Added a instrumentation of load calls

src/main/java/org/dataloader/DataLoaderHelper.java

@@ -148,12 +148,16 @@ CompletableFuture<V> load(K key, Object loadContext) {
             boolean cachingEnabled = loaderOptions.cachingEnabled();
 
             stats.incrementLoadCount(new IncrementLoadCountStatisticsContext<>(key, loadContext));
-
+            DataLoaderInstrumentationContext<Object> ctx = ctxOrNoopCtx(instrumentation().beginLoad(dataLoader, key,loadContext));
+            CompletableFuture<V> cf;
             if (cachingEnabled) {
-                return loadFromCache(key, loadContext, batchingEnabled);
+                cf = loadFromCache(key, loadContext, batchingEnabled);
             } else {
-                return queueOrInvokeLoader(key, loadContext, batchingEnabled, false);
+                cf = queueOrInvokeLoader(key, loadContext, batchingEnabled, false);
             }
+            ctx.onDispatched();
+            cf.whenComplete(ctx::onCompleted);
+            return cf;
         }
     }
 

src/main/java/org/dataloader/instrumentation/ChainedDataLoaderInstrumentation.java

@@ -69,6 +69,12 @@ public ChainedDataLoaderInstrumentation addAll(Collection<DataLoaderInstrumentat
         return new ChainedDataLoaderInstrumentation(list);
     }
 
+
+    @Override
+    public DataLoaderInstrumentationContext<Object> beginLoad(DataLoader<?, ?> dataLoader, Object key, Object loadContext) {
+        return chainedCtx(it -> it.beginLoad(dataLoader, key, loadContext));
+    }
+
     @Override
     public DataLoaderInstrumentationContext<DispatchResult<?>> beginDispatch(DataLoader<?, ?> dataLoader) {
         return chainedCtx(it -> it.beginDispatch(dataLoader));

src/main/java/org/dataloader/instrumentation/DataLoaderInstrumentation.java

@@ -12,6 +12,21 @@
  */
 @PublicSpi
 public interface DataLoaderInstrumentation {
+    /**
+     * This call back is done just before the {@link DataLoader#load(Object)} methods are invoked,
+     * and it completes when the load promise is completed.  If the value is a cached {@link java.util.concurrent.CompletableFuture}
+     * then it might return almost immediately, otherwise it will return
+     * when the batch load function is invoked and values get returned
+     *
+     * @param dataLoader  the {@link DataLoader} in question
+     * @param key         the key used during the {@link DataLoader#load(Object)} call
+     * @param loadContext the load context used during the {@link DataLoader#load(Object, Object)} call
+     * @return a DataLoaderInstrumentationContext or null to be more performant
+     */
+    default DataLoaderInstrumentationContext<Object> beginLoad(DataLoader<?, ?> dataLoader, Object key, Object loadContext) {
+        return null;
+    }
+
     /**
      * This call back is done just before the {@link DataLoader#dispatch()} is invoked,
      * and it completes when the dispatch call promise is done.

src/test/java/org/dataloader/DataLoaderCacheMapTest.java

@@ -43,7 +43,7 @@ public void should_access_to_future_dependants() {
         Collection<CompletableFuture<Integer>> futures = dataLoader.getCacheMap().getAll();
 
         List<CompletableFuture<Integer>> futuresList = new ArrayList<>(futures);
-        assertThat(futuresList.get(0).getNumberOfDependents(), equalTo(2));
-        assertThat(futuresList.get(1).getNumberOfDependents(), equalTo(1));
+        assertThat(futuresList.get(0).getNumberOfDependents(), equalTo(4)); // instrumentation is depending on the CF completing
+        assertThat(futuresList.get(1).getNumberOfDependents(), equalTo(2));
     }
 }

src/test/java/org/dataloader/instrumentation/CapturingInstrumentation.java

@@ -6,15 +6,49 @@
 
 import java.util.ArrayList;
 import java.util.List;
+import java.util.stream.Collectors;
 
 class CapturingInstrumentation implements DataLoaderInstrumentation {
-    String name;
-    List<String> methods = new ArrayList<>();
+    protected String name;
+    protected List<String> methods = new ArrayList<>();
 
     public CapturingInstrumentation(String name) {
         this.name = name;
     }
 
+    public String getName() {
+        return name;
+    }
+
+    public List<String> methods() {
+        return methods;
+    }
+
+    public List<String> notLoads() {
+        return methods.stream().filter(method -> !method.contains("beginLoad")).collect(Collectors.toList());
+    }
+
+    public List<String> onlyLoads() {
+        return methods.stream().filter(method -> method.contains("beginLoad")).collect(Collectors.toList());
+    }
+
+
+    @Override
+    public DataLoaderInstrumentationContext<Object> beginLoad(DataLoader<?, ?> dataLoader, Object key, Object loadContext) {
+        methods.add(name + "_beginLoad" +"_k:" + key);
+        return new DataLoaderInstrumentationContext<>() {
+            @Override
+            public void onDispatched() {
+                methods.add(name + "_beginLoad_onDispatched"+"_k:" + key);
+            }
+
+            @Override
+            public void onCompleted(Object result, Throwable t) {
+                methods.add(name + "_beginLoad_onCompleted"+"_k:" + key);
+            }
+        };
+    }
+
     @Override
     public DataLoaderInstrumentationContext<DispatchResult<?>> beginDispatch(DataLoader<?, ?> dataLoader) {
         methods.add(name + "_beginDispatch");

src/test/java/org/dataloader/instrumentation/CapturingInstrumentationReturnsNull.java

@@ -12,6 +12,12 @@ public CapturingInstrumentationReturnsNull(String name) {
         super(name);
     }
 
+    @Override
+    public DataLoaderInstrumentationContext<Object> beginLoad(DataLoader<?, ?> dataLoader, Object key, Object loadContext) {
+        methods.add(name + "_beginLoad" +"_k:" + key);
+        return null;
+    }
+
     @Override
     public DataLoaderInstrumentationContext<DispatchResult<?>> beginDispatch(DataLoader<?, ?> dataLoader) {
         methods.add(name + "_beginDispatch");

src/test/java/org/dataloader/instrumentation/ChainedDataLoaderInstrumentationTest.java

@@ -61,16 +61,21 @@ void canChainTogetherOneInstrumentation() {
 
         DataLoader<String, String> dl = DataLoaderFactory.newDataLoader(TestKit.keysAsValues(), options);
 
-        dl.load("A");
-        dl.load("B");
+        dl.load("X");
+        dl.load("Y");
 
         CompletableFuture<List<String>> dispatch = dl.dispatch();
 
         await().until(dispatch::isDone);
 
-        assertThat(capturingA.methods, equalTo(List.of("A_beginDispatch",
+        assertThat(capturingA.notLoads(), equalTo(List.of("A_beginDispatch",
                 "A_beginBatchLoader", "A_beginBatchLoader_onDispatched", "A_beginBatchLoader_onCompleted",
                 "A_beginDispatch_onDispatched", "A_beginDispatch_onCompleted")));
+
+        assertThat(capturingA.onlyLoads(), equalTo(List.of(
+                "A_beginLoad_k:X", "A_beginLoad_onDispatched_k:X", "A_beginLoad_k:Y", "A_beginLoad_onDispatched_k:Y",
+                "A_beginLoad_onCompleted_k:X", "A_beginLoad_onCompleted_k:Y"
+        )));
     }
 
 
@@ -87,8 +92,8 @@ public void canChainTogetherManyInstrumentationsWithDifferentBatchLoaders(TestDa
 
         DataLoader<String, String> dl = factory.idLoader(options);
 
-        dl.load("A");
-        dl.load("B");
+        dl.load("X");
+        dl.load("Y");
 
         CompletableFuture<List<String>> dispatch = dl.dispatch();
 
@@ -98,16 +103,21 @@ public void canChainTogetherManyInstrumentationsWithDifferentBatchLoaders(TestDa
         // A_beginBatchLoader happens before A_beginDispatch_onDispatched because these are sync
         // and no async - a batch scheduler or async batch loader would change that
         //
-        assertThat(capturingA.methods, equalTo(List.of("A_beginDispatch",
+        assertThat(capturingA.notLoads(), equalTo(List.of("A_beginDispatch",
                 "A_beginBatchLoader", "A_beginBatchLoader_onDispatched", "A_beginBatchLoader_onCompleted",
                 "A_beginDispatch_onDispatched", "A_beginDispatch_onCompleted")));
 
-        assertThat(capturingB.methods, equalTo(List.of("B_beginDispatch",
+        assertThat(capturingA.onlyLoads(), equalTo(List.of(
+                "A_beginLoad_k:X", "A_beginLoad_onDispatched_k:X", "A_beginLoad_k:Y", "A_beginLoad_onDispatched_k:Y",
+                "A_beginLoad_onCompleted_k:X", "A_beginLoad_onCompleted_k:Y"
+        )));
+
+        assertThat(capturingB.notLoads(), equalTo(List.of("B_beginDispatch",
                 "B_beginBatchLoader", "B_beginBatchLoader_onDispatched", "B_beginBatchLoader_onCompleted",
                 "B_beginDispatch_onDispatched", "B_beginDispatch_onCompleted")));
 
         // it returned null on all its contexts - nothing to call back on
-        assertThat(capturingButReturnsNull.methods, equalTo(List.of("NULL_beginDispatch", "NULL_beginBatchLoader")));
+        assertThat(capturingButReturnsNull.notLoads(), equalTo(List.of("NULL_beginDispatch", "NULL_beginBatchLoader")));
     }
 
     @Test

src/test/java/org/dataloader/instrumentation/DataLoaderInstrumentationTest.java

@@ -29,6 +29,61 @@ public class DataLoaderInstrumentationTest {
         return keys;
     });
 
+    @Test
+    void canMonitorLoading() {
+        AtomicReference<DataLoader<?, ?>> dlRef = new AtomicReference<>();
+
+        CapturingInstrumentation instrumentation = new CapturingInstrumentation("x") {
+
+            @Override
+            public DataLoaderInstrumentationContext<Object> beginLoad(DataLoader<?, ?> dataLoader, Object key, Object loadContext) {
+                DataLoaderInstrumentationContext<Object> superCtx = super.beginLoad(dataLoader, key, loadContext);
+                dlRef.set(dataLoader);
+                return superCtx;
+            }
+
+            @Override
+            public DataLoaderInstrumentationContext<List<?>> beginBatchLoader(DataLoader<?, ?> dataLoader, List<?> keys, BatchLoaderEnvironment environment) {
+                return DataLoaderInstrumentationHelper.noOpCtx();
+            }
+        };
+
+        DataLoaderOptions options = new DataLoaderOptions()
+                .setInstrumentation(instrumentation)
+                .setMaxBatchSize(5);
+
+        DataLoader<String, String> dl = DataLoaderFactory.newDataLoader(snoozingBatchLoader, options);
+
+        List<String> keys = new ArrayList<>();
+        for (int i = 0; i < 3; i++) {
+            String key = "X" + i;
+            keys.add(key);
+            dl.load(key);
+        }
+
+        // load a key that is cached
+        dl.load("X0");
+
+        CompletableFuture<List<String>> dispatch = dl.dispatch();
+
+        await().until(dispatch::isDone);
+        assertThat(dlRef.get(), is(dl));
+        assertThat(dispatch.join(), equalTo(keys));
+
+        // the batch loading means they start and are instrumentation dispatched before they all end up completing
+        assertThat(instrumentation.onlyLoads(),
+                equalTo(List.of(
+                        "x_beginLoad_k:X0", "x_beginLoad_onDispatched_k:X0",
+                        "x_beginLoad_k:X1", "x_beginLoad_onDispatched_k:X1",
+                        "x_beginLoad_k:X2", "x_beginLoad_onDispatched_k:X2",
+                        "x_beginLoad_k:X0", "x_beginLoad_onDispatched_k:X0", // second cached call counts
+                        "x_beginLoad_onCompleted_k:X0",
+                        "x_beginLoad_onCompleted_k:X0", // each load call counts
+                        "x_beginLoad_onCompleted_k:X1", "x_beginLoad_onCompleted_k:X2")));
+
+    }
+
+
     @Test
     void canMonitorDispatching() {
         Stopwatch stopwatch = Stopwatch.stopwatchUnStarted();

src/test/java/org/dataloader/instrumentation/DataLoaderRegistryInstrumentationTest.java

@@ -224,7 +224,7 @@ public void endToEndIntegrationTest(TestDataLoaderFactory factory) {
         await().until(loadA::isDone);
         assertThat(loadA.join(), equalTo("A"));
 
-        assertThat(instrA.methods, equalTo(List.of("A_beginDispatch",
+        assertThat(instrA.notLoads(), equalTo(List.of("A_beginDispatch",
                 "A_beginBatchLoader", "A_beginBatchLoader_onDispatched", "A_beginBatchLoader_onCompleted",
                 "A_beginDispatch_onDispatched", "A_beginDispatch_onCompleted")));
     }