Codec improvements

Ensure DecoderContext null checks the decoder
PojoCodec improve error message if the cached codec is null
Remove creation race condition when creating automatic PojoCodecs

JAVA-3606

Author: rozza

bson/src/main/org/bson/codecs/DecoderContext.java

@@ -18,6 +18,8 @@
 
 import org.bson.BsonReader;
 
+import static org.bson.assertions.Assertions.notNull;
+
 /**
  * The context for decoding values to BSON.
  *
@@ -90,6 +92,7 @@ public DecoderContext build() {
      * @since 3.5
      */
     public <T> T decodeWithChildContext(final Decoder<T> decoder, final BsonReader reader) {
+        notNull("decoder", decoder);
         return decoder.decode(reader, DEFAULT_CONTEXT);
     }
 

bson/src/main/org/bson/codecs/pojo/PojoCodecImpl.java

@@ -210,15 +210,17 @@ private <S> void decodePropertyModel(final BsonReader reader, final DecoderConte
                 if (reader.getCurrentBsonType() == BsonType.NULL) {
                     reader.readNull();
                 } else {
-                    value = decoderContext.decodeWithChildContext(propertyModel.getCachedCodec(), reader);
+                    Codec<S> codec = propertyModel.getCachedCodec();
+                    if (codec == null) {
+                        throw new CodecConfigurationException(format("Missing codec in '%s' for '%s'",
+                                classModel.getName(), propertyModel.getName()));
+                    }
+                    value = decoderContext.decodeWithChildContext(codec, reader);
                 }
                 if (propertyModel.isWritable()) {
                     instanceCreator.set(value, propertyModel);
                 }
-            } catch (BsonInvalidOperationException e) {
-                throw new CodecConfigurationException(format("Failed to decode '%s'. Decoding '%s' errored with: %s",
-                        classModel.getName(), name, e.getMessage()), e);
-            } catch (CodecConfigurationException e) {
+            } catch (BsonInvalidOperationException | CodecConfigurationException e) {
                 throw new CodecConfigurationException(format("Failed to decode '%s'. Decoding '%s' errored with: %s",
                         classModel.getName(), name, e.getMessage()), e);
             }

bson/src/main/org/bson/internal/CodecCache.java

@@ -36,6 +36,16 @@ public void put(final Class<?> clazz, final Codec<?> codec){
         codecCache.put(clazz, Optional.of(codec));
     }
 
+    @SuppressWarnings("unchecked")
+    public synchronized <T> Codec<T> putIfMissing(final Class<T> clazz, final Codec<T> codec){
+        if (codecCache.containsKey(clazz)) {
+            return (Codec<T>) codecCache.get(clazz).get();
+        } else {
+            codecCache.put(clazz, Optional.of(codec));
+            return codec;
+        }
+    }
+
     @SuppressWarnings("unchecked")
     public <T> Codec<T> getOrThrow(final Class<T> clazz) {
         if (codecCache.containsKey(clazz)) {

bson/src/main/org/bson/internal/ProvidersCodecRegistry.java

@@ -56,8 +56,7 @@ public <T> Codec<T> get(final ChildCodecRegistry<T> context) {
             for (CodecProvider provider : codecProviders) {
                 Codec<T> codec = provider.get(context.getCodecClass(), context);
                 if (codec != null) {
-                    codecCache.put(context.getCodecClass(), codec);
-                    return codec;
+                    return codecCache.putIfMissing(context.getCodecClass(), codec);
                 }
             }
             codecCache.put(context.getCodecClass(), null);