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Rollup merge of #105239 - gh2o:no-heap-alloc-on-thread-start, r=cuviper

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Avoid heap allocation when truncating thread names

Ensure that heap allocation does not occur in a thread until `std::thread` is ready. This fixes issues with custom allocators that call `std:🧵:current()`, since doing so prematurely initializes `THREAD_INFO` and causes the following `thread_info::set()` to fail.
This commit is contained in:
Matthias Krüger 2022-12-10 15:01:44 +01:00 committed by GitHub
commit 43bee03a67
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1 changed files with 7 additions and 12 deletions
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19
library/std/src/sys/unix/thread.rs
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@ -136,7 +136,7 @@ pub fn set_name(name: &CStr) {
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);
@ -153,7 +153,7 @@ pub fn set_name(name: &CStr) {
#[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);
@ -285,17 +285,12 @@ fn drop(&mut self) {
}
#[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> {