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	diff --git a/src/applications/drydock/worker/DrydockLeaseUpdateWorker.php b/src/applications/drydock/worker/DrydockLeaseUpdateWorker.php
	index 676401937e..0402276696 100644
	--- a/src/applications/drydock/worker/DrydockLeaseUpdateWorker.php
	+++ b/src/applications/drydock/worker/DrydockLeaseUpdateWorker.php
	@@ -1,1128 +1,1129 @@
	<?php

	/**
	* @task update Updating Leases
	* @task command Processing Commands
	* @task allocator Drydock Allocator
	* @task acquire Acquiring Leases
	* @task activate Activating Leases
	* @task release Releasing Leases
	* @task break Breaking Leases
	* @task destroy Destroying Leases
	*/
	final class DrydockLeaseUpdateWorker extends DrydockWorker {

	protected function doWork() {
	$lease_phid = $this->getTaskDataValue('leasePHID');

	$hash = PhabricatorHash::digestForIndex($lease_phid);
	$lock_key = 'drydock.lease:'.$hash;

	$lock = PhabricatorGlobalLock::newLock($lock_key)
	->lock(1);

	try {
	$lease = $this->loadLease($lease_phid);
	$this->handleUpdate($lease);
	} catch (Exception $ex) {
	$lock->unlock();
	$this->flushDrydockTaskQueue();
	throw $ex;
	}

	$lock->unlock();
	}


	/* -( Updating Leases )---------------------------------------------------- */


	/**
	* @task update
	*/
	private function handleUpdate(DrydockLease $lease) {
	try {
	$this->updateLease($lease);
	} catch (DrydockAcquiredBrokenResourceException $ex) {
	// If this lease acquired a resource but failed to activate, we don't
	// need to break the lease. We can throw it back in the pool and let
	// it take another shot at acquiring a new resource.

	// Before we throw it back, release any locks the lease is holding.
	DrydockSlotLock::releaseLocks($lease->getPHID());

	$lease
	->setStatus(DrydockLeaseStatus::STATUS_PENDING)
	->setResourcePHID(null)
	->save();

	$lease->logEvent(
	DrydockLeaseReacquireLogType::LOGCONST,
	array(
	'class' => get_class($ex),
	'message' => $ex->getMessage(),
	));

	$this->yieldLease($lease, $ex);
	} catch (Exception $ex) {
	if ($this->isTemporaryException($ex)) {
	$this->yieldLease($lease, $ex);
	} else {
	$this->breakLease($lease, $ex);
	}
	}
	}


	/**
	* @task update
	*/
	private function updateLease(DrydockLease $lease) {
	$this->processLeaseCommands($lease);

	$lease_status = $lease->getStatus();
	switch ($lease_status) {
	case DrydockLeaseStatus::STATUS_PENDING:
	$this->executeAllocator($lease);
	break;
	case DrydockLeaseStatus::STATUS_ACQUIRED:
	$this->activateLease($lease);
	break;
	case DrydockLeaseStatus::STATUS_ACTIVE:
	// Nothing to do.
	break;
	case DrydockLeaseStatus::STATUS_RELEASED:
	case DrydockLeaseStatus::STATUS_BROKEN:
	$this->destroyLease($lease);
	break;
	case DrydockLeaseStatus::STATUS_DESTROYED:
	break;
	}

	$this->yieldIfExpiringLease($lease);
	}


	/**
	* @task update
	*/
	private function yieldLease(DrydockLease $lease, Exception $ex) {
	$duration = $this->getYieldDurationFromException($ex);

	$lease->logEvent(
	DrydockLeaseActivationYieldLogType::LOGCONST,
	array(
	'duration' => $duration,
	));

	throw new PhabricatorWorkerYieldException($duration);
	}


	/* -( Processing Commands )------------------------------------------------ */


	/**
	* @task command
	*/
	private function processLeaseCommands(DrydockLease $lease) {
	if (!$lease->canReceiveCommands()) {
	return;
	}

	$this->checkLeaseExpiration($lease);

	$commands = $this->loadCommands($lease->getPHID());
	foreach ($commands as $command) {
	if (!$lease->canReceiveCommands()) {
	break;
	}

	$this->processLeaseCommand($lease, $command);

	$command
	->setIsConsumed(true)
	->save();
	}
	}


	/**
	* @task command
	*/
	private function processLeaseCommand(
	DrydockLease $lease,
	DrydockCommand $command) {
	switch ($command->getCommand()) {
	case DrydockCommand::COMMAND_RELEASE:
	$this->releaseLease($lease);
	break;
	}
	}


	/* -( Drydock Allocator )-------------------------------------------------- */


	/**
	* Find or build a resource which can satisfy a given lease request, then
	* acquire the lease.
	*
	* @param DrydockLease Requested lease.
	* @return void
	* @task allocator
	*/
	private function executeAllocator(DrydockLease $lease) {
	$blueprints = $this->loadBlueprintsForAllocatingLease($lease);

	// If we get nothing back, that means no blueprint is defined which can
	// ever build the requested resource. This is a permanent failure, since
	// we don't expect to succeed no matter how many times we try.
	if (!$blueprints) {
	throw new PhabricatorWorkerPermanentFailureException(
	pht(
	'No active Drydock blueprint exists which can ever allocate a '.
	'resource for lease "%s".',
	$lease->getPHID()));
	}

	// First, try to find a suitable open resource which we can acquire a new
	// lease on.
	$resources = $this->loadAcquirableResourcesForLease($blueprints, $lease);

	list($free_resources, $used_resources) = $this->partitionResources(
	$lease,
	$resources);

	$resource = $this->leaseAnyResource($lease, $free_resources);
	if ($resource) {
	return $resource;
	}

	// We're about to try creating a resource. If we're already creating
	// something, just yield until that resolves.

	$this->yieldForPendingResources($lease);

	// We haven't been able to lease an existing resource yet, so now we try to
	// create one. We may still have some less-desirable "used" resources that
	// we'll sometimes try to lease later if we fail to allocate a new resource.

	$resource = $this->newLeasedResource($lease, $blueprints);
	if ($resource) {
	return $resource;
	}

	// We haven't been able to lease a desirable "free" resource or create a
	// new resource. Try to lease a "used" resource.

	$resource = $this->leaseAnyResource($lease, $used_resources);
	if ($resource) {
	return $resource;
	}

	// If this lease has already triggered a reclaim, just yield and wait for
	// it to resolve.
	$this->yieldForReclaimingResources($lease);

	// Try to reclaim a resource. This will yield if it reclaims something.
	$this->reclaimAnyResource($lease, $blueprints);

	// We weren't able to lease, create, or reclaim any resources. We just have
	// to wait for resources to become available.

	$lease->logEvent(
	DrydockLeaseWaitingForResourcesLogType::LOGCONST,
	array(
	'blueprintPHIDs' => mpull($blueprints, 'getPHID'),
	));

	throw new PhabricatorWorkerYieldException(15);
	}

	private function reclaimAnyResource(DrydockLease $lease, array $blueprints) {
	assert_instances_of($blueprints, 'DrydockBlueprint');

	$blueprints = $this->rankBlueprints($blueprints, $lease);

	// Try to actively reclaim unused resources. If we succeed, jump back
	// into the queue in an effort to claim it.

	foreach ($blueprints as $blueprint) {
	$reclaimed = $this->reclaimResources($blueprint, $lease);
	if ($reclaimed) {

	$lease->logEvent(
	DrydockLeaseReclaimLogType::LOGCONST,
	array(
	'resourcePHIDs' => array($reclaimed->getPHID()),
	));

	// Yield explicitly here: we'll be awakened when the resource is
	// reclaimed.

	throw new PhabricatorWorkerYieldException(15);
	}
	}
	}

	private function yieldForPendingResources(DrydockLease $lease) {
	// See T13677. If this lease has already triggered the allocation of
	// one or more resources and they are still pending, just yield and
	// wait for them.

	$viewer = $this->getViewer();

	$phids = $lease->getAllocatedResourcePHIDs();
	if (!$phids) {
	return null;
	}

	$resources = id(new DrydockResourceQuery())
	->setViewer($viewer)
	->withPHIDs($phids)
	->withStatuses(
	array(
	DrydockResourceStatus::STATUS_PENDING,
	))
	->setLimit(1)
	->execute();
	if (!$resources) {
	return;
	}

	$lease->logEvent(
	DrydockLeaseWaitingForActivationLogType::LOGCONST,
	array(
	'resourcePHIDs' => mpull($resources, 'getPHID'),
	));

	throw new PhabricatorWorkerYieldException(15);
	}

	private function yieldForReclaimingResources(DrydockLease $lease) {
	$viewer = $this->getViewer();

	$phids = $lease->getReclaimedResourcePHIDs();
	if (!$phids) {
	return;
	}

	$resources = id(new DrydockResourceQuery())
	->setViewer($viewer)
	->withPHIDs($phids)
	->withStatuses(
	array(
	DrydockResourceStatus::STATUS_ACTIVE,
	+ DrydockResourceStatus::STATUS_RELEASED,
	))
	->setLimit(1)
	->execute();
	if (!$resources) {
	return;
	}

	$lease->logEvent(
	DrydockLeaseWaitingForReclamationLogType::LOGCONST,
	array(
	'resourcePHIDs' => mpull($resources, 'getPHID'),
	));

	throw new PhabricatorWorkerYieldException(15);
	}

	private function newLeasedResource(
	DrydockLease $lease,
	array $blueprints) {
	assert_instances_of($blueprints, 'DrydockBlueprint');

	$usable_blueprints = $this->removeOverallocatedBlueprints(
	$blueprints,
	$lease);

	// If we get nothing back here, some blueprint claims it can eventually
	// satisfy the lease, just not right now. This is a temporary failure,
	// and we expect allocation to succeed eventually.

	// Return, try to lease a "used" resource, and continue from there.

	if (!$usable_blueprints) {
	return null;
	}

	$usable_blueprints = $this->rankBlueprints($usable_blueprints, $lease);

	$new_resources = $this->newResources($lease, $usable_blueprints);
	if (!$new_resources) {
	// If we were unable to create any new resources, return and
	// try to lease a "used" resource.
	return null;
	}

	$new_resources = $this->removeUnacquirableResources(
	$new_resources,
	$lease);
	if (!$new_resources) {
	// If we make it here, we just built a resource but aren't allowed
	// to acquire it. We expect this to happen if the resource prevents
	// acquisition until it activates, which is common when a resource
	// needs to perform setup steps.

	// Explicitly yield and wait for activation, since we don't want to
	// lease a "used" resource.

	throw new PhabricatorWorkerYieldException(15);
	}

	$resource = $this->leaseAnyResource($lease, $new_resources);
	if ($resource) {
	return $resource;
	}

	// We may not be able to lease a resource even if we just built it:
	// another process may snatch it up before we can lease it. This should
	// be rare, but is not concerning. Just try to build another resource.

	// We likely could try to build the next resource immediately, but err on
	// the side of caution and yield for now, at least until this code is
	// better vetted.

	throw new PhabricatorWorkerYieldException(15);
	}

	private function partitionResources(
	DrydockLease $lease,
	array $resources) {

	assert_instances_of($resources, 'DrydockResource');
	$viewer = $this->getViewer();

	$lease_statuses = array(
	DrydockLeaseStatus::STATUS_PENDING,
	DrydockLeaseStatus::STATUS_ACQUIRED,
	DrydockLeaseStatus::STATUS_ACTIVE,
	);

	// Partition resources into "free" resources (which we can try to lease
	// immediately) and "used" resources, which we can only to lease after we
	// fail to allocate a new resource.

	// "Free" resources are unleased and/or prefer reuse over allocation.
	// "Used" resources are leased and prefer allocation over reuse.

	$free_resources = array();
	$used_resources = array();

	foreach ($resources as $resource) {
	$blueprint = $resource->getBlueprint();

	if (!$blueprint->shouldAllocateSupplementalResource($resource, $lease)) {
	$free_resources[] = $resource;
	continue;
	}

	$leases = id(new DrydockLeaseQuery())
	->setViewer($viewer)
	->withResourcePHIDs(array($resource->getPHID()))
	->withStatuses($lease_statuses)
	->setLimit(1)
	->execute();
	if (!$leases) {
	$free_resources[] = $resource;
	continue;
	}

	$used_resources[] = $resource;
	}

	return array($free_resources, $used_resources);
	}

	private function newResources(
	DrydockLease $lease,
	array $blueprints) {
	assert_instances_of($blueprints, 'DrydockBlueprint');

	$resources = array();
	$exceptions = array();
	foreach ($blueprints as $blueprint) {
	$caught = null;
	try {
	$resources[] = $this->allocateResource($blueprint, $lease);

	// Bail after allocating one resource, we don't need any more than
	// this.
	break;
	} catch (Exception $ex) {
	$caught = $ex;
	} catch (Throwable $ex) {
	$caught = $ex;
	}

	if ($caught) {
	// This failure is not normally expected, so log it. It can be
	// caused by something mundane and recoverable, however (see below
	// for discussion).

	// We log to the blueprint separately from the log to the lease:
	// the lease is not attached to a blueprint yet so the lease log
	// will not show up on the blueprint; more than one blueprint may
	// fail; and the lease is not really impacted (and won't log) if at
	// least one blueprint actually works.

	$blueprint->logEvent(
	DrydockResourceAllocationFailureLogType::LOGCONST,
	array(
	'class' => get_class($caught),
	'message' => $caught->getMessage(),
	));

	$exceptions[] = $caught;
	}
	}

	if (!$resources) {
	// If one or more blueprints claimed that they would be able to allocate
	// resources but none are actually able to allocate resources, log the
	// failure and yield so we try again soon.

	// This can happen if some unexpected issue occurs during allocation
	// (for example, a call to build a VM fails for some reason) or if we
	// raced another allocator and the blueprint is now full.

	$ex = new PhutilAggregateException(
	pht(
	'All blueprints failed to allocate a suitable new resource when '.
	'trying to allocate lease ("%s").',
	$lease->getPHID()),
	$exceptions);

	$lease->logEvent(
	DrydockLeaseAllocationFailureLogType::LOGCONST,
	array(
	'class' => get_class($ex),
	'message' => $ex->getMessage(),
	));

	return null;
	}

	return $resources;
	}


	private function leaseAnyResource(
	DrydockLease $lease,
	array $resources) {
	assert_instances_of($resources, 'DrydockResource');

	if (!$resources) {
	return null;
	}

	$resources = $this->rankResources($resources, $lease);

	$exceptions = array();
	$yields = array();

	$allocated = null;
	foreach ($resources as $resource) {
	try {
	$this->acquireLease($resource, $lease);
	$allocated = $resource;
	break;
	} catch (DrydockResourceLockException $ex) {
	// We need to lock the resource to actually acquire it. If we aren't
	// able to acquire the lock quickly enough, we can yield and try again
	// later.
	$yields[] = $ex;
	} catch (DrydockSlotLockException $ex) {
	// This also just indicates we ran into some kind of contention,
	// probably from another lease. Just yield.
	$yields[] = $ex;
	} catch (DrydockAcquiredBrokenResourceException $ex) {
	// If a resource was reclaimed or destroyed by the time we actually
	// got around to acquiring it, we just got unlucky.
	$yields[] = $ex;
	} catch (PhabricatorWorkerYieldException $ex) {
	// We can be told to yield, particularly by the supplemental allocator
	// trying to give us a supplemental resource.
	$yields[] = $ex;
	} catch (Exception $ex) {
	$exceptions[] = $ex;
	}
	}

	if ($allocated) {
	return $allocated;
	}

	if ($yields) {
	throw new PhabricatorWorkerYieldException(15);
	}

	throw new PhutilAggregateException(
	pht(
	'Unable to acquire lease "%s" on any resource.',
	$lease->getPHID()),
	$exceptions);
	}


	/**
	* Get all the concrete @{class:DrydockBlueprint}s which can possibly
	* build a resource to satisfy a lease.
	*
	* @param DrydockLease Requested lease.
	* @return list<DrydockBlueprint> List of qualifying blueprints.
	* @task allocator
	*/
	private function loadBlueprintsForAllocatingLease(
	DrydockLease $lease) {
	$viewer = $this->getViewer();

	$impls = DrydockBlueprintImplementation::getAllForAllocatingLease($lease);
	if (!$impls) {
	return array();
	}

	$blueprint_phids = $lease->getAllowedBlueprintPHIDs();
	if (!$blueprint_phids) {
	$lease->logEvent(DrydockLeaseNoBlueprintsLogType::LOGCONST);
	return array();
	}

	$query = id(new DrydockBlueprintQuery())
	->setViewer($viewer)
	->withPHIDs($blueprint_phids)
	->withBlueprintClasses(array_keys($impls))
	->withDisabled(false);

	// The Drydock application itself is allowed to authorize anything. This
	// is primarily used for leases generated by CLI administrative tools.
	$drydock_phid = id(new PhabricatorDrydockApplication())->getPHID();

	$authorizing_phid = $lease->getAuthorizingPHID();
	if ($authorizing_phid != $drydock_phid) {
	$blueprints = id(clone $query)
	->withAuthorizedPHIDs(array($authorizing_phid))
	->execute();
	if (!$blueprints) {
	// If we didn't hit any blueprints, check if this is an authorization
	// problem: re-execute the query without the authorization constraint.
	// If the second query hits blueprints, the overall configuration is
	// fine but this is an authorization problem. If the second query also
	// comes up blank, this is some other kind of configuration issue so
	// we fall through to the default pathway.
	$all_blueprints = $query->execute();
	if ($all_blueprints) {
	$lease->logEvent(
	DrydockLeaseNoAuthorizationsLogType::LOGCONST,
	array(
	'authorizingPHID' => $authorizing_phid,
	));
	return array();
	}
	}
	} else {
	$blueprints = $query->execute();
	}

	$keep = array();
	foreach ($blueprints as $key => $blueprint) {
	if (!$blueprint->canEverAllocateResourceForLease($lease)) {
	continue;
	}

	$keep[$key] = $blueprint;
	}

	return $keep;
	}


	/**
	* Load a list of all resources which a given lease can possibly be
	* allocated against.
	*
	* @param list<DrydockBlueprint> Blueprints which may produce suitable
	* resources.
	* @param DrydockLease Requested lease.
	* @return list<DrydockResource> Resources which may be able to allocate
	* the lease.
	* @task allocator
	*/
	private function loadAcquirableResourcesForLease(
	array $blueprints,
	DrydockLease $lease) {
	assert_instances_of($blueprints, 'DrydockBlueprint');
	$viewer = $this->getViewer();

	$resources = id(new DrydockResourceQuery())
	->setViewer($viewer)
	->withBlueprintPHIDs(mpull($blueprints, 'getPHID'))
	->withTypes(array($lease->getResourceType()))
	->withStatuses(
	array(
	DrydockResourceStatus::STATUS_ACTIVE,
	))
	->execute();

	return $this->removeUnacquirableResources($resources, $lease);
	}


	/**
	* Remove resources which can not be acquired by a given lease from a list.
	*
	* @param list<DrydockResource> Candidate resources.
	* @param DrydockLease Acquiring lease.
	* @return list<DrydockResource> Resources which the lease may be able to
	* acquire.
	* @task allocator
	*/
	private function removeUnacquirableResources(
	array $resources,
	DrydockLease $lease) {
	$keep = array();
	foreach ($resources as $key => $resource) {
	$blueprint = $resource->getBlueprint();

	if (!$blueprint->canAcquireLeaseOnResource($resource, $lease)) {
	continue;
	}

	$keep[$key] = $resource;
	}

	return $keep;
	}


	/**
	* Remove blueprints which are too heavily allocated to build a resource for
	* a lease from a list of blueprints.
	*
	* @param list<DrydockBlueprint> List of blueprints.
	* @return list<DrydockBlueprint> List with blueprints that can not allocate
	* a resource for the lease right now removed.
	* @task allocator
	*/
	private function removeOverallocatedBlueprints(
	array $blueprints,
	DrydockLease $lease) {
	assert_instances_of($blueprints, 'DrydockBlueprint');

	$keep = array();

	foreach ($blueprints as $key => $blueprint) {
	if (!$blueprint->canAllocateResourceForLease($lease)) {
	continue;
	}

	$keep[$key] = $blueprint;
	}

	return $keep;
	}


	/**
	* Rank blueprints by suitability for building a new resource for a
	* particular lease.
	*
	* @param list<DrydockBlueprint> List of blueprints.
	* @param DrydockLease Requested lease.
	* @return list<DrydockBlueprint> Ranked list of blueprints.
	* @task allocator
	*/
	private function rankBlueprints(array $blueprints, DrydockLease $lease) {
	assert_instances_of($blueprints, 'DrydockBlueprint');

	// TODO: Implement improvements to this ranking algorithm if they become
	// available.
	shuffle($blueprints);

	return $blueprints;
	}


	/**
	* Rank resources by suitability for allocating a particular lease.
	*
	* @param list<DrydockResource> List of resources.
	* @param DrydockLease Requested lease.
	* @return list<DrydockResource> Ranked list of resources.
	* @task allocator
	*/
	private function rankResources(array $resources, DrydockLease $lease) {
	assert_instances_of($resources, 'DrydockResource');

	// TODO: Implement improvements to this ranking algorithm if they become
	// available.
	shuffle($resources);

	return $resources;
	}


	/**
	* Perform an actual resource allocation with a particular blueprint.
	*
	* @param DrydockBlueprint The blueprint to allocate a resource from.
	* @param DrydockLease Requested lease.
	* @return DrydockResource Allocated resource.
	* @task allocator
	*/
	private function allocateResource(
	DrydockBlueprint $blueprint,
	DrydockLease $lease) {
	$resource = $blueprint->allocateResource($lease);
	$this->validateAllocatedResource($blueprint, $resource, $lease);

	// If this resource was allocated as a pending resource, queue a task to
	// activate it.
	if ($resource->getStatus() == DrydockResourceStatus::STATUS_PENDING) {

	$lease->addAllocatedResourcePHIDs(
	array(
	$resource->getPHID(),
	));
	$lease->save();

	PhabricatorWorker::scheduleTask(
	'DrydockResourceUpdateWorker',
	array(
	'resourcePHID' => $resource->getPHID(),

	// This task will generally yield while the resource activates, so
	// wake it back up once the resource comes online. Most of the time,
	// we'll be able to lease the newly activated resource.
	'awakenOnActivation' => array(
	$this->getCurrentWorkerTaskID(),
	),
	),
	array(
	'objectPHID' => $resource->getPHID(),
	));
	}

	return $resource;
	}


	/**
	* Check that the resource a blueprint allocated is roughly the sort of
	* object we expect.
	*
	* @param DrydockBlueprint Blueprint which built the resource.
	* @param wild Thing which the blueprint claims is a valid resource.
	* @param DrydockLease Lease the resource was allocated for.
	* @return void
	* @task allocator
	*/
	private function validateAllocatedResource(
	DrydockBlueprint $blueprint,
	$resource,
	DrydockLease $lease) {

	if (!($resource instanceof DrydockResource)) {
	throw new Exception(
	pht(
	'Blueprint "%s" (of type "%s") is not properly implemented: %s must '.
	'return an object of type %s or throw, but returned something else.',
	$blueprint->getBlueprintName(),
	$blueprint->getClassName(),
	'allocateResource()',
	'DrydockResource'));
	}

	if (!$resource->isAllocatedResource()) {
	throw new Exception(
	pht(
	'Blueprint "%s" (of type "%s") is not properly implemented: %s '.
	'must actually allocate the resource it returns.',
	$blueprint->getBlueprintName(),
	$blueprint->getClassName(),
	'allocateResource()'));
	}

	$resource_type = $resource->getType();
	$lease_type = $lease->getResourceType();

	if ($resource_type !== $lease_type) {
	throw new Exception(
	pht(
	'Blueprint "%s" (of type "%s") is not properly implemented: it '.
	'built a resource of type "%s" to satisfy a lease requesting a '.
	'resource of type "%s".',
	$blueprint->getBlueprintName(),
	$blueprint->getClassName(),
	$resource_type,
	$lease_type));
	}
	}

	private function reclaimResources(
	DrydockBlueprint $blueprint,
	DrydockLease $lease) {
	$viewer = $this->getViewer();

	$resources = id(new DrydockResourceQuery())
	->setViewer($viewer)
	->withBlueprintPHIDs(array($blueprint->getPHID()))
	->withStatuses(
	array(
	DrydockResourceStatus::STATUS_ACTIVE,
	))
	->execute();

	// TODO: We could be much smarter about this and try to release long-unused
	// resources, resources with many similar copies, old resources, resources
	// that are cheap to rebuild, etc.
	shuffle($resources);

	foreach ($resources as $resource) {
	if ($this->canReclaimResource($resource)) {
	$this->reclaimResource($resource, $lease);
	return $resource;
	}
	}

	return null;
	}


	/* -( Acquiring Leases )--------------------------------------------------- */


	/**
	* Perform an actual lease acquisition on a particular resource.
	*
	* @param DrydockResource Resource to acquire a lease on.
	* @param DrydockLease Lease to acquire.
	* @return void
	* @task acquire
	*/
	private function acquireLease(
	DrydockResource $resource,
	DrydockLease $lease) {

	$blueprint = $resource->getBlueprint();
	$blueprint->acquireLease($resource, $lease);

	$this->validateAcquiredLease($blueprint, $resource, $lease);

	// If this lease has been acquired but not activated, queue a task to
	// activate it.
	if ($lease->getStatus() == DrydockLeaseStatus::STATUS_ACQUIRED) {
	$this->queueTask(
	__CLASS__,
	array(
	'leasePHID' => $lease->getPHID(),
	),
	array(
	'objectPHID' => $lease->getPHID(),
	));
	}
	}


	/**
	* Make sure that a lease was really acquired properly.
	*
	* @param DrydockBlueprint Blueprint which created the resource.
	* @param DrydockResource Resource which was acquired.
	* @param DrydockLease The lease which was supposedly acquired.
	* @return void
	* @task acquire
	*/
	private function validateAcquiredLease(
	DrydockBlueprint $blueprint,
	DrydockResource $resource,
	DrydockLease $lease) {

	if (!$lease->isAcquiredLease()) {
	throw new Exception(
	pht(
	'Blueprint "%s" (of type "%s") is not properly implemented: it '.
	'returned from "%s" without acquiring a lease.',
	$blueprint->getBlueprintName(),
	$blueprint->getClassName(),
	'acquireLease()'));
	}

	$lease_phid = $lease->getResourcePHID();
	$resource_phid = $resource->getPHID();

	if ($lease_phid !== $resource_phid) {
	throw new Exception(
	pht(
	'Blueprint "%s" (of type "%s") is not properly implemented: it '.
	'returned from "%s" with a lease acquired on the wrong resource.',
	$blueprint->getBlueprintName(),
	$blueprint->getClassName(),
	'acquireLease()'));
	}
	}


	/* -( Activating Leases )-------------------------------------------------- */


	/**
	* @task activate
	*/
	private function activateLease(DrydockLease $lease) {
	$resource = $lease->getResource();
	if (!$resource) {
	throw new Exception(
	pht('Trying to activate lease with no resource.'));
	}

	$resource_status = $resource->getStatus();

	if ($resource_status == DrydockResourceStatus::STATUS_PENDING) {
	throw new PhabricatorWorkerYieldException(15);
	}

	if ($resource_status != DrydockResourceStatus::STATUS_ACTIVE) {
	throw new DrydockAcquiredBrokenResourceException(
	pht(
	'Trying to activate lease ("%s") on a resource ("%s") in '.
	'the wrong status ("%s").',
	$lease->getPHID(),
	$resource->getPHID(),
	$resource_status));
	}

	// NOTE: We can race resource destruction here. Between the time we
	// performed the read above and now, the resource might have closed, so
	// we may activate leases on dead resources. At least for now, this seems
	// fine: a resource dying right before we activate a lease on it should not
	// be distinguishable from a resource dying right after we activate a lease
	// on it. We end up with an active lease on a dead resource either way, and
	// can not prevent resources dying from lightning strikes.

	$blueprint = $resource->getBlueprint();
	$blueprint->activateLease($resource, $lease);
	$this->validateActivatedLease($blueprint, $resource, $lease);
	}

	/**
	* @task activate
	*/
	private function validateActivatedLease(
	DrydockBlueprint $blueprint,
	DrydockResource $resource,
	DrydockLease $lease) {

	if (!$lease->isActivatedLease()) {
	throw new Exception(
	pht(
	'Blueprint "%s" (of type "%s") is not properly implemented: it '.
	'returned from "%s" without activating a lease.',
	$blueprint->getBlueprintName(),
	$blueprint->getClassName(),
	'acquireLease()'));
	}

	}


	/* -( Releasing Leases )--------------------------------------------------- */


	/**
	* @task release
	*/
	private function releaseLease(DrydockLease $lease) {
	$lease
	->setStatus(DrydockLeaseStatus::STATUS_RELEASED)
	->save();

	$lease->logEvent(DrydockLeaseReleasedLogType::LOGCONST);

	$resource = $lease->getResource();
	if ($resource) {
	$blueprint = $resource->getBlueprint();
	$blueprint->didReleaseLease($resource, $lease);
	}

	$this->destroyLease($lease);
	}


	/* -( Breaking Leases )---------------------------------------------------- */


	/**
	* @task break
	*/
	protected function breakLease(DrydockLease $lease, Exception $ex) {
	switch ($lease->getStatus()) {
	case DrydockLeaseStatus::STATUS_BROKEN:
	case DrydockLeaseStatus::STATUS_RELEASED:
	case DrydockLeaseStatus::STATUS_DESTROYED:
	throw new PhutilProxyException(
	pht(
	'Unexpected failure while destroying lease ("%s").',
	$lease->getPHID()),
	$ex);
	}

	$lease
	->setStatus(DrydockLeaseStatus::STATUS_BROKEN)
	->save();

	$lease->logEvent(
	DrydockLeaseActivationFailureLogType::LOGCONST,
	array(
	'class' => get_class($ex),
	'message' => $ex->getMessage(),
	));

	$lease->awakenTasks();

	$this->queueTask(
	__CLASS__,
	array(
	'leasePHID' => $lease->getPHID(),
	),
	array(
	'objectPHID' => $lease->getPHID(),
	));

	throw new PhabricatorWorkerPermanentFailureException(
	pht(
	'Permanent failure while activating lease ("%s"): %s',
	$lease->getPHID(),
	$ex->getMessage()));
	}


	/* -( Destroying Leases )-------------------------------------------------- */


	/**
	* @task destroy
	*/
	private function destroyLease(DrydockLease $lease) {
	$resource = $lease->getResource();

	if ($resource) {
	$blueprint = $resource->getBlueprint();
	$blueprint->destroyLease($resource, $lease);
	}

	DrydockSlotLock::releaseLocks($lease->getPHID());

	$lease
	->setStatus(DrydockLeaseStatus::STATUS_DESTROYED)
	->save();

	$lease->logEvent(DrydockLeaseDestroyedLogType::LOGCONST);

	$lease->awakenTasks();
	}

	}

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