Avoid potential race conditions on collecting process tags (#8799)

* Avoid potential race conditions on collecting process tags

* Add synchronisation on test methods

Author: amarziali

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

@@ -102,11 +102,13 @@ static void calculate() {
   private ProcessTags() {}
 
   // need to be synchronized on writing. As optimization, it does not need to be sync on read.
-  public static synchronized void addTag(String key, String value) {
+  public static void addTag(String key, String value) {
     if (enabled) {
-      Lazy.TAGS.put(key, value);
-      Lazy.serializedForm = null;
-      Lazy.listForm = null;
+      synchronized (Lazy.TAGS) {
+        Lazy.TAGS.put(key, value);
+        Lazy.serializedForm = null;
+        Lazy.listForm = null;
+      }
     }
   }
 
@@ -136,15 +138,19 @@ public static UTF8BytesString getTagsForSerialization() {
 
   /** Visible for testing. */
   static void empty() {
-    Lazy.TAGS.clear();
-    Lazy.serializedForm = null;
-    Lazy.listForm = null;
+    synchronized (Lazy.TAGS) {
+      Lazy.TAGS.clear();
+      Lazy.serializedForm = null;
+      Lazy.listForm = null;
+    }
   }
 
   /** Visible for testing. */
   static void reset() {
-    empty();
-    enabled = Config.get().isExperimentalPropagateProcessTagsEnabled();
-    Lazy.TAGS.putAll(Lazy.loadTags());
+    synchronized (Lazy.TAGS) {
+      empty();
+      enabled = Config.get().isExperimentalPropagateProcessTagsEnabled();
+      Lazy.TAGS.putAll(Lazy.loadTags());
+    }
   }
 }