Async Scheduler

Async Scheduler is a lightweight asynchronous task scheduler and runtime written in C.

Inspired by Rust's std::future, async/await, and tokio-style runtimes, it demonstrates how to implement efficient asynchronous programming in a garbage collector–free environment.

Features

• Manual implementation of Future and async/await: Recreates Rust's Future trait and async/await semantics in C.
• Coroutine-based task system: Stackless coroutine model for task scheduling.
• epoll-based asynchronous I/O: Efficient I/O event handling using Linux's epoll.
• Graceful shutdown: Cleans up all resources safely before server termination.

System Design

---

Build

Quick Build

source BUILD

Manual Build

Configure:

export CC=clang
export CFLAGS="-g -O2 -Wall -Wextra"

autoreconf -i
mkdir -p build
cd build
../configure

Build:

make
# or, with compilation database
bear -- make

Clean Build

cd build
make clean
make distclean

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Run

Server

./build/server

Example output:

Welcome to the Echo Server.
Usage: telnet localhost 10000
Press Ctrl+C to stop the Server.
Accept (6): 127.0.0.1
Echo (6): Hello?
Accept (7): 127.0.0.1
Echo (7): Good evening!
Echo (7): Goodbye.
Close (7)
Echo (6): Bye.
Close (6)
^C[SIG: 2]
Executor Stop.
Clean (5)
Goodbye.

Client

Telnet

telnet localhost 10000

Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
Hello?
Hello?
Bye.
Bye.
^]
telnet> quit
Connection closed.

Netcat

Disconnect immediately after sending data to the server. In this case, the connection is terminated before the client's fd is registered with the server.

echo "Hello?" | nc -q 0 localhost 10000

---

Valgrind

Compile for Debugging

export CC=clang
export CFLAGS="-gdwarf-4 -O0"
autoreconf -i
mkdir -p build && cd build
../configure
bear -- make

Run with Valgrind

valgrind --leak-check=full --show-leak-kinds=all --track-origins=yes ./build/server

Example Output with Valgrind

==49402== Memcheck, a memory error detector
==49402== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==49402== Using Valgrind-3.18.1 and LibVEX; rerun with -h for copyright info
==49402== Command: ./build/server
==49402==
Welcome to the Echo Server.
Usage: telnet localhost 10000
Press Ctrl+C to stop the Server.
Accept (6): 127.0.0.1
Echo (6): hi
Close (6)
^C[SIG: 2]
Executor Stop.
Clean (5)
Goodbye.
==49402==
==49402== HEAP SUMMARY:
==49402==     in use at exit: 0 bytes in 0 blocks
==49402==   total heap usage: 57 allocs, 57 frees, 11,194 bytes allocated
==49402==
==49402== All heap blocks were freed -- no leaks are possible
==49402==
==49402== For lists of detected and suppressed errors, rerun with: -s
==49402== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

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Code Formatting

• torvalds/linux: .clang-format

find . -iname '*.h' -o -iname '*.c' | xargs clang-format -i