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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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49
lib/socketpair.h
View file

@ -26,19 +26,42 @@
#include "curl_setup.h"
#ifdef HAVE_PIPE
#if defined(HAVE_EVENTFD) && \
defined(__x86_64__) && \
defined(__aarch64__) && \
defined(__ia64__) && \
defined(__ppc64__) && \
defined(__mips64) && \
defined(__sparc64__) && \
defined(__riscv_64e) && \
defined(__s390x__)
/* Use eventfd only with 64-bit CPU architectures because eventfd has a
* stringent rule of requiring the 8-byte buffer when calling read(2) and
* write(2) on it. In some rare cases, the C standard library implementation
* on a 32-bit system might choose to define uint64_t as a 32-bit type for
* various reasons (memory limitations, compatibility with older code),
* which makes eventfd broken.
*/
#define USE_EVENTFD 1
#define wakeup_write write
#define wakeup_read read
#define wakeup_close close
#define wakeup_create(p) Curl_pipe(p)
#define wakeup_create(p,nb) Curl_eventfd(p,nb)
#ifdef HAVE_FCNTL
#include <curl/curl.h>
int Curl_pipe(curl_socket_t socks[2]);
#else
#define Curl_pipe(p) pipe(p)
#endif
int Curl_eventfd(curl_socket_t socks[2], bool nonblocking);
#elif defined(HAVE_PIPE)
#define wakeup_write write
#define wakeup_read read
#define wakeup_close close
#define wakeup_create(p,nb) Curl_pipe(p,nb)
#include <curl/curl.h>
int Curl_pipe(curl_socket_t socks[2], bool nonblocking);
#else /* HAVE_PIPE */
@ -60,19 +83,13 @@ int Curl_pipe(curl_socket_t socks[2]);
#define SOCKETPAIR_TYPE SOCK_STREAM
#endif
#define wakeup_create(p)\
Curl_socketpair(SOCKETPAIR_FAMILY, SOCKETPAIR_TYPE, 0, p)
#define wakeup_create(p,nb)\
Curl_socketpair(SOCKETPAIR_FAMILY, SOCKETPAIR_TYPE, 0, p, nb)
#endif /* HAVE_PIPE */
#ifndef HAVE_SOCKETPAIR
#include <curl/curl.h>
int Curl_socketpair(int domain, int type, int protocol,
curl_socket_t socks[2]);
#else
#define Curl_socketpair(a,b,c,d) socketpair(a,b,c,d)
#endif
curl_socket_t socks[2], bool nonblocking);
#endif /* HEADER_CURL_SOCKETPAIR_H */