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Auto merge of #149481 - RalfJung:threadid-fallback, r=joboet

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ThreadId generation fallback path: avoid spurious yields

Fixes https://github.com/rust-lang/miri/issues/4737
Alternative to https://github.com/rust-lang/rust/pull/149476
Cc `@orlp` `@joboet`
This commit is contained in:
bors 2025-12-01 10:47:13 +00:00
commit 9b82a4fffe
1 changed files with 4 additions and 1 deletions
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5
library/std/src/thread/id.rs
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@ -70,7 +70,9 @@ impl ThreadId {
// Acquire lock.
let mut spin = 0;
while COUNTER_LOCKED.compare_exchange_weak(false, true, Ordering::Acquire, Ordering::Relaxed).is_err() {
// Miri doesn't like it when we yield here as it interferes with deterministically
// scheduling threads, so avoid `compare_exchange_weak` to avoid spurious yields.
while COUNTER_LOCKED.swap(true, Ordering::Acquire) {
if spin <= 3 {
for _ in 0..(1 << spin) {
spin_loop();
@ -80,6 +82,7 @@ impl ThreadId {
}
spin += 1;
}
// This was `false` before the swap, so we got the lock.
// SAFETY: we have an exclusive lock on the counter.
unsafe {