thread1 = new Thread(() -> {
            // do something
            communication.setFlag(true);
        });

        Thread thread2 = new Thread(() -> {
            while (!communication.getFlag()) {
                // waiting
            }
            // continue execution
        });

        thread1.start();
        thread2.start();

        thread1.join();
        thread2.join();
    }
}

In the above code, thread thread1 sets the flag to true through the setFlag method, and thread thread2 continuously checks the value of the flag through the getFlag method. Continue to perform subsequent operations until it is true.

2. Use wait and notify methods to communicate

Java provides the wait and notify methods of the Object class, which can be used for waiting and waking up operations between threads. The thread suspends its own execution through the wait method and releases the object's lock, while other threads wake up the waiting thread through the notify method and continue execution.

The following is a sample code using the wait and notify methods:

public class WaitNotifyCommunication {
    private boolean flag = false;

    public synchronized void setFlag(boolean value) {
        flag = value;
        notify();
    }

    public synchronized void getFlag() throws InterruptedException {
        while (!flag) {
            wait();
        }
    }

    public static void main(String[] args) throws InterruptedException {
        WaitNotifyCommunication communication = new WaitNotifyCommunication();

        Thread thread1 = new Thread(() -> {
            // do something
            communication.setFlag(true);
        });

        Thread thread2 = new Thread(() -> {
            try {
                communication.getFlag();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            // continue execution
        });

        thread1.start();
        thread2.start();

        thread1.join();
        thread2.join();
    }
}

In the above code, thread thread1 sets the flag to true through the setFlag method, and calls the notify method to wake up the waiting thread thread2. Thread thread2 waits through the wait method inside the getFlag method until it is awakened by thread1 and continues to perform subsequent operations.

3. Use Lock and Condition to communicate

In addition to using the synchronized keyword, Java also provides the Lock and Condition interfaces to control thread synchronization and communication in a more fine-grained manner . The Condition interface provides methods such as await, signal, and signalAll, which can be used for waiting and waking up operations between threads.

The following is a sample code using Lock and Condition:

import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class LockConditionCommunication {
    private boolean flag = false;
    private Lock lock = new ReentrantLock();
    private Condition condition = lock.newCondition();

    public void setFlag(boolean value) {
        lock.lock();
        try {
            flag = value;
            condition.signal();
        } finally {
            lock.unlock();
        }
    }

    public void getFlag() throws InterruptedException {
        lock.lock();
        try {
            while (!flag) {
                condition.await();
            }
        } finally {
            lock.unlock();
        }
    }

    public static void main(String[] args) throws InterruptedException {
        LockConditionCommunication communication = new LockConditionCommunication();

        Thread thread1 = new Thread(() -> {
            // do something
            communication.setFlag(true);
        });

        Thread thread2 = new Thread(() -> {
            try {
                communication.getFlag();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            // continue execution
        });

        thread1.start();
        thread2.start();

        thread1.join();
        thread2.join();
    }
}

In the above sample code, ReentrantLock and Condition are used to ensure thread synchronization and communication. Thread thread1 sets the flag to true through the setFlag method, and calls the condition.signal method to wake up the waiting thread thread2. Thread thread2 waits through the condition.await method inside the getFlag method until it is awakened by thread1 and continues to perform subsequent operations.

Summary: There are many ways to solve the problem of inter-thread communication in Java. Choosing the appropriate method depends on the specific application scenarios and requirements. Whether you use shared variables, wait and notify methods, or Lock and Condition interfaces, you need to pay attention to correctly handling the synchronization and mutual exclusion relationships between threads to avoid concurrency problems and deadlocks. We hope that the above code examples can help readers better understand and apply related technologies of inter-thread communication.

(Note: The above code is only an example and may have shortcomings. Readers need to make appropriate modifications and improvements according to specific needs in actual applications.)

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