lindig/polly

OCaml bindings for Linux epoll(2)

Polly

Polly is an OCaml binding for the Linux epoll system call:

• Small, simple, and self-contained
• Avoids most allocation in the event loop
• MIT licensed

Note that epoll is specific to Linux and that this library won't compile on macOS, for example.

Installation

As of version 0.2.2, Polly is now in Opam and can be installed from there:

opam install polly

Most recently version 0.4.1 was submitted to Opam.

Using inside utop

• make utop or
• dune utop

launches a utop toplevel that has the library loaded for interactive use.

Other Epoll Bindings

• OCaml Backpack
• Jane Street Core

Contribute

If you find this useful, please contribute back by raising pull requests for improvements you made.

polly's Issues

release runtime lock around syscalls

Polly should probably release the runtime lock in a few more places, e.g. epoll_create1 and eventfd are both syscalls that may allocate resources and currently they'd block the entire process for their duration.
epoll_ctl is a syscall too, but it may be invoked very frequently (depending how the application) is written, so that one should probably be benchmarked whether releasing the runtime lock is beneficial or not (although in general we should probably release the runtime lock around any syscall - we don't know how long they might take).
The only place where keeping the runtime lock held is beneficial are small library functions that on their fastpaths don't invoke any syscalls.

Polly does release the runtime lock around the very long syscall that waits, so that is fine.

OTOH releasing the runtime lock makes optimizations like #12 impossible, so if we make changes in this area we should probably measure all 3 scenarios (current polly, noalloc polly, and polly with runtime lock released in _ctl), also measuring the impact on other threads that may be blocked.

Optimise stub

The function caml_polly_ctl and the three functions calling it could be called frequently in some applications. We could tag them with noalloc and untagged, raising the exception from OCaml in case of error ?

Adding evenfd inside polly

Could it be possible to add binding for
`̀``
#include <sys/eventfd.h>

int eventfd(unsigned int initval, int flags);

This is only one function, frequently used to wait on mutex/semaphore with epoll. So a binding for just that may be a bit overkill ?

make lint

make lint is not configured in the same way as lint in the worflow ?
on my machine, make lint reports no error while the workflow fails with the same code.