Always clear thumbnails after full completes.

Fixes #244

library/src/androidTest/java/com/bumptech/glide/request/GenericRequestTest.java

@@ -432,6 +432,15 @@ public class GenericRequestTest {
         assertTrue(request.isCancelled());
     }
 
+    @Test
+    public void testDoesNotNotifyTargetTwiceIfClearedTwiceInARow() {
+        GenericRequest request = harness.getRequest();
+        request.clear();
+        request.clear();
+
+        verify(harness.target, times(1)).onLoadCleared(any(Drawable.class));
+    }
+
     @Test
     public void testResourceIsNotCompleteWhenAskingCoordinatorIfCanSetImage() {
         RequestCoordinator requestCoordinator = mock(RequestCoordinator.class);

library/src/androidTest/java/com/bumptech/glide/request/ThumbnailRequestCoordinatorTest.java

@@ -282,11 +282,11 @@ public class ThumbnailRequestCoordinatorTest {
     }
 
     @Test
-    public void testDoesNotClearThumbRequestOnFullRequestComplete_withNonNullParent() {
+    public void testClearsThumbRequestOnFullRequestComplete_withNonNullParent() {
         coordinator = new ThumbnailRequestCoordinator(parent);
         coordinator.setRequests(full, thumb);
         coordinator.onRequestSuccess(full);
-        verify(thumb, never()).clear();
+        verify(thumb).clear();
     }
 
     @Test

library/src/main/java/com/bumptech/glide/request/GenericRequest.java

@@ -46,10 +46,12 @@ public final class GenericRequest<A, T, Z, R> implements Request, SizeReadyCallb
         WAITING_FOR_SIZE,
         /** Finished loading media successfully. */
         COMPLETE,
-        /** Failed to load media. */
+        /** Failed to load media, may be restarted. */
         FAILED,
         /** Cancelled by the user, may not be restarted. */
         CANCELLED,
+        /** Cleared by the user with a placeholder set, may not be restarted. */
+        CLEARED,
         /** Temporarily paused by the system, may be restarted. */
         PAUSED,
     }
@@ -298,6 +300,9 @@ public final class GenericRequest<A, T, Z, R> implements Request, SizeReadyCallb
     @Override
     public void clear() {
         Util.assertMainThread();
+        if (status == Status.CLEARED) {
+            return;
+        }
         cancel();
         // Resource must be released before canNotifyStatusChanged is called.
         if (resource != null) {
@@ -306,6 +311,8 @@ public final class GenericRequest<A, T, Z, R> implements Request, SizeReadyCallb
         if (canNotifyStatusChanged()) {
             target.onLoadCleared(getPlaceholderDrawable());
         }
+        // Must be after cancel().
+        status = Status.CLEARED;
     }
 
     @Override
@@ -353,7 +360,7 @@ public final class GenericRequest<A, T, Z, R> implements Request, SizeReadyCallb
      */
     @Override
     public boolean isCancelled() {
-        return status == Status.CANCELLED;
+        return status == Status.CANCELLED || status == Status.CLEARED;
     }
 
     /**

library/src/main/java/com/bumptech/glide/request/ThumbnailRequestCoordinator.java

@@ -60,14 +60,13 @@ public class ThumbnailRequestCoordinator implements RequestCoordinator, Request
 
     @Override
     public void onRequestSuccess(Request request) {
-      if (request.equals(thumb)) {
-        return;
-      }
-      if (coordinator == null) {
+        if (request.equals(thumb)) {
+            return;
+        }
+        if (coordinator != null) {
+            coordinator.onRequestSuccess(this);
+        }
         thumb.clear();
-      } else {
-        coordinator.onRequestSuccess(this);
-      }
     }
 
     private boolean parentIsAnyResourceSet() {