Adding a ScheduledDataLoaderRegistry

README.md

@@ -478,6 +478,33 @@ and there are also gains to this different mode of operation:
 However, with batch execution control comes responsibility! If you forget to make the call to `dispatch()` then the futures
 in the load request queue will never be batched, and thus _will never complete_! So be careful when crafting your loader designs.
 
+## Scheduled Dispatching
+
+`ScheduledDataLoaderRegistry` is a registry that allows for dispatching to be done on a schedule. It contains a
+predicate that is evaluated (per data loader contained within) when `dispatchAll` is invoked.
+
+If that predicate is true, it will make a `dispatch` call on the data loader, otherwise is will schedule a task to
+perform that check again. Once a predicate evaluated to true, it will not reschedule and another call to
+`dispatchAll` is required to be made.
+
+This allows you to do things like "dispatch ONLY if the queue depth is > 10 deep or more than 200 millis have passed
+since it was last dispatched".
+
+```java
+
+        DispatchPredicate depthOrTimePredicate = DispatchPredicate
+            .dispatchIfDepthGreaterThan(10)
+            .or(DispatchPredicate.dispatchIfLongerThan(Duration.ofMillis(200)));
+
+        ScheduledDataLoaderRegistry registry = ScheduledDataLoaderRegistry.newScheduledRegistry()
+            .dispatchPredicate(depthOrTimePredicate)
+            .schedule(Duration.ofMillis(10))
+            .register("users",userDataLoader)
+            .build();
+```
+
+The above acts as a kind of minimum batch depth, with a time overload. It won't dispatch if the loader depth is less
+than or equal to 10 but if 200ms pass it will dispatch.
 
 ## Let's get started!
 

src/main/java/org/dataloader/DataLoaderRegistry.java

@@ -6,6 +6,7 @@
 import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.HashSet;
+import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
@@ -19,7 +20,7 @@
  */
 @PublicApi
 public class DataLoaderRegistry {
-    private final Map<String, DataLoader<?, ?>> dataLoaders = new ConcurrentHashMap<>();
+    protected final Map<String, DataLoader<?, ?>> dataLoaders = new ConcurrentHashMap<>();
 
     public DataLoaderRegistry() {
     }
@@ -28,6 +29,7 @@ private DataLoaderRegistry(Builder builder) {
         this.dataLoaders.putAll(builder.dataLoaders);
     }
 
+
     /**
      * This will register a new dataloader
      *
@@ -84,6 +86,13 @@ public DataLoaderRegistry combine(DataLoaderRegistry registry) {
         return new ArrayList<>(dataLoaders.values());
     }
 
+    /**
+     * @return the currently registered data loaders as a map
+     */
+    public Map<String, DataLoader<?, ?>> getDataLoadersMap() {
+        return new LinkedHashMap<>(dataLoaders);
+    }
+
     /**
      * This will unregister a new dataloader
      *

src/main/java/org/dataloader/annotations/ExperimentalApi.java

@@ -0,0 +1,23 @@
+package org.dataloader.annotations;
+
+import java.lang.annotation.Documented;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+import static java.lang.annotation.ElementType.CONSTRUCTOR;
+import static java.lang.annotation.ElementType.FIELD;
+import static java.lang.annotation.ElementType.METHOD;
+import static java.lang.annotation.ElementType.TYPE;
+
+/**
+ * This represents code that the graphql-java project considers experimental API and while our intention is that it will
+ * progress to be {@link PublicApi}, its existence, signature of behavior may change between releases.
+ *
+ * In general unnecessary changes will be avoided but you should not depend on experimental classes being stable
+ */
+@Retention(RetentionPolicy.RUNTIME)
+@Target(value = {CONSTRUCTOR, METHOD, TYPE, FIELD})
+@Documented
+public @interface ExperimentalApi {
+}

src/main/java/org/dataloader/registries/DispatchPredicate.java

@@ -0,0 +1,92 @@
+package org.dataloader.registries;
+
+import org.dataloader.DataLoader;
+
+import java.time.Duration;
+import java.util.Objects;
+
+/**
+ * A predicate class used by {@link ScheduledDataLoaderRegistry} to decide whether to dispatch or not
+ */
+@FunctionalInterface
+public interface DispatchPredicate {
+    /**
+     * This predicate tests whether the data loader should be dispatched or not.
+     *
+     * @param dataLoaderKey the key of the data loader when registered
+     * @param dataLoader    the dataloader to dispatch
+     *
+     * @return true if the data loader SHOULD be dispatched
+     */
+    boolean test(String dataLoaderKey, DataLoader<?, ?> dataLoader);
+
+
+    /**
+     * Returns a composed predicate that represents a short-circuiting logical
+     * AND of this predicate and another.
+     *
+     * @param other a predicate that will be logically-ANDed with this
+     *              predicate
+     *
+     * @return a composed predicate that represents the short-circuiting logical
+     * AND of this predicate and the {@code other} predicate
+     */
+    default DispatchPredicate and(DispatchPredicate other) {
+        Objects.requireNonNull(other);
+        return (k, dl) -> test(k, dl) && other.test(k, dl);
+    }
+
+    /**
+     * Returns a predicate that represents the logical negation of this
+     * predicate.
+     *
+     * @return a predicate that represents the logical negation of this
+     * predicate
+     */
+    default DispatchPredicate negate() {
+        return (k, dl) -> !test(k, dl);
+    }
+
+    /**
+     * Returns a composed predicate that represents a short-circuiting logical
+     * OR of this predicate and another.
+     *
+     * @param other a predicate that will be logically-ORed with this
+     *              predicate
+     *
+     * @return a composed predicate that represents the short-circuiting logical
+     * OR of this predicate and the {@code other} predicate
+     */
+    default DispatchPredicate or(DispatchPredicate other) {
+        Objects.requireNonNull(other);
+        return (k, dl) -> test(k, dl) || other.test(k, dl);
+    }
+
+    /**
+     * This predicate will return true if the {@link DataLoader} has not be dispatched
+     * for at least the duration length of time.
+     *
+     * @param duration the length of time to check
+     *
+     * @return true if the data loader has not been dispatched in duration time
+     */
+    static DispatchPredicate dispatchIfLongerThan(Duration duration) {
+        return (dataLoaderKey, dataLoader) -> {
+            int i = dataLoader.getTimeSinceDispatch().compareTo(duration);
+            return i > 0;
+        };
+    }
+
+    /**
+     * This predicate will return true if the {@link DataLoader#dispatchDepth()} is greater than the specified depth.
+     *
+     * This will act as minimum batch size.  There must be more than `depth` items queued for the predicate to return true.
+     *
+     * @param depth the value to be greater than
+     *
+     * @return true if the {@link DataLoader#dispatchDepth()} is greater than the specified depth.
+     */
+    static DispatchPredicate dispatchIfDepthGreaterThan(int depth) {
+        return (dataLoaderKey, dataLoader) -> dataLoader.dispatchDepth() > depth;
+    }
+}

src/main/java/org/dataloader/registries/ScheduledDataLoaderRegistry.java

@@ -0,0 +1,186 @@
+package org.dataloader.registries;
+
+import org.dataloader.DataLoader;
+import org.dataloader.DataLoaderRegistry;
+import org.dataloader.annotations.ExperimentalApi;
+
+import java.time.Duration;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.concurrent.Executors;
+import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.TimeUnit;
+
+import static org.dataloader.impl.Assertions.nonNull;
+
+/**
+ * This {@link DataLoaderRegistry} will use a {@link DispatchPredicate} when {@link #dispatchAll()} is called
+ * to test (for each {@link DataLoader} in the registry) if a dispatch should proceed.  If the predicate returns false, then a task is scheduled
+ * to perform that predicate dispatch again via the {@link ScheduledExecutorService}.
+ * <p>
+ * This will continue to loop (test false and reschedule) until such time as the predicate returns true, in which case
+ * no rescheduling will occur and you will need to call dispatch again to restart the process.
+ * <p>
+ * If you wanted to create a ScheduledDataLoaderRegistry that started a rescheduling immediately, just create one and
+ * call {@link #rescheduleNow()}.
+ * <p>
+ * This code is currently marked as {@link ExperimentalApi}
+ */
+@ExperimentalApi
+public class ScheduledDataLoaderRegistry extends DataLoaderRegistry implements AutoCloseable {
+
+    private final ScheduledExecutorService scheduledExecutorService;
+    private final DispatchPredicate dispatchPredicate;
+    private final Duration schedule;
+    private volatile boolean closed;
+
+    private ScheduledDataLoaderRegistry(Builder builder) {
+        this.dataLoaders.putAll(builder.dataLoaders);
+        this.scheduledExecutorService = builder.scheduledExecutorService;
+        this.dispatchPredicate = builder.dispatchPredicate;
+        this.schedule = builder.schedule;
+        this.closed = false;
+    }
+
+    /**
+     * Once closed this registry will never again reschedule checks
+     */
+    @Override
+    public void close() {
+        closed = true;
+    }
+
+    /**
+     * @return how long the {@link ScheduledExecutorService} task will wait before checking the predicate again
+     */
+    public Duration getScheduleDuration() {
+        return schedule;
+    }
+
+    @Override
+    public void dispatchAll() {
+        dispatchAllWithCount();
+    }
+
+    @Override
+    public int dispatchAllWithCount() {
+        int sum = 0;
+        for (Map.Entry<String, DataLoader<?, ?>> entry : dataLoaders.entrySet()) {
+            DataLoader<?, ?> dataLoader = entry.getValue();
+            String key = entry.getKey();
+            if (dispatchPredicate.test(key, dataLoader)) {
+                sum += dataLoader.dispatchWithCounts().getKeysCount();
+            } else {
+                reschedule(key, dataLoader);
+            }
+        }
+        return sum;
+    }
+
+    /**
+     * This will immediately dispatch the {@link DataLoader}s in the registry
+     * without testing the predicate
+     */
+    public void dispatchAllImmediately() {
+        super.dispatchAll();
+    }
+
+    /**
+     * This will immediately dispatch the {@link DataLoader}s in the registry
+     * without testing the predicate
+     *
+     * @return total number of entries that were dispatched from registered {@link org.dataloader.DataLoader}s.
+     */
+    public int dispatchAllWithCountImmediately() {
+        return super.dispatchAllWithCount();
+    }
+
+    /**
+     * This will schedule a task to check the predicate and dispatch if true right now.  It will not do
+     * a pre check of the preodicate like {@link #dispatchAll()} would
+     */
+    public void rescheduleNow() {
+        dataLoaders.forEach(this::reschedule);
+    }
+
+    private void reschedule(String key, DataLoader<?, ?> dataLoader) {
+        if (!closed) {
+            Runnable runThis = () -> dispatchOrReschedule(key, dataLoader);
+            scheduledExecutorService.schedule(runThis, schedule.toMillis(), TimeUnit.MILLISECONDS);
+        }
+    }
+
+    private void dispatchOrReschedule(String key, DataLoader<?, ?> dataLoader) {
+        if (dispatchPredicate.test(key, dataLoader)) {
+            dataLoader.dispatch();
+        } else {
+            reschedule(key, dataLoader);
+        }
+    }
+
+    /**
+     * By default this will create use a {@link Executors#newSingleThreadScheduledExecutor()}
+     * and a schedule duration of 10 milli seconds.
+     *
+     * @return A builder of {@link ScheduledDataLoaderRegistry}s
+     */
+    public static Builder newScheduledRegistry() {
+        return new Builder();
+    }
+
+    public static class Builder {
+
+        private ScheduledExecutorService scheduledExecutorService = Executors.newSingleThreadScheduledExecutor();
+        private DispatchPredicate dispatchPredicate = (key, dl) -> true;
+        private Duration schedule = Duration.ofMillis(10);
+        private final Map<String, DataLoader<?, ?>> dataLoaders = new HashMap<>();
+
+        public Builder scheduledExecutorService(ScheduledExecutorService executorService) {
+            this.scheduledExecutorService = nonNull(executorService);
+            return this;
+        }
+
+        public Builder schedule(Duration schedule) {
+            this.schedule = schedule;
+            return this;
+        }
+
+        public Builder dispatchPredicate(DispatchPredicate dispatchPredicate) {
+            this.dispatchPredicate = nonNull(dispatchPredicate);
+            return this;
+        }
+
+        /**
+         * This will register a new dataloader
+         *
+         * @param key        the key to put the data loader under
+         * @param dataLoader the data loader to register
+         *
+         * @return this builder for a fluent pattern
+         */
+        public Builder register(String key, DataLoader<?, ?> dataLoader) {
+            dataLoaders.put(key, dataLoader);
+            return this;
+        }
+
+        /**
+         * This will combine together the data loaders in this builder with the ones
+         * from a previous {@link DataLoaderRegistry}
+         *
+         * @param otherRegistry the previous {@link DataLoaderRegistry}
+         *
+         * @return this builder for a fluent pattern
+         */
+        public Builder registerAll(DataLoaderRegistry otherRegistry) {
+            dataLoaders.putAll(otherRegistry.getDataLoadersMap());
+            return this;
+        }
+
+        /**
+         * @return the newly built {@link ScheduledDataLoaderRegistry}
+         */
+        public ScheduledDataLoaderRegistry build() {
+            return new ScheduledDataLoaderRegistry(this);
+        }
+    }
+}