K
Thread.stop()There is the method Thread.stop() that has this purpose. However it is obsolete (deprecated). It still works if used, but there are strong reasons why you do not use it.When a thread is stopped suddenly, it can leave important operations unfinished. For example, imagine that it was saving information in a file and when it was suddenly stopped the file gets corrupted. Or suppose she was doing some critical operation with some object in memory and being suddenly interrupted, does this object end up being inconsistent and corrupted? This is the reason why Thread.stop() was discontinued.O Thread.stop() works by sudden launching a ThreadDeath inside the thread that was stopped force. That means the thread will still have the blocks finally executed, and if she gives one catch (ThreadDeath e) or one catch (Throwable e), she can capture ThreadDeath and end up not being stopped. That may seem good, but if ThreadDeath is released from inside a block finally, finally ends up being interrupted leaving something very important unfinished. If you try to treat this by capturing ThreadDeath, another Thread.stop() can cause a new ThreadDeath inside the code that should be treating ThreadDeath, and because of this, in practice it is impossible to treat ThreadDeath adequately.To make it worse, let's assume that the thread was inside a code belonging to some library that was doing any operation with arrays, in short, something that had nothing to do with the Thread.stop() or with ThreadDeath. You even have one catch (ThreadDeath e) somewhere outside the library in a method you use it. When ThreadDeath is captured, the library code executed only by half leaving a lot of inconsistent things. So how do you fix those things? How do you even find out what was inconsistent?Thread.stop(Throwable), Thread.suspend() and Thread.destroy()Beyond Thread.stop() there is a variant Thread.stop(Throwable) (also obsolete) that for the thread with an arbitrary exception, rather than a ThreadDeath. This is even worse because you continue with the same problem Thread.stop()but now instead of one ThreadDeath you have any exception and therefore it is harder to write code that you can handle it. In more modern versions of JDK, this method only launches one UnsupportedOperationException, being one of the very few cases where there was a propositional retrocompatibility break in Java.There is the method Thread.suspend() that for the thread and let it continue later with Thread.resume(). However, this method may also end up leaving incomplete important operations and inconsistent objects due to sudden termination of the thread. Besides, it can result in deadlocks, since any locks on objects (those that are obtained in blocks and methods synchronized) remain locked for the suspended thread. For this reason, these methods are also obsolete.There is also the method Thread.destroy() (obsolete) that should stop the thread immediately and destroy it. This method has never been implemented and trying to use it results in an exception. If it had been implemented, the result would be similar to one Thread.suspend() where there is no option to make a Thread.resume().Breaking threads gracefullyTo stop a thread gracefully, it must be running code that predicts its interruption gracefully. This can simply encode the thread so as to check from time to time if a variable boolean or AtomicBoolean or some special condition in order to determine whether the thread should stop or not. That is, the thread code is designed to know when it should be interrupted and voluntarily do it gracefully.Thread.interrupt()The recommended way to interrupt threads is with the method Thread.interrupt(). This method does not interrupt the thread in fact, only arrows a flag in it (the break status). You can know if the current thread was interrupted by the use of methods Thread.interrupted() and Thread.isInterrupted(). These methods return one boolean saying whether the thread was interrupted or not. The difference between them is that Thread.interrupted() cleans the break status (defines how false), while the Thread.isInterrupted() doesn't change it. In addition, the Thread.interrupted() is a static method that checks and cleans the thread break state that invoked it (Thread.currentThread()), while the Thread.isInterrupted() is a class instance method Thread.Several JDK methods (e.g. Thread.sleep and Object.wait) throw the exception InterruptedException. This exception is released when the thread is running these methods (Thread.sleep, Object.wait or others) is interrupted by the use of Thread.interrupt(). In this way, it is possible to interrupt a thread that is stuck in a Thread.sleep or Object.wait. It is important that the interrupted thread treats the InterruptedException satisfactorily (simply catching it and ignoring it without thinking straight about what is doing, it is not a good programming practice). When InterruptedException is released, the thread break status is cleaned (sected to false), since when the exception is being captured, the interruption is already being treated.If you are designing a method that can get stuck for a long time, a good alternative is to check out the Thread.isInterrupted() or Thread.interrupted() and launch InterruptedException. For example:public void metodoDemorado() throws InterruptedException {
while (/*alguma coisa*/) {
// faz qualquer coisa
if (Thread.interrupted()) throw new InterruptedException();
}
}
