Execute Python function in Main thread from call in Dummy thread

Question

I have a Python script that handles aynchronous callbacks from .NET Remoting. These callbacks execute in a dummy (worker) thread. From inside my callback handler, I need to call a function I've defined in my script, but I need the function to execute in the main thread.

The Main thread is a remote client that sends commands to a server. Some of these commands result in asynchronous callbacks.

Basically, I need the equivalent of .NET's Invoke method. Is this possible?

Answer 1

You want to use the Queue (now queue from python 3) class to set up a queue that your dummy threads populate with functions and that your main thread consumes.

import Queue  #somewhere accessible to both: callback_queue = Queue.Queue()  def from_dummy_thread(func_to_call_from_main_thread):     callback_queue.put(func_to_call_from_main_thread)  def from_main_thread_blocking():     callback = callback_queue.get() #blocks until an item is available     callback()  def from_main_thread_nonblocking():     while True:         try:             callback = callback_queue.get(False) #doesn't block         except Queue.Empty: #raised when queue is empty             break         callback() 

Demo:

import threading import time  def print_num(dummyid, n):     print "From %s: %d" % (dummyid, n) def dummy_run(dummyid):     for i in xrange(5):         from_dummy_thread(lambda: print_num(dummyid, i))         time.sleep(0.5)      threading.Thread(target=dummy_run, args=("a",)).start() threading.Thread(target=dummy_run, args=("b",)).start()  while True:     from_main_thread_blocking() 

Prints:

From a: 0 From b: 0 From a: 1 From b: 1 From b: 2 From a: 2 From b: 3 From a: 3 From b: 4 From a: 4 

and then blocks forever