python response slow when running external DLL

[jfong at ms4.hinet.net]

Peter Otten at 2015/11/28 UTC+8 6:14:09PM wrote：
> No, the point of both recipes is that tkinter operations are only ever 
> invoked from the main thread. The main thread has polling code that 
> repeatedly looks if there are results from the helper thread. As far I 
> understand the polling method has the structure
> 
> f():
>    # did we get something back from the other thread?
>    # a queue is used to avoid race conditions
> 
>    # if yes react.
>    # var_status.set() goes here
> 
>    # reschedule f to run again in a few millisecs; 
>    # that's what after() does

Have no idea how the main thread poll on all those events (or it use a queue)?
All I know now is that the main thread(mainloop()?) can be easily blocked by event handlers if the handler didn't run as a separate thread.

> >     .....
> >     .....
> >     #do the rest
> >     var_status.set('Download...')
> >     _thread.start_new_thread(td_download, ())  #must use threading
> > 
> > def td_download():
> >     result = mydll.SayHello()
> >     if result:
> >         var_status.set("Download Fail at %s" % hex(result))
> >         showerror('Romter', 'Download Fail')
> >     else:
> >         var_status.set('Download OK')
> >         showinfo('Romter', 'Download OK')
> 
> As td_download() runs in the other thread the var_status.set() methods are 
> problematic.

No idea what kind of problem it will encounter. Can you explain?

> Another complication that inevitably comes with concurrency: what if the 
> user triggers another download while one download is already running? If you 
> don't keep track of all downloads the message will already switch to 
> "Download OK" while one download is still running.

Hummm...this thought never comes to my mind. After take a quick test I found, you are right, a second "download" was triggered immediately. That's a shock to me. I suppose the same event shouldn't be triggered again, or at least not triggered immediately, before its previous handler was completed. ...I will take a check later on Borland C++ builder to see how it reacts!

Anyway to prevent this happens? if Python didn't take care it for us.