An introduction to libuv (2016)

https://nikhilm.github.io/uvbook/

by eatonphil • 8 years ago

125 38 8 years ago

nikhilm.github.io

ridiculous_fish3• 8 years ago

libuv supports child processes via fork, such as in uv_spawn. It also uses multiple threads to support uv_fs_stat, etc.

How does it handle the well known incompatibility between fork and threads?

oconnor663• 8 years ago

Which incompatibility do you mean? If you're forking to create a child process, usually you're just careful not to do anything that might acquire a lock (including allocating memory) in between the fork and the exec, and then I think you're good?

Forking for something else, though, god help you.

ridiculous_fish3• 8 years ago

The tricky part of this approach is error handling. What if a system call fails in between fork and exec, or exec itself?

It looks like libuv creates a pipe for every new process, and uses that to send errno back on any failing system call. This has the disadvantage that you only get the error code, and none of the context. You get ENOENT, but you don't know which path was invalid.

tapirl• 8 years ago

This book and the code is based on libuv version v1.3.0.

libuv v1.30 was release at on Jan 28, 2015. It is at v1.22.0.

nsm• 8 years ago

Original author here. Yes this book was written a long time ago when I was into the node ecosystem.

A lot of the book was copied into the official docs later https://github.com/libuv/libuv/pull/1246.

The book definitely does not capture new things. I do not intend to update it, but I still look at pull requests.

saghul2• 8 years ago

I merged it into the official docs, thanks a lot for all your work nsm! <3

newnewpdro5• 8 years ago

Why is the hello world example [0] unnecessarily allocating and freeing the uv_loop_t? When I see this kind of crap right out of the gate I immediately begin suspecting this is probably a pile of awful code written by a novice C programmer then documented and published as if it's the best thing since sliced bread.

Much of the value in making a struct (and hence its size) public and supplying a pointer to the initializer is the potential to embed or avoid heap allocation of the thing altogether, and here in an example which would benefit from both the simplified code in addition to demonstrating the advantage, it's completely missed.

Fixed form:

  int main() {
    uv_loop_t loop;
    
    uv_loop_init(&loop);

    printf("Now quitting.\n");
    uv_run(&loop, UV_RUN_DEFAULT);

    uv_loop_close(&loop);

    return 0;
  }

[0] https://nikhilm.github.io/uvbook/basics.html#hello-world

CJefferson• 8 years ago

Generally, you only create one uv_loop_t, and it is vital it is never copied (which is easy to do accisentally if you stack allocate it).

mallocing is the entirely sensible thing to do here.

newnewpdro5• 8 years ago

Then uv_loop_t should be an opaque type so its size isn't known at all, and uv_loop_init() should instead be uv_loop_new() returning the heap-allocated uv_loop_t, and uv_loop_close() renamed to uv_loop_free().

As-is the API and the way its use is being demonstrated in that example appear amateur to say the least.

int0x803• 8 years ago

What do you mean by accidentally copy?

struct embbed { ... uv_loop_t loop; ... } e1, e2; ... e1 = e2; ?

beached_whale• 8 years ago

I just assumed it was because if the memory location ever changes it would invalidate all the pointers to it. It has to have a fixed memory location

nosefrog• 8 years ago

I work with Nikhil. He's incredibly smart and a fantastic programmer. Didn't know he wrote a book on libuv though!

saghul2• 8 years ago

We merged this guide into http://docs.libuv.org/en/v1.x/guide.html which got some updates to match API changes.

Keyframe• 8 years ago

Is libuv used anywhere else outside of node?

snarfy• 8 years ago

I'm pretty sure aspnetcore uses it.

sasmithjr• 8 years ago

The default for Kestrel has been moved off of libuv, but you can choose to use libuv if you'd like.

https://blogs.msdn.microsoft.com/webdev/2018/04/12/asp-net-c...

gajjanag• 8 years ago

The Julia programming language uses it.

piquadrat• 8 years ago

There's an event loop implementation for Python based on libuv: https://github.com/MagicStack/uvloop

It's compatible with the native asyncio event loop and can be used as a drop-in replacement.

insertnickname• 8 years ago

https://github.com/libuv/libuv/wiki/Projects-that-use-libuv

bmease• 8 years ago

neovim uses libuv.

djs55• 8 years ago

There's a very good OCaml binding: https://github.com/fdopen/uwt . It works really well in the networking component of the Docker for Mac and Windows desktop apps (see https://github.com/moby/vpnkit)

An introduction to libuv (2016)

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