Github user StephanEwen commented on a diff in the pull request:
https://github.com/apache/flink/pull/3394#discussion_r106513577
--- Diff:
flink-runtime/src/main/java/org/apache/flink/runtime/resourcemanager/slotmanager/SlotManager.java
---
@@ -21,519 +21,897 @@
import org.apache.flink.annotation.VisibleForTesting;
import org.apache.flink.api.common.time.Time;
import org.apache.flink.runtime.clusterframework.types.AllocationID;
-import org.apache.flink.runtime.clusterframework.types.ResourceID;
-import org.apache.flink.runtime.clusterframework.types.ResourceSlot;
+import org.apache.flink.runtime.clusterframework.types.ResourceProfile;
+import org.apache.flink.runtime.clusterframework.types.TaskManagerSlot;
import org.apache.flink.runtime.clusterframework.types.SlotID;
import org.apache.flink.runtime.concurrent.BiFunction;
+import org.apache.flink.runtime.concurrent.CompletableFuture;
import org.apache.flink.runtime.concurrent.Future;
-import org.apache.flink.runtime.resourcemanager.ResourceManagerServices;
+import org.apache.flink.runtime.concurrent.ScheduledExecutor;
+import org.apache.flink.runtime.concurrent.impl.FlinkCompletableFuture;
+import org.apache.flink.runtime.instance.InstanceID;
+import org.apache.flink.runtime.messages.Acknowledge;
import org.apache.flink.runtime.resourcemanager.SlotRequest;
-import
org.apache.flink.runtime.resourcemanager.messages.jobmanager.RMSlotRequestRegistered;
-import
org.apache.flink.runtime.resourcemanager.messages.taskexecutor.TMSlotRequestRejected;
-import
org.apache.flink.runtime.resourcemanager.messages.taskexecutor.TMSlotRequestReply;
-import
org.apache.flink.runtime.resourcemanager.registration.TaskExecutorRegistration;
+import
org.apache.flink.runtime.resourcemanager.exceptions.ResourceManagerException;
+import
org.apache.flink.runtime.resourcemanager.registration.TaskExecutorConnection;
import org.apache.flink.runtime.taskexecutor.SlotReport;
import org.apache.flink.runtime.taskexecutor.SlotStatus;
+import org.apache.flink.runtime.taskexecutor.TaskExecutorGateway;
+import
org.apache.flink.runtime.taskexecutor.exceptions.SlotAllocationException;
+import
org.apache.flink.runtime.taskexecutor.exceptions.SlotOccupiedException;
import org.apache.flink.util.Preconditions;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.Map;
-
-import static org.apache.flink.util.Preconditions.checkNotNull;
+import java.util.Objects;
+import java.util.UUID;
+import java.util.concurrent.CancellationException;
+import java.util.concurrent.Executor;
+import java.util.concurrent.ScheduledFuture;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.TimeoutException;
/**
- * SlotManager is responsible for receiving slot requests and do slot
allocations. It allows to request
- * slots from registered TaskManagers and issues container allocation
requests in case of there are not
- * enough available slots. Besides, it should sync its slot allocation
with TaskManager's heartbeat.
- * <p>
- * The main operation principle of SlotManager is:
- * <ul>
- * <li>1. All slot allocation status should be synced with TaskManager,
which is the ground truth.</li>
- * <li>2. All slots that have registered must be tracked, either by free
pool or allocated pool.</li>
- * <li>3. All slot requests will be handled by best efforts, there is no
guarantee that one request will be
- * fulfilled in time or correctly allocated. Conflicts or timeout or some
special error will happen, it should
- * be handled outside SlotManager. SlotManager will make each decision
based on the information it currently
- * holds.</li>
- * </ul>
- * <b>IMPORTANT:</b> This class is <b>Not Thread-safe</b>.
+ * The slot manager is responsible for maintaining a view on all
registered task manager slots,
+ * their allocation and all pending slot requests. Whenever a new slot is
registered or and
+ * allocated slot is freed, then it tries to fulfill another pending slot
request. Whenever there
+ * are not enough slots available the slot manager will notify the
resource manager about it via
+ * {@link ResourceManagerActions#allocateResource(ResourceProfile)}.
+ *
+ * In order to free resources and avoid resource leaks, idling task
managers (task managers whose
+ * slots are currently not used) and not fulfilled pending slot requests
time out triggering their
+ * release and failure, respectively.
*/
-public abstract class SlotManager {
+public class SlotManager implements AutoCloseable {
+
+ private static final Logger LOG =
LoggerFactory.getLogger(SlotManager.class);
+
+ /** Scheduled executor for timeouts */
+ private final ScheduledExecutor scheduledExecutor;
+
+ /** Timeout for slot requests to the task manager */
+ private final Time taskManagerRequestTimeout;
+
+ /** Timeout after which an allocation is discarded */
+ private final Time slotRequestTimeout;
+
+ /** Timeout after which an unused TaskManager is released */
+ private final Time taskManagerTimeout;
+
+ /** Map for all registered slots */
+ private final HashMap<SlotID, TaskManagerSlot> slots;
- protected final Logger LOG = LoggerFactory.getLogger(getClass());
+ /** Index of all currently free slots */
+ private final LinkedHashMap<SlotID, TaskManagerSlot> freeSlots;
- /** The Resource allocation provider */
- protected final ResourceManagerServices rmServices;
+ /** All currently registered task managers */
+ private final HashMap<InstanceID, TaskManagerRegistration>
taskManagerRegistrations;
- /** All registered task managers with ResourceID and gateway. */
- private final Map<ResourceID, TaskExecutorRegistration> taskManagers;
+ /** Map of fulfilled and active allocations for request deduplication
purposes */
+ private final HashMap<AllocationID, SlotID> fulfilledSlotRequests;
- /** All registered slots, including free and allocated slots */
- private final Map<ResourceID, Map<SlotID, ResourceSlot>>
registeredSlots;
+ /** Map of pending/unfulfilled slot allocation requests */
+ private final HashMap<AllocationID, PendingSlotRequest>
pendingSlotRequests;
- /** All pending slot requests, waiting available slots to fulfil */
- private final Map<AllocationID, SlotRequest> pendingSlotRequests;
+ /** Leader id of the containing component */
+ private UUID leaderId;
- /** All free slots that can be used to be allocated */
- private final Map<SlotID, ResourceSlot> freeSlots;
+ /** Executor for future callbacks which have to be "synchronized" */
+ private Executor mainThreadExecutor;
- /** All allocations, we can lookup allocations either by SlotID or
AllocationID */
- private final AllocationMap allocationMap;
+ /** Callbacks for resource (de-)allocations */
+ private ResourceManagerActions resourceManagerActions;
- private final Time timeout;
+ /** True iff the component has been started */
+ private boolean started;
- public SlotManager(ResourceManagerServices rmServices) {
- this.rmServices = checkNotNull(rmServices);
- this.registeredSlots = new HashMap<>(16);
- this.pendingSlotRequests = new LinkedHashMap<>(16);
- this.freeSlots = new HashMap<>(16);
- this.allocationMap = new AllocationMap();
- this.taskManagers = new HashMap<>();
- this.timeout = Time.seconds(10);
+ public SlotManager(
+ ScheduledExecutor scheduledExecutor,
+ Time taskManagerRequestTimeout,
+ Time slotRequestTimeout,
+ Time taskManagerTimeout) {
+ this.scheduledExecutor =
Preconditions.checkNotNull(scheduledExecutor);
+ this.taskManagerRequestTimeout =
Preconditions.checkNotNull(taskManagerRequestTimeout);
+ this.slotRequestTimeout =
Preconditions.checkNotNull(slotRequestTimeout);
+ this.taskManagerTimeout =
Preconditions.checkNotNull(taskManagerTimeout);
+
+ slots = new HashMap<>(16);
+ freeSlots = new LinkedHashMap<>(16);
+ taskManagerRegistrations = new HashMap<>(4);
+ fulfilledSlotRequests = new HashMap<>(16);
+ pendingSlotRequests = new HashMap<>(16);
+
+ leaderId = null;
+ resourceManagerActions = null;
+ started = false;
}
- //
------------------------------------------------------------------------
- // slot managements
- //
------------------------------------------------------------------------
+ //
---------------------------------------------------------------------------------------------
+ // Component lifecycle methods
+ //
---------------------------------------------------------------------------------------------
/**
- * Request a slot with requirements, we may either fulfill the request
or pending it. Trigger container
- * allocation if we don't have enough resource. If we have free slot
which can match the request, record
- * this allocation and forward the request to TaskManager through
ResourceManager (we want this done by
- * RPC's main thread to avoid race condition).
+ * Starts the slot manager with the given leader id and resource
manager actions.
*
- * @param request The detailed request of the slot
- * @return RMSlotRequestRegistered The confirmation message to be send
to the caller
+ * @param newLeaderId to use for communication with the task managers
+ * @param newResourceManagerActions to use for resource (de-)allocations
+ */
+ public void start(UUID newLeaderId, Executor newMainThreadExecutor,
ResourceManagerActions newResourceManagerActions) {
+ leaderId = Preconditions.checkNotNull(newLeaderId);
+ mainThreadExecutor =
Preconditions.checkNotNull(newMainThreadExecutor);
+ resourceManagerActions =
Preconditions.checkNotNull(newResourceManagerActions);
+
+ started = true;
+ }
+
+ /**
+ * Suspends the component. This clears the internal state of the slot
manager.
*/
- public RMSlotRequestRegistered requestSlot(final SlotRequest request) {
- final AllocationID allocationId = request.getAllocationId();
- if (isRequestDuplicated(request)) {
- LOG.warn("Duplicated slot request, AllocationID:{}",
allocationId);
- return new RMSlotRequestRegistered(allocationId);
+ public void suspend() {
+ for (PendingSlotRequest pendingSlotRequest :
pendingSlotRequests.values()) {
+ cancelPendingSlotRequest(pendingSlotRequest);
}
- // try to fulfil the request with current free slots
- final ResourceSlot slot = chooseSlotToUse(request, freeSlots);
- if (slot != null) {
- LOG.info("Assigning SlotID({}) to AllocationID({}),
JobID:{}", slot.getSlotId(),
- allocationId, request.getJobId());
+ pendingSlotRequests.clear();
+
+ HashSet<InstanceID> registeredTaskManagers = new
HashSet<>(taskManagerRegistrations.keySet());
+
+ for (InstanceID registeredTaskManager : registeredTaskManagers)
{
+ unregisterTaskManager(registeredTaskManager);
+ }
+
+ leaderId = null;
+ resourceManagerActions = null;
+ started = false;
+ }
+
+ /**
+ * Closes the slot manager.
+ *
+ * @throws Exception if the close operation fails
+ */
+ @Override
+ public void close() throws Exception {
+ suspend();
+ }
+
+ //
---------------------------------------------------------------------------------------------
+ // Public API
+ //
---------------------------------------------------------------------------------------------
+
+ /**
+ * Requests a slot with the respective resource profile.
+ *
+ * @param slotRequest specifying the requested slot specs
+ * @return true if the slot request was registered; false if the
request is a duplicate
+ * @throws SlotManagerException if the slot request failed (e.g. not
enough resources left)
+ */
+ public boolean registerSlotRequest(SlotRequest slotRequest) throws
SlotManagerException {
+ checkInit();
- // record this allocation in bookkeeping
- allocationMap.addAllocation(slot.getSlotId(),
allocationId);
- // remove selected slot from free pool
- freeSlots.remove(slot.getSlotId());
+ if (checkDuplicateRequest(slotRequest.getAllocationId())) {
+ LOG.debug("Ignoring a duplicate slot request with
allocation id {}.", slotRequest.getAllocationId());
- sendSlotRequest(slot, request);
+ return false;
} else {
- LOG.info("Cannot fulfil slot request, try to allocate a
new container for it, " +
- "AllocationID:{}, JobID:{}", allocationId,
request.getJobId());
- Preconditions.checkState(rmServices != null,
- "Attempted to allocate resources but no
ResourceManagerServices set.");
-
rmServices.allocateResource(request.getResourceProfile());
- pendingSlotRequests.put(allocationId, request);
+ PendingSlotRequest pendingSlotRequest = new
PendingSlotRequest(slotRequest);
+
+ pendingSlotRequests.put(slotRequest.getAllocationId(),
pendingSlotRequest);
+
+ try {
+ internalRequestSlot(pendingSlotRequest);
+ } catch (ResourceManagerException e) {
+ // requesting the slot failed --> remove
pending slot request
+
pendingSlotRequests.remove(slotRequest.getAllocationId());
+
+ throw new SlotManagerException("Could not
fulfill slot request " + slotRequest.getAllocationId() + '.', e);
+ }
+
+ return true;
}
+ }
- return new RMSlotRequestRegistered(allocationId);
+ /**
+ * Cancels and removes a pending slot request with the given allocation
id. If there is no such
+ * pending request, then nothing is done.
+ *
+ * @param allocationId identifying the pending slot request
+ * @return True if a pending slot request was found; otherwise false
+ */
+ public boolean unregisterSlotRequest(AllocationID allocationId) {
+ checkInit();
+
+ PendingSlotRequest pendingSlotRequest =
pendingSlotRequests.remove(allocationId);
+
+ if (null != pendingSlotRequest) {
+ cancelPendingSlotRequest(pendingSlotRequest);
+
+ return true;
+ } else {
+ LOG.debug("No pending slot request with allocation id
{} found.", allocationId);
+
+ return false;
+ }
}
/**
- * Notifies the SlotManager that a slot is available again after being
allocated.
- * @param slotID slot id of available slot
+ * Registers a new task manager at the slot manager. This will make the
task managers slots
+ * known and, thus, available for allocation.
+ *
+ * @param taskExecutorConnection for the new task manager
+ * @param initialSlotReport for the new task manager
*/
- public void notifySlotAvailable(ResourceID resourceID, SlotID slotID) {
- if (!allocationMap.isAllocated(slotID)) {
- throw new IllegalStateException("Slot was not
previously allocated but " +
- "TaskManager reports it as available again");
+ public void registerTaskManager(final TaskExecutorConnection
taskExecutorConnection, SlotReport initialSlotReport) {
+ checkInit();
+
+ // we identify task managers by their instance id
+ if
(!taskManagerRegistrations.containsKey(taskExecutorConnection.getInstanceID()))
{
+ TaskManagerRegistration taskManagerRegistration = new
TaskManagerRegistration(taskExecutorConnection);
+
taskManagerRegistrations.put(taskExecutorConnection.getInstanceID(),
taskManagerRegistration);
}
- allocationMap.removeAllocation(slotID);
- final Map<SlotID, ResourceSlot> slots =
registeredSlots.get(resourceID);
- ResourceSlot freeSlot = slots.get(slotID);
- if (freeSlot == null) {
- throw new IllegalStateException("Slot was not
registered with SlotManager but " +
- "TaskManager reported it to be available.");
+
+ reportSlotStatus(taskExecutorConnection.getInstanceID(),
initialSlotReport);
+ }
+
+ /**
+ * Unregisters the task manager identified by the given instance id and
its associated slots
+ * from the slot manager.
+ *
+ * @param instanceId identifying the task manager to unregister
+ * @return True if there existed a registered task manager with the
given instance id
+ */
+ public boolean unregisterTaskManager(InstanceID instanceId) {
+ checkInit();
+
+ TaskManagerRegistration taskManagerRegistration =
taskManagerRegistrations.remove(instanceId);
+
+ if (null != taskManagerRegistration) {
+ removeSlots(taskManagerRegistration.getSlots());
+
+ taskManagerRegistration.cancelTimeout();
+
+ return true;
+ } else {
+ LOG.debug("There is no task manager registered with
instance ID {}. Ignoring this message.", instanceId);
+
+ return false;
}
- handleFreeSlot(freeSlot);
}
/**
- * The slot request to TaskManager may be either failed by rpc
communication (timeout, network error, etc.)
- * or really rejected by TaskManager. We shall retry this request by:
- * <ul>
- * <li>1. verify and clear all the previous allocate information for
this request
- * <li>2. try to request slot again
- * </ul>
- * <p>
- * This may cause some duplicate allocation, e.g. the slot request to
TaskManager is successful but the response
- * is lost somehow, so we may request a slot in another TaskManager,
this causes two slots assigned to one request,
- * but it can be taken care of by rejecting registration at JobManager.
+ * Reports the current slot allocations for a task manager identified
by the given instance id.
*
- * @param originalRequest The original slot request
- * @param slotId The target SlotID
+ * @param instanceId identifying the task manager for which to report
the slot status
+ * @param slotReport containing the status for all of its slots
+ * @return true if the slot status has been updated successfully,
otherwise false
*/
- void handleSlotRequestFailedAtTaskManager(final SlotRequest
originalRequest, final SlotID slotId) {
- final AllocationID originalAllocationId =
originalRequest.getAllocationId();
- LOG.info("Slot request failed at TaskManager, SlotID:{},
AllocationID:{}, JobID:{}",
- slotId, originalAllocationId,
originalRequest.getJobId());
-
- if (allocationMap.isAllocated(slotId)) {
- final AllocationID expectedAllocationId =
allocationMap.getAllocationID(slotId);
-
- // check whether we have an agreement on whom this slot
belongs to
- if (originalAllocationId.equals(expectedAllocationId)) {
- LOG.info("De-allocate this request and retry");
-
allocationMap.removeAllocation(expectedAllocationId);
-
pendingSlotRequests.put(originalRequest.getAllocationId(), originalRequest);
- ResourceSlot slot =
checkNotNull(getRegisteredSlot(slotId));
- // treat this slot as empty and retry with a
different request
- handleFreeSlot(slot);
+ public boolean reportSlotStatus(InstanceID instanceId, SlotReport
slotReport) {
+ checkInit();
+
+ TaskManagerRegistration taskManagerRegistration =
taskManagerRegistrations.get(instanceId);
+
+ if (null != taskManagerRegistration) {
+ HashSet<SlotID> slotsToRemove = new
HashSet<>(taskManagerRegistration.getSlots());
+ boolean idle = true;
+
+ for (SlotStatus slotStatus : slotReport) {
+ if
(slotsToRemove.remove(slotStatus.getSlotID())) {
+ // slot which was already registered
+ updateSlot(slotStatus.getSlotID(),
slotStatus.getAllocationID());
+ } else {
+ // new slot
+ registerSlot(
+ instanceId,
+ slotStatus.getSlotID(),
+ slotStatus.getAllocationID(),
+ slotStatus.getResourceProfile(),
+
taskManagerRegistration.getTaskManagerConnection());
+ }
+
+ TaskManagerSlot slot =
slots.get(slotStatus.getSlotID());
+
+ idle &= slot.isFree();
+ }
+
+ // remove the slots for which we haven't received a
slot status message
+ removeSlots(slotsToRemove);
+
+ if (idle) {
+ // no slot of this task manager is being used
--> register timer to free this resource
+
registerTaskManagerTimeout(taskManagerRegistration);
+ }
+
+ return true;
+ } else {
+ LOG.debug("Received slot report for unknown task
manager with instance id {}. Ignoring this report.", instanceId);
+
+ return false;
+ }
+ }
+
+ /**
+ * Free the given slot from the given allocation. If the slot is still
allocated by the given
+ * allocation id, then the slot will be marked as free and will be
subject to new slot requests.
+ *
+ * @param slotId identifying the slot to free
+ * @param allocationId with which the slot is presumably allocated
+ */
+ public void freeSlot(SlotID slotId, AllocationID allocationId) {
+ checkInit();
+
+ TaskManagerSlot slot = slots.get(slotId);
+
+ if (null != slot) {
+ if (slot.isAllocated()) {
+ if (Objects.equals(allocationId,
slot.getAllocationId())) {
+ // free the slot
+ slot.setAllocationId(null);
+
fulfilledSlotRequests.remove(allocationId);
+
+ if (slot.isFree()) {
+ handleFreeSlot(slot);
+ }
+
+ TaskManagerRegistration
taskManagerRegistration = taskManagerRegistrations.get(slot.getInstanceId());
+
+ if (null != taskManagerRegistration &&
!anySlotUsed(taskManagerRegistration.getSlots())) {
+
registerTaskManagerTimeout(taskManagerRegistration);
+ }
+ } else {
+ LOG.debug("Received request to free
slot {} with expected allocation id {}, " +
+ "but actual allocation id {}
differs. Ignoring the request.", slotId, allocationId, slot.getAllocationId());
+ }
} else {
- LOG.error("Slot request failed for slot {} with
allocation id {}:" +
- " Allocation id did not match
the expected allocation id {}.",
- slotId, originalAllocationId,
expectedAllocationId);
+ LOG.debug("Slot {} has not been allocated.",
allocationId);
}
} else {
- LOG.error("Slot request failed for slot {} with
allocation id {}: " +
- "Slot was not previously registered.",
- slotId, originalAllocationId);
+ LOG.debug("Trying to free a slot {} which has not been
registered. Ignoring this message.", slotId);
}
}
+ //
---------------------------------------------------------------------------------------------
+ // Behaviour methods
+ //
---------------------------------------------------------------------------------------------
+
/**
- * Registers a TaskExecutor
- * @param resourceID TaskExecutor's ResourceID
- * @param registration TaskExecutor's registration
- * @param slotReport TaskExecutor's free and allocated slots
+ * Finds a matching slot request for a given resource profile. If there
is no such request,
+ * the method returns null.
+ *
+ * Note: If you want to change the behaviour of the slot manager wrt
slot allocation and
+ * request fulfillment, then you should override this method.
+ *
+ * @param slotResourceProfile defining the resources of an available
slot
+ * @return A matching slot request which can be deployed in a slot with
the given resource
+ * profile. Null if there is no such slot request pending.
*/
- public void registerTaskExecutor(
- ResourceID resourceID,
- TaskExecutorRegistration registration,
- SlotReport slotReport) {
+ protected PendingSlotRequest findMatchingRequest(ResourceProfile
slotResourceProfile) {
- if (taskManagers.get(resourceID) != null) {
- notifyTaskManagerFailure(resourceID);
+ for (PendingSlotRequest pendingSlotRequest :
pendingSlotRequests.values()) {
+ if (!pendingSlotRequest.isAssigned() &&
slotResourceProfile.isMatching(pendingSlotRequest.getResourceProfile())) {
+ return pendingSlotRequest;
+ }
}
- this.taskManagers.put(resourceID, registration);
+ return null;
+ }
+
+ /**
+ * Finds a matching slot for a given resource profile. A matching slot
has at least as many
+ * resources available as the given resource profile. If there is no
such slot available, then
+ * the method returns null.
+ *
+ * Note: If you want to change the behaviour of the slot manager wrt
slot allocation and
+ * request fulfillment, then you should override this method.
+ *
+ * @param requestResourceProfile specifying the resource requirements
for the a slot request
+ * @return A matching slot which fulfills the given resource profile.
Null if there is no such
+ * slot available.
+ */
+ protected TaskManagerSlot findMatchingSlot(ResourceProfile
requestResourceProfile) {
+ Iterator<Map.Entry<SlotID, TaskManagerSlot>> iterator =
freeSlots.entrySet().iterator();
+
+ while (iterator.hasNext()) {
+ TaskManagerSlot taskManagerSlot =
iterator.next().getValue();
- for (SlotStatus slotStatus : slotReport.getSlotsStatus()) {
- final SlotID slotId = slotStatus.getSlotID();
+ // sanity check
+ Preconditions.checkState(taskManagerSlot.isFree());
- final TaskExecutorRegistration taskExecutorRegistration
= taskManagers.get(slotId.getResourceID());
- if (taskExecutorRegistration == null) {
- LOG.info("Received SlotStatus but ResourceID {}
is unknown to the SlotManager",
- slotId.getResourceID());
- return;
+ if
(taskManagerSlot.getResourceProfile().isMatching(requestResourceProfile)) {
+ iterator.remove();
+ return taskManagerSlot;
}
+ }
- final ResourceSlot slot = new ResourceSlot(slotId,
slotStatus.getProfiler(), taskExecutorRegistration);
+ return null;
+ }
- registerNewSlot(slot);
- LOG.info("New slot appeared, SlotID:{},
AllocationID:{}", slotId, slotStatus.getAllocationID());
+ //
---------------------------------------------------------------------------------------------
+ // Internal slot operations
+ //
---------------------------------------------------------------------------------------------
- if (slotStatus.getAllocationID() != null) {
- // slot in use, record this in bookkeeping
- allocationMap.addAllocation(slotId,
slotStatus.getAllocationID());
- } else {
+ /**
+ * Registers a slot for the given task manager at the slot manager. The
task manager is
+ * identified by the given instance id and the slot is identified by
the given slot id. The
+ * given resource profile defines the available resources for the slot.
The task manager
+ * connection can be used to communicate with the task manager.
+ *
+ * @param instanceId identifying the task manager on which the slot
lives
+ * @param slotId identifying the slot on the task manager
+ * @param allocationId which is currently deployed in the slot
+ * @param resourceProfile of the slot
+ * @param taskManagerConnection to communicate with the remote task
manager
+ */
+ private void registerSlot(
--- End diff --
I would pass the `TaskManagerRegistration` into this method. Looking it up
again is redundant work and leads to the "what if it is not found" case (where
the question comes up whether to log or to throw an exception), which can be
avoided.
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