多线程07：《疯狂Java讲义》学习笔记——线程组和未处理的异常

注：此文为学习《疯狂Java讲义》的笔记，因此内容全部来自于该书中。

1.线程组

        ThreadGroup表示线程组，可以对一批线程进行分类管理。对线程组的控制相当于同时控制这批线程。用户创建的所有现场都属于指定线程组，如果没有指定，则线程数与默认线程组。默认情况下，子线程和创建它的父线程属于同一个线程组。线程运行中途不能改变它所属的线程组。

        一旦某个线程加入了指定线程组之后，该线程将一直属于该线程组，直到该线程死亡，线程运行中不能改变它所属的线程组。

        Thread类中相关构造方法。

Thread(ThreadGroup group, Runnable target)

Allocates a new Thread object.

Thread(ThreadGroup group, Runnable target, String name)

Allocates a new Thread object so that it has target as its run object, has the specified name as its name, and belongs to the thread group referred to by group.

Thread(ThreadGroup group, Runnable target, String name, long stackSize)

Allocates a new Thread object so that it has target as its run object, has the specified name as its name, and belongs to the thread group referred to by group, and has the specified stack size.

Thread(ThreadGroup group, String name)

Allocates a new Thread object.

        ThreadGroup类的构造方法。

Constructor and Description

ThreadGroup(String name)

Constructs a new thread group.

ThreadGroup(ThreadGroup parent, String name)

Creates a new thread group.

        ThreadGroup方法。

Modifier and Type

Method and Description

int

activeCount()

Returns an estimate of the number of active threads in this thread group and its subgroups.

int

activeGroupCount()

Returns an estimate of the number of active groups in this thread group and its subgroups.

int

getMaxPriority()

Returns the maximum priority of this thread group.

void

interrupt()

Interrupts all threads in this thread group.

boolean

isDaemon()

Tests if this thread group is a daemon thread group.

boolean

isDestroyed()

Tests if this thread group has been destroyed.

void

setDaemon(boolean daemon)

Changes the daemon status of this thread group.

void

setMaxPriority(int pri)

Sets the maximum priority of the group.

void

uncaughtException(Thread t, Throwable e)

Called by the Java Virtual Machine when a thread in this thread group stops because of an uncaught exception, and the thread does not have a specific Thread.UncaughtExceptionHandler installed.

 

2.未处理的异常

        如果线程执行过程中抛出了一个未处理异常，JVM在结束该线程之前自动查找是否有对应的UncaughtExceptionHandler对象，如果找到该处理器对象，调用该对象的uncaughtException(Thread t,Throwable e)方法处理异常。

        Thread.UncaughtExceptionHandler是Thread类一个内部接口，只有一个方法，即voiduncaughtException()。

        Thread类中设置异常处理器的方法如下。

Modifier and Type

Method and Description

static void

setDefaultUncaughtExceptionHandler(Thread.UncaughtExceptionHandler eh)

Set the default handler invoked when a thread abruptly terminates due to an uncaught exception, and no other handler has been defined for that thread.

void

setUncaughtExceptionHandler(Thread.UncaughtExceptionHandler eh)

Set the handler invoked when this thread abruptly terminates due to an uncaught exception.

 

        ThreadGroup实现了Thread.UncaughtExceptionHandler接口。线程组会作为默认异常处理器。当一个线程抛出异常，JVM首先查找该异常对应的异常处理器，如果找到则调用该异常处理器处理该异常；否则JVM将会调用该线程组对象的uncaughtException()方法来处理该异常。

        线程组处理异常的默认流程。(1)如果该线程组有父线程组，则调用父线程组的uncaughtException()方法来处理该异常。(2)如果该线程实例所属的线程类有默认的异常处理器，那么调用该异常处理器来处理该异常。(3)如果该异常对象时ThreadDeath的对象，则不做任何处理，否则，将异常跟踪栈的信息打印到System.err输出流，并结束该线程。