QFutureWatcher and "cancel" on a QtConcurrent filter...

[wysota]

If you do not connect any signals from the watcher tthen I don't see how throttling is of any use to you. It makes sense only if the producer is faster than the consumer for really large data sets where resource consumption matters. If you are not processing entries as they appear in the result (which would require the use of signals) then if throttling kicked in your operation would never complete.

Maybe you should describe what you are trying to achieve with QtConcurrent, why you need throttling and how you process the results.

[t_3]

If you do not connect any signals from the watcher tthen I don't see how throttling is of any use to you. It makes sense only if the producer is faster than the consumer for really large data sets where resource consumption matters. If you are not processing entries as they appear in the result (which would require the use of signals) then if throttling kicked in your operation would never complete.

Maybe you should describe what you are trying to achieve with QtConcurrent, why you need throttling and how you process the results.

i process [some of the] future results in the main/ui thread, but for particular reasons i'm using own signals instead of the watcher ones.

i work on a plugin that needs to access two different, both non thread safe api's (one from a Qt based host application, and external other one), so whenever i like to offload processing to keep the ui responsive it gets complicated, not the last because i have only very limited control - for example the threadpool threads limit; in this particular case the thread limit is already way beyond what is healthy for the particular modules task (thumbnails rendering on a gpu), so i need a way to limit concurrent processing on my own.

the key part in the docs description is the wording "pending signals". i of course see that to calculate a "pending" number (to test against a limit) needs something that adds and removes signals from a "pending" list (however that works). means you are probably right that watcher throttling won't work if i don't use the internal methods to consume results. after some test it seems that the setting has just no effect at all in this case - even if i set the limit to "1" the filter still runs down the sequence without being ever paused... so i'm going to use a semaphore.

thanks for your help...