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Memoize the I/O vector count limit

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Keep the I/O vector count limit in a `SyncOnceCell` to avoid the overhead of
repeatedly calling `sysconf` as these limits are guaranteed to not change during
the lifetime of a process by POSIX.
This commit is contained in:
Adam Reichold 2020-08-01 14:29:42 +02:00
parent 9468752581
commit 6672f7be03
1 changed files with 16 additions and 11 deletions
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27
library/std/src/sys/unix/fd.rs
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@ -2,6 +2,7 @@
use crate::cmp;
use crate::io::{self, Initializer, IoSlice, IoSliceMut, Read};
use crate::lazy::SyncOnceCell;
use crate::mem;
use crate::sys::cvt;
use crate::sys_common::AsInner;
@ -28,18 +29,22 @@ const READ_LIMIT: usize = libc::ssize_t::MAX as usize;
#[cfg(any(target_os = "linux", target_os = "macos"))]
fn max_iov() -> c_int {
let ret = unsafe {
libc::sysconf(
#[cfg(target_os = "linux")]
libc::_SC_IOV_MAX,
#[cfg(target_os = "macos")]
libc::_SC_UIO_MAXIOV,
)
};
static LIM: SyncOnceCell<c_int> = SyncOnceCell::new();
// 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.get_or_init(|| {
let ret = unsafe {
libc::sysconf(
#[cfg(target_os = "linux")]
libc::_SC_IOV_MAX,
#[cfg(target_os = "macos")]
libc::_SC_UIO_MAXIOV,
)
};
// 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 }
})
}
#[cfg(not(any(target_os = "linux", target_os = "macos")))]