romenskiy2012/curl
1
0
Fork 0
mirror of https://github.com/curl/curl.git synced 2026-06-01 22:14:17 +03:00
Code Issues Projects Releases Packages Wiki Activity

socketpair: add eventfd and use SOCK_NONBLOCK for socketpair()

Browse source 
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
No known key found for this signature in database
GPG key ID: 5CC908FDB71E12C2
10 changed files with 149 additions and 41 deletions
Download patch file Download diff file Expand all files Collapse all files

25
lib/multi.c
View file

@ -426,14 +426,7 @@ struct Curl_multi *Curl_multi_handle(size_t hashsize, /* socket hash */
goto error;
#else
#ifdef ENABLE_WAKEUP
if(wakeup_create(multi->wakeup_pair) < 0) {
multi->wakeup_pair[0] = CURL_SOCKET_BAD;
multi->wakeup_pair[1] = CURL_SOCKET_BAD;
}
else if(curlx_nonblock(multi->wakeup_pair[0], TRUE) < 0 ||
curlx_nonblock(multi->wakeup_pair[1], TRUE) < 0) {
wakeup_close(multi->wakeup_pair[0]);
wakeup_close(multi->wakeup_pair[1]);
if(wakeup_create(multi->wakeup_pair, TRUE) < 0) {
multi->wakeup_pair[0] = CURL_SOCKET_BAD;
multi->wakeup_pair[1] = CURL_SOCKET_BAD;
}
@ -1639,6 +1632,15 @@ CURLMcode curl_multi_wakeup(struct Curl_multi *multi)
it has to be careful only to access parts of the
Curl_multi struct that are constant */
#if defined(ENABLE_WAKEUP) && !defined(USE_WINSOCK)
#ifdef USE_EVENTFD
const void *buf;
const uint64_t val = 1;
#else
char buf[1];
#endif
#endif
/* GOOD_MULTI_HANDLE can be safely called */
if(!GOOD_MULTI_HANDLE(multi))
return CURLM_BAD_HANDLE;
@ -1652,8 +1654,11 @@ CURLMcode curl_multi_wakeup(struct Curl_multi *multi)
making it safe to access from another thread after the init part
and before cleanup */
if(multi->wakeup_pair[1] != CURL_SOCKET_BAD) {
char buf[1];
#ifdef USE_EVENTFD
buf = &val;
#else
buf[0] = 1;
#endif
while(1) {
/* swrite() is not thread-safe in general, because concurrent calls
can have their messages interleaved, but in this case the content
@ -2882,8 +2887,10 @@ CURLMcode curl_multi_cleanup(struct Curl_multi *multi)
#else
#ifdef ENABLE_WAKEUP
wakeup_close(multi->wakeup_pair[0]);
#ifndef USE_EVENTFD
wakeup_close(multi->wakeup_pair[1]);
#endif
#endif
#endif
multi_xfer_bufs_free(multi);