How to Terminate a Thread When Main Program Ends

How to terminate a thread when main program ends?

Check this question. The correct answer has great explanation on how to terminate threads the right way:
Is there any way to kill a Thread in Python?

To make the thread stop on Keyboard Interrupt signal (ctrl+c) you can catch the exception "KeyboardInterrupt" and cleanup before exiting. Like this:

try:
    start_thread()  
except (KeyboardInterrupt, SystemExit):
    cleanup_stop_thread()
    sys.exit()

This way you can control what to do whenever the program is abruptly terminated.

You can also use the built-in signal module that lets you setup signal handlers (in your specific case the SIGINT signal): http://docs.python.org/library/signal.html

Java - Stop a thread automatically when program ends

The thread you are creating is independent and does not depend on the Main Thread termination. You can use Daemon thread for the same. Daemon threads will be terminated by the JVM when there are none of the other non- daemon threads running, it includes a main thread of execution as well.

public static void main(String[] args) {
    Thread t = new Thread(new Runnable() {
        @Override
        public void run() {
            while (true) {
                System.out.println("Daemon thread");
            }
        }
    });
    t.setDaemon(true);
    t.start();

    System.out.println("End of main");
}

Is there any way to kill a Thread?

It is generally a bad pattern to kill a thread abruptly, in Python, and in any language. Think of the following cases:

• the thread is holding a critical resource that must be closed properly
• the thread has created several other threads that must be killed as well.

The nice way of handling this, if you can afford it (if you are managing your own threads), is to have an exit_request flag that each thread checks on a regular interval to see if it is time for it to exit.

For example:

import threading

class StoppableThread(threading.Thread):
    """Thread class with a stop() method. The thread itself has to check
    regularly for the stopped() condition."""

    def __init__(self,  *args, **kwargs):
        super(StoppableThread, self).__init__(*args, **kwargs)
        self._stop_event = threading.Event()

    def stop(self):
        self._stop_event.set()

    def stopped(self):
        return self._stop_event.is_set()

In this code, you should call stop() on the thread when you want it to exit, and wait for the thread to exit properly using join(). The thread should check the stop flag at regular intervals.

There are cases, however, when you really need to kill a thread. An example is when you are wrapping an external library that is busy for long calls, and you want to interrupt it.

The following code allows (with some restrictions) to raise an Exception in a Python thread:

def _async_raise(tid, exctype):
    '''Raises an exception in the threads with id tid'''
    if not inspect.isclass(exctype):
        raise TypeError("Only types can be raised (not instances)")
    res = ctypes.pythonapi.PyThreadState_SetAsyncExc(ctypes.c_long(tid),
                                                     ctypes.py_object(exctype))
    if res == 0:
        raise ValueError("invalid thread id")
    elif res != 1:
        # "if it returns a number greater than one, you're in trouble,
        # and you should call it again with exc=NULL to revert the effect"
        ctypes.pythonapi.PyThreadState_SetAsyncExc(ctypes.c_long(tid), None)
        raise SystemError("PyThreadState_SetAsyncExc failed")

class ThreadWithExc(threading.Thread):
    '''A thread class that supports raising an exception in the thread from
       another thread.
    '''
    def _get_my_tid(self):
        """determines this (self's) thread id

        CAREFUL: this function is executed in the context of the caller
        thread, to get the identity of the thread represented by this
        instance.
        """
        if not self.isAlive():
            raise threading.ThreadError("the thread is not active")

        # do we have it cached?
        if hasattr(self, "_thread_id"):
            return self._thread_id

        # no, look for it in the _active dict
        for tid, tobj in threading._active.items():
            if tobj is self:
                self._thread_id = tid
                return tid

        # TODO: in python 2.6, there's a simpler way to do: self.ident

        raise AssertionError("could not determine the thread's id")

    def raiseExc(self, exctype):
        """Raises the given exception type in the context of this thread.

        If the thread is busy in a system call (time.sleep(),
        socket.accept(), ...), the exception is simply ignored.

        If you are sure that your exception should terminate the thread,
        one way to ensure that it works is:

            t = ThreadWithExc( ... )
            ...
            t.raiseExc( SomeException )
            while t.isAlive():
                time.sleep( 0.1 )
                t.raiseExc( SomeException )

        If the exception is to be caught by the thread, you need a way to
        check that your thread has caught it.

        CAREFUL: this function is executed in the context of the
        caller thread, to raise an exception in the context of the
        thread represented by this instance.
        """
        _async_raise( self._get_my_tid(), exctype )

(Based on Killable Threads by Tomer Filiba. The quote about the return value of PyThreadState_SetAsyncExc appears to be from an old version of Python.)

As noted in the documentation, this is not a magic bullet because if the thread is busy outside the Python interpreter, it will not catch the interruption.

A good usage pattern of this code is to have the thread catch a specific exception and perform the cleanup. That way, you can interrupt a task and still have proper cleanup.

How can I kill all threads?

No. Individual threads can't be terminated forcibly (it's unsafe, since it could leave locks held, leading to deadlocks, among other things).

Two ways to do something like this would be to either:

1. Have all threads launched as daemon threads, with the main thread waiting on an Event/Condition and exiting as soon as one of the threads sets the Event or notifies the Condition. The process terminates as soon as the (sole) non-daemon thread exits, ending all the daemon threads
2. Use a shared Event that all the threads poll intermittently, so they cooperatively exit shortly after it is set.

How to close a thread from within?

When you start a thread, it begins executing a function you give it (if you're extending threading.Thread, the function will be run()). To end the thread, just return from that function.

According to this, you can also call thread.exit(), which will throw an exception that will end the thread silently.

How to close a thread when multithreading?

To terminate an Thread controlled, using a threadsafe threading.Event():

import threading, time

def Thread_Function(running):
    while running.is_set():
        print('running')
        time.sleep(1)

if __name__ == '__main__':
    running = threading.Event()
    running.set()

    thread = threading.Thread(target=Thread_Function, args=(running,))
    thread.start()

    time.sleep(1)
    print('Event running.clear()')
    running.clear()

    print('Wait until Thread is terminating')
    thread.join()
    print("EXIT __main__")

Output:

running  
running  
Event running.clear()  
Wait until Thread is terminating  
EXIT __main__

Tested with Python:3.4.2

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