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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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GPG key ID: 5CC908FDB71E12C2
10 changed files with 149 additions and 41 deletions
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63
lib/socketpair.c
View file

@ -27,14 +27,31 @@
#include "urldata.h"
#include "rand.h"
#if defined(HAVE_PIPE) && defined(HAVE_FCNTL)
#include <fcntl.h>
#if defined(USE_EVENTFD)
#ifdef HAVE_SYS_EVENTFD_H
#include <sys/eventfd.h>
#endif
int Curl_pipe(curl_socket_t socks[2])
int Curl_eventfd(curl_socket_t socks[2], bool nonblocking)
{
int efd = eventfd(0, nonblocking ? EFD_CLOEXEC | EFD_NONBLOCK : EFD_CLOEXEC);
if(efd == -1) {
socks[0] = socks[1] = CURL_SOCKET_BAD;
return -1;
}
socks[0] = socks[1] = efd;
return 0;
}
#elif defined(HAVE_PIPE)
#ifdef HAVE_FCNTL
#include <fcntl.h>
#endif
int Curl_pipe(curl_socket_t socks[2], bool nonblocking)
{
if(pipe(socks))
return -1;
#ifdef HAVE_FCNTL
if(fcntl(socks[0], F_SETFD, FD_CLOEXEC) ||
fcntl(socks[1], F_SETFD, FD_CLOEXEC) ) {
close(socks[0]);
@ -42,6 +59,16 @@ int Curl_pipe(curl_socket_t socks[2])
socks[0] = socks[1] = CURL_SOCKET_BAD;
return -1;
}
#endif
if(nonblocking) {
if(curlx_nonblock(socks[0], TRUE) < 0 ||
curlx_nonblock(socks[1], TRUE) < 0) {
close(socks[0]);
close(socks[1]);
socks[0] = socks[1] = CURL_SOCKET_BAD;
return -1;
}
}
return 0;
}
@ -80,7 +107,7 @@ int Curl_pipe(curl_socket_t socks[2])
#include "memdebug.h"
int Curl_socketpair(int domain, int type, int protocol,
curl_socket_t socks[2])
curl_socket_t socks[2], bool nonblocking)
{
union {
struct sockaddr_in inaddr;
@ -198,6 +225,10 @@ int Curl_socketpair(int domain, int type, int protocol,
} while(1);
}
if(nonblocking)
if(curlx_nonblock(socks[0], TRUE) < 0 ||
curlx_nonblock(socks[1], TRUE) < 0)
goto error;
sclose(listener);
return 0;
@ -207,5 +238,25 @@ error:
sclose(socks[1]);
return -1;
}
#else
int Curl_socketpair(int domain, int type, int protocol,
curl_socket_t socks[2], bool nonblocking)
{
#ifdef SOCK_NONBLOCK
type = nonblocking ? type | SOCK_NONBLOCK : type;
#endif
if(socketpair(domain, type, protocol, socks))
return -1;
#ifndef SOCK_NONBLOCK
if(nonblocking) {
if(curlx_nonblock(socks[0], TRUE) < 0 ||
curlx_nonblock(socks[1], TRUE) < 0) {
close(socks[0]);
close(socks[1]);
return -1;
}
}
#endif
return 0;
}
#endif /* ! HAVE_SOCKETPAIR */