JVM内存模型

场景：一个进程中有多个进程，其中一个线程down 或者OOM  其它线程是否还能正常工作？

下面我们来看下JVM 的内存模型：

代码测试：

public static void main(String[] args) {
    ThreadGroup group = new ThreadGroup("test");
    new Thread(group, () -> {
        List<byte[]> list = new ArrayList<>();
        while (true) {
            System.out.println(new Date().toString() + Thread.currentThread().getName());
            byte[] b = new byte[1024 * 1024 * 1];
            list.add(b);
            try {
                Thread.sleep(1000);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }).start();
    new Thread(group, () -> {
        while (true) {
            System.out.println(new Date().toString() + Thread.currentThread().getName());
            try {
                Thread.sleep(1000);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }).start();

}

IDEA  vm 参数设置：-Xms10m   -Xmx10m 

运行后发现一个线程OOM 后另一个线程还可以继续执行

跟踪Thrad 的源码：

public Thread(ThreadGroup group, Runnable target) {
    init(group, target, "Thread-" + nextThreadNum(), 0);
}

进一步跟踪

private void init(ThreadGroup g, Runnable target, String name,
                  long stackSize) {
    init(g, target, name, stackSize, null, true);
}

private void init(ThreadGroup g, Runnable target, String name,
                  long stackSize, AccessControlContext acc,
                  boolean inheritThreadLocals) {
    if (name == null) {
        throw new NullPointerException("name cannot be null");
    }

    this.name = name;

    Thread parent = currentThread();    //关键
    SecurityManager security = System.getSecurityManager();
    if (g == null) {
        /* Determine if it's an applet or not */

        /* If there is a security manager, ask the security manager
           what to do. */
        if (security != null) {
            g = security.getThreadGroup();
        }

        /* If the security doesn't have a strong opinion of the matter
           use the parent thread group. */
        if (g == null) {
            g = parent.getThreadGroup();
        }
    }

    /* checkAccess regardless of whether or not threadgroup is
       explicitly passed in. */
    g.checkAccess();

    /*
     * Do we have the required permissions?
     */
    if (security != null) {
        if (isCCLOverridden(getClass())) {
            security.checkPermission(SUBCLASS_IMPLEMENTATION_PERMISSION);
        }
    }

    g.addUnstarted();

    this.group = g;
    this.daemon = parent.isDaemon();
    this.priority = parent.getPriority();
    if (security == null || isCCLOverridden(parent.getClass()))
        this.contextClassLoader = parent.getContextClassLoader();
    else
        this.contextClassLoader = parent.contextClassLoader;
    this.inheritedAccessControlContext =
            acc != null ? acc : AccessController.getContext();
    this.target = target;
    setPriority(priority);
    if (inheritThreadLocals && parent.inheritableThreadLocals != null)
        this.inheritableThreadLocals =
            ThreadLocal.createInheritedMap(parent.inheritableThreadLocals);
    /* Stash the specified stack size in case the VM cares */
    this.stackSize = stackSize;

    /* Set thread ID */
    tid = nextThreadID();
}
在进入 currentThread() 方法

/**
 * Returns a reference to the currently executing thread object.
 *
 * @return  the currently executing thread.
 */
public static native Thread currentThread();

结论： new Thread () 底层其实是new 一个 native Thread  由上面的 java 内存图 可知 native 方法属于线程私有 所有

一个进程中的某个线程 down 其它线程仍然能继续执行