Crate cooptex

cooptex provides deadlock-free Mutexes. The CoopMutex::lock method wraps the std::sync::Mutex return value with a Result that will request the caller to drop other held locks so another thread could make progress. This behavior is easily accomplished by using the retry_loop function.

use cooptex::*;
let a = CoopMutex::new(42);
let b = CoopMutex::new(43);

retry_loop(|| {
  let a_lock = a.lock()?.unwrap();
  let b_lock = b.lock()?.unwrap();
  assert_eq!(*a_lock + *b_lock, 85);
  Ok(())
});

The crate also provides a lower-overhead function lock which acquires a set of std::sync::Mutexes in a consistent order, to guarantee no deadlocks. Use that function if you can acquire all necessary locks at once.

If you conditionally acquire locks, CoopMutex and retry_loop are likely necessary.

CoopMutex Guarantees

This crate aims to guarantee that multiple threads cannot possibly deadlock by acquiring locks.

This crate also will prefer threads that have lived the “longest” without completing work. Meaning, when retry_loop successfully completes, it will move that thread to the end of the queue for acquiring future locks. This provides an approximately fair scheduler.

The crate is still in early development, so there may be cases that aren’t covered. Please open an issue if you can reproduce a deadlock.

Non-Guarantees

This crate explicitly allows the following potentially undesired behavior:

• CoopMutex::lock may return Retry when it could wait and acquire the lock without a deadlock.
• CoopMutex::lock may wait arbitrarily long before returning Retry.

Incomplete

• We have not fully analyzed the behavior during panics. There is no unsafe code, so we could only possibly deadlock.

Re-exports

pub use lock_in_order::lock;

Modules

lock_in_order

Support for the lock function.

Structs

CoopMutex

A deadlock-free version of Mutex.

MutexGuard

A guard for a CoopMutex. Access the underlying data through Deref and DerefMut.

Retry

Marker struct indicating that a thread requesting a CoopMutex should drop all its currently held MutexGuards and attempt to reacquire them.

Functions

retry_loop

Helper function for implementing the behavior of dropping held MutexGuards when a CoopMutex::lock call returns Retry.