本文主要總結線程共享數(shù)據(jù)的相關知識,主要包括兩方面:一是某個線程內(nèi)如何共享數(shù)據(jù),保證各個線程的數(shù)據(jù)不交叉;一是多個線程間如何共享數(shù)據(jù),保證數(shù)據(jù)的一致性。
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自己實現(xiàn)的話,是定義一個Map,線程為鍵,數(shù)據(jù)為值,表中的每一項即是為每個線程準備的數(shù)據(jù),這樣在一個線程中數(shù)據(jù)是一致的。
例子
package com.iot.thread; import java.util.HashMap; import java.util.Map; import java.util.Random; /** * Created by brian on 2016/2/4. */ public class ThreadScopeShareData { //準備一個哈希表,為每個線程準備數(shù)據(jù) private static Map<Thread,Integer> threadData = new HashMap<>(); public static void main(String[] args) { for (int i=0;i<2;i++){ new Thread( new Runnable() { @Override public void run() { int data = new Random().nextint(); threadData.put(Thread.currentThread(),data); System.out.println(Thread.currentThread()+" put data:"+data); new A().get(); new B().get(); } } ).start(); } } static class A{ public void get(){ int data = threadData.get(Thread.currentThread()); System.out.println("A from "+Thread.currentThread()+" get data "+data); } } static class B{ public void get(){ int data = threadData.get(Thread.currentThread()); System.out.println("B from "+Thread.currentThread()+" get data "+data); } } }
上述代碼偶爾會報異常:
Exception in thread "Thread-0" java.lang.NullPointerException
at com.iot.thread.ThreadScopeShareData$A.get(ThreadScopeShareData.java:29)
at com.iot.thread.ThreadScopeShareData$1.run(ThreadScopeShareData.java:21)
at java.lang.Thread.run(Thread.java:745)
具體原因還不知道
API:
java.lang:Class ThreadLocal<T>
使用ThreadLocal類型的對象代替上面的Map即可
定義一個對象來封裝多個變量,然后在ThreadLocal中存儲整個對象
多變量時,最好將ThreadLocal類放在數(shù)據(jù)類的內(nèi)部,數(shù)據(jù)類采用單例模式,這樣,新建對象和獲取對象都會更方便,同時封裝性更強。
package com.iot.thread; import java.util.Random; /** * Created by brian on 2016/2/4. */ public class ThreadLocalTest { private static ThreadLocal<Integer> threadInger = new ThreadLocal<>(); public static void main(String[] args) { for (int i=0;i<2;i++){ new Thread(new Runnable() { @Override public void run() { int data = new Random().nextint(100); threadInger.set(data); System.out.println(Thread.currentThread()+" put data:"+data); MyThreadScopeData.getThreadInstance().setName(Thread.currentThread().toString()); MyThreadScopeData.getThreadInstance().setAge(data%10); new A().get(); new B().get(); } } ).start(); } } static class A{ public void get(){ int data = threadInger.get(); System.out.println("A from "+Thread.currentThread()+" get data "+data); MyThreadScopeData myThreadScopeData = MyThreadScopeData.getThreadInstance(); System.out.println("A from "+myThreadScopeData); } } static class B{ public void get(){ int data = threadInger.get(); System.out.println("B from "+Thread.currentThread()+" get data "+data); MyThreadScopeData myThreadScopeData = MyThreadScopeData.getThreadInstance(); System.out.println("B from "+myThreadScopeData); } } } /** * 將多變量封裝起來的數(shù)據(jù)類 * 單例模式,內(nèi)置ThreadLocal類型變量 */ class MyThreadScopeData{ private MyThreadScopeData(){ } private static ThreadLocal<MyThreadScopeData> data = new ThreadLocal<>(); public static MyThreadScopeData getThreadInstance(){ MyThreadScopeData instance = data.get(); if(instance == null){ instance = new MyThreadScopeData(); data.set(instance); } return instance; } private String name; private int age; public String getName() { return name; } public void setName(String name) { this.name = name; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } @Override public String toString() { String reVal = super.toString()+"-{name,age}"+":{"+getName()+","+getAge()+"}"; return reVal; } }
幾種方式
最后一種方式的示例:
設計5個線程,其中三個線程每次對j增加1,另外兩個線程對j每次減少1
package com.iot.thread; /** * Created by brian on 2016/2/4. */ public class MutiThreadShareData { private static MutiShareData mutiShareData = new MutiShareData(); public static void main(String[] args) { for (int i=0;i<3;i++){ new Thread( new Runnable() { @Override public void run() { System.out.println(Thread.currentThread()+":{j from "+ mutiShareData.getJ()+" + to: "+mutiShareData.increment()+"}"); } } ).start(); } for (int i=0;i<2;i++){ new Thread( new Runnable() { @Override public void run() { System.out.println(Thread.currentThread()+":{j from "+ mutiShareData.getJ()+" - to: "+mutiShareData.decrement()+"}"); } } ).start(); } } } /** * 將共享數(shù)據(jù)封裝在另一對象中(操作數(shù)據(jù)的方法也在該對象完成) */ class MutiShareData{ private int j = 0; public synchronized int increment(){ return ++j; } public synchronized int decrement(){ return --j; } public synchronized int getJ() { return j; } public synchronized void setJ(int j) { this.j = j; } }
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