coio

A C++ asynchronous I/O library built on the sender/receiver model (std::execution), with first-class coroutine support.

#include <coio/core.h>
#include <coio/execution_context.h>
#include <coio/utils/timer.h>

using namespace std::chrono_literals;

auto job(coio::time_loop::scheduler sched, int value, std::chrono::seconds delay) -> coio::task<int> {
    coio::timer timer{sched};
    co_await timer.async_wait(delay);
    co_return value;
}

auto main() -> int {
    coio::time_loop context;
    auto [i, j] = coio::this_thread::sync_wait(coio::when_all(
        job(context.get_scheduler(), 114, 2s),
        job(context.get_scheduler(), 514, 1s),
        [&context]() -> coio::task<> { context.run(); co_return; }()
    )).value();
    // i == 114, j == 514, total wall time ≈ 2s
}

Features

• Sender/receiver model — every asynchronous operation is a sender, composable with std::execution algorithms and directly co_await-able inside coio coroutines.
• Coroutine types — task<T, Allocator, Scheduler> for asynchronous computations, generator<Ref, Val, Allocator> for lazy synchronous sequences.
• Execution contexts — the portable time_loop, plus native async I/O backends: epoll_context and uring_context on Linux, iocp_context on Windows.
• Networking — TCP/UDP sockets with synchronous and asynchronous operations, address types and a resolver.
• Files and pipes — stream and random-access files, pipes, and complete-transfer read/write algorithms.
• Synchronization — async_mutex, async_semaphore, async_latch: primitives that suspend coroutines instead of blocking threads.
• Utilities — timers, structured concurrency scopes, signal handling, buffers and concurrent queues.

Note

Async I/O and networking backends are currently implemented on Linux (epoll and io_uring; the io_uring backend requires kernel 5.19 or newer) and Windows (IOCP).

Where to start

Goal	Page
Build and install the library	Getting Started
Understand senders, coroutines, and cancellation in coio	Concepts
Write your first async program	task, time_loop
Do network I/O	Sockets, I/O Model & Lifetime
Understand the threading contracts	Execution Contexts, Thread Safety Summary

License

coio is distributed under the MIT License.