mailing list of musl libc

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 #include "pthread_impl.h"
#include <threads.h>

int __mtx_trylock(__mtx_t *mtx)
{
	int tid, old, own, ret = 0;
	pthread_t self;
	if (mtx->_mt_typ == PTHREAD_MUTEX_NORMAL) {
		return a_cas(&mtx->_mt_lck, 0, thrd_busy) & thrd_busy;
	} else {
		self = __pthread_self();
		tid = self->tid;
		old = mtx->_mt_lck;
		own = old & 0x7fffffff;
		if (own == tid) {
			if ((unsigned)mtx->_mt_cnt >= INT_MAX) return thrd_error;
			else mtx->_mt_cnt++;
		} else {
			if ((own && !(own & 0x40000000)) || a_cas(&mtx->_mt_lck, old, tid)!=old)
				return thrd_busy;
		}
	}
	return thrd_success;
}

int mtx_trylock(mtx_t *mut)
{
	__mtx_t * m = __mtx_getref(mut);
	if (!m) return thrd_error;
	int ret = __mtx_trylock(m);
	__mtx_unref(m);
	return ret;
}