fix: change Session events list to a threadsafe implementation by default

google-genai-bot · copybara-github · commit 0b5ac9214926 · 2026-02-26T15:21:12.000-08:00
Session appends to event, so any readers of events will get a ConcurrentModificationException.

PiperOrigin-RevId: 875914576
diff --git a/core/src/main/java/com/google/adk/sessions/Session.java b/core/src/main/java/com/google/adk/sessions/Session.java
@@ -25,6 +25,7 @@
 import java.time.Duration;
 import java.time.Instant;
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.List;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ConcurrentMap;
@@ -54,7 +55,7 @@ public static final class Builder {
     private String appName;
     private String userId;
     private State state = new State(new ConcurrentHashMap<>());
-    private List<Event> events = new ArrayList<>();
+    private List<Event> events = Collections.synchronizedList(new ArrayList<>());
     private Instant lastUpdateTime = Instant.EPOCH;
 
     public Builder(String id) {
@@ -101,7 +102,7 @@ public Builder userId(String userId) {
     @CanIgnoreReturnValue
     @JsonProperty("events")
     public Builder events(List<Event> events) {
-      this.events = events;
+      this.events = Collections.synchronizedList(events);
       return this;
     }
 
