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.
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