#async #futures #concurrency


A hassle-free data type for asynchronous programming

16 releases

0.7.0 Nov 30, 2020
0.6.2 Jun 7, 2020
0.6.1 Mar 23, 2020
0.5.0 Dec 23, 2019
0.1.1 Nov 7, 2017

#88 in Concurrency

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124 downloads per month
Used in 13 crates (9 directly)


1.5K SLoC


desync = "0.7"

Desync is a concurrency library for Rust that protects data by scheduling operations in order instead of locking and blocking threads. It provides a simple API that works well with Rust's notion of lifetimes, alongside a concurrency model with a dramatically reduced set of moving parts.

This approach has several advantages over the traditional method:

  • It's simpler: almost the entire set of thread methods and synchronisation primitives can be replaced with the two fundamental scheduling functions, sync() and desync().
  • There's less boilerplate: code is less about starting threads and sending messages and more literally expresses intent.
  • It's easier to reason about: scheduled operations are always performed in the order they're queued so race conditions and similar issues due to out-of-order execution are both much rarer and easier to debug.
  • Borrowing and asynchronous code can mix much more seamlessly than in other concurrency models.
  • It makes it easier to write highly concurrent code: desync makes moving between performing operations synchronously and asynchronously trivial, with no need to deal with adding code to start threads or communicate between them.

In addition to the two fundamental methods, desync provides methods for generating futures and processing streams.

Quick start

Desync provides a single type, Desync<T> that can be used to replace both threads and mutexes. This type schedules operations for a contained data structure so that they are always performed in order and optionally in the background.

Such a Desync object can be created like so:

use desync::Desync;
let number = Desync::new(0);

It supports two main operations. async will schedule a new job for the object that will run in a background thread. It's useful for deferring long-running operations and moving updates so they can run in parallel.

let number = Desync::new(0);
number.desync(|val| {
    // Long update here
    *val = 42;

// We can carry on what we're doing with the update now running in the background

The other operation is sync, which schedules a job to run synchronously on the data structure. This is useful for retrieving values from a Desync.

let new_number = number.sync(|val| *val);           // = 42

Desync objects always run operations in the order that is provided, so all operations are serialized from the point of view of the data that they contain. When combined with the ability to perform operations asynchronously, this provides a useful way to immediately parallelize long-running operations.

Working with futures

Desync has support for the futures library. The simplest operation is future_sync(), which creates a future that runs asynchronously on a Desync object but - unlike desync() can return a result. It works like this:

let future_number = number.future_sync(|val| future::ready(*val).boxed());
assert!(executor::block_on(async { future_number.await.unwrap() }) == 42 )

There is also a future_desync() operation, which can be used in cases where the thread is expected to block. It can be used in the same situations as future_sync() but has a detach() method to leave the task running in the background, or a sync() method to wait for the result to be computed.

Desync can run streams in the background too, via the pipe_in() and pipe() functions. These work on Arc<Desync<T>> references and provide a way to process a stream asynchronously. These two functions provide a powerful way to process input and also to connect Desync objects together using message-passing for communication.

let some_object = Arc::new(Desync::new(some_object));

pipe_in(Arc::clone(&number), some_stream, 
    |some_object, input| some_object.process(input));

let output_stream = pipe(Arc::clone(&number), some_stream, 
    |some_object, input| some_object.process_with_output(input));


~17K SLoC