Re: [pysystray-users] Threads and "global variable"

[Christian K. <chr...@gm...>]

Hi Essien,

Thanks for your response!

 > > I am stuck at what seems like a simple thing: I have spawned one 
thread
 > > automatically on load of the taskbar icon. That was easy. Now I need
 > > this thread to change it's behaviour depending on what menu items I
 > > selected. I have a global variable that each menu item can set, but 
the
 > > thread doesn't see it.
 > >
 > > After what I could google on it it seems the threads run in their own
 > > space. I found some examples for communication between threads but 
only
 > > for class-threads and not the type function-thread that pysystray 
uses,
 > > plus it seems complicated.
 > >  
 > Indeed threads can't communicate via 'global' anythings really, unless
 > via some complex mechanisms... Windows I think builds up that frame work
 > for threads into a message passing system i think. must have read that
 > somewhere.
 > > What is the most simplistic approach to change a parameter 
"globally" so
 > > that the thread can see it? I tried a get_val() function but that
 > > doesn't work either and the thread always sees 0.
 > >  
 >
 > The way I see, it, what you could do would be to use sockets. On UNIX i
 > would say use socket.AF_LOCAL but in windows, you can just use the
 > normal INET sockets.
 >
 > It seems to me that your on_load thread is the main thread that others
 > can control no? In that case, you can make it a server, that listens for
 > values from clients. Then each of your menu items will do a simple
 > socket.socket(), connect(), send(). The server picks up the message and
 > works with it.
 >
 > You can make this all simple by building a simple module to abstract the
 > client messages, so you could have:
 >
 >
 > foobar.client_send(foobar.COOL_VALUE)
 >
 > then in the server you could do,
 >
 > while 1:
 >  msg = foobar_server.get_msg()
 >  if msg == foobar.COOL_VALUE:
 >     #meh
 >  if msg == foobar.UNCOOL_VALUE:
 >     #more meh!
 >
 > that's the way I would do it :)

Thanks again for the suggestion, but it raised more questions from a 
n00b like me when it comes to Win32 programming. How do I open the 
socket? How do I check if a message is waiting before I get it, in case 
I need the thread to be always running? I actually tried to open a local 
socket using 'localhost' and '127.0.0.1' and got a "connection refused" 
error, so I gave up.

However, I found an (IMHO) easier option using a queue. Here is my solution:

import Queue
...
msg_queue = Queue.Queue()
...
@systray.threaded
def my_lil_thread():
    new_value = 0
    while (1):
        if not msg_queue.empty():
            new_value = msg_queue.get()
        if new_value == 123  # Do whatever...
        ...

# Then in the callback for a menu item:

    msg_queue.put(123)  # Cause my_lil_thread to do whatever


I believe it works because the thread "inherits" all global objects that 
exist in the module at the time the thread is started (or defined, I 
don't know) and because msg_queue is a reference that remains static 
once the queue is opened, and the queue itself is a sharable object that 
is accessible from all threads. It is probably not the right way to do 
it and a Python expert might scream in horror but it works fine! :-)

Cheers,
Chris