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socketpair: add eventfd and use SOCK_NONBLOCK for socketpair()

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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 change 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

Closes #13874
This commit is contained in:
Andy Pan 2024-06-02 02:26:11 +08:00 • committed by Daniel Stenberg
parent b71916b859
commit 23fe1a52dc
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10 changed files with 149 additions and 41 deletions
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2
CMakeLists.txt
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@ -1168,6 +1168,7 @@ if(WIN32)
endif()
endif()
check_include_file_concat("sys/eventfd.h" HAVE_SYS_EVENTFD_H)
check_include_file_concat("sys/filio.h" HAVE_SYS_FILIO_H)
check_include_file_concat("sys/wait.h" HAVE_SYS_WAIT_H)
check_include_file_concat("sys/ioctl.h" HAVE_SYS_IOCTL_H)
@ -1288,6 +1289,7 @@ check_symbol_exists(getaddrinfo "${CURL_INCLUDES};stdlib.h;string.h" HAVE_GET
check_symbol_exists(getifaddrs "${CURL_INCLUDES};stdlib.h" HAVE_GETIFADDRS)
check_symbol_exists(freeaddrinfo "${CURL_INCLUDES}" HAVE_FREEADDRINFO)
check_symbol_exists(pipe "${CURL_INCLUDES}" HAVE_PIPE)
check_symbol_exists(eventfd "${CURL_INCLUDES};sys/eventfd.h" HAVE_EVENTFD)
check_symbol_exists(ftruncate "${CURL_INCLUDES}" HAVE_FTRUNCATE)
check_symbol_exists(_fseeki64 "${CURL_INCLUDES};stdio.h" HAVE__FSEEKI64)
check_symbol_exists(getpeername "${CURL_INCLUDES}" HAVE_GETPEERNAME)