Crossfire

High-performance lockless spsc/mpsc/mpmc channels, algorithm derives crossbeam with improvements.

It supports async contexts and bridges the gap between async and blocking contexts.

For the concept, please refer to the wiki.

Version history

• v1.0: Used in production since 2022.12.

• v2.0: [2025.6] Refactored the codebase and API by removing generic types from the ChannelShared type, which made it easier to code with.

• v2.1: [2025.9] Removed the dependency on crossbeam-channel and implemented with a modified version of crossbeam-queue, brings 2x performance improvements for both async and blocking contexts.

• v3.0: [2026.1] Refactored API back to generic flavor interface, added select. Dedicated optimization: Bounded SPSC +70%, MPSC +30%, one-size +20%. Eliminate enum dispatch cost, async performance improved for another 33%. Checkout compat for migration from v2.x.

Performance

Being a lockless channel, crossfire outperforms other async-capable channels. And thanks to a lighter notification mechanism, in a blocking context, most cases are even better than the original crossbeam-channel,

More benchmark data is posted on wiki.

Also, being a lockless channel, the algorithm relies on spinning and yielding. Spinning is good on multi-core systems, but not friendly to single-core systems (like virtual machines). So we provide a function detect_backoff_cfg() to detect the running platform. Calling it within the initialization section of your code, will get a 2x performance boost on VPS.

The benchmark is written in the criterion framework. You can run the benchmark by:

make bench crossfire
make bench crossfire_select

APIs

Concurrency Modules

• spsc, mpsc, mpmc. Each has different underlying implementation optimized to its concurrent model. The SP or SC interface is only for non-concurrent operation. It's more memory-efficient in waker registration, and has atomic ops cost reduced in the lockless algorithm.

• oneshot has its special sender/receiver type because using Tx / Rx will be too heavy.

• select:

  • Select<'a>: crossbeam-channel style type erased API, borrows receiver address and select with "token"
  • Multiplex: Multiplex stream that owns multiple receiver, select from the same type of channel flavors, for the same type of message.

Flavors

The following lockless queues are expose in flavor module, and each one have type alias in spsc/mpsc/mpmc:

• List (which use crossbeam SegQueue)
• Array (which is an enum that wraps crossbeam ArrayQueue, and a One if init with size<=1)
  • For a bounded channel, a 0 size case is not supported yet. (rewrite as 1 size).
  • The implementation for spsc & mpsc is simplified from mpmc version.
• One (which derives from ArrayQueue algorithm, but have better performance in size=1 scenario, because it have two slots to allow reader and writer works concurrently)
• Null (See the doc null), for cancellation purpose channel, that only wakeup on closing.

NOTE : Although the name Array, List are the same between spsc/mpsc/mpmc module, they are different type alias local to its parent module. We suggest distinguish by namespace when import for use.

Channel builder function

Aside from function bounded_*, unbounded_* which specify the sender / receiver type, each module has build() and new() function, which can apply to any channel flavors, and any async/blocking combinations.

Types

Safety: For the SP / SC version, AsyncTx, AsyncRx, Tx, and Rx are not Clone and without Sync. Although can be moved to other threads, but not allowed to use send/recv while in an Arc. (Refer to the compile_fail examples in the type document).

The benefit of using the SP / SC API is completely lockless waker registration, in exchange for a performance boost.

The sender/receiver can use the From trait to convert between blocking and async context counterparts (refer to the example below)

Error types

Error types are the same as crossbeam-channel:

TrySendError, SendError, SendTimeoutError, TryRecvError, RecvError, RecvTimeoutError

Async compatibility

Tested on tokio-1.x and async-std-1.x, crossfire is runtime-agnostic.

The following scenarios are considered:

• The AsyncTx::send() and AsyncRx::recv() operations are cancellation-safe in an async context. You can safely use the select! macro and timeout() function in tokio/futures in combination with recv(). On cancellation, SendFuture and RecvFuture will trigger drop(), which will clean up the state of the waker, making sure there is no memory-leak and deadlock. But you cannot know the true result from SendFuture, since it's dropped upon cancellation. Thus, we suggest using AsyncTx::send_timeout() instead.

• When the "tokio" or "async_std" feature is enabled, we also provide two additional functions:

• AsyncTx::send_timeout(), which will return the message that failed to be sent in SendTimeoutError. We guarantee the result is atomic. Alternatively, you can use AsyncTx::send_with_timer().

• AsyncRx::recv_timeout(), we guarantee the result is atomic. Alternatively, you can use AsyncRx::recv_with_timer().

• The waker footprint:

When using a multi-producer and multi-consumer scenario, there's a small memory overhead to pass along a Weak reference of wakers. Because we aim to be lockless, when the sending/receiving futures are canceled (like tokio::time::timeout()), it might trigger an immediate cleanup if the try-lock is successful, otherwise will rely on lazy cleanup. (This won't be an issue because weak wakers will be consumed by actual message send and recv). On an idle-select scenario, like a notification for close, the waker will be reused as much as possible if poll() returns pending.

• Handle written future:

The future object created by AsyncTx::send(), AsyncTx::send_timeout(), AsyncRx::recv(), AsyncRx::recv_timeout() is Sized. You don't need to put them in Box.

If you like to use poll function directly for complex behavior, you can call AsyncSink::poll_send() or AsyncStream::poll_item() with Context.

Usage

Cargo.toml:

[dependencies]
crossfire = "3.0"

Feature flags

• compat: Enable the compat model, which has the same API namespace struct as V2.x

• tokio: Enable send_timeout(), recv_timeout() with tokio sleep function. (conflict with async_std feature)

• async_std: Enable send_timeout, recv_timeout with async-std sleep function. (conflict with tokio feature)

• trace_log: Development mode, to enable internal log while testing or benchmark, to debug deadlock issues.

Example

blocking / async sender receiver mixed together

extern crate crossfire;
use crossfire::*;
#[macro_use]
extern crate tokio;
use tokio::time::{sleep, interval, Duration};

#[tokio::main]
async fn main() {
    let (tx, rx) = mpmc::bounded_async::<usize>(100);
    let mut recv_counter = 0;
    let mut co_tx = Vec::new();
    let mut co_rx = Vec::new();
    const ROUND: usize = 1000;

    let _tx: MTx<mpmc::Array<usize>> = tx.clone().into_blocking();
    co_tx.push(tokio::task::spawn_blocking(move || {
        for i in 0..ROUND {
            _tx.send(i).expect("send ok");
        }
    }));
    co_tx.push(tokio::spawn(async move {
        for i in 0..ROUND {
            tx.send(i).await.expect("send ok");
        }
    }));
    let _rx: MRx<mpmc::Array<usize>> = rx.clone().into_blocking();
    co_rx.push(tokio::task::spawn_blocking(move || {
        let mut count: usize = 0;
        'A: loop {
            match _rx.recv() {
                Ok(_i) => {
                    count += 1;
                }
                Err(_) => break 'A,
            }
        }
        count
    }));
    co_rx.push(tokio::spawn(async move {
        let mut count: usize = 0;
        'A: loop {
            match rx.recv().await {
                Ok(_i) => {
                    count += 1;
                }
                Err(_) => break 'A,
            }
        }
        count
    }));
    for th in co_tx {
        let _ = th.await.unwrap();
    }
    for th in co_rx {
        recv_counter += th.await.unwrap();
    }
    assert_eq!(recv_counter, ROUND * 2);
}

Test status

NOTE: Because we has push the speed to a level no one has gone before, it can put a pure pressure to the async runtime. Some hidden bug (especially atomic ops on weaker ordering platform) might occur:

The test is placed in test-suite directory, run with:

make test

Debugging deadlock issue

Debug locally:

Use --features trace_log to run the bench or test until it hangs, then press ctrl+c or send SIGINT, there will be latest log dump to /tmp/crossfire_ring.log (refer to tests/common.rs _setup_log())

Debug with github workflow: https://github.com/frostyplanet/crossfire-rs/issues/37