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keep using poll as fast path and only use fcntl as fallback

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this minimizes the amount of syscalls performed during startup
This commit is contained in:
The 8472 2022-06-04 11:34:02 +02:00
parent e0a53ed63a
commit d3465a8f21
2 changed files with 65 additions and 19 deletions
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1
library/std/src/lib.rs
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@ -239,6 +239,7 @@
#![feature(dropck_eyepatch)]
#![feature(exhaustive_patterns)]
#![feature(intra_doc_pointers)]
#![feature(label_break_value)]
#![feature(lang_items)]
#![feature(let_chains)]
#![feature(linkage)]

83
library/std/src/sys/unix/mod.rs
View File

@ -67,25 +67,70 @@ pub unsafe fn init(argc: isize, argv: *const *const u8) {
args::init(argc, argv);
unsafe fn sanitize_standard_fds() {
cfg_if::cfg_if! {
if #[cfg(not(any(
// The standard fds are always available in Miri.
miri,
target_os = "emscripten",
target_os = "fuchsia",
target_os = "vxworks",
target_os = "l4re",
)))] {
use crate::sys::os::errno;
for fd in 0..3 {
if libc::fcntl(fd, libc::F_GETFD) == -1 && errno() == libc::EBADF {
if libc::open("/dev/null\0".as_ptr().cast(), libc::O_RDWR, 0) == -1 {
// If the stream is closed but we failed to reopen it, abort the
// process. Otherwise we wouldn't preserve the safety of
// operations on the corresponding Rust object Stdin, Stdout, or
// Stderr.
libc::abort();
}
// fast path with a single syscall for systems with poll()
#[cfg(not(any(
miri,
target_os = "emscripten",
target_os = "fuchsia",
target_os = "vxworks",
// The poll on Darwin doesn't set POLLNVAL for closed fds.
target_os = "macos",
target_os = "ios",
target_os = "redox",
target_os = "l4re",
)))]
'poll: {
use crate::sys::os::errno;
let pfds: &mut [_] = &mut [
libc::pollfd { fd: 0, events: 0, revents: 0 },
libc::pollfd { fd: 1, events: 0, revents: 0 },
libc::pollfd { fd: 2, events: 0, revents: 0 },
];
while libc::poll(pfds.as_mut_ptr(), 3, 0) == -1 {
if errno() == libc::EINTR {
continue;
}
if errno() == libc::EINVAL {
// RLIMIT_NOFILE may be preventing use of poll()
break 'poll;
}
libc::abort();
}
for pfd in pfds {
if pfd.revents & libc::POLLNVAL == 0 {
continue;
}
if libc::open("/dev/null\0".as_ptr().cast(), libc::O_RDWR, 0) == -1 {
// If the stream is closed but we failed to reopen it, abort the
// process. Otherwise we wouldn't preserve the safety of
// operations on the corresponding Rust object Stdin, Stdout, or
// Stderr.
libc::abort();
}
}
return;
}
// fallback in case poll isn't available or limited by RLIMIT_NOFILE
#[cfg(not(any(
// The standard fds are always available in Miri.
miri,
target_os = "emscripten",
target_os = "fuchsia",
target_os = "vxworks",
target_os = "l4re",
)))]
{
use crate::sys::os::errno;
for fd in 0..3 {
if libc::fcntl(fd, libc::F_GETFD) == -1 && errno() == libc::EBADF {
if libc::open("/dev/null\0".as_ptr().cast(), libc::O_RDWR, 0) == -1 {
// If the stream is closed but we failed to reopen it, abort the
// process. Otherwise we wouldn't preserve the safety of
// operations on the corresponding Rust object Stdin, Stdout, or
// Stderr.
libc::abort();
}
}
}