Remove blocking ClassInfo.of (#643)

* Remove blocking ClassInfo.of

Replaces blocking logic in ClassInfo.of with ConcurrentMap.computeIfAbsent.

Also removes WeakHashMap as it wasn't actually doing the intended operation. The ClassInfo value has a strong reference to the Class which prevents the weak key reference from ever being collected.

* Remove dependency on JDK8 API

computeIfAbsent isn't available in all supported environments. Replace with the same logic as the default computeIfAbsent implementation.

Author: edalquist

google-http-client/src/main/java/com/google/api/client/util/ClassInfo.java

@@ -24,7 +24,8 @@
 import java.util.Locale;
 import java.util.Map;
 import java.util.TreeSet;
-import java.util.WeakHashMap;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentMap;
 
 /**
  * Computes class information to determine data key name/value pairs associated with the class.
@@ -37,11 +38,12 @@
 public final class ClassInfo {
 
   /** Class information cache, with case-sensitive field names. */
-  private static final Map<Class<?>, ClassInfo> CACHE = new WeakHashMap<Class<?>, ClassInfo>();
+  private static final ConcurrentMap<Class<?>, ClassInfo> CACHE =
+      new ConcurrentHashMap<Class<?>, ClassInfo>();
 
   /** Class information cache, with case-insensitive fields names. */
-  private static final Map<Class<?>, ClassInfo> CACHE_IGNORE_CASE =
-      new WeakHashMap<Class<?>, ClassInfo>();
+  private static final ConcurrentMap<Class<?>, ClassInfo> CACHE_IGNORE_CASE =
+      new ConcurrentHashMap<Class<?>, ClassInfo>();
 
   /** Class. */
   private final Class<?> clazz;
@@ -81,16 +83,15 @@ public static ClassInfo of(Class<?> underlyingClass, boolean ignoreCase) {
     if (underlyingClass == null) {
       return null;
     }
-    final Map<Class<?>, ClassInfo> cache = ignoreCase ? CACHE_IGNORE_CASE : CACHE;
-    ClassInfo classInfo;
-    synchronized (cache) {
-      classInfo = cache.get(underlyingClass);
-      if (classInfo == null) {
-        classInfo = new ClassInfo(underlyingClass, ignoreCase);
-        cache.put(underlyingClass, classInfo);
-      }
-    }
-    return classInfo;
+    final ConcurrentMap<Class<?>, ClassInfo> cache = ignoreCase ? CACHE_IGNORE_CASE : CACHE;
+
+    // Logic copied from ConcurrentMap.computeIfAbsent
+    ClassInfo v, newValue;
+    return ((v = cache.get(underlyingClass)) == null
+            && (newValue = new ClassInfo(underlyingClass, ignoreCase)) != null
+            && (v = cache.putIfAbsent(underlyingClass, newValue)) == null)
+        ? newValue
+        : v;
   }
 
   /**