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Reduce synchronization overhead of I/O vector count memoization

This commit is contained in:
Adam Reichold 2020-08-01 15:38:08 +02:00
parent 6672f7be03
commit 87edccf0f0
1 changed files with 14 additions and 10 deletions
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24
library/std/src/sys/unix/fd.rs
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@ -2,8 +2,8 @@
use crate::cmp;
use crate::io::{self, Initializer, IoSlice, IoSliceMut, Read};
use crate::lazy::SyncOnceCell;
use crate::mem;
use crate::sync::atomic::{AtomicUsize, Ordering};
use crate::sys::cvt;
use crate::sys_common::AsInner;
@ -28,10 +28,11 @@ const READ_LIMIT: usize = c_int::MAX as usize - 1;
const READ_LIMIT: usize = libc::ssize_t::MAX as usize;
#[cfg(any(target_os = "linux", target_os = "macos"))]
fn max_iov() -> c_int {
static LIM: SyncOnceCell<c_int> = SyncOnceCell::new();
fn max_iov() -> usize {
static LIM: AtomicUsize = AtomicUsize::new(0);
*LIM.get_or_init(|| {
let mut lim = LIM.load(Ordering::Relaxed);
if lim == 0 {
let ret = unsafe {
libc::sysconf(
#[cfg(target_os = "linux")]
@ -43,13 +44,16 @@ fn max_iov() -> c_int {
// 1024 is the default value on modern Linux systems
// and hopefully more useful than `c_int::MAX`.
if ret > 0 { ret as c_int } else { 1024 }
})
lim = if ret > 0 { ret as usize } else { 1024 };
LIM.store(lim, Ordering::Relaxed);
}
lim
}
#[cfg(not(any(target_os = "linux", target_os = "macos")))]
fn max_iov() -> c_int {
c_int::MAX
fn max_iov() -> usize {
c_int::MAX as usize
}
impl FileDesc {
@ -80,7 +84,7 @@ impl FileDesc {
libc::readv(
self.fd,
bufs.as_ptr() as *const libc::iovec,
cmp::min(bufs.len(), max_iov() as usize) as c_int,
cmp::min(bufs.len(), max_iov()) as c_int,
)
})?;
Ok(ret as usize)
@ -137,7 +141,7 @@ impl FileDesc {
libc::writev(
self.fd,
bufs.as_ptr() as *const libc::iovec,
cmp::min(bufs.len(), max_iov() as usize) as c_int,
cmp::min(bufs.len(), max_iov()) as c_int,
)
})?;
Ok(ret as usize)