perf(core): Reduce context serialization allocations

Use sorted key arrays when serializing contexts to avoid allocating an ArrayList for each serialization. This preserves deterministic key ordering while keeping the snapshot representation smaller.

Co-Authored-By: Claude <noreply@anthropic.com>

Author: adinauer

sentry/src/main/java/io/sentry/MonitorContexts.java

@@ -3,15 +3,15 @@
 import io.sentry.util.Objects;
 import io.sentry.vendor.gson.stream.JsonToken;
 import java.io.IOException;
-import java.util.Collections;
-import java.util.List;
+import java.util.Arrays;
 import java.util.concurrent.ConcurrentHashMap;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
 public final class MonitorContexts extends ConcurrentHashMap<String, Object>
     implements JsonSerializable {
   private static final long serialVersionUID = 3987329379811822556L;
+  private static final String[] EMPTY_KEYS = new String[0];
 
   public MonitorContexts() {}
 
@@ -49,8 +49,8 @@ public void serialize(final @NotNull ObjectWriter writer, final @NotNull ILogger
       throws IOException {
     writer.beginObject();
     // Serialize in alphabetical order to keep determinism.
-    final List<String> sortedKeys = Collections.list(keys());
-    Collections.sort(sortedKeys);
+    final String[] sortedKeys = keySet().toArray(EMPTY_KEYS);
+    Arrays.sort(sortedKeys);
     for (final String key : sortedKeys) {
       final Object value = get(key);
       if (value != null) {

sentry/src/main/java/io/sentry/protocol/Contexts.java

@@ -14,10 +14,9 @@
 import io.sentry.util.Objects;
 import io.sentry.vendor.gson.stream.JsonToken;
 import java.io.IOException;
-import java.util.Collections;
+import java.util.Arrays;
 import java.util.Enumeration;
 import java.util.HashMap;
-import java.util.List;
 import java.util.Map;
 import java.util.Set;
 import java.util.concurrent.ConcurrentHashMap;
@@ -28,6 +27,7 @@
 public class Contexts implements JsonSerializable {
   private static final long serialVersionUID = 252445813254943011L;
   public static final String REPLAY_ID = "replay_id";
+  private static final String[] EMPTY_KEYS = new String[0];
 
   private final @NotNull ConcurrentHashMap<String, Object> internalStorage =
       new ConcurrentHashMap<>();
@@ -302,8 +302,8 @@ public void serialize(final @NotNull ObjectWriter writer, final @NotNull ILogger
       throws IOException {
     writer.beginObject();
     // Serialize in alphabetical order to keep determinism.
-    final List<String> sortedKeys = Collections.list(keys());
-    Collections.sort(sortedKeys);
+    final String[] sortedKeys = internalStorage.keySet().toArray(EMPTY_KEYS);
+    Arrays.sort(sortedKeys);
     for (final String key : sortedKeys) {
       final Object value = get(key);
       if (value != null) {

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

@@ -0,0 +1,19 @@
+package io.sentry
+
+import io.sentry.protocol.SerializationUtils
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import org.mockito.kotlin.mock
+
+class MonitorContextsTest {
+  @Test
+  fun `serializes entries in alphabetical order`() {
+    val contexts =
+      MonitorContexts().apply {
+        put("b", 2)
+        put("a", 1)
+      }
+
+    assertEquals("{\"a\":1,\"b\":2}", SerializationUtils.serializeToString(contexts, mock()))
+  }
+}