Java 学习笔记-阻塞 和 死锁

 首先从 Thread中的两个deprecated方法说起 ： suspend 和 resume

废除的原因很简单，because it s  deadlock-prone。

/*This method has been deprecated, as it is inherently deadlock-prone. If the target thread holds a lock on the monitor protecting a critical system resource when it is suspended, no thread can access this resource until the target thread is resumed. If the thread that would resume the target thread attempts to lock this monitor  calling resume, deadlock results. Such deadlocks typically manifest themselves as "frozen" processes. For more information*/

suspend 方法使一个线程挂起 ，设想一个情况 线程A占用着系统关键的共享资源，并且在保护该资源的monitor上有lock，此时如果线程B调用了线程A的suspend方法，则线程进入挂起状态，除非该线程被唤醒，否则锁一直没释放，其他线程无法竞争获得锁

 

另外 还要理解 thread . state枚举类

public static enum Thread.State
extends Enum<Thread.State>
A thread state. A thread can be in one of the following states:
NEW
A thread that has not yet started is in this state.
RUNNABLE
A thread executing in the Java virtual machine is in this state.
BLOCKED
A thread that is blocked waiting for a monitor lock is in this state.
WAITING
A thread that is waiting indefinitely for another thread to perform a particular action is in this state.
TIMED_WAITING
A thread that is waiting for another thread to perform an action for up to a specified waiting time is in this state.
TERMINATED
A thread that has exited is in this state.
A thread can be in only one state at a given point in time. These states are virtual machine states which do not reflect any operating system thread states.

通过 Thread.currentThread.getName & Thread.currentThread.getState 两个方法 测试put 和 take方法（《线程通讯 1 中的代码》）

可以很好理解 suspend 与Object.wait 和 lock.newCondition的区别

suspend直接把线程挂起 ， 可理解为线程中断，只有其他线程 调用它的resume方法才能唤醒它

而其他两个 在执行this.wait 或者 condition.await 后并不会马上释放锁，而是继续把同步代码块执行完毕再释放锁（当然你要在finally里 lock.unlock）

这样避免了deadlock - prone ，所以废除了suspend 

 

另外，线程阻塞就是线程并没有被停止，只是一种待机状态（如执行了wait后），等待其他线程操作唤醒他

Java 提供了 Thread.Interrupt（） 方法用于线程跳出run方法体