From 3c55af5b09877c22405ed345c2873b9c5b33a20a Mon Sep 17 00:00:00 2001 From: Gavin Li Date: Sat, 3 Dec 2022 21:54:38 -0800 Subject: [PATCH] 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::thread::current(), since doing so prematurely initializes THREAD_INFO and causes the following thread_info::set() to fail. --- library/std/src/sys/unix/thread.rs | 19 +++++++------------ 1 file changed, 7 insertions(+), 12 deletions(-) diff --git a/library/std/src/sys/unix/thread.rs b/library/std/src/sys/unix/thread.rs index c1d30dd9d521b..6ecf5bdcf86d2 100644 --- a/library/std/src/sys/unix/thread.rs +++ b/library/std/src/sys/unix/thread.rs @@ -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); @@ -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); @@ -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(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 {