Java 多线程死锁

1、死锁出现：线程1占有锁A，线程2占有锁B，线程1必须等待锁B释放后才能继续（进而才能释放锁A），线程2必须等待锁A释放后才能继续（进而才能释放锁B），因此导致了死循环等待

2、代码模拟死锁

public class ThreadDeadLock {

	public static void main(String[] args) {
		final String str1 = "resource1";
		final String str2 = "resource2";
		
		Thread t1 = new Thread(new Runnable() {
			
			@Override
			public void run() {
				synchronized (str1) {
					System.out.println(Thread.currentThread().getName() + " get lock on resource1");
					
					try {
						Thread.sleep(3000);  // 执行一些逻辑处理
					} catch (InterruptedException e) {
						e.printStackTrace();
					}
					
					synchronized (str2) {
						System.out.println(Thread.currentThread().getName() + " get lock on resource2");
					}
				}
			}
		});
		
		Thread t2 = new Thread(new Runnable() {
			
			@Override
			public void run() {
				synchronized (str2) {
					System.out.println(Thread.currentThread().getName() + " get lock on resource2");
					
					try {
						Thread.sleep(3000); // 执行一些逻辑处理
					} catch (InterruptedException e) {
						e.printStackTrace();
					}
					
					synchronized (str1) {
						System.out.println(Thread.currentThread().getName() + " get lock on resource1");
					}
				}
			
			}
		});
		
		
		t1.start();
		t2.start();
	}
}

3、如果两个线程获取锁顺序一致，则不会出现死锁

public class ThreadDeadLock {

	public static void main(String[] args) {
		final String str1 = "resource1";
		final String str2 = "resource2";
		
		Thread t1 = new Thread(new Runnable() {
			
			@Override
			public void run() {
				synchronized (str1) {
					System.out.println(Thread.currentThread().getName() + " get lock on resource1");
					
					try {
						Thread.sleep(3000);  // 执行一些逻辑处理
					} catch (InterruptedException e) {
						e.printStackTrace();
					}
					
					synchronized (str2) {
						System.out.println(Thread.currentThread().getName() + " get lock on resource2");
					}
				}
			}
		});
		
		Thread t2 = new Thread(new Runnable() {
			
			@Override
			public void run() {
				synchronized (str1) {
					System.out.println(Thread.currentThread().getName() + " get lock on resource1");
					
					try {
						Thread.sleep(3000); // 执行一些逻辑处理
					} catch (InterruptedException e) {
						e.printStackTrace();
					}
					
					synchronized (str2) {
						System.out.println(Thread.currentThread().getName() + " get lock on resource2");
					}
				}
			
			}
		});
		
		
		t1.start();
		t2.start();
	}
}