add proper fuxed-based locking for stdio

[musl] / src / stdio / ftrylockfile.c

#include "stdio_impl.h"
#include "pthread_impl.h"

int ftrylockfile(FILE *f)
{
        int tid = pthread_self()->tid;
        if (f->lock == tid) {
                if (f->lockcount == LONG_MAX)
                        return -1;
                f->lockcount++;
                return 0;
        }
        if (f->lock < 0) f->lock = 0;
        if (f->lock || a_cas(&f->lock, 0, tid))
                return -1;
        f->lockcount = 1;
        return 0;
}