Fix NoSuchElementException in CircularFifoQueue when cloning a Scope (#2328)

Author: markushi

CHANGELOG.md

@@ -5,6 +5,7 @@
 ### Fixes
 
 - Use correct set-cookie for the HTTP Client response object ([#2326](https://github.com/getsentry/sentry-java/pull/2326))
+- Fix NoSuchElementException in CircularFifoQueue when cloning a Scope ([#2328](https://github.com/getsentry/sentry-java/pull/2328))
 
 ### Features
 

sentry/src/main/java/io/sentry/Scope.java

@@ -97,7 +97,7 @@ public Scope(final @NotNull SentryOptions options) {
     this.fingerprint = new ArrayList<>(scope.fingerprint);
     this.eventProcessors = new CopyOnWriteArrayList<>(scope.eventProcessors);
 
-    final Queue<Breadcrumb> breadcrumbsRef = scope.breadcrumbs;
+    final Breadcrumb[] breadcrumbsRef = scope.breadcrumbs.toArray(new Breadcrumb[0]);
 
     Queue<Breadcrumb> breadcrumbsClone = createBreadcrumbsList(scope.options.getMaxBreadcrumbs());
 

sentry/src/main/java/io/sentry/SynchronizedQueue.java

@@ -131,4 +131,18 @@ public E remove() {
       return decorated().remove();
     }
   }
+
+  @Override
+  public Object[] toArray() {
+    synchronized (lock) {
+      return decorated().toArray();
+    }
+  }
+
+  @Override
+  public <T> T[] toArray(T[] object) {
+    synchronized (lock) {
+      return decorated().toArray(object);
+    }
+  }
 }

sentry/src/test/java/io/sentry/ScopeTest.kt

@@ -217,6 +217,31 @@ class ScopeTest {
         assertTrue(clone.attachments is CopyOnWriteArrayList)
     }
 
+    @Test
+    fun `copying scope won't crash if there are concurrent operations`() {
+        val options = SentryOptions().apply {
+            maxBreadcrumbs = 10000
+        }
+        val scope = Scope(options)
+        for (i in 0 until options.maxBreadcrumbs) {
+            scope.addBreadcrumb(Breadcrumb.info("item"))
+        }
+
+        // remove one breadcrumb after the other on an extra thread
+        Thread({
+            while (scope.breadcrumbs.isNotEmpty()) {
+                scope.breadcrumbs.remove()
+            }
+        }, "thread-breadcrumb-remover").start()
+
+        // clone in the meantime
+        while (scope.breadcrumbs.isNotEmpty()) {
+            Scope(scope)
+        }
+
+        // expect no exception to be thrown ¯\_(ツ)_/¯
+    }
+
     @Test
     fun `clear scope resets scope to default state`() {
         val scope = Scope(SentryOptions())