/**
* Switch the active activity if there are other activities
* waiting to run.
*
* @param activity The current active activity.
*/
void ActivityManager::relinquish(Activity *activity)
{
// if we have waiting activities, then let one of them
// in next.
if (hasWaiters())
{
addWaitingActivity(activity, true);
}
}
/**
* Add a waiting activity to the waiting queue.
*
* @param waitingAct The activity to queue up.
* @param release If true, the kernel lock should be released on completion.
*/
void ActivityManager::addWaitingActivity(RexxActivity *waitingAct, bool release )
{
ResourceSection lock("ActivityManager::addWaitingActivity", 0); // need the control block locks
addWaitingActivityCount += 1;
// nobody waiting yet? If the release flag is true, we already have the
// kernel lock, but nobody is waiting. In theory, this can't really
// happen, but we can return immediately if that is true.
if (waitingActivities.empty())
{
// we're done if we already have the lock and the queue is empty.
if (release)
{
return;
}
// add to the end
waitingActivities.push_back(waitingAct);
// this will ensure this happens before the lock is released
sentinel = false;
// we should end up getting the lock immediately, but you never know.
lock.release(); // release the lock now
}
else
{
// add to the end
waitingActivities.push_back(waitingAct);
// this will ensure this happens before the lock is released
sentinel = false;
// we're going to wait until posted, so make sure the run semaphore is cleared
waitingAct->clearWait();
sentinel = true;
lock.release(); // release the lock now
sentinel = false;
// if we are the current kernel semaphore owner, time to release this
// so other waiters can
if (release)
{
unlockKernel();
}
SysActivity::yield(); // yield the thread
waitingAct->waitForDispatch(); // wait for this thread to get dispatched again
}
sentinel = true;
lockKernel(); // get the kernel lock now
// belt and braces. it is possible the dispatcher was
// reentered on the same thread, in which case we have an
// earlier stack frame waiting on the same semaphore. Clear it so it
// get get reposted later.
waitingAct->clearWait();
sentinel = false;
lock.reacquire(); // get the resource lock back
sentinel = false; // another memory barrier
// We only get dispatched if we end up at the front of the queue again,
// so just pop the front element.
waitingActivities.pop_front();
sentinel = true;
// if there's something else in the queue, then post the run semaphore of
// the head element so that it wakes up next and starts waiting on the
// run semaphore
if (hasWaiters())
{
waitingActivities.front()->postDispatch();
}
// the setting of the sentinel variables acts as a memory barrier to
// ensure that the assignment of currentActivitiy occurs precisely at this point.
sentinel = false;
currentActivity = waitingAct; /* set new current activity */
sentinel = true;
/* and new active settings */
Numerics::setCurrentSettings(waitingAct->getNumericSettings());
}
bool gps_hasWaiters()
{ return hasWaiters(&wait_gps); }