| /* |
| * Licensed to the Apache Software Foundation (ASF) under one |
| * or more contributor license agreements. See the NOTICE file |
| * distributed with this work for additional information |
| * regarding copyright ownership. The ASF licenses this file |
| * to you under the Apache License, Version 2.0 (the |
| * "License"); you may not use this file except in compliance |
| * with the License. You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| package org.apache.beam.runners.core; |
| |
| import java.util.Collection; |
| import java.util.Set; |
| import org.apache.beam.sdk.transforms.windowing.BoundedWindow; |
| import org.apache.beam.sdk.transforms.windowing.WindowFn; |
| import org.apache.beam.vendor.guava.v20_0.com.google.common.annotations.VisibleForTesting; |
| |
| /** |
| * Track which windows are <i>active</i>, and the <i>state address window(s)</i> under which their |
| * state is stored. Also help with the multi-step process of merging windows and their associated |
| * state. |
| * |
| * <p>When windows are merged we must also merge their state. For example, we may need to |
| * concatenate buffered elements, sum a count of elements, or find a new minimum timestamp. If we |
| * start with two windows {@code Wa} and {@code Wb} and later discover they should be merged into |
| * window {@code Wab} then, naively, we must copy and merge the states of {@code Wa} and {@code Wab} |
| * into {@code Wab}. |
| * |
| * <p>However, the common case for merging windows is for a new window to be merged into an existing |
| * window. Thus, if {@code Wa} is the existing window and {@code Wb} the new window it is more |
| * efficient to leave the state for {@code Wa} where it is, and simply redirect {@code Wab} to it. |
| * In this case we say {@code Wab} has a state address window of {@code Wa}. |
| * |
| * <p>Even if windows {@code Wa} and {@code Wb} already have state, it can still be more efficient |
| * to append the state of {@code Wb} onto {@code Wa} rather than copy the state from {@code Wa} and |
| * {@code Wb} into {@code Wab}. |
| * |
| * <p>We use the following terminology for windows: |
| * |
| * <ol> |
| * <li><b>ACTIVE</b>: A window that has state associated with it and has not itself been merged |
| * away. The window may have one (or more) state address windows under which its non-empty |
| * state is stored. A state value for an ACTIVE window must be derived by reading the state in |
| * (all of) its state address windows. Note that only pre 1.4 pipelines use multiple state |
| * address windows per active window. From 1.4 onwards we eagerly merge window state into a |
| * single state address window. |
| * <li><b>NEW</b>: The initial state for a window of an incoming element which is not already |
| * ACTIVE. We have not yet called {@link WindowFn#mergeWindows}, and so don't yet know whether |
| * the window will be be merged into another NEW or ACTIVE window, or will become an ACTIVE |
| * window in its own right. |
| * </ol> |
| * |
| * <p>If no windows will ever be merged we can use the trivial implementation {@link |
| * NonMergingActiveWindowSet}. Otherwise, the actual implementation of this data structure is in |
| * {@link MergingActiveWindowSet}. |
| * |
| * @param <W> the type of window being managed |
| */ |
| public interface ActiveWindowSet<W extends BoundedWindow> { |
| /** Callback for {@link #merge}. */ |
| public interface MergeCallback<W extends BoundedWindow> { |
| /** |
| * Called when windows are about to be merged, but before any {@link #onMerge} callback has been |
| * made. |
| * |
| * @param toBeMerged the windows about to be merged. |
| * @param mergeResult the result window, either a member of {@code toBeMerged} or new. |
| */ |
| void prefetchOnMerge(Collection<W> toBeMerged, W mergeResult) throws Exception; |
| |
| /** |
| * Called when windows are about to be merged, after all {@link #prefetchOnMerge} calls have |
| * been made, but before the active window set has been updated to reflect the merge. |
| * |
| * @param toBeMerged the windows about to be merged. |
| * @param mergeResult the result window, either a member of {@code toBeMerged} or new. |
| */ |
| void onMerge(Collection<W> toBeMerged, W mergeResult) throws Exception; |
| } |
| |
| /** |
| * Remove any remaining NEW windows since they were not promoted to being ACTIVE by {@link |
| * #ensureWindowIsActive} and we don't need to record anything about them. |
| */ |
| void cleanupTemporaryWindows(); |
| |
| /** Save any state changes needed. */ |
| void persist(); |
| |
| /** Return (a view of) the set of currently ACTIVE and NEW windows. */ |
| Set<W> getActiveAndNewWindows(); |
| |
| /** Return {@code true} if {@code window} is ACTIVE. */ |
| boolean isActive(W window); |
| |
| /** Return {@code true} if {@code window} is ACTIVE or NEW. */ |
| boolean isActiveOrNew(W window); |
| |
| /** |
| * Called when an incoming element indicates it is a member of {@code window}, but before we have |
| * started processing that element. If {@code window} is not already known to be ACTIVE, then add |
| * it as NEW. |
| */ |
| void ensureWindowExists(W window); |
| |
| /** |
| * Called when a NEW or ACTIVE window is now known to be ACTIVE. Ensure that if it is NEW then it |
| * becomes ACTIVE (with itself as its only state address window). |
| */ |
| void ensureWindowIsActive(W window); |
| |
| /** |
| * If {@code window} is not already known to be ACTIVE then add it as ACTIVE. For testing only. |
| */ |
| @VisibleForTesting |
| void addActiveForTesting(W window); |
| |
| /** Remove {@code window} from the set. */ |
| void remove(W window); |
| |
| /** |
| * Invoke {@link WindowFn#mergeWindows} on the {@code WindowFn} associated with this window set, |
| * merging as many of the NEW and ACTIVE windows as possible. {@code mergeCallback} will be |
| * invoked for each group of windows that are merged. After this all merge result windows will be |
| * ACTIVE, and all windows which have been merged away will be neither ACTIVE nor NEW. |
| */ |
| void merge(MergeCallback<W> mergeCallback) throws Exception; |
| |
| /** |
| * Signal that all state in {@link #readStateAddresses} for {@code window} has been merged into |
| * the {@link #writeStateAddress} for {@code window}. |
| */ |
| void merged(W window); |
| |
| /** |
| * Return the state address windows for ACTIVE {@code window} from which all state associated |
| * should be read and merged. |
| */ |
| Set<W> readStateAddresses(W window); |
| |
| /** |
| * Return the state address window of ACTIVE {@code window} into which all new state should be |
| * written. Always one of the results of {@link #readStateAddresses}. |
| */ |
| W writeStateAddress(W window); |
| |
| /** |
| * Return the state address window into which all new state should be written after ACTIVE windows |
| * {@code toBeMerged} have been merged into {@code mergeResult}. |
| */ |
| W mergedWriteStateAddress(Collection<W> toBeMerged, W mergeResult); |
| } |