主要是针对 synchronized 。
加锁对象是谁
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| package com.redisc;
import lombok.extern.slf4j.Slf4j;
@Slf4j(topic = "c.Test")
public class Test {
public static void main(String[] args) throws InterruptedException {
Room room = new Room();
Thread t1 = new Thread(() -> {
for (int i = 0; i < 5000; i++) {
room.decrement();
}
});
Thread t2 = new Thread(() -> {
for (int i = 0; i < 5000; i++) {
room.increment();
}
});
t1.start();
t2.start();
t1.join();
t2.join();
log.debug("{}", room.getCounter());
}
}
class Room {
private int counter = 0;
public synchronized void increment() {
counter++;
}
public synchronized void decrement() {
counter--;
}
public synchronized int getCounter() {
return this.counter;
}
}
|
加锁对象是 Room 的 this。
可以 1 优先吗
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| package com.redisc;
import lombok.extern.slf4j.Slf4j;
import java.util.concurrent.TimeUnit;
@Slf4j(topic = "c.Test")
public class Test {
public static void main(String[] args) throws InterruptedException {
Room room = new Room();
Thread t1 = new Thread(room::decrement);
Thread t2 = new Thread(() -> {
try {
room.increment();
} catch (InterruptedException e) {
e.printStackTrace();
}
});
t1.start();
t2.start();
t1.join();
t2.join();
log.debug("{}", room.getCounter());
}
}
@Slf4j(topic = "c.Room")
class Room {
private int counter = 0;
public synchronized void increment() throws InterruptedException {
TimeUnit.SECONDS.sleep(1);
counter++;
log.debug("1");
}
public synchronized void decrement() {
counter--;
log.debug("2");
}
public synchronized int getCounter() {
return this.counter;
}
}
|
答案有机会出现 1 先于 2 的情况。因为，虽然，1 中有 sleep ，但是，cpu 给两个线程谁先上锁是随机的。
c 方法有互斥吗
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| package com.redisc;
import lombok.extern.slf4j.Slf4j;
import java.util.concurrent.TimeUnit;
@Slf4j(topic = "c.Test")
public class Test {
public static void main(String[] args) throws InterruptedException {
Room room = new Room();
Thread t1 = new Thread(()->{
try {
room.a();
} catch (InterruptedException e) {
e.printStackTrace();
}
});
Thread t2 = new Thread(()->{
room.b();
});
Thread t3 = new Thread(()->{
room.c();
});
t1.start();
t2.start();
t3.start();
}
}
@Slf4j(topic = "c.Room")
class Room {
public synchronized void a() throws InterruptedException {
TimeUnit.SECONDS.sleep(1);
log.debug("1");
}
public synchronized void b() {
log.debug("2");
}
public void c() {
log.debug("3");
}
}
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c 没有互斥效果。
room1 和 room2 互斥吗
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| package com.redisc;
import lombok.extern.slf4j.Slf4j;
import java.util.concurrent.TimeUnit;
@Slf4j(topic = "c.Test")
public class Test {
public static void main(String[] args) throws InterruptedException {
Room room1 = new Room();
Room room2 = new Room();
Thread t2 = new Thread(() -> {
room1.b();
});
Thread t3 = new Thread(() -> {
room2.c();
});
t2.start();
t3.start();
}
}
@Slf4j(topic = "c.Room")
class Room {
public synchronized void b() {
log.debug("2");
}
public synchronized void c() {
log.debug("3");
}
}
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不互斥，分属于两个对象。
后面的题目都很简单，只要把 java | synchronized 对象锁 看懂就好了。
