How to use two threads (GUI and backend)

[jmp]

On 10/27/2016 12:22 PM, pozz wrote:
> Anyway I don't like this approach, because the main (and single) thread
> should check in_waiting every X milliseconds.
> If X is too high, I could wait for the answer even if it is already
> ready in the input buffer.
> If X is too low, the application consumes a lot of clocks to check
> in_waiting.
>
> I would prefer to have a callback automatically called when the read
> operation is complete.  And I think the only method is using another
> (blocking) thread. The blocking function read returns *immediately* when
> all the bytes are received.  And I think during blocking time, the
> thread isn't consuming CPU clocks.

Threads do consume CPU clocks.
An operation within a thread will not consume less CPU clocks, however, 
the scheduler will interrupt the thread and give other 
threads/operations a chance to process as well.
Threads implement paralellism, not performances.

 From what I understand of your context, you don't want you GUI to 
"freeze" when waiting for the remote application. That's a valid concern.

You can use threads to fix that(or you can use already written working 
python libraries that would mask this low level programing, it's up to you).

What you should not do is focus on gaining "CPU clocks". You just don't 
care. It's probably not an issue. If it is, drop python and implement 
your app in C.

JM