third_party/ulib/musl/src/stdio/fputc.c

#include "stdio_impl.h"

int fputc(int c, FILE* f) {
    if (atomic_load(&f->lock) < 0 || !__lockfile(f))
        return putc_unlocked(c, f);
    c = putc_unlocked(c, f);
    __unlockfile(f);
    return c;
}