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A-atomicArea: Atomics, barriers, and sync primitivesArea: Atomics, barriers, and sync primitivesA-docsArea: Documentation for any part of the project, including the compiler, standard library, and toolsArea: Documentation for any part of the project, including the compiler, standard library, and toolsC-bugCategory: This is a bug.Category: This is a bug.T-libsRelevant to the library team, which will review and decide on the PR/issue.Relevant to the library team, which will review and decide on the PR/issue.T-libs-apiRelevant to the library API team, which will review and decide on the PR/issue.Relevant to the library API team, which will review and decide on the PR/issue.
Description
The code below verifies that the only one thread holds the ReentrantLock by recording the owner thread id inside. It should be true since the lock is never unlocked (note that the lock guard is leaked). In practice, in some executions the assertion fails:
#![feature(reentrant_lock)]
#![feature(thread_id_value)]
use std::cell::Cell;
use std::mem::ManuallyDrop;
use std::sync::ReentrantLock;
use std::thread;
fn main() {
let lock = ReentrantLock::new(Cell::new(None));
let run = || {
let id = ManuallyDrop::new(lock.lock());
match id.get() {
None => id.set(Some(thread::current().id())),
Some(id) => assert_eq!(id, thread::current().id()),
}
};
thread::scope(|s| {
s.spawn(run);
});
thread::scope(|s| {
s.spawn(run);
});
}
$ cargo run
thread '<unnamed>' panicked at src/main.rs:15:25:
assertion `left == right` failed
left: ThreadId(2)
right: ThreadId(3)
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
thread 'main' panicked at src/main.rs:21:5:
a scoped thread panicked
Inspired by report from rust-lang/miri#3450, which also explains why this fails.
Ideally the assertion failure wouldn't be among possible executions.
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A-atomicArea: Atomics, barriers, and sync primitivesArea: Atomics, barriers, and sync primitivesA-docsArea: Documentation for any part of the project, including the compiler, standard library, and toolsArea: Documentation for any part of the project, including the compiler, standard library, and toolsC-bugCategory: This is a bug.Category: This is a bug.T-libsRelevant to the library team, which will review and decide on the PR/issue.Relevant to the library team, which will review and decide on the PR/issue.T-libs-apiRelevant to the library API team, which will review and decide on the PR/issue.Relevant to the library API team, which will review and decide on the PR/issue.