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So I'm writing some multithreaded shit in C that is supposed to work cross-platform. MingW has Posix threads for Windows, so that saved already half of the platform dependency. The other half was that these threads need to run external programs.

Well, there's system(), right? Uhm yes, but it sucks. It's incredibly slow on Windows, and it looks like you can have only one system() call ongoing at the same time. Which kinda defeats the multithreaded driver. Ok, but there's CreateProcessA(), and that doesn't suck.

Fine, now for Linux. The fork/exec hack is quite ugly, but it works and is even fast. Just never use fork() without immediate exec(). First try under Cygwin... crap I fork bombed my system! What is this shit? Ah I fucked up the path names so that the external executable couldn't be run.

Lesson learnt: put an exit() right after the exec() in the path for child process. Should never be reached, but if it goes there, the exit() at least prevents a fork bomb.

Well yeah, sort of works under Cygwin, but only with up to 3 threads. Beyond that, it seems like fork() at some point gives two processes the same PID, and then shit hangs.

Even slapping a mutex around the fork and releasing it only in the parent process didn't help. Fork in Cygwin is like a fork in the ass. posix_spawn() should work better because it can be mapped more easily to the Windows model, but still no dice.

OK, testing under real Linux. Yeah, no issues with that one! But instead, I get some obscure "free(): invalid size" abort. What the fuck would that even mean?! Checking my free() calls: all fine.

Time to fire up GDB in the terminal! Put a catch on the abort signal, mh got just hex data. Shit I forgot to compile with -O0 and -g. Next try. Backtrace shows the full call trace, back to the originating line in my program - which is fclose() on a file.

Ahhh I remember! Under Linux, fclosing a file that is already closed makes the program crash. So probably I was closing it twice. Checking back.. yeah that's where it was.

Shit runs fast on several cores now!