Isn’t that good advice? Rewriting it in C can prove that the problem is not in your programmin language.

Outdated OS can be the problem as well.

What kind of advice did you expect?

> Rewriting it in C can prove that the problem is not in your programmin language

It's a lot of work of rewriting it in C. It's doable, but impractical. And such rewrite may introduce new bugs.

Proving that the problem isn't in my language wasn't necessary - there were no room for it to introduce such kind of bug. Language bugs are usually manifest themselves in a way different way, (like broken binary code leading to crashes or accepting invalid code). That's why I have created my question in a first place - while I was sure, that it wasn't a language bug.

> Outdated OS can be the problem as well.

Outdated OS can't be a problem. Basic socket functionality was implemented eons ago and all known bugs should be fixed even in pretty outdated versions of the kernel.

> What kind of advice did you expect?

Eventually I have found myself, that in my test program I create too much connections for a TCP server and its internal connection queue overflows. But it took some time to find it, way longer compared to what could be achieved if my SO was answered. The problem was not so hard to spot considering that I have described what exactly I do. Even providing code examples wasn't necessary - textual description was enough.