Open
Description
openedon Sep 28, 2023
See also #116179:
When a scoped thread is implicitly joined, the destructors of thread-local variables are not guaranteed to have completed when the scope is exited. When a scoped thread is explicitly joined, however, the destructors of thread-local variables do complete before the scope is exited.
Scoped thread implicit join fails 'happens before' guarantee
As documented in the Rust Atomics and Locks book by Mara Bos, "joining a thread creates a happens-before relationship between the joined thread and what happens after the join() call". This is not true for implicit joins on scoped threads.
I tried this code:
use std::{hint::black_box, mem::replace, thread};
static mut CONTROL: Option<String> = None;
fn main() {
// Explicit join of scoped thread.
{
for _ in 0..5000 {
thread::scope(|s| {
let h = s.spawn(|| {
FOO.with(|v| {
black_box(v);
});
});
h.join().unwrap();
});
// SAFETY: this happens after the thread join, which provides a `happens before` guarantee
let v = unsafe { &CONTROL };
black_box(format!("{:?}", v));
print!(".");
}
println!("Completed EXPLICIT join loop.");
}
println!();
// Implicit join of scoped thread.
{
for _ in 0..5000 {
thread::scope(|s| {
let _h = s.spawn(|| {
FOO.with(|v| {
black_box(v);
});
});
});
// SAFETY: this happens after the implicit thread join, which should provide a `happens before` guarantee
let v = unsafe { &CONTROL };
black_box(format!("{:?}", v));
print!(".");
}
println!("Completed IMPLICIT join loop.");
}
}
struct Foo(());
impl Drop for Foo {
fn drop(&mut self) {
// SAFETY: this happens before the thread join, which provides a `happens before` guarantee
let _: Option<String> = unsafe { replace(&mut CONTROL, Some("abcd".to_owned())) };
}
}
thread_local! {
static FOO: Foo = Foo(());
}I expected to see this happen: Both the explicit join and implicit join portions of the code should terminate normally.
Instead, this happened: The explicit join portion terminates normally as expected, but the implicit join portion panics (the number of iterations on the loop before it panics varies) .
This issue is related to issue #116179.
Meta
The same behaviour is observed on the nightly version nightly-x86_64-unknown-linux-gnu unchanged - rustc 1.74.0-nightly (0288f2e 2023-09-25).
rustc --version --verbose:
rustc 1.72.1 (d5c2e9c34 2023-09-13)
binary: rustc
commit-hash: d5c2e9c342b358556da91d61ed4133f6f50fc0c3
commit-date: 2023-09-13
host: x86_64-unknown-linux-gnu
release: 1.72.1
LLVM version: 16.0.5
Backtrace
thread 'main' panicked at 'byte index 5 is out of bounds of `hP�^`', library/core/src/fmt/mod.rs:2324:30
stack backtrace:
0: rust_begin_unwind
at /rustc/d5c2e9c342b358556da91d61ed4133f6f50fc0c3/library/std/src/panicking.rs:593:5
1: core::panicking::panic_fmt
at /rustc/d5c2e9c342b358556da91d61ed4133f6f50fc0c3/library/core/src/panicking.rs:67:14
2: core::str::slice_error_fail_rt
3: core::str::slice_error_fail
at /rustc/d5c2e9c342b358556da91d61ed4133f6f50fc0c3/library/core/src/str/mod.rs:87:9
4: core::str::traits::<impl core::slice::index::SliceIndex<str> for core::ops::range::Range<usize>>::index
at /rustc/d5c2e9c342b358556da91d61ed4133f6f50fc0c3/library/core/src/str/traits.rs:235:21
5: core::str::traits::<impl core::ops::index::Index<I> for str>::index
at /rustc/d5c2e9c342b358556da91d61ed4133f6f50fc0c3/library/core/src/str/traits.rs:61:15
6: <str as core::fmt::Debug>::fmt
at /rustc/d5c2e9c342b358556da91d61ed4133f6f50fc0c3/library/core/src/fmt/mod.rs:2324:30
7: <alloc::string::String as core::fmt::Debug>::fmt
at /rustc/d5c2e9c342b358556da91d61ed4133f6f50fc0c3/library/alloc/src/string.rs:2271:9
8: <&T as core::fmt::Debug>::fmt
at /rustc/d5c2e9c342b358556da91d61ed4133f6f50fc0c3/library/core/src/fmt/mod.rs:2268:62
9: core::fmt::builders::DebugTuple::field::{{closure}}
at /rustc/d5c2e9c342b358556da91d61ed4133f6f50fc0c3/library/core/src/fmt/builders.rs:322:17
10: core::result::Result<T,E>::and_then
at /rustc/d5c2e9c342b358556da91d61ed4133f6f50fc0c3/library/core/src/result.rs:1319:22
11: core::fmt::builders::DebugTuple::field
at /rustc/d5c2e9c342b358556da91d61ed4133f6f50fc0c3/library/core/src/fmt/builders.rs:309:35
12: core::fmt::Formatter::debug_tuple_field1_finish
at /rustc/d5c2e9c342b358556da91d61ed4133f6f50fc0c3/library/core/src/fmt/mod.rs:2035:9
13: <core::option::Option<T> as core::fmt::Debug>::fmt
at /rustc/d5c2e9c342b358556da91d61ed4133f6f50fc0c3/library/core/src/option.rs:559:37
14: <&T as core::fmt::Debug>::fmt
at /rustc/d5c2e9c342b358556da91d61ed4133f6f50fc0c3/library/core/src/fmt/mod.rs:2268:62
15: core::fmt::rt::Argument::fmt
at /rustc/d5c2e9c342b358556da91d61ed4133f6f50fc0c3/library/core/src/fmt/rt.rs:138:9
16: core::fmt::write
at /rustc/d5c2e9c342b358556da91d61ed4133f6f50fc0c3/library/core/src/fmt/mod.rs:1094:21
17: core::fmt::Write::write_fmt
at /rustc/d5c2e9c342b358556da91d61ed4133f6f50fc0c3/library/core/src/fmt/mod.rs:192:9
18: alloc::fmt::format::format_inner
at /rustc/d5c2e9c342b358556da91d61ed4133f6f50fc0c3/library/alloc/src/fmt.rs:610:16
19: alloc::fmt::format::{{closure}}
at /rustc/d5c2e9c342b358556da91d61ed4133f6f50fc0c3/library/alloc/src/fmt.rs:614:34
20: core::option::Option<T>::map_or_else
at /rustc/d5c2e9c342b358556da91d61ed4133f6f50fc0c3/library/core/src/option.rs:1180:21
21: alloc::fmt::format
at /rustc/d5c2e9c342b358556da91d61ed4133f6f50fc0c3/library/alloc/src/fmt.rs:614:5
22: thread_local_destruction_in_scoped_thread2::main
at ./general/src/bin/thread_local_destruction_in_scoped_thread2.rs:41:23
23: core::ops::function::FnOnce::call_once
at /rustc/d5c2e9c342b358556da91d61ed4133f6f50fc0c3/library/core/src/ops/function.rs:250:5
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
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