Java多线程间同步
1、什么是线程安全
class SellTicketRunnable implements Runnable {
public int count = 100;
@Override
public void run() {
while (count > 0) {
try {
Thread.sleep(500);
} catch (InterruptedException e) {
e.printStackTrace();
}
int index = 100 - count + 1;
System.out.println(Thread.currentThread().getName() + "卖出第" + index + "张票");
count--;
}
}
}
public class JavaSyncDemo {
public static void main(String[] args) {
SellTicketRunnable runnable = new SellTicketRunnable();
Thread sellThread1 = new Thread(runnable);
Thread sellThread2 = new Thread(runnable);
sellThread1.start();
sellThread2.start();
}
}
2、线程安全问题的解决办法
(1)使用同步代码块
class SellTicketRunnable implements Runnable {
public int count = 100;
private Object lock = new Object();
@Override
public void run() {
while (count > 0) {
try {
Thread.sleep(500);
} catch (InterruptedException e) {
e.printStackTrace();
}
synchronized (lock) {
if (count > 0) {
int index = 100 - count + 1;
System.out.println(Thread.currentThread().getName() + "卖出第" + index + "张票");
count--;
}
}
}
}
}
public class JavaSyncDemo {
public static void main(String[] args) {
SellTicketRunnable runnable = new SellTicketRunnable();
Thread sellThread1 = new Thread(runnable);
Thread sellThread2 = new Thread(runnable);
sellThread1.start();
sellThread2.start();
}
}
(2)使用同步函数
class SellTicketRunnable01 implements Runnable {
public int count = 100;
@Override
public void run() {
while (count > 0) {
try {
Thread.sleep(500);
} catch (InterruptedException e) {
e.printStackTrace();
}
this.sale();
}
}
synchronized void sale() {
if (count > 0) {
int index = 100 - count + 1;
System.out.println(Thread.currentThread().getName() + "卖出第" + index + "张票");
count--;
}
}
}
public class JavaSyncDemo01 {
public static void main(String[] args) {
SellTicketRunnable01 runnable = new SellTicketRunnable01();
Thread sellThread1 = new Thread(runnable);
Thread sellThread2 = new Thread(runnable);
sellThread1.start();
sellThread2.start();
}
}
class SellTicketRunnable02 implements Runnable {
public static int count = 100;
@Override
public void run() {
while (count > 0) {
try {
Thread.sleep(500);
} catch (InterruptedException e) {
e.printStackTrace();
}
SellTicketRunnable02.sale();
}
}
static void sale() {
synchronized (SellTicketRunnable02.class) {
if (count > 0) {
int index = 100 - count + 1;
System.out.println(Thread.currentThread().getName() + "卖出第" + index + "张票");
count--;
}
}
}
}
public class JavaSyncDemo02 {
public static void main(String[] args) {
SellTicketRunnable02 runnable = new SellTicketRunnable02();
Thread sellThread1 = new Thread(runnable);
Thread sellThread2 = new Thread(runnable);
sellThread1.start();
sellThread2.start();
}
}
(3)使用lock锁
class SellTicketRunnable03 implements Runnable {
public int count = 100;
private Lock lock = new ReentrantLock();
@Override
public void run() {
while (count > 0) {
try {
Thread.sleep(500);
} catch (InterruptedException e) {
e.printStackTrace();
}
lock.lock();
if (count > 0) {
int index = 100 - count + 1;
System.out.println(Thread.currentThread().getName() + "卖出第" + index + "张票");
count--;
}
lock.unlock();
}
}
}
public class JavaSyncDemo03 {
public static void main(String[] args) {
SellTicketRunnable03 runnable = new SellTicketRunnable03();
Thread sellThread1 = new Thread(runnable);
Thread sellThread2 = new Thread(runnable);
sellThread1.start();
sellThread2.start();
}
}
// lock锁的安全使用方法
class lockDemo {
Lock lock = new ReentrantLock();
void demoFun() {
lock.lock();
try {
// 可能出现线程安全的操作
} finally {
lock.unlock();
}
}
}
(4)使用Java原子类
class SellTicketRunnable04 implements Runnable {
public AtomicInteger count = new AtomicInteger(100);
@Override
public void run() {
while (true) {
try {
Thread.sleep(50);
} catch (InterruptedException e) {
e.printStackTrace();
}
if (count.get() > 0) {
int index = 100 - count.getAndDecrement() + 1;
System.out.println(Thread.currentThread().getName() + "卖出第" + index + "张票");
}
}
}
}
public class JavaSyncDemo04 {
public static void main(String[] args) {
SellTicketRunnable04 runnable = new SellTicketRunnable04();
Thread sellThread1 = new Thread(runnable);
Thread sellThread2 = new Thread(runnable);
sellThread1.start();
sellThread2.start();
}
}
3、死锁
public class DeadLockDemo01 {
private static Object lock1 = new Object();
private static Object lock2 = new Object();
public static void main(String[] args) {
new Thread() { //线程1
public void run() {
while (true) {
synchronized (lock1) {
System.out.println(this.getName() + ":获取lock1锁");
synchronized (lock2) {
System.out.println(this.getName() + ":获取lock2锁");
}
}
}
}
}.start();
new Thread() { //线程2
public void run() {
while (true) {
synchronized (lock2) {
System.out.println(this.getName() + ":获取lock2锁");
synchronized (lock1) {
System.out.println(this.getName() + "::获取lock1锁");
}
}
}
}
}.start();
}
}
源码地址