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Java編程之多線程死鎖與線程間通信簡單實(shí)現(xiàn)代碼

來源：本站原創(chuàng)|時(shí)間：2020-01-10|欄目：Java編程|點(diǎn)擊： 次

死鎖定義

死鎖是指兩個(gè)或者多個(gè)線程被永久阻塞的一種局面，產(chǎn)生的前提是要有兩個(gè)或兩個(gè)以上的線程，并且來操作兩個(gè)或者多個(gè)以上的共同資源；我的理解是用兩個(gè)線程來舉例，現(xiàn)有線程A和B同時(shí)操作兩個(gè)共同資源a和b，A操作a的時(shí)候上鎖LockA,繼續(xù)執(zhí)行的時(shí)候，A還需要LockB進(jìn)行下面的操作，這個(gè)時(shí)候b資源在被B線程操作，剛好被上了鎖LockB，假如此時(shí)線程B剛好釋放了LockB則沒有問題，但沒有釋放LockB鎖的時(shí)候，線程A和B形成了對LockB鎖資源的爭奪，從而造成阻塞，形成死鎖；具體其死鎖代碼如下：

public class MyDeadLockTest {
 public static void main(String[] args){
  Object obj1 = new Object();
  Thread thread1 = new Thread(new DeadRes(true,obj1));
  Thread thread2 = new Thread(new DeadRes(false,obj1));
  thread1.start();
  thread2.start();
 }
}
class DeadRes implements Runnable{
 boolean flag;
 Object obj;
 public DeadRes(boolean flag, Object obj1) {
  this.flag = flag;
  this.obj = obj1;
 }
 @Override
 public void run() {
   if(flag){
    synchronized (DeadRes.class){
     System.out.println(Thread.currentThread().getName()+" acquie lock is DeadRes.class");
     synchronized (obj){
      System.out.println(Thread.currentThread().getName()+" acquie lock is obj");
     }
    }
   }else{
    synchronized (obj){
     System.out.println(Thread.currentThread().getName()+" acquie lock is obj");
     synchronized (DeadRes.class){
      System.out.println(Thread.currentThread().getName()+" acquie lock is DeadRes.class");
     }
    }
   }
 }
}

執(zhí)行結(jié)果如下圖：

Thread-1 acquie lock is obj
Thread-0 acquie lock is DeadRes.class

當(dāng)然每次執(zhí)行的結(jié)果不一樣，有可能是一種和諧狀態(tài)，沒有發(fā)生死鎖，此時(shí)為保證每次死鎖，可以讓run()方法中，執(zhí)行while(true)循環(huán)，這樣保證了每次必定發(fā)生死鎖；當(dāng)然實(shí)際應(yīng)用中，我們應(yīng)該盡量避免死鎖，當(dāng)有多線程操作多個(gè)共同資源的時(shí)候，避免發(fā)生同一鎖對象的同步嵌套。

線程間的通訊—-生產(chǎn)者與消費(fèi)者模式

1、讓兩個(gè)線程交替進(jìn)行操作，當(dāng)生產(chǎn)了一個(gè)數(shù)字后，緊接著消費(fèi)一個(gè)，首先采用Object對象中的wait-notify來實(shí)現(xiàn)，具體代碼如下:

public class ThreadProConsume {
 public static void main(String[] args){
  Product product = new Product();
  Thread thread1 = new Thread(new Producer(product));
  Thread thread2 = new Thread(new Consumer(product));
  thread1.start();
  thread2.start();
 }
}
class Product{
 String name;
 private int count = 1;
 boolean flag = false;
 public synchronized void set(String name){
  if(flag){
   try {
    this.wait();
   } catch (InterruptedException e) {
    e.printStackTrace();
   }
  }
  this.name = name +"--"+count++;
  flag = true;
  System.out.println(Thread.currentThread().getName()+" produce num : "+this.name);
  this.notify();
 }
 public synchronized void out(){
  if(!flag){
   try {
    this.wait();
   } catch (InterruptedException e) {
    e.printStackTrace();
   }
  }
  System.out.println(Thread.currentThread().getName()+" consume num is : "+this.name);
  flag = false;
  this.notify();
 }
}
class Producer implements Runnable{
 Product res;
 public Producer(Product product) {
  this.res = product;
 }
 @Override
 public void run() {
  while(true){
   res.set("guyue");
  }
 }
}
class Consumer implements Runnable{
 Product res;
 public Consumer(Product product) {
  this.res = product;
 }
 @Override
 public void run() {
  while(true){
   res.out();
  }
 }
}

執(zhí)行結(jié)果如圖：

Thread-1 consume num is : guyue--3938
Thread-0 produce num : guyue--3939
Thread-1 consume num is : guyue--3939
Thread-0 produce num : guyue--3940
Thread-1 consume num is : guyue--3940
Thread-0 produce num : guyue--3941
Thread-1 consume num is : guyue--3941

當(dāng)超過兩個(gè)以上線程操作的時(shí)候，這里需要在set()與out()方法中的if判斷改為while，并且notif方法，改為notifyAll()，這樣多個(gè)線程操作的時(shí)候，便可以交替進(jìn)行，具體代碼如下：

public class ThreadProConsume {
 public static void main(String[] args){
  Product product = new Product();
  Thread thread1 = new Thread(new Producer(product));
  Thread thread3 = new Thread(new Producer(product));
  Thread thread2 = new Thread(new Consumer(product));
  Thread thread4 = new Thread(new Consumer(product));
  thread1.start();
  thread3.start();
  thread2.start();
  thread4.start();
 }
}
class Product{
 String name;
 private int count = 1;
 boolean flag = false;
 public synchronized void set(String name){
  while(flag){
   try {
    this.wait();
   } catch (InterruptedException e) {
    e.printStackTrace();
   }
  }
  this.name = name +"--"+count++;
  flag = true;
  System.out.println(Thread.currentThread().getName()+" produce num : "+this.name);
  this.notifyAll();
 }
 public synchronized void out(){
  while (!flag){
   try {
    this.wait();
   } catch (InterruptedException e) {
    e.printStackTrace();
   }
  }
  System.out.println(Thread.currentThread().getName()+" consume num is : "+this.name);
  flag = false;
  this.notifyAll();
 }
}

執(zhí)行結(jié)果如下：

Thread-0 produce num : guyue--50325
Thread-2 consume num is : guyue--50325
Thread-1 produce num : guyue--50326
Thread-3 consume num is : guyue--50326
Thread-0 produce num : guyue--50327
Thread-2 consume num is : guyue--50327
Thread-1 produce num : guyue--50328
Thread-3 consume num is : guyue--50328

2、采用Lock-Condition方法實(shí)現(xiàn)如下：

class Product{
 String name;
 private int count = 1;
 boolean flag = false;
 Lock lock = new ReentrantLock();
 Condition conditon = lock.newCondition();
 public void set(String name){
  try{
   lock.lock();
   while(flag){
    conditon.await();
   }
   this.name = name +"--"+count++;
   flag = true;
   System.out.println(Thread.currentThread().getName()+" produce num : "+this.name);
   conditon.signalAll();
  }catch (Exception e){
  }finally {
   lock.unlock();
  }
 }
 public void out(){
  try{
   lock.lock();
   while(!flag){
    conditon.await();
   }
   flag = false;
   System.out.println(Thread.currentThread().getName()+" consumer num is : "+this.name);
   conditon.signalAll();
  }catch (Exception e){
  }finally {
   lock.unlock();
  }
 }
}

執(zhí)行結(jié)果如下：

Thread-0 produce num : guyue--20305
Thread-3 consumer num is : guyue--20305
Thread-1 produce num : guyue--20306
Thread-2 consumer num is : guyue--20306
Thread-0 produce num : guyue--20307
Thread-3 consumer num is : guyue--20307
Thread-1 produce num : guyue--20308
Thread-2 consumer num is : guyue--20308

以上就是本文關(guān)于Java編程之多線程死鎖與線程間通信簡單實(shí)現(xiàn)代碼的全部內(nèi)容，希望對大家有所幫助。關(guān)于Java多線程以及線程間通信的例子，本站還有幾篇文章可以參考：

詳解java中的互斥鎖信號量和多線程等待機(jī)制、Java多線程編程小實(shí)例模擬停車場系統(tǒng)、Java網(wǎng)絡(luò)編程基礎(chǔ)篇之單向通信

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