Java memory model and deadlock: in-depth understanding of deadlock issues in concurrent programming

php editor Youzi will analyze the Java memory model and deadlock issues in detail, and deeply explore the key challenges in concurrent programming. Understanding and mastering the causes and solutions of deadlocks is crucial to improving your concurrent programming skills. Let's delve into it together and solve this common but difficult problem.

DeadLock is a common problem in concurrent programming. It occurs when two or more threads are waiting for each other to release locks. When a thread holds a lock, if another thread also attempts to acquire the lock, the second thread will be blocked. If two threads hold locks that each other needs, a deadlock occurs.

In order to solve the deadlock problem, you can use the following methods:

• Avoid deadlock: Try to avoid creating deadlock conditions in your code. For example, don't use multiple locks on the same object, and don't have one thread wait for another thread to release the lock.
• Use lock timeout: Specify a timeout when acquiring the lock. If the lock cannot be acquired within the timeout, the thread will throw an exception and continue execution.
• Use interrupt: When a thread is waiting for another thread to release the lock, it can send an interrupt signal to the waiting thread. If the thread receives an interrupt signal, an InterruptedException exception is thrown and execution continues.

The following is a sample code that demonstrates deadlock:

public class DeadlockExample {

private static Object lock1 = new Object();
private static Object lock2 = new Object();

public static void main(String[] args) {
Thread thread1 = new Thread(() -> {
synchronized (lock1) {
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
synchronized (lock2) {
System.out.println("Thread 1 acquired both locks");
}
}
});

Thread thread2 = new Thread(() -> {
synchronized (lock2) {
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
synchronized (lock1) {
System.out.println("Thread 2 acquired both locks");
}
}
});

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

In this example code, two threads try to acquire two locks at the same time. Thread 1 first acquires lock 1 and then attempts to acquire lock 2. Thread 2 acquires lock 2 first and then attempts to acquire lock 1. A deadlock occurs because both threads hold locks that each other needs.

In order to solve this deadlock problem, the code can be modified as follows:

public class DeadlockExample {

private static Object lock1 = new Object();
private static Object lock2 = new Object();

public static void main(String[] args) {
Thread thread1 = new Thread(() -> {
synchronized (lock1) {
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
synchronized (lock2) {
System.out.println("Thread 1 acquired both locks");
}
}
});

Thread thread2 = new Thread(() -> {
synchronized (lock2) {
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
synchronized (lock1) {
System.out.println("Thread 2 acquired both locks");
}
}
});

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

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

In this modified code, we use the join() method to wait for the thread to complete execution. In this way, you can ensure that thread 1 acquires lock 2 after acquiring lock 1, and thread 2 acquires lock 1 after acquiring lock 2. In this way, deadlock will not occur.

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