Avoid concurrent modification in lifecycle impl.

Fixes #375.

library/src/main/java/com/bumptech/glide/manager/ActivityFragmentLifecycle.java

 package com.bumptech.glide.manager;
 
+import com.bumptech.glide.util.Util;
+
 import java.util.Collections;
 import java.util.Set;
 import java.util.WeakHashMap;
@@ -44,21 +46,21 @@ class ActivityFragmentLifecycle implements Lifecycle {
 
     void onStart() {
         isStarted = true;
-        for (LifecycleListener lifecycleListener : lifecycleListeners) {
+        for (LifecycleListener lifecycleListener : Util.getSnapshot(lifecycleListeners)) {
             lifecycleListener.onStart();
         }
     }
 
     void onStop() {
         isStarted = false;
-        for (LifecycleListener lifecycleListener : lifecycleListeners) {
+        for (LifecycleListener lifecycleListener : Util.getSnapshot(lifecycleListeners)) {
             lifecycleListener.onStop();
         }
     }
 
     void onDestroy() {
         isDestroyed = true;
-        for (LifecycleListener lifecycleListener : lifecycleListeners) {
+        for (LifecycleListener lifecycleListener : Util.getSnapshot(lifecycleListeners)) {
             lifecycleListener.onDestroy();
         }
     }

library/src/main/java/com/bumptech/glide/manager/RequestTracker.java

 package com.bumptech.glide.manager;
 
 import com.bumptech.glide.request.Request;
+import com.bumptech.glide.util.Util;
 
 import java.util.ArrayList;
 import java.util.Collections;
@@ -64,7 +65,7 @@ public class RequestTracker {
      */
     public void pauseRequests() {
         isPaused = true;
-        for (Request request : getSnapshot()) {
+        for (Request request : Util.getSnapshot(requests)) {
             if (request.isRunning()) {
                 request.pause();
                 pendingRequests.add(request);
@@ -77,7 +78,7 @@ public class RequestTracker {
      */
     public void resumeRequests() {
         isPaused = false;
-        for (Request request : getSnapshot()) {
+        for (Request request : Util.getSnapshot(requests)) {
             if (!request.isComplete() && !request.isCancelled() && !request.isRunning()) {
                 request.begin();
             }
@@ -89,7 +90,7 @@ public class RequestTracker {
      * Cancels all requests and clears their resources.
      */
     public void clearRequests() {
-        for (Request request : getSnapshot()) {
+        for (Request request : Util.getSnapshot(requests)) {
             request.clear();
         }
         pendingRequests.clear();
@@ -99,7 +100,7 @@ public class RequestTracker {
      * Restarts failed requests and cancels and restarts in progress requests.
      */
     public void restartRequests() {
-        for (Request request : getSnapshot()) {
+        for (Request request : Util.getSnapshot(requests)) {
             if (!request.isComplete() && !request.isCancelled()) {
                 // Ensure the request will be restarted in onResume.
                 request.pause();
@@ -111,17 +112,4 @@ public class RequestTracker {
             }
         }
     }
-
-    // Avoids a ConcurrentModificationException when requests are started by another request completing. See #303.
-    private List<Request> getSnapshot() {
-        // toArray creates a new ArrayList internally and this way we can guarantee entries will not be
-        // null. See #322.
-        List<Request> result = new ArrayList<Request>(requests.size());
-        // We could also just call new ArrayList<Request>(requests) but that actually creates two new ArrayLists because
-        // that constructor in ArrayList calls toArray().
-        for (Request request : requests) {
-            result.add(request);
-        }
-        return result;
-    }
 }

library/src/main/java/com/bumptech/glide/util/Util.java

@@ -8,6 +8,9 @@ import android.os.Looper;
 import com.bumptech.glide.request.target.Target;
 
 import java.util.ArrayDeque;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.List;
 import java.util.Queue;
 
 /**
@@ -157,9 +160,25 @@ public final class Util {
     }
 
     /**
-     * Creates a {@link java.util.Queue} of the given size using Glide's preferred implementation.
+     * Returns a {@link java.util.Queue} of the given size using Glide's preferred implementation.
      */
     public static <T> Queue<T> createQueue(int size) {
         return new ArrayDeque<T>(size);
     }
+
+    /**
+     * Returns a copy of the given list that is safe to iterate over and perform actions that may
+     * modify the original list.
+     *
+     * <p> See #303 and #375. </p>
+     */
+    public static <T> List<T> getSnapshot(Collection<T> other) {
+        // toArray creates a new ArrayList internally and this way we can guarantee entries will not
+        // be null. See #322.
+        List<T> result = new ArrayList<T>(other.size());
+        for (T item : other) {
+            result.add(item);
+        }
+        return result;
+    }
 }