diff --git a/tests/pass/concurrency/tls_lib_drop.rs b/tests/pass/concurrency/tls_lib_drop.rs index 86f03bac34f..552b371cc7f 100644 --- a/tests/pass/concurrency/tls_lib_drop.rs +++ b/tests/pass/concurrency/tls_lib_drop.rs @@ -71,7 +71,116 @@ fn check_blocking() { thread::yield_now(); } +// This test tests that TLS destructors have run before the thread joins. The +// test has no false positives (meaning: if the test fails, there's actually +// an ordering problem). It may have false negatives, where the test passes but +// join is not guaranteed to be after the TLS destructors. However, false +// negatives should be exceedingly rare due to judicious use of +// thread::yield_now and running the test several times. +fn join_orders_after_tls_destructors() { + use std::sync::atomic::{AtomicU8, Ordering}; + + // We emulate a synchronous MPSC rendezvous channel using only atomics and + // thread::yield_now. We can't use std::mpsc as the implementation itself + // may rely on thread locals. + // + // The basic state machine for an SPSC rendezvous channel is: + // FRESH -> THREAD1_WAITING -> MAIN_THREAD_RENDEZVOUS + // where the first transition is done by the “receiving” thread and the 2nd + // transition is done by the “sending” thread. + // + // We add an additional state `THREAD2_LAUNCHED` between `FRESH` and + // `THREAD1_WAITING` to block until all threads are actually running. + // + // A thread that joins on the “receiving” thread completion should never + // observe the channel in the `THREAD1_WAITING` state. If this does occur, + // we switch to the “poison” state `THREAD2_JOINED` and panic all around. + // (This is equivalent to “sending” from an alternate producer thread.) + const FRESH: u8 = 0; + const THREAD2_LAUNCHED: u8 = 1; + const THREAD1_WAITING: u8 = 2; + const MAIN_THREAD_RENDEZVOUS: u8 = 3; + const THREAD2_JOINED: u8 = 4; + static SYNC_STATE: AtomicU8 = AtomicU8::new(FRESH); + + for _ in 0..10 { + SYNC_STATE.store(FRESH, Ordering::SeqCst); + + let jh = thread::Builder::new() + .name("thread1".into()) + .spawn(move || { + struct TlDrop; + + impl Drop for TlDrop { + fn drop(&mut self) { + let mut sync_state = SYNC_STATE.swap(THREAD1_WAITING, Ordering::SeqCst); + loop { + match sync_state { + THREAD2_LAUNCHED | THREAD1_WAITING => thread::yield_now(), + MAIN_THREAD_RENDEZVOUS => break, + THREAD2_JOINED => panic!( + "Thread 1 still running after thread 2 joined on thread 1" + ), + v => unreachable!("sync state: {}", v), + } + sync_state = SYNC_STATE.load(Ordering::SeqCst); + } + } + } + + thread_local! { + static TL_DROP: TlDrop = TlDrop; + } + + TL_DROP.with(|_| {}); + + loop { + match SYNC_STATE.load(Ordering::SeqCst) { + FRESH => thread::yield_now(), + THREAD2_LAUNCHED => break, + v => unreachable!("sync state: {}", v), + } + } + }) + .unwrap(); + + let jh2 = thread::Builder::new() + .name("thread2".into()) + .spawn(move || { + assert_eq!(SYNC_STATE.swap(THREAD2_LAUNCHED, Ordering::SeqCst), FRESH); + jh.join().unwrap(); + match SYNC_STATE.swap(THREAD2_JOINED, Ordering::SeqCst) { + MAIN_THREAD_RENDEZVOUS => return, + THREAD2_LAUNCHED | THREAD1_WAITING => { + panic!("Thread 2 running after thread 1 join before main thread rendezvous") + } + v => unreachable!("sync state: {:?}", v), + } + }) + .unwrap(); + + loop { + match SYNC_STATE.compare_exchange( + THREAD1_WAITING, + MAIN_THREAD_RENDEZVOUS, + Ordering::SeqCst, + Ordering::SeqCst, + ) { + Ok(_) => break, + Err(FRESH) => thread::yield_now(), + Err(THREAD2_LAUNCHED) => thread::yield_now(), + Err(THREAD2_JOINED) => { + panic!("Main thread rendezvous after thread 2 joined thread 1") + } + v => unreachable!("sync state: {:?}", v), + } + } + jh2.join().unwrap(); + } +} + fn main() { check_destructors(); check_blocking(); + join_orders_after_tls_destructors(); }