What causes "No serializer for ${instanceClass}: ${instance}" in oracle/graal?

Take the class name from the message and register an ObjectSerializer (clazz/tag/serialize/deserialize) for it in JsonReplayCodec

oracle/graal · error · IllegalArgumentException

No serializer for ${instanceClass}: ${instance}

Error message

No serializer for ${instanceClass}: ${instance}

What it means

RecursiveSerializer.serialize(Object, ValueBuilder) dispatches by looking up an ObjectSerializer: first an exact-class map, then a scan of interface-keyed serializers (with result caching into the exact-class map). If neither finds a handler, it throws IllegalArgumentException naming the class and instance — the recorded object graph contains a type the codec was never taught to serialize.

Source

Thrown at compiler/src/jdk.graal.compiler/src/jdk/graal/compiler/hotspot/replaycomp/JsonReplayCodec.java:1900

    private final RecursiveSerializer recursiveSerializer = new RecursiveSerializer() {
        @Override
        public void serialize(Object instance, JsonBuilder.ValueBuilder valueBuilder) throws IOException {
            if (instance == null) {
                valueBuilder.value(null);
                return;
            }
            ObjectSerializer serializer = exactClassSerializers.get(instance.getClass());
            if (serializer == null) {
                var cursor = interfaceSerializers.getEntries();
                while (cursor.advance()) {
                    if (cursor.getKey().isInstance(instance)) {
                        serializer = cursor.getValue();
                        exactClassSerializers.put(instance.getClass(), serializer);
                        break;
                    }
                }
                if (serializer == null) {
                    throw new IllegalArgumentException("No serializer for " + instance.getClass() + ": " + instance);
                }
            }
            try (JsonBuilder.ObjectBuilder builder = valueBuilder.object()) {
                builder.append("tag", serializer.tag());
                serializer.serialize(instance, builder, this);
            }
        }

        @Override
        public void serialize(Object instance, JsonBuilder.ValueBuilder valueBuilder, String tag) throws IOException {
            if (instance == null) {
                valueBuilder.value(null);
                return;
            }
            ObjectSerializer serializer = tagSerializers.get(tag);
            if (serializer == null) {
                throw new IllegalArgumentException("No serializer registered for the given tag " + tag);
            }

View on GitHub (pinned to a66e9ccd1d)

Solutions

Take the class name from the message and register an ObjectSerializer (clazz/tag/serialize/deserialize) for it in JsonReplayCodec
If it is a JDK type, serialize it structurally (e.g. by name string) rather than by proxy
Re-record and serialize with the same GraalVM build so the type sets match
Filter the offending value out of recording if it is not needed for replay

Defensive patterns

Strategy: try-catch

Try / catch

try {
    serializer.serialize(value, valueBuilder);
} catch (IllegalArgumentException e) {
    if (e.getMessage().startsWith("No serializer for")) {
        // log class name, skip or structurally encode the value; do not corrupt the stream silently
        LOG.warning("Unhandled replay type: " + e.getMessage());
    } else { throw e; }
}

Prevention

Keep serializer coverage in lockstep with the recorded compiler interface: one change adds the type and its serializer
Add a canSerialize(Object) probe API in forks to assert coverage before a long recording run
Run a smoke serialize right after recording so gaps fail fast, not at replay time

When it happens

Trigger: Any recorded value whose class implements none of the registered serializer classes/interfaces — typically a new JDK/Graal type introduced by version drift, or an object reaching the recorder through a custom compiler-interface method.

Common situations: Upgrading one side (recorder or serializer) of a replay workflow without the other; custom compiler-interface extensions recording domain objects; unexpected java.* types (Class, MethodHandles, lambdas) leaking into recorded results.

Related errors

AI-assisted analysis of oracle/graal@a66e9ccd1d (2026-08-14). Data as JSON: /api/errors/a2452c17303fa31b. Report an issue: GitHub.