update configuration to use concurrentlinkedqueue for holding callbacks

sdk/src/main/java/com/bugsnag/android/Configuration.java

@@ -13,6 +13,7 @@
 import java.util.Map;
 import java.util.Observable;
 import java.util.Observer;
+import java.util.concurrent.ConcurrentLinkedQueue;
 
 /**
  * User-specified configuration storage object, contains information
@@ -50,9 +51,9 @@ public class Configuration extends Observable implements Observer {
 
     @NonNull
     private MetaData metaData;
-    private final Collection<BeforeNotify> beforeNotifyTasks = new LinkedHashSet<>();
+    private final Collection<BeforeNotify> beforeNotifyTasks = new ConcurrentLinkedQueue<>();
     private final Collection<BeforeRecordBreadcrumb> beforeRecordBreadcrumbTasks
-        = new LinkedHashSet<>();
+        = new ConcurrentLinkedQueue<>();
     private String codeBundleId;
     private String notifierType;
 
@@ -547,7 +548,9 @@ protected boolean shouldIgnoreClass(String className) {
      * @param beforeNotify the new before notify task
      */
     protected void beforeNotify(BeforeNotify beforeNotify) {
-        this.beforeNotifyTasks.add(beforeNotify);
+        if (!beforeNotifyTasks.contains(beforeNotify)) {
+            beforeNotifyTasks.add(beforeNotify);
+        }
     }
 
     /**
@@ -556,7 +559,9 @@ protected void beforeNotify(BeforeNotify beforeNotify) {
      * @param beforeRecordBreadcrumb the new before breadcrumb task
      */
     protected void beforeRecordBreadcrumb(BeforeRecordBreadcrumb beforeRecordBreadcrumb) {
-        this.beforeRecordBreadcrumbTasks.add(beforeRecordBreadcrumb);
+        if (!beforeRecordBreadcrumbTasks.contains(beforeRecordBreadcrumb)) {
+            beforeRecordBreadcrumbTasks.add(beforeRecordBreadcrumb);
+        }
     }
 
     /**