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Avoid heap allocation when truncating thread names #105239

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merged 1 commit into from
Dec 10, 2022
Merged

Avoid heap allocation when truncating thread names #105239

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19 changes: 7 additions & 12 deletions library/std/src/sys/unix/thread.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -136,7 +136,7 @@ impl Thread {

unsafe {
// Available since glibc 2.12, musl 1.1.16, and uClibc 1.0.20.
let name = truncate_cstr(name, TASK_COMM_LEN);
let name = truncate_cstr::<{ TASK_COMM_LEN }>(name);
let res = libc::pthread_setname_np(libc::pthread_self(), name.as_ptr());
// We have no good way of propagating errors here, but in debug-builds let's check that this actually worked.
debug_assert_eq!(res, 0);
Expand All @@ -153,7 +153,7 @@ impl Thread {
#[cfg(any(target_os = "macos", target_os = "ios", target_os = "watchos"))]
pub fn set_name(name: &CStr) {
unsafe {
let name = truncate_cstr(name, libc::MAXTHREADNAMESIZE);
let name = truncate_cstr::<{ libc::MAXTHREADNAMESIZE }>(name);
let res = libc::pthread_setname_np(name.as_ptr());
// We have no good way of propagating errors here, but in debug-builds let's check that this actually worked.
debug_assert_eq!(res, 0);
Expand Down Expand Up @@ -285,17 +285,12 @@ impl Drop for Thread {
}

#[cfg(any(target_os = "linux", target_os = "macos", target_os = "ios", target_os = "watchos"))]
fn truncate_cstr(cstr: &CStr, max_with_nul: usize) -> crate::borrow::Cow<'_, CStr> {
use crate::{borrow::Cow, ffi::CString};

if cstr.to_bytes_with_nul().len() > max_with_nul {
let bytes = cstr.to_bytes()[..max_with_nul - 1].to_vec();
// SAFETY: the non-nul bytes came straight from a CStr.
// (CString will add the terminating nul.)
Cow::Owned(unsafe { CString::from_vec_unchecked(bytes) })
} else {
Cow::Borrowed(cstr)
fn truncate_cstr<const MAX_WITH_NUL: usize>(cstr: &CStr) -> [libc::c_char; MAX_WITH_NUL] {
let mut result = [0; MAX_WITH_NUL];
for (src, dst) in cstr.to_bytes().iter().zip(&mut result[..MAX_WITH_NUL - 1]) {
*dst = *src as libc::c_char;
}
result
}

pub fn available_parallelism() -> io::Result<NonZeroUsize> {
Expand Down