mirror of
https://github.com/kovidgoyal/calibre.git
synced 2026-01-07 20:50:20 -05:00
a62ad5f70c
Theory: the producer (Qt GUI cover function) exists only once per instance of FunctionDispatcher. This follows from the fact that the dispatcher instance is created on the recipient thread. The consumer (the cover cache) could in theory be multiple threads (but it isn't). Because the items produced by the producer are not equivalent, we need to ensure that the order of items put in the queue by the producer is equal to the order of the requests. To guarantee this order, regardless of the number of consumer threads, we ensure that only one request to the producer can be outstanding.