OutOfMemoryError: unable to create new native thread

OutOfMemoryError: unable to create new native thread

這個錯誤是因爲建立了太多的線程致使的。建立線程的數量能夠由下面公式計算出來：

(MaxProcessMemory - JVMMemory - ReservedOsMemory) / (ThreadStackSize) = Number of threads 

MaxProcessMemory：進程最大尋址空間。
JVMMMEMORY：jvm的內存空間（堆+永久區）-Xmx大小 (應該是實際分配大小)
ReservedOsMemory：操做系統預留內存
ThreadStackSize：-Xss大小

計算過程請參考：http://www.javashuo.com/article/p-wrvfheip-hc.html

重現該異常以下，

import java.util.concurrent.CountDownLatch;

class TestThread extends Thread {


    CountDownLatch count = new CountDownLatch(1);

    public TestThread() {
        this.setDaemon(true);
    }

    /**
     * 線程一直等待
     */
    @Override
    public void run() {
        try {
            count.await();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

    }
}

public class XssTest {
    public static void main(String args[]) {

        for (int i = 0; ; i++) {
            System.out.println("i = " + i);
            new Thread(new TestThread()).start();
        }
    }
}

運行結果：

i = 2027
Exception in thread "main" java.lang.OutOfMemoryError: unable to create new native thread
	at java.lang.Thread.start0(Native Method)
	at java.lang.Thread.start(Thread.java:714)
	at XssTest.main(XssTest.java:37)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:497)
	at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)

-Xss（ThreadStackSize）參數的做用

－－－the stack size for each thread

JDK5.0之後每一個線程堆棧大小爲1M,之前每一個線程堆棧大小爲256K。在相同物理內存下，減少這個值能生成更多的線程。可是操做系統對一個進程內的線程數仍是有限制的，不能無限生成。

使用不一樣的Xss參數來運行下面這個程序，

public class XssDemo {

    private static int count = 0;

    public static void recursion() {
        //減小局部變量的聲明，能夠節省棧幀大小，增長調用深度
        long a = 1, b = 2, c = 3, d = 4, e = 5, f = 6, q = 7, x = 8, y = 9, z = 10;
        count++;
        recursion();
    }

    public static void main(String args[]) {
        try {
            recursion();
        } catch (Throwable e) {
            System.out.println("deep of calling = " + count);
//            e.printStackTrace();
        }
    }
}

運行以下，

➜  helloworld java -Xmx128m -Xms128m -Xss1024k XssDemo
deep of calling = 12401
➜  helloworld java -Xmx128m -Xms128m -Xss512k XssDemo
deep of calling = 3524

當線程棧設置的較大時，棧的深度會比較大。

-Xmx -Xms -Xss對線程建立數量的影響

參見http://jzhihui.iteye.com/blog/1271122

-Xms

intial java heap size

-Xmx

maximum java heap size

-Xss

the stack size for each thread

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