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Rollup merge of #103379 - cuviper:truncate-thread-name, r=thomcc
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Truncate thread names on Linux and Apple targets

These targets have system limits on the thread names, 16 and 64 bytes
respectively, and `pthread_setname_np` returns an error if the name is
longer. However, we're not in a context that can propagate errors when
we call this, and we used to implicitly truncate on Linux with `prctl`,
so now we manually truncate these names ahead of time.

r? ``@thomcc``
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Dylan-DPC authored Oct 24, 2022
2 parents 89d2387 + 15cfeb3 commit a3618d4
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Showing 2 changed files with 49 additions and 0 deletions.
18 changes: 18 additions & 0 deletions library/std/src/sys/unix/thread.rs
Original file line number Diff line number Diff line change
Expand Up @@ -132,8 +132,11 @@ impl Thread {

#[cfg(target_os = "linux")]
pub fn set_name(name: &CStr) {
const TASK_COMM_LEN: usize = 16;

unsafe {
// Available since glibc 2.12, musl 1.1.16, and uClibc 1.0.20.
let name = truncate_cstr(name, TASK_COMM_LEN);
libc::pthread_setname_np(libc::pthread_self(), name.as_ptr());
}
}
Expand All @@ -148,6 +151,7 @@ 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);
libc::pthread_setname_np(name.as_ptr());
}
}
Expand Down Expand Up @@ -276,6 +280,20 @@ 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)
}
}

pub fn available_parallelism() -> io::Result<NonZeroUsize> {
cfg_if::cfg_if! {
if #[cfg(any(
Expand Down
31 changes: 31 additions & 0 deletions library/std/src/thread/tests.rs
Original file line number Diff line number Diff line change
Expand Up @@ -37,6 +37,37 @@ fn test_named_thread() {
.unwrap();
}

#[cfg(any(
// Note: musl didn't add pthread_getname_np until 1.2.3
all(target_os = "linux", target_env = "gnu"),
target_os = "macos",
target_os = "ios",
target_os = "watchos"
))]
#[test]
fn test_named_thread_truncation() {
use crate::ffi::CStr;

let long_name = crate::iter::once("test_named_thread_truncation")
.chain(crate::iter::repeat(" yada").take(100))
.collect::<String>();

let result = Builder::new().name(long_name.clone()).spawn(move || {
// Rust remembers the full thread name itself.
assert_eq!(thread::current().name(), Some(long_name.as_str()));

// But the system is limited -- make sure we successfully set a truncation.
let mut buf = vec![0u8; long_name.len() + 1];
unsafe {
libc::pthread_getname_np(libc::pthread_self(), buf.as_mut_ptr().cast(), buf.len());
}
let cstr = CStr::from_bytes_until_nul(&buf).unwrap();
assert!(cstr.to_bytes().len() > 0);
assert!(long_name.as_bytes().starts_with(cstr.to_bytes()));
});
result.unwrap().join().unwrap();
}

#[test]
#[should_panic]
fn test_invalid_named_thread() {
Expand Down

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