OutOfMemoryError: unable to create new native thread

这个错误是由于创建了太多的线程导致的。创建线程的数量可以由下面公式计算出来：

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

MaxProcessMemory：进程最大寻址空间。
JVMMMEMORY：jvm的内存空间（堆+永久区）-Xmx大小 (应该是实际分配大小)
ReservedOsMemory：操作系统预留内存
ThreadStackSize：-Xss大小

计算过程请参考：https://segmentfault.com/a/1190000004694232

重现该异常如下，

import java.util.concurrent.CountDownLatch;

class TestThread extends Thread {


    CountDownLatch count = new CountDownLatch(1);

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

    /**
     * 线程一直等待
     */
    @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();
        }
    }
}

运行结果：

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）参数的作用

－－－the stack size for each thread

JDK5.0以后每个线程堆栈大小为1M,以前每个线程堆栈大小为256K。在相同物理内存下，减小这个值能生成更多的线程。但是操作系统对一个进程内的线程数还是有限制的，不能无限生成。

使用不同的Xss参数来运行下面这个程序，

public class XssDemo {

    private static int count = 0;

    public static void recursion() {
        //减少局部变量的声明，可以节省栈帧大小，增加调用深度
        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();
        }
    }
}

运行如下，

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

当线程栈设置的较大时，栈的深度会比较大。

-Xmx -Xms -Xss对线程创建数量的影响

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

-Xms

intial java heap size

-Xmx

maximum java heap size

-Xss

the stack size for each thread

===========END===========

来源：oschina

链接：https://my.oschina.net/u/1469576/blog/744462

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countdownlatch