Implement backpressure mechanism for iced_winit::Proxy
#2389
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The
EventLoopProxyinwinitis implemented using an unboundedmpscchannel. In practice, this means that we have to be careful when publishing to this channel, as it will simply keep allocating additional memory when needed. And guess what? We are not careful at all!Currently, if a
Subscriptiondecides to start producing messages very quickly—faster thanupdatecan process them—the messages will start piling up in theEventLoopProxyand memory usage will increase indefinitely. Furthermore, this memory will stay allocated as channel capacity once the application catches up and the messages are processed. I suspect this could be the root cause of some high memory usage reports (like squidowl/halloy#309).The solution implemented in this PR consists in connecting the output of an async, bounded
mpscchannel to theEventLoopProxyinput while freeing new message slots when published messages are processed byupdate—effectively achieving backpressure for all of our async abstractions.