1 unstable release
|0.1.0||Feb 18, 2020|
#6 in #waker
In Rust async programming it is somewhat common to need to keep track of a set of
Wakers that should be notified when something happens. This is useful for implementing many synchronization abstractions including mutexes, channels, condition variables, etc. This library provides an implementation of a queue of
Wakers, that can be used for this purpose.
The implementation (and API) pulls heavily from the
waker_set module in
async-std, and the storage structure was inspired by
slab, although the actual details differ somewhat to optimize for the uses of
This implementation differs from the
waker_set implementation and patterns followed in the
futures-util crate. Specifically:
- The order in which tasks are notified is more fair.
Waitlistuses a FIFO queue for notifying waiting tasks, whereas the usage of
slabin other implementations can result in task starvation in certains situations (see https://users.rust-lang.org/t/concerns-about-using-slab-to-track-wakers/33653).
- Removing an entry from the list is potentially
O(1). This is a bit of a tradeoff. Using slab gets
O(1)removal because it doesn't care about the order of the entries. On the other hand, notifying a single entry is
Waitlist, and notifying all waiting only has to iterate through waiting entries, whereas with slab it is necessary to iterate through the entire capacity of the slab. Also, if an entry has already been woken in
Waitlist, "removal" is still only
O(1)(because it is really just decrementing a counter).
WaitListuses std::sync::Mutex to synchronize similar to
async-stdwhich uses a