reactor: Use writeable_eventfd for reactor::_notify_eventfd #2895
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The member in question is initialized with eventfd descriptor and is then used by reactor to wakeup backend from sleep. The writeable_eventfd class provides "compatible" signalling facility that can be re-used. The reading part of writeable_eventfd is readable_eventfd, which is too much for the backend usage, so the writeable_eventfd::consume() helper is added. Next, the read-side of the eventfd nowdays works via fd_kernel_completion-s inheritants, that are patched to call the newly introduced method. In the end of the day, the patch generalizes the "protocol" that notify eventfd peers use to kick each other -- the 8 bytes dummy tranfer. Signed-off-by: Pavel Emelyanov <[email protected]>
avikivity
reviewed
Aug 3, 2025
| std::optional<size_t> writeable_eventfd::consume() { | ||
| uint64_t c; | ||
| return _fd.read(&c, sizeof(c)); | ||
| } |
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Shouldn't this be part of the read side?
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The read-side uses await-able wrapper around pollable_fd, which is not needed by the users of this new method. Actually the writeable_eventfd and readable_eventfd are supposed to play with each other, while reactor only needs the writeable end. I'll think on it a bit more
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The member in question is initialized with eventfd descriptor and is then used by reactor to wakeup backend from sleep. The writeable_eventfd class provides "compatible" signalling facility that can be re-used.
The reading part of writeable_eventfd is readable_eventfd, which is too much for the backend usage, so the writeable_eventfd::consume() helper is added. Next, the read-side of the eventfd nowdays works via fd_kernel_completion-s inheritants, that are patched to call the newly introduced method.
In the end of the day, the patch generalizes the "protocol" that notify eventfd peers use to kick each other -- the 8 bytes dummy tranfer.