Java启动新线程的额外开销

在启动一个新线程的时候会有一定时间的额外开销，因此并不是所有情况下都应使用多线程。如下的代码段进行简单实验探讨：

//TimeCostToStartNewThread.java

public class TimeCostToStartNewThread{

public static void main(String[] args){
long now1 = System.nanoTime();
for(int i = 0; i < 10000000; i++){// i依次取值100,1000,10000,100000,1000000,10000000

}
long current1 = System.nanoTime();
System.out.println("current - now 1 = " + (current1 - now1));
long now2 = System.nanoTime();
new Thread(new Runnable(){
public void run(){
for(int i = 0; i < 10000000; i++){

}
}
}).start();
long current2 = System.nanoTime();
System.out.println( "current - now 2 = " + (current2 - now2));
}
}

D:\CodingLearning\Java多线程设计>javac TimeCostToStartNewThread.java

D:\CodingLearning\Java多线程设计>java TimeCostToStartNewThread

current - now 1 = 906

current - now 2 = 427110

D:\CodingLearning\Java多线程设计>javac TimeCostToStartNewThread.java

D:\CodingLearning\Java多线程设计>java TimeCostToStartNewThread

current - now 1 = 4527

current - now 2 = 435864

D:\CodingLearning\Java多线程设计>javac TimeCostToStartNewThread.java

D:\CodingLearning\Java多线程设计>java TimeCostToStartNewThread

current - now 1 = 45277

current - now 2 = 394511

D:\CodingLearning\Java多线程设计>javac TimeCostToStartNewThread.java

D:\CodingLearning\Java多线程设计>java TimeCostToStartNewThread

current - now 1 = 419263

current - now 2 = 456993

D:\CodingLearning\Java多线程设计>javac TimeCostToStartNewThread.java

D:\CodingLearning\Java多线程设计>java TimeCostToStartNewThread

current - now 1 = 683679

current - now 2 = 429525

D:\CodingLearning\Java多线程设计>javac TimeCostToStartNewThread.java

D:\CodingLearning\Java多线程设计>java TimeCostToStartNewThread

current - now 1 = 3157601

current - now 2 = 447938

D:\CodingLearning\Java多线程设计>

从上面的结果上我们可以得知启动一个新线程的额外开销大约在4*(10的6次方)纳秒的时间，当使用顺序编程的开销时间大于这个值时，我们可以考虑使用多线程。