Replace non-reentrant C stdlib calls with thread-safe alternatives

[capocasa]

Summary

During pharao development I noticed some theoretical and reproducible non-thread-safe C calls in the Nim stdlib. Here is a list of C functions known not to be thread safe. I could reproduce data corruption on some of them for threaded access, while others seem to be thread safe in glibc but possibly not in other C libs. Performance should be equivalent.

Module	Non-reentrant	Replacement
times	localtime	localtime_s (MSVC) / localtime_r (MinGW, POSIX)
oserrors, syncio, osproc	strerror	strerror_r (via shared helper)
nativesockets	getprotobyname	getprotobyname_r
nativesockets	getservbyname	getservbyname_r
nativesockets	getservbyport	getservbyport_r
nativesockets	gethostbyname	getaddrinfo
nativesockets	gethostbyaddr	getnameinfo

strerror_r uses a bit of C code to detect a glibc function signature special case. An explicit tzset is added to localtime_r instead of localtime's implicit one.

This is a bit more change than I'd hope for but I'm not sure how to be more concise about it. Questions welcome.

[Araq]

The only thing that matters if the glibc / the OS's libc isn't threadsafe, in reality, in 2026. "Known not to be threadsafe on SunOS in 1998" -- I couldn't care less.

[capocasa]

Okay so first off that patch was way too invasive, it's clean now.

Here is a test program and is results:

nim e run.nims
Hint: used config file '/home/carlo/.choosenim/toolchains/nim-2.2.8/config/nim.cfg' [Conf]
Hint: used config file '/home/carlo/.choosenim/toolchains/nim-2.2.8/config/config.nims' [Conf]
Hint: used config file '/home/carlo/.config/nim/nim.cfg' [Conf]
Hint: used config file '/home/carlo/.config/nim/config.nims' [Conf]
  getProtoByName (glibc)
  getProtoByName (musl)
  getServByName (glibc)
  getServByName (musl)
  getServByPort (glibc)
  getServByPort (musl)
  getHostByName (glibc)
  getHostByName (musl)
  localtime (glibc)
  localtime (musl)

Thread-safety corruption test (8 threads, 50k iterations each)

Function          glibc                  musl
----------------- ---------------------- -------------------
getProtoByName    30/400000 CORRUPTED    ERROR
getServByName     6/40000 CORRUPTED      1/40000 CORRUPTED
getServByPort     1/8000 CORRUPTED       93/8000 CORRUPTED
getHostByName     SIGSEGV                SIGSEGV
localtime         524/400000 CORRUPTED   18/400000 CORRUPTED

[capocasa]

TLDR; the test program proves that 2026 glibc and musl are not, in fact, thread safe in the way the Nim stdlib is currently calling them.

[Araq]

Hint: used config file 'D:\a\Nim\Nim\compiler\nim.cfg' [Conf]
d:/a/nim/nim/dist/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/11.1.0/../../../../x86_64-w64-mingw32/bin/ld.exe: D:/a/Nim/Nim/nimcache/r_windows_amd64/@ptimes.nim.c.o:@ptimes.nim.c:(.text+0x40df): undefined reference to localtime_r' d:/a/nim/nim/dist/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/11.1.0/../../../../x86_64-w64-mingw32/bin/ld.exe: D:/a/Nim/Nim/nimcache/r_windows_amd64/@ptimes.nim.c.o:@ptimes.nim.c:(.text+0x4166): undefined reference to localtime_r'
collect2.exe: error: ld returned 1 exit status

[capocasa]

Testing platforms

[capocasa]

Done- replaces non-thread-safe calls that glibc and windows keep around for their extreme backwards compatibility with respective thread-safe extensions, does not touch anything else.

There's one hitch, I resorted to an ugly hack to prevent a musl regression. Clean way forward has been previously discussed.

[Araq]

That's too ugly, we need to find a better solution for it. Or we simply add our own locks around the existing getprotobyname() calls. The new Muslim libC is the future; if it lacks the new awesome getprotobyname_r with its 5 parameter ptr ptr shit we can't use it.