Python Threading: Making The Thread Function Return From An External Signal

Could anyone please point out whats wrong with this code. I am trying to return the thread through a variable flag, which I want to control in my main thread. test27.py import thr

Solution 1:

The Thread class can be instantiated with the target argument. Then you just give it a function which should be executed in a new thread. It is a convenient way to start a simple thread, but for more control it is usually easier to have a class inherited from Thread, which has additional member variables, like the flag for aborting.

For example:

import time
import threading

classMyThread(threading.Thread):
    def__init__(self, x, y):
        super().__init__()
        # or in Python 2:# super(MyThread, self).__init__()
        self.x = x
        self.y = y
        self._stop_requested = Falsedefrun(self):
        whilenot self._stop_requested:
            z = self.x + self.y
            w = self.x - self.y
            print (z * w)
            time.sleep(1)

    defstop(self, timeout=None):
        self._stop_requested = True
        self.join(timeout)

Then, to start the thread, call start() and then to stop it call stop():

>>>defrun_thread_for_5_seconds():...    t = MyThread(3, 4)...    t.start()...    time.sleep(5)...    t.stop()...>>>run_thread_for_5_seconds()
-7
-7
-7
-7
-7
>>>

Solution 2:

Regular variables should not be tracked in threads. This is done to prevent race condition. You must use thread-safe constructs to communicate between threads. For a simple flag use threading.Event. Also you cannot access local variable flag via thread object. It is local, and is only visible from scope. You must either use a global variable, as in my example below or create an Object before calling your thread and use a member variable.

from threading import Event
flag = Event()

defRead(x,y):
    global flag
    flag.clear()
    ...
    if flag.is_set():
        return

main thread:

sleep(5)
flag.set()

P.S.: I just noticed that you attempted to use lock() in the thread, but failed to use it in the main thread. For a simple flag go with Event. For a lock() you need to lock both parts and mitigate a risk of a deadlock.