线上死锁问题排查和处理

Java 死锁排查

通过 jps + jstack 来定位和排查

如果线程长时间处于阻塞，就需要考虑是否是死锁了。

模拟死锁

public class DeadlockDemo {private static final Object lock1 = new Object();private static final Object lock2 = new Object();public static void main(String[] args) {// 创建线程1Thread t1 = new Thread(() -> {synchronized (lock1) {System.out.println("Thread 1: Holding lock 1...");try {Thread.sleep(100);} catch (InterruptedException e) {e.printStackTrace();}System.out.println("Thread 1: Waiting for lock 2...");synchronized (lock2) {System.out.println("Thread 1: Holding lock 1 & 2...");}}});// 创建线程2Thread t2 = new Thread(() -> {synchronized (lock2) {System.out.println("Thread 2: Holding lock 2...");try {Thread.sleep(100);} catch (InterruptedException e) {e.printStackTrace();}System.out.println("Thread 2: Waiting for lock 1...");synchronized (lock1) {System.out.println("Thread 2: Holding lock 1 & 2...");}}});// 启动线程t1.start();
//        try {
//            Thread.sleep(1000);
//        } catch (InterruptedException e) {
//            throw new RuntimeException(e);
//        }t2.start();}
}

Thread 1: Holding lock 1...
Thread 2: Holding lock 2...
Thread 1: Waiting for lock 2...
Thread 2: Waiting for lock 1...

通过 jps + jstack 来定位和排查

PS D:\xxx> jps   查看java进程状态
19504
16356 RemoteMavenServer36
20692 Launcher
9044 DeadlockDemo
13064 Jps

PS D:\xxx> jstack 9044   打印java进程堆栈

Found one Java-level deadlock:
=============================
"Thread-1":
waiting to lock monitor 0x0000000026a08df8 (object 0x00000007174cc1b8, a java.lang.Object),
which is held by "Thread-0"
"Thread-0":
waiting to lock monitor 0x0000000026a0b898 (object 0x00000007174cc1c8, a java.lang.Object),
which is held by "Thread-1"

Java stack information for the threads listed above:
===================================================
"Thread-1":
        at DeadlockDemo.lambda$main$1(DeadlockDemo.java:33)
        - waiting to lock <0x00000007174cc1b8> (a java.lang.Object)
        - locked <0x00000007174cc1c8> (a java.lang.Object)
        at DeadlockDemo$$Lambda$2/1078694789.run(Unknown Source)
        at java.lang.Thread.run(Thread.java:748)
"Thread-0":
        at DeadlockDemo.lambda$main$0(DeadlockDemo.java:17)
        - waiting to lock <0x00000007174cc1c8> (a java.lang.Object)
        - locked <0x00000007174cc1b8> (a java.lang.Object)
        at DeadlockDemo$$Lambda$1/1324119927.run(Unknown Source)
        at java.lang.Thread.run(Thread.java:748)

Found 1 deadlock.

预防和处理死锁

1.考虑顺序获取需要的资源；

2.考虑无锁的方案；

MySQL死锁排查

使用 SHOW ENGINE INNODB STATUS # 查看死锁日志

模拟死锁

建表语句


-- 创建users表
CREATE TABLE users (id INT PRIMARY KEY,          -- 主键，唯一标识用户name VARCHAR(50) NOT NULL,   -- 用户名称balance DECIMAL(10, 2)       -- 用户余额
);-- 为name字段创建普通索引
CREATE INDEX idx_name ON users (name);-- 插入测试数据
INSERT INTO users (id, name, balance) VALUES
(1, 'Bob', 1000.00),       -- 用户Bob，余额1000
(2, 'Alice', 1000.00);     -- 用户Alice，余额1000UPDATE `users`
set balance = 1000;

事务1

-- 会话1
BEGIN;
UPDATE users SET balance = balance - 100 WHERE name = 'Bob';  -- 更新Bob的余额
UPDATE users SET balance = balance + 100 WHERE name = 'Alice';  -- 更新COMMIT;

事务2

-- 会话2
BEGIN;
UPDATE users SET balance = balance + 100 WHERE name = 'Alice';  -- 更新Alice的余额
UPDATE users SET balance = balance - 100 WHERE name = 'Bob';  -- 更新Bob的余额COMMIT;

死锁检测设置


show variables like 'innodb_deadlock_detect';set global innodb_deadlock_detect = 1;  # 开启死锁检测   如有死锁 会回滚某一个事务
set global innodb_deadlock_detect = 0;SHOW ENGINE INNODB STATUS    # 查看 死锁日志