Adding configuration variable

Added configuration variable to toggle between the two map implementations

Author: dougqh

dd-trace-api/src/main/java/datadog/trace/api/config/GeneralConfig.java

@@ -100,5 +100,7 @@ public final class GeneralConfig {
   public static final String APM_TRACING_ENABLED = "apm.tracing.enabled";
   public static final String JDK_SOCKET_ENABLED = "jdk.socket.enabled";
 
+  public static final String OPTIMIZED_MAP_ENABLED = "optimized.map.enabled";
+
   private GeneralConfig() {}
 }

internal-api/src/main/java/datadog/trace/api/Config.java

@@ -540,6 +540,7 @@ public static String getHostName() {
   private final boolean longRunningTraceEnabled;
   private final long longRunningTraceInitialFlushInterval;
   private final long longRunningTraceFlushInterval;
+
   private final boolean cassandraKeyspaceStatementExtractionEnabled;
   private final boolean couchbaseInternalSpansEnabled;
   private final boolean elasticsearchBodyEnabled;
@@ -576,6 +577,8 @@ public static String getHostName() {
 
   private final boolean jdkSocketEnabled;
 
+  private final boolean optimizedMapEnabled;
+
   // Read order: System Properties -> Env Variables, [-> properties file], [-> default value]
   private Config() {
     this(ConfigProvider.createDefault());
@@ -2027,6 +2030,9 @@ PROFILING_DATADOG_PROFILER_ENABLED, isDatadogProfilerSafeInCurrentEnvironment())
 
     this.jdkSocketEnabled = configProvider.getBoolean(JDK_SOCKET_ENABLED, true);
 
+    this.optimizedMapEnabled =
+        configProvider.getBoolean(GeneralConfig.OPTIMIZED_MAP_ENABLED, false);
+
     log.debug("New instance: {}", this);
   }
 
@@ -3653,6 +3659,10 @@ public boolean isJdkSocketEnabled() {
     return jdkSocketEnabled;
   }
 
+  public boolean isOptimizedMapEnabled() {
+    return optimizedMapEnabled;
+  }
+
   /** @return A map of tags to be applied only to the local application root span. */
   public TagMap getLocalRootSpanTags() {
     final Map<String, String> runtimeTags = getRuntimeTags();

internal-api/src/main/java/datadog/trace/api/TagMap.java

@@ -1056,7 +1056,10 @@ public EntryChange next() {
  * That will allow all of the calls to create methods to be devirtualized without a guard
  */
 abstract class TagMapFactory<MapT extends TagMap> {
-  public static final TagMapFactory<?> INSTANCE = new OptimizedTagMapFactory();
+  public static final TagMapFactory<?> INSTANCE =
+      Config.get().isOptimizedMapEnabled()
+          ? new OptimizedTagMapFactory()
+          : new LegacyTagMapFactory();
 
   public abstract MapT create();