CODEWITHSUNDEEP
multithreadingqt4synchronizationpthreads
maxpayne
maxpayne

Reputation: 2499

interesting thread synchronization problem

I am trying to come up with a synchronization model for the following scenario:

I have a GUI thread that is responsible for CPU intensive animation + blocking I/O. The GUI thread retrieves images from the network (puts them in a shared buffer) , these images are processed (CPU intensive operation..done by a worker thread) and then these images are animated ( again CPU intensive..done by the GUI thread).

The processing of images is done by a worker thread..it retrieves images from the shared buffer processes them and puts them in an output buffer.

There is only once CPU and the GUI thread should not get scheduled out while it is animating the images (the animation has to be really smooth). This means that the work thread should get the CPU only when the GUI thread is waiting for I/O operation to complete.

How do i go about achieving this? This looks like a classic producer consumer problem...but i am not quite sure how i can guarantee that the animation will be as smooth as possible ( i am open to using more threads).

I would like to use QThreads (Qt framework) for platform independence but i can consider pthreads for more control ( as currently we are only aiming for linux).

Any ideas?

EDIT:

i guess the problems boils down to one thing..how do i ensure that the animation thread is not interrupted while it is animating the images ( the animation runs when the user goes from one page to the other..all the images in the new page are animated before shown in their proper place..this is a small operation but it must be really smooth).The worker thread can only run when the animation is over..

Upvotes: 0

Views: 1056

Answers (2)

Derick Schoonbee
Derick Schoonbee

Reputation: 3021

The first big question is: Do I really need threads? Qt 's event system and network objects make it easy to not having the technical burden of threads and all the snags that comes with it.

Have a look at alternative ways to address issues here and here. These techniques great if you are sticking to pure Qt code and do not depend on a 3rd party library. If you must use a 3rd party lib that does blocking calls then sure, you can use threads.

Here is an example of a consumer producer.

Also have a look at Advanced Qt Programming: Creating Great Software with C++ and Qt 4

My advice is to start without threads and see how it fares. You can always refactor to threads after. So, best is to design your objects/architecture without too much coupling.

If you want you can post some code to give more context.

Upvotes: 1

aroth
aroth

Reputation: 54796

Just thinking out loud here, but it sounds like you have two compute-intensive tasks, animation and processing, and you want animation to always have priority over processing. If that is correct then maybe instead of having these tasks in separate threads you could have a single thread that handles both animation and processing.

For instance, the thread could have two task-queues, one for animation jobs and one for processing jobs, and it only starts a job from the processing queue when the animation queue is empty. But, this will only work well if each individual processing job is relatively small and/or interruptible at arbitrary positions (otherwise animation jobs will get delayed, which is not what you want).

Upvotes: 1

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