Subversion Repositories HelenOS-historic

/*

/*

 * Note about race conditions.

 * Note about race conditions.

 * Because of non-atomic nature of operations performed sequentially on the futex

 * Because of non-atomic nature of operations performed sequentially on the futex

 * counter and the futex wait queue, there is a race condition:

 * counter and the futex wait queue, there is a race condition:

 *

 *

 *

 *

 * Scenario 1 (wait queue timeout vs. futex_up()):

 * Scenario 1 (wait queue timeout vs. futex_up()):

 * 1. assume wq->missed_wakeups == 0 && futex->count == -1

 * 1. assume wq->missed_wakeups == 0 && futex->count == -1

 *    (ie. thread A sleeping, thread B in the critical section)

 *    (ie. thread A sleeping, thread B in the critical section)

 * 2. A receives timeout and gets removed from the wait queue

 * 2. A receives timeout and gets removed from the wait queue

/** Up the futex.

/** Up the futex.

 *

 *

 * @param futex Futex.

 * @param futex Futex.

 *

 *

 */

 */

int futex_up(atomic_t *futex)

int futex_up(atomic_t *futex)

{

{

    long val;

    long val;