Avoid overriding user's MDC in Log4j (open-telemetry#13479)

Author: 123liuziming

instrumentation/log4j/log4j-context-data/log4j-context-data-2.17/library-autoconfigure/src/main/java/io/opentelemetry/instrumentation/log4j/contextdata/v2_17/OpenTelemetryContextDataProvider.java

@@ -16,6 +16,7 @@
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.Map;
+import org.apache.logging.log4j.ThreadContext;
 import org.apache.logging.log4j.core.util.ContextDataProvider;
 
 /**
@@ -67,6 +68,11 @@ public Map<String, String> supplyContextData() {
       return staticContextData;
     }
 
+    if (ThreadContext.containsKey(ContextDataKeys.TRACE_ID_KEY)) {
+      // Assume already instrumented event if traceId is present.
+      return staticContextData;
+    }
+
     Map<String, String> contextData = new HashMap<>(staticContextData);
     SpanContext spanContext = currentSpan.getSpanContext();
     contextData.put(ContextDataKeys.TRACE_ID_KEY, spanContext.getTraceId());

instrumentation/log4j/log4j-context-data/log4j-context-data-common/testing/src/main/java/io/opentelemetry/instrumentation/log4j/contextdata/Log4j2Test.java

@@ -15,6 +15,7 @@
 import java.util.concurrent.atomic.AtomicReference;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
+import org.apache.logging.log4j.ThreadContext;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
@@ -132,4 +133,29 @@ void testIdsWhenSpan() {
     assertThat(events.get(3).getContextData().get(getLoggingKey("trace_flags"))).isEqualTo("01");
     assertThat(events.get(3).getContextData().get("baggage.baggage_key")).isNull();
   }
+
+  @Test
+  void testNoOverrideTraceId() {
+    Logger logger = LogManager.getLogger("TestLogger");
+
+    ThreadContext.put(getLoggingKey("trace_id"), "test_traceId");
+    ThreadContext.put(getLoggingKey("span_id"), "test_spanId");
+    ThreadContext.put(getLoggingKey("trace_flags"), "test_traceFlag");
+    getInstrumentationExtension()
+        .runWithSpan(
+            "test",
+            () -> {
+              logger.info("log span parent");
+            });
+    List<ListAppender.LoggedEvent> events = ListAppender.get().getEvents();
+    ThreadContext.clearAll();
+    assertThat(events.size()).isEqualTo(1);
+    assertThat(events.get(0).getMessage()).isEqualTo("log span parent");
+    assertThat(events.get(0).getContextData().get(getLoggingKey("trace_id")))
+        .isEqualTo("test_traceId");
+    assertThat(events.get(0).getContextData().get(getLoggingKey("span_id")))
+        .isEqualTo("test_spanId");
+    assertThat(events.get(0).getContextData().get(getLoggingKey("trace_flags")))
+        .isEqualTo("test_traceFlag");
+  }
 }