/**
* Called by the executor to fetch something to build next.
*
* <p>This method blocks until a next project becomes buildable.
*/
public Queue.Item pop() throws InterruptedException {
final Executor exec = Executor.currentExecutor();
try {
while (true) {
final JobOffer offer = new JobOffer(exec);
long sleep = -1;
synchronized (this) {
// consider myself parked
assert !parked.containsKey(exec);
parked.put(exec, offer);
// reuse executor thread to do a queue maintenance.
// at the end of this we get all the buildable jobs
// in the buildables field.
maintain();
// allocate buildable jobs to executors
Iterator<BuildableItem> itr = buildables.iterator();
while (itr.hasNext()) {
BuildableItem p = itr.next();
// one last check to make sure this build is not blocked.
if (isBuildBlocked(p.task)) {
itr.remove();
blockedProjects.put(p.task, new BlockedItem(p));
continue;
}
JobOffer runner = loadBalancer.choose(p.task, new ApplicableJobOfferList(p.task));
if (runner == null)
// if we couldn't find the executor that fits,
// just leave it in the buildables list and
// check if we can execute other projects
continue;
assert runner.canTake(p.task);
// found a matching executor. use it.
runner.set(p);
itr.remove();
}
// we went over all the buildable projects and awaken
// all the executors that got work to do. now, go to sleep
// until this thread is awakened. If this executor assigned a job to
// itself above, the block method will return immediately.
if (!waitingList.isEmpty()) {
// wait until the first item in the queue is due
sleep = peek().timestamp.getTimeInMillis() - new GregorianCalendar().getTimeInMillis();
if (sleep < 100) sleep = 100; // avoid wait(0)
}
}
// this needs to be done outside synchronized block,
// so that executors can maintain a queue while others are sleeping
if (sleep == -1) offer.event.block();
else offer.event.block(sleep);
synchronized (this) {
// retract the offer object
assert parked.get(exec) == offer;
parked.remove(exec);
// am I woken up because I have a project to build?
if (offer.item != null) {
// if so, just build it
LOGGER.fine("Pop returning " + offer.item + " for " + exec.getName());
offer.item.future.startExecuting(exec);
return offer.item;
}
// otherwise run a queue maintenance
}
}
} finally {
synchronized (this) {
// remove myself from the parked list
JobOffer offer = parked.remove(exec);
if (offer != null && offer.item != null) {
// we are already assigned a project,
// ask for someone else to build it.
// note that while this thread is waiting for CPU
// someone else can schedule this build again,
// so check the contains method first.
if (!contains(offer.item.task)) buildables.put(offer.item.task, offer.item);
}
// since this executor might have been chosen for
// maintenance, schedule another one. Worst case
// we'll just run a pointless maintenance, and that's
// fine.
scheduleMaintenance();
}
}
}
protected void doRun() {
Queue q = queue.get();
if (q != null) q.maintain();
else cancel();
}