1. 線程間的通信
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線程間通信
- 生產(chǎn)者+消費(fèi)者
- 通知等待喚醒機(jī)制
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多線程編程模板
- 判斷 干活 通知
- 判斷需使用while碍遍，以防止中斷和虛假喚醒(見java.lang.Object的API)
A thread can also wake up without being notified, interrupted, or timing out, a so-called spurious wakeup. While this will rarely occur in practice, applications must guard against it by testing for the condition that should have caused the thread to be awakened, and continuing to wait if the condition is not satisfied. In other words, waits should always occur in loops, like this one
synchronized (obj) { while (<condition does not hold>) obj.wait(timeout); ... // Perform action appropriate to condition }線程也可以在沒有通知耸彪、中斷或超時(shí)的情況下被喚醒撑螺，這就是所謂的假喚醒瓦宜。雖然這種情況在實(shí)踐中很少發(fā)生躯舔，但應(yīng)用程序必須通過測(cè)試導(dǎo)致線程被喚醒的條件來防止這種情況發(fā)生亡电，如果條件不滿足疚顷，則繼續(xù)等待髓迎。換句話說峦朗，等待應(yīng)該總是出現(xiàn)在循環(huán)中，就像這個(gè)循環(huán)一樣
1.1 synchronized版
-
synchronized實(shí)現(xiàn)
- 先2個(gè)線程操作資源類排龄，資源中的操作判斷使用if波势，如線程A和線程B，可以正常運(yùn)行1 0 1 0 1 0...
- 增加2個(gè)線程C和D，模擬虛假喚醒尺铣，判斷依舊是if拴曲，運(yùn)行的結(jié)果數(shù)字不是全部為1、0
- 原因：在java多線程判斷時(shí)凛忿，不能用if澈灼，程序出事出在了判斷上面，突然有一添加的線程進(jìn)到if了侄非，突然中斷了交出控制權(quán)蕉汪，沒有進(jìn)行驗(yàn)證，而是直接走下去了逞怨，加了兩次者疤，甚至多次
- 在4線程中，將資源類的if判斷改為while判斷叠赦，while是只要喚醒就要拉回來再判斷一次
package juc.demo; import java.util.concurrent.locks.Condition; import java.util.concurrent.locks.Lock; import java.util.concurrent.locks.ReentrantLock; /** * @Description: * 現(xiàn)在兩個(gè)線程驹马， * 可以操作初始值為零的一個(gè)變量， * 實(shí)現(xiàn)一個(gè)線程對(duì)該變量加1除秀，一個(gè)線程對(duì)該變量減1糯累， * 交替，來10輪册踩。 * @Package: juc.demo * @ClassName NotifyWaitDemo * @author: wuwb * @date: 2020/10/19 13:30 */ public class NotifyWaitDemo { public static void main(String[] args) { int turn = 1000; //資源類 ShareData data = new ShareData(); new Thread(() -> { for (int i = 0; i < turn; i++) { try { data.increment(); } catch (Exception e) { e.printStackTrace(); } } }, "A").start(); new Thread(() -> { for (int i = 0; i < turn; i++) { try { data.decrement(); } catch (Exception e) { e.printStackTrace(); } } }, "B").start(); new Thread(() -> { for (int i = 0; i < turn; i++) { try { data.increment(); } catch (Exception e) { e.printStackTrace(); } } }, "C").start(); new Thread(() -> { for (int i = 0; i < turn; i++) { try { data.decrement(); } catch (Exception e) { e.printStackTrace(); } } }, "D").start(); } } //資源類 class ShareData{ private int number = 0; public synchronized void increment() throws InterruptedException { //判斷 if換while while (number != 0) { this.wait(); } //干活 number++; System.out.println(Thread.currentThread().getName() + ":" + number); //通知 this.notifyAll(); } public synchronized void decrement() throws InterruptedException { while (number == 0) { this.wait(); } number--; System.out.println(Thread.currentThread().getName() + ":" + number); this.notifyAll(); } }
1.2 JUC版
1608004387960.png
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Lock 及 Condition
package juc.demo; import java.util.concurrent.locks.Condition; import java.util.concurrent.locks.Lock; import java.util.concurrent.locks.ReentrantLock; /** * @Description: * 現(xiàn)在兩個(gè)線程泳姐， * 可以操作初始值為零的一個(gè)變量， * 實(shí)現(xiàn)一個(gè)線程對(duì)該變量加1暂吉，一個(gè)線程對(duì)該變量減1胖秒， * 交替，來10輪慕的。 * @Package: juc.demo * @ClassName NotifyWaitDemo * @author: wuwb * @date: 2020/10/19 13:30 */ public class NotifyWaitDemo { public static void main(String[] args) { int turn = 1000; //資源類 ShareData data = new ShareData(); new Thread(() -> { for (int i = 0; i < turn; i++) { try { data.increment(); } catch (Exception e) { e.printStackTrace(); } } }, "A").start(); new Thread(() -> { for (int i = 0; i < turn; i++) { try { data.decrement(); } catch (Exception e) { e.printStackTrace(); } } }, "B").start(); new Thread(() -> { for (int i = 0; i < turn; i++) { try { data.increment(); } catch (Exception e) { e.printStackTrace(); } } }, "C").start(); new Thread(() -> { for (int i = 0; i < turn; i++) { try { data.decrement(); } catch (Exception e) { e.printStackTrace(); } } }, "D").start(); } } //資源類 class ShareData{ private int number = 0; private Lock lock = new ReentrantLock(); private Condition condition = lock.newCondition(); public void increment() { lock.lock(); try { //判斷 while (number != 0) { condition.await();//this.wait(); } //干活 number++; System.out.println(Thread.currentThread().getName() + ":" + number); //通知 condition.signalAll();//this.notifyAll(); } catch (Exception e) { e.printStackTrace(); } finally { lock.unlock(); } } public void decrement() { lock.lock(); try { while (number == 0) { condition.await(); } number--; System.out.println(Thread.currentThread().getName() + ":" + number); condition.signalAll(); } catch (Exception e) { e.printStackTrace(); } finally { lock.unlock(); } } }
1.3 定制化調(diào)用通信
- 使用Lock阎肝、Condition指定調(diào)用順序，指定喚醒哪個(gè)線程
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/**
* @Description
* 多線程之間按順序調(diào)用肮街，實(shí)現(xiàn)A->B->C
* ......來10輪
*/
public class ThreadOrderAccess {
public static void main(String[] args) {
ShareResource resource = new ShareResource();
new Thread(() -> {
for (int i = 0; i < 10; i++) {
resource.printA();
}
}, "A").start();
new Thread(() -> {
for (int i = 0; i < 10; i++) {
resource.printB();
}
}, "B").start();
new Thread(() -> {
for (int i = 0; i < 10; i++) {
resource.printC();
}
}, "C").start();
}
}
class ShareResource{
/**標(biāo)志位*/
private int number = 1;
private Lock lock = new ReentrantLock();
/**3把鑰匙*/
private Condition condition1 = lock.newCondition();
private Condition condition2 = lock.newCondition();
private Condition condition3 = lock.newCondition();
public void printA() {
lock.lock();
try {
while (number != 1) {
condition1.await();
}
System.out.println(Thread.currentThread().getName()+"==>AAAAAAAAAA");
number = 2;
condition2.signal();
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
public void printB() {
lock.lock();
try {
while (number != 2) {
condition2.await();
}
System.out.println(Thread.currentThread().getName()+"==>BBBBBBBBBB");
number = 3;
condition3.signal();
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
public void printC() {
lock.lock();
try {
while (number != 3) {
condition3.await();
}
System.out.println(Thread.currentThread().getName()+"==>CCCCCCCCCC");
number = 1;
condition1.signal();
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
}
