This document provides an overview of the libuv library. Libuv is a cross-platform asynchronous I/O and event loop library written in C. It is used by Node.js and many other projects. The document discusses libuv's architecture, features like the event loop, handles, and requests. It also covers libuv's use in Node.js and the current state and future plans for libuv.

1. A DEEP DIVE INTO LIBUV
Saúl Ibarra Corretgé
NodeConf EU 2016

2. A DEEP DIVE INTO LIBUV
DIA DHAOIBH A ÉIRE!
▸ @saghul
▸ libuv core janitor
▸ Nodejs collaborator
▸ Open Source enthusiast

3. LIBUV

4. A DEEP DIVE INTO LIBUV
LIBUV
▸ Cross-platform async I/O and more
▸ Small (relatively) C library: ~30K LOC (without tests)
▸ Extensive test suite and CI coverage
▸ Designed for C programs that miss the joy of JavaScript
callback hell
▸ Used by Node and many other projects:
https://github.com/libuv/libuv/wiki/Projects-that-use-libuv

5. A DEEP DIVE INTO LIBUV
LIBUV: FEATURES
▸ Event loop
▸ Timers
▸ TCP / UDP sockets
▸ Named pipes
▸ Filesystem operations
▸ Signal handling
▸ Child processes
▸ ANSI escaped TTY
▸ Threading utilities
▸ Coolest logo ever

6. A DEEP DIVE INTO LIBUV
LIBUV: ARCHITECTURE
▸ The event loop: uv_loop_t
▸ Handles: uv_handle_t
▸ Requests: uv_req_t
▸ Other utilities

7. A DEEP DIVE INTO LIBUV
LIBUV: ARCHITECTURE
OPERATING SYSTEM
NETWORK I/O FILE I/O OTHER STUFF
OS INDEPENDENT
STUFF

8. A DEEP DIVE INTO LIBUV
LIBUV ARCHITECTURE: NETWORK I/O
OPERATING SYSTEM
UV_TCP_T UV_PIPE_T UV_TTY_T
UV_UDP_T UV_POLL_TUV_STREAM_T
UV__IO_T (UNIX ONLY)

9. A DEEP DIVE INTO LIBUV
LIBUV ARCHITECTURE: FILE I/O
UV_FS_T UV_GETADDRINFO_T UV_GETNAMEINFO_T
UV__WORK_T
THREAD POOL
UV_WORK_T

10. A DEEP DIVE INTO LIBUV
LIBUV: A WORD ON THREADS
▸ We only use threads for file i/o and getaddrinfo
▸ http://blog.libtorrent.org/2012/10/asynchronous-disk-io/
▸ Default thread pool size is 4
(runtime env var: UV_THREADPOOL_SIZE)
▸ NOT FOR NETWORK I/O
▸ NOT FOR NETWORK I/O
▸ NOT FOR NETWORK I/O

11. THE LIBUV EVENT LOOP IS
SINGLE THREADED. THE THREAD
POOL IS ONLY USED FOR FILE I/O.
The libuv police
A DEEP DIVE INTO LIBUV

12. A DEEP DIVE INTO LIBUV
LIBUV ARCHITECTURE: OTHER
▸ OS independent
▸ uv_timer_t
▸ uv_idle_t, uv_prepare_t, uv_check_t
aka “loop watchers”
▸ The thread pool
▸ OS dependent
▸ uv_signal_t
▸ uv_process_t
▸ Threading and miscellaneous utilities

13. A DEEP DIVE INTO LIBUV
LIBUV: THE EVENT LOOP

14. int uv_run(uv_loop_t* loop, uv_run_mode mode) {
int timeout, r, ran_pending;
r = uv__loop_alive(loop);
if (!r)
uv__update_time(loop);
while (r != 0 && loop->stop_flag == 0) {
uv__update_time(loop);
uv__run_timers(loop);
ran_pending = uv__run_pending(loop);
uv__run_idle(loop);
uv__run_prepare(loop);
timeout = 0;
if ((mode == UV_RUN_ONCE && !ran_pending) || mode == UV_RUN_DEFAULT)
timeout = uv_backend_timeout(loop);
uv__io_poll(loop, timeout);
uv__run_check(loop);
uv__run_closing_handles(loop);
if (mode == UV_RUN_ONCE) {
uv__update_time(loop);
uv__run_timers(loop);
}
r = uv__loop_alive(loop);
if (mode == UV_RUN_ONCE || mode == UV_RUN_NOWAIT)
break;
}
loop->stop_flag = 0;
return r;
}

15. static int uv__loop_alive(const uv_loop_t* loop) {
return uv__has_active_handles(loop) ||
uv__has_active_reqs(loop) ||
loop->closing_handles != NULL;
}

16. int uv_backend_timeout(const uv_loop_t* loop) {
if (loop->stop_flag != 0)
return 0;
if (!uv_loop_alive(loop))
return 0;
if (!QUEUE_EMPTY(&loop->idle_handles))
return 0;
if (!QUEUE_EMPTY(&loop->pending_queue))
return 0;
return uv__next_timeout(loop);
}

17. void uv__run_timers(uv_loop_t* loop) {
struct heap_node* heap_node;
uv_timer_t* handle;
for (;;) {
heap_node = heap_min((struct heap*) &loop->timer_heap);
if (heap_node == NULL)
break;
handle = container_of(heap_node, uv_timer_t, heap_node);
if (handle->timeout > loop->time)
break;
uv_timer_stop(handle);
uv_timer_again(handle);
handle->timer_cb(handle);
}
}

18. LIBUV IN NODE

19. A DEEP DIVE INTO LIBUV
LIBUV: THE EVENT LOOP
REMEMBER?

20. A DEEP DIVE INTO LIBUV
NODE EVENT LOOP
COALESCED, 1 NODE
TIMER != 1 LIBUV
TIMER
RUN
ON A CHECK + IDLE
HANDLE
NEXT TICK CALLBACKS RUN FROM
NODE::MAKECALLBACK

21. A DEEP DIVE INTO LIBUV
ONION ARCHITECTURE (TM)
net.Socket
TCPWrap
uv_tcp_t
Socket._handle
TCPWrap.handle_
fd / HANDLE

22. STATE OF
THE UNICORN

23. A DEEP DIVE INTO LIBUV
STATE OF THE UNICORN: V1.X
▸ 1.10 release imminent
▸ Enterprise Ready (R)
▸ Release champion: @cjihrig
▸ 12 new APIs since 1.0.0
▸ ABI remained stable!
▸ 7 maintainers (~ 5 active)

24. A DEEP DIVE INTO LIBUV
STATE OF THE UNICORN: MASTER
▸ ~ 2kloc less!
▸ Supported platforms cleanup
▸ A number of pending PRs (sorry!)

25. A DEEP DIVE INTO LIBUV
STATE OF THE UNICORN: THE PLAN FOR V2
▸ Improve documentation
▸ Improve thread pool
▸ uv_timeout_t and uv_read_t requests
▸ libuv-extras: companion library
▸ uv_link_t, uv_ssl_t
▸ uv_serial_t ?

26. RESOURCES
libuv.org
docs.libuv.org
#libuv on IRC
libuv Google Group
#libuv on StackOverflow

27. WHEN THERE IS
SOMETHING STRANGE
IN YOUR
EVENT LOOP

28. A DEEP DIVE INTO LIBUV
WHO YOU GONNA CALL? @LIBUV/COLLABORATORS
▸ @piscisaureus
▸ @bnoordhuis
▸ @indutny
▸ @saghul
▸ @cjihrig
▸ @iWuzHere
▸ @santigimeno

29. QUESTIONS?
@saghul
bettercallsaghul.com