Kill a thread in Python

[C. Barnes]

This code module allows you to kill threads.  The
class KThread is a drop-in replacement for
threading.Thread.  It adds the kill() method, which
should stop most threads in their tracks.

#
---------------------------------------------------------------------
# KThread.py: A killable Thread implementation.
#
---------------------------------------------------------------------

import sys
import trace
import threading

class KThread(threading.Thread):
  """A subclass of threading.Thread, with a kill()
method."""
  def __init__(self, *args, **keywords):
    threading.Thread.__init__(self, *args, **keywords)
    self.killed = False

  def start(self):
    """Start the thread."""
    self.__run_backup = self.run
    self.run = self.__run      # Force the Thread to
install our trace.
    threading.Thread.start(self)

  def __run(self):
    """Hacked run function, which installs the
trace."""
    sys.settrace(self.globaltrace)
    self.__run_backup()
    self.run = self.__run_backup

  def globaltrace(self, frame, why, arg):
    if why == 'call':
      return self.localtrace
    else:
      return None

  def localtrace(self, frame, why, arg):
    if self.killed:
      if why == 'line':
        raise SystemExit()
    return self.localtrace

  def kill(self):
    self.killed = True


------------------------------------------------------------------------
Example usage:
------------------------------------------------------------------------

This illustrates running a function in a separate
thread.  The thread is
killed before the function finishes.

from KThread import *

def func():
  print 'Function started'
  for i in xrange(1000000):
    pass
  print 'Function finished'

A = KThread(target=func)
A.start()
for i in xrange(1000000):
  pass
A.kill()

print 'End of main program'


Output:

  Function started
  End of main program


-----------------------------------------------------------------------
How It Works:
-----------------------------------------------------------------------

The KThread class works by installing a trace in the
thread.  The trace
checks at every line of execution whether it should
terminate itself.
So it's possible to instantly kill any actively
executing Python code.
However, if your code hangs at a lower level than
Python, then the
thread will not actually be killed until the next
Python statement is
executed.

-----------------------------------------------------------------------
Considerations:
-----------------------------------------------------------------------

Certain IDEs may install their own threading trace
code, for debugging
purposes.  This module is incompatible with those
IDEs.

Consider bugging the Python folks, until they give us
a thread kill
method.  The code has already been written:

http://mail.python.org/pipermail/python-list/2003-February/148999.html


Regards,
Connelly Barnes



	
		
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