死鎖定義
死鎖是指兩個或者多個線程被永久阻塞的一種局面，產生的前提是要有兩個或兩個以上的線程，并且來操作兩個或者多個以上的共同資源；我的理解是用兩個線程來舉例，現有線程A和B同時操作兩個共同資源a和b，A操作a的時候上鎖LockA,繼續執行的時候，A還需要LockB進行下面的操作，這個時候b資源在被B線程操作，剛好被上了鎖LockB，假如此時線程B剛好釋放了LockB則沒有問題，但沒有釋放LockB鎖的時候，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：
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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"); } } } }} |
執行結果如下圖：
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Thread-1 acquie lock is objThread-0 acquie lock is DeadRes.class |
當然每次執行的結果不一樣，有可能是一種和諧狀態，沒有發生死鎖，此時為保證每次死鎖，可以讓run()方法中，執行while(true)循環，這樣保證了每次必定發生死鎖；當然實際應用中，我們應該盡量避免死鎖，當有多線程操作多個共同資源的時候，避免發生同一鎖對象的同步嵌套。
線程間的通訊—-生產者與消費者模式
1、讓兩個線程交替進行操作，當生產了一個數字后，緊接著消費一個，首先采用Object對象中的wait-notify來實現，具體代碼如下:
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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(); } }} |
執行結果如圖：
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Thread-1 consume num is : guyue--3938Thread-0 produce num : guyue--3939Thread-1 consume num is : guyue--3939Thread-0 produce num : guyue--3940Thread-1 consume num is : guyue--3940Thread-0 produce num : guyue--3941Thread-1 consume num is : guyue--3941 |
當超過兩個以上線程操作的時候，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()，這樣多個線程操作的時候，便可以交替進行，具體代碼如下：
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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(); }} |
執行結果如下：
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Thread-0 produce num : guyue--50325Thread-2 consume num is : guyue--50325Thread-1 produce num : guyue--50326Thread-3 consume num is : guyue--50326Thread-0 produce num : guyue--50327Thread-2 consume num is : guyue--50327Thread-1 produce num : guyue--50328Thread-3 consume num is : guyue--50328 |
2、采用Lock-Condition方法實現如下：
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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(); } }} |
執行結果如下：
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Thread-0 produce num : guyue--20305Thread-3 consumer num is : guyue--20305Thread-1 produce num : guyue--20306Thread-2 consumer num is : guyue--20306Thread-0 produce num : guyue--20307Thread-3 consumer num is : guyue--20307Thread-1 produce num : guyue--20308Thread-2 consumer num is : guyue--20308 |
以上就是本文關于Java編程之多線程死鎖與線程間通信簡單實現代碼的全部內容，希望對大家有所幫助。關于Java多線程以及線程間通信的例子，如有不足之處，歡迎留言指出。感謝朋友們對本站的支持！
原文鏈接：http://blog.csdn.net/yongxihu/article/details/70277372
