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Comment by kentonv | Hacker News Reader

Doesn't almost every C library function potentially call getenv()? printf()ing a number requires checking the locale which can be configured via the environment, after all.

I'd say you shouldn't be calling setenv() at all once you've spawned threads.

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The environment variables don't affect locale immediately; only when you call setlocale().

> I'd say you shouldn't be calling setenv() at all once you've spawned threads.

Or, you know, get a better C library. https://src.illumos.org/source/xref/illumos-gate/usr/src/lib...

Can you explain what point you are trying to get across? I just see a page of code.

That appears to be the OpenSolaris C library.

I imagine that it is meant to convey that the quality is higher in this library than in GNU libc.

As the link contains a specific line number, I believe gp suggests to read comment blocks. I’m not very interested to dive into details atm, but at least the explanations seem to be on point.

Just read the code! /s

Grandparent didn't just link to "code"; they linked to a five-paragraph comment explaining what is going on. Did you read those comments before you posted your snarky reply?

I think the gist of it is that unlike the glibc implementation, the Illumos implementation of getenv() is lock-free and thread-safe.

you are a joy

Correct. libc is largely thread unsafe.

Thread unsafe is too kind a qualifier, libc is largely thread-broken.

Doesn't have to be. Even `strtok()`, `getpwnam()`, etc. can be thread-safe (just not reentrant).

I have to admit the conclusion I have reached is that threads are the problem not libc.

We really should have embraced a better primitive than "shared memory execution environment"

I think a lot could be fixed with functions that don't access global state, but get that state as an additional parameter. E.g. I would really like `snprintf_l()`/`fprintf_l()` to be supported by glibc. It is supported by FreeBSD, macOS (Darwin), and even Windows (with a `_` prefix for some reason)! Not by GNU libc.

I think that it is generally not reasonable to convert existing large projects to be multithreaded, in the same way that it is generally not reasonable to fully rewrite existing large projects from scratch.

The alternative that I have seen be successful, is to achieve parallelism by forking separate processes wherever you would have spawned threads, and then communicate through shared memory regions.

It's a lot like having Rust-style unsafe blocks, in that you know that if you are having a thread-safety issue it will definitely be in one of the code sections where you are touching the shared memory region, and not anywhere else.

Obviously there's a higher startup cost for forking, but this makes it possible to gain parallelism without breaking all the thread-unsafe code that is certainly in an existing large project.

> I'd say you shouldn't be calling setenv() at all once you've spawned threads.

That's why I hate ZeroMQ. They spawn threads and do magics behind your back.

ZeroMQ is a big abstraction over sockets. The higher the level of abstractions, the more these things are usually necessary.

If you're using a library like that it comes with the territory, and you have to decide for yourself the cost-benefit of using non blocking sockets and async io yourself, or trust a library.

Much more fun to write these things yourself sometimes, but I find e.g. libevent a nice somewhere-in-between abstraction level I can be happy with.

Sure, but library that spawn threads are a pain. It is convenient for the library writer but it always end up being a significant inconvenience for the user.

But the question is: Who knows what and what not to do with libc?

"But Go compiled it just fine..."

I build most of my Go binaries with cgo disabled for this, and many other reasons.

In case you don't know, cross-building with GOOS/GOARCH will imply CGO_ENABLED=0 unless you also specify CC_FOR_${GOOS}_${GOARCH}; I cross-build most of my code for (and test it on) amd64, arm64, linux, openbsd, and darwin.

Go will sometimes link to the local libc for network-related functionality if you don't disable cgo.

That's the entire point of the post and the earlier posts it links to.

The post is about getaddrinfo() specifically. It just struck me as odd to call that one out when there are far more common C library calls that use getenv().

There's a strong tendency to think of network calls as entirely universal and not tied in any way to to locale settings in the environment.

Time, date, physical spellings, ... many things are locale dependant, but socket stuff?.

It comes as a Surprise!!, and not the good kind, to many a network programmer with just a few years under their belt to discover threaded networking can segfault because of this.

Once you know, you know and don't forget (until next time), but I suspect this was the motivation behind the blog posting, the principal of potentially most surprise.

They did a post on mktime()

But, yes, in general for libc, if the manpage didn't say it's thread-safe, it is unsafe.

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