socketpair: add eventfd and use SOCK_NONBLOCK for socketpair()
#13874
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panjf2000
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Currently, we use `pipe` for `wakeup_create`, which requires ***two***
file descriptors. Furthermore, given its complexity inside, `pipe` is a
bit heavyweight for just a simple event wait/notify mechanism.
`eventfd` would be a more suitable solution for this kind of scenario,
kernel also advocates for developers to use `eventfd` instead of `pipe`
in some simple use cases:
> Applications can use an eventfd file descriptor instead of a pipe
(see pipe(2) in all cases where a pipe is used simply to signal
events. The kernel overhead of an eventfd file descriptor is
much lower than that of a pipe, and only one file descriptor is
required (versus the two required for a pipe).
This PR adds the new backend of `eventfd` for `wakeup_create` and uses
it where available, eliminating the overhead of `pipe`. Also, it optimizes
the `wakeup_create` to eliminate the system calls that make file descriptors
non-blocking by moving the logic of setting non-blocking flags on file
descriptors to `socketpair.c` and using `SOCK_NONBLOCK` for `socketpair(2)`,
`EFD_NONBLOCK` for `eventfd(2)`.
Ref:
https://man7.org/linux/man-pages/man7/pipe.7.html
https://man7.org/linux/man-pages/man2/eventfd.2.html
https://man7.org/linux/man-pages/man2/socketpair.2.html
https://www.gnu.org/software/gnulib/manual/html_node/eventfd.html
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Thanks! |
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Unfortunately, this breaks |
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How did it break? What's the error info? |
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I'm investigating this. |
Is this breakage perhaps specific to Windows? I built |
I've run |
Follow-up to 23fe1a5 curl#13874
Follow-up to 23fe1a5 curl#13874 Closes curl#15561
Currently, we use
pipeforwakeup_create, which requires two file descriptors. Furthermore, given its complexity inside,pipeis a bit heavyweight for just a simple event wait/notify mechanism.eventfdwould be a more suitable solution for this kind of scenario, kernel also advocates for developers to useeventfdinstead ofpipefor some simple use cases:This PR adds the new backend of
eventfdforwakeup_createand uses it where available, eliminating the overhead ofpipe. Also, it optimizes thewakeup_createto eliminate the system calls that make file descriptors non-blocking by moving the logic of setting non-blocking flags on file descriptors tosocketpair.cand usingSOCK_NONBLOCKforsocketpair(2),EFD_NONBLOCKforeventfd(2).Ref:
https://man7.org/linux/man-pages/man7/pipe.7.html
https://man7.org/linux/man-pages/man2/eventfd.2.html
https://man7.org/linux/man-pages/man2/socketpair.2.html
https://www.gnu.org/software/gnulib/manual/html_node/eventfd.html