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…e polling for I/O After running the ready callbacks, BaseEventLoop._run_once() now keeps running the callbacks they schedule, in batches, before it polls for I/O again. This saves one I/O poll per hop of a callback chain, for example when a completed future wakes up a task. Eager processing is bounded by the new asyncio.EventLoopSettings, set with loop.set_settings() and read with loop.get_settings(): eager_max_time (default 100 microseconds) and eager_max_callbacks (default 100). asyncio.sleep(0) ends eager processing, so that the task resumes only after the next I/O poll. When stop() is called during eager processing, run_forever() runs one more iteration, which polls for I/O and runs what the loop would have run without eager processing. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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Run callbacks that are scheduled during an event loop iteration eagerly, within a small budget, instead of always waiting for the next I/O poll. This removes one
select()/epoll_wait()call per hop in code that resolves futures or wakes tasks in chains.asyncio.EventLoopSettings(eager_max_time, eager_max_callbacks)andloop.get_settings()/loop.set_settings(). The defaults are 100 µs and 100 callbacks;eager_max_time=0turns eager processing off.asyncio.sleep(0), which still guarantees an I/O poll, and onloop.stop(), which keeps its documented "current batch only" behaviour.Benchmarks (release build): a
call_soon()chain is 38% faster,Queueping-pong 25% faster, and a task awaiting a child task 33% faster. Servers with many connections are unchanged. While a long run of callbacks keeps going, timers and I/O can be delayed by up to about 100–200 µs.A few tests that assumed "one task hop = one I/O poll" were adjusted.