Allow SchemaLoader to use a callback to lazily load schema nodes, including…

Allow SchemaLoader to use a callback to lazily load schema nodes, including dependencies of loaded nodes.

c++/src/capnp/generated-header-support.h

@@ -147,11 +147,16 @@ struct RawSchema {
   //
   // This is an internal structure which could change in the future.
 
+  uint64_t id;
+
   const word* encodedNode;
   // Encoded SchemaNode, readable via readMessageUnchecked<schema::Node>(encodedNode).
 
   const RawSchema* const* dependencies;
-  // Pointers to other types on which this one depends, sorted by ID.
+  // Pointers to other types on which this one depends, sorted by ID.  The schemas in this table
+  // may be uninitialized -- you must call ensureInitialized() on the one you wish to use before
+  // using it.
+  //
   // TODO(someday):  Make this a hashtable.
 
   struct MemberInfo {
@@ -171,6 +176,23 @@ struct RawSchema {
   // Points to the RawSchema of a compiled-in type to which it is safe to cast any DynamicValue
   // with this schema.  This is null for all compiled-in types; it is only set by SchemaLoader on
   // dynamically-loaded types.
+
+  class Initializer {
+  public:
+    virtual void init(const RawSchema* schema) const = 0;
+  };
+
+  const Initializer* lazyInitializer;
+  // Lazy initializer, invoked by ensureInitialized().
+
+  inline void ensureInitialized() const {
+    // Lazy initialization support.  Invoke to ensure that initialization has taken place.  This
+    // is required in particular when traversing the dependency list.  RawSchemas for compiled-in
+    // types are always initialized; only dynamically-loaded schemas may be lazy.
+
+    const Initializer* i = __atomic_load_n(&lazyInitializer, __ATOMIC_ACQUIRE);
+    if (i != nullptr) i->init(this);
+  }
 };
 
 template <typename T>

c++/src/capnp/schema-loader-test.c++

@@ -208,6 +208,8 @@ TEST(SchemaLoader, Incompatible) {
       loadUnderAlternateTypeId<test::TestAllTypes>(loader, typeId<test::TestListDefaults>()));
 }
 
+// TODO(test):  More extensively test upgrade/downgrade checks.
+
 TEST(SchemaLoader, Enumerate) {
   SchemaLoader loader;
   loader.loadCompiledTypeAndDependencies<TestAllTypes>();
@@ -222,7 +224,88 @@ TEST(SchemaLoader, Enumerate) {
   }
 }
 
-// TODO(test):  More extensively test upgrade/downgrade checks.
+TEST(SchemaLoader, EnumerateNoPlaceholders) {
+  SchemaLoader loader;
+  Schema schema = loader.load(Schema::from<TestDefaults>().getProto());
+
+  {
+    auto list = loader.getAllLoaded();
+    ASSERT_EQ(1u, list.size());
+    EXPECT_TRUE(list[0] == schema);
+  }
+
+  Schema dep = schema.getDependency(typeId<TestAllTypes>());
+
+  {
+    auto list = loader.getAllLoaded();
+    ASSERT_EQ(2u, list.size());
+    if (list[0] == schema) {
+      EXPECT_TRUE(list[1] == dep);
+    } else {
+      EXPECT_TRUE(list[0] == dep);
+      EXPECT_TRUE(list[1] == schema);
+    }
+  }
+}
+
+class FakeLoaderCallback: public SchemaLoader::LazyLoadCallback {
+public:
+  FakeLoaderCallback(const schema::Node::Reader node): node(node), loaded(false) {}
+
+  bool isLoaded() { return loaded; }
+
+  void load(const SchemaLoader& loader, uint64_t id) const override {
+    if (id == 1234) {
+      // Magic "not found" ID.
+      return;
+    }
+
+    EXPECT_EQ(node.getId(), id);
+    EXPECT_FALSE(loaded);
+    loaded = true;
+    loader.loadIfNew(node);
+  }
+
+private:
+  const schema::Node::Reader node;
+  mutable bool loaded = false;
+};
+
+TEST(SchemaLoader, LazyLoad) {
+  FakeLoaderCallback callback(Schema::from<TestAllTypes>().getProto());
+  SchemaLoader loader(callback);
+
+  EXPECT_TRUE(loader.tryGet(1234) == nullptr);
+
+  EXPECT_FALSE(callback.isLoaded());
+  Schema schema = loader.get(typeId<TestAllTypes>());
+  EXPECT_TRUE(callback.isLoaded());
+
+  EXPECT_EQ(schema.getProto().getDisplayName(),
+            Schema::from<TestAllTypes>().getProto().getDisplayName());
+
+  EXPECT_EQ(schema, schema.getDependency(typeId<TestAllTypes>()));
+  EXPECT_EQ(schema, loader.get(typeId<TestAllTypes>()));
+}
+
+TEST(SchemaLoader, LazyLoadGetDependency) {
+  FakeLoaderCallback callback(Schema::from<TestAllTypes>().getProto());
+  SchemaLoader loader(callback);
+
+  Schema schema = loader.load(Schema::from<TestDefaults>().getProto());
+
+  EXPECT_FALSE(callback.isLoaded());
+
+  Schema dep = schema.getDependency(typeId<TestAllTypes>());
+
+  EXPECT_TRUE(callback.isLoaded());
+
+  EXPECT_EQ(dep.getProto().getDisplayName(),
+            Schema::from<TestAllTypes>().getProto().getDisplayName());
+
+  EXPECT_EQ(dep, schema.getDependency(typeId<TestAllTypes>()));
+  EXPECT_EQ(dep, loader.get(typeId<TestAllTypes>()));
+}
 
 }  // namespace
 }  // namespace _ (private)

c++/src/capnp/schema-loader.c++

@@ -33,22 +33,50 @@
 
 namespace capnp {
 
+class SchemaLoader::InitializerImpl: public _::RawSchema::Initializer {
+public:
+  inline explicit InitializerImpl(const SchemaLoader& loader): loader(loader), callback(nullptr) {}
+  inline InitializerImpl(const SchemaLoader& loader, const LazyLoadCallback& callback)
+      : loader(loader), callback(callback) {}
+
+  inline kj::Maybe<const LazyLoadCallback&> getCallback() const { return callback; }
+
+  void init(const _::RawSchema* schema) const override;
+
+  inline bool operator==(decltype(nullptr)) const { return callback == nullptr; }
+
+private:
+  const SchemaLoader& loader;
+  kj::Maybe<const LazyLoadCallback&> callback;
+};
+
 class SchemaLoader::Impl {
 public:
-  _::RawSchema* load(const schema::Node::Reader& reader);
+  inline explicit Impl(const SchemaLoader& loader): initializer(loader) {}
+  inline Impl(const SchemaLoader& loader, const LazyLoadCallback& callback)
+      : initializer(loader, callback) {}
+
+  _::RawSchema* load(const schema::Node::Reader& reader, bool isPlaceholder);
 
   _::RawSchema* loadNative(const _::RawSchema* nativeSchema);
 
   _::RawSchema* loadEmpty(uint64_t id, kj::StringPtr name, schema::Node::Body::Which kind);
   // Create a dummy empty schema of the given kind for the given id and load it.
 
-  _::RawSchema* tryGet(uint64_t typeId) const;
+  struct TryGetResult {
+    _::RawSchema* schema;
+    kj::Maybe<const LazyLoadCallback&> callback;
+  };
+
+  TryGetResult tryGet(uint64_t typeId) const;
   kj::Array<Schema> getAllLoaded() const;
 
   kj::Arena arena;
 
 private:
   std::unordered_map<uint64_t, _::RawSchema*> schemas;
+
+  InitializerImpl initializer;
 };
 
 // =======================================================================================
@@ -396,7 +424,7 @@ private:
   }
 
   void validateTypeId(uint64_t id, schema::Node::Body::Which expectedKind) {
-    _::RawSchema* existing = loader.tryGet(id);
+    _::RawSchema* existing = loader.tryGet(id).schema;
     if (existing != nullptr) {
       auto node = readMessageUnchecked<schema::Node>(existing->encodedNode);
       VALIDATE_SCHEMA(node.getBody().which() == expectedKind,
@@ -406,9 +434,8 @@ private:
       return;
     }
 
-    // TODO(cleanup):  str() really needs to return something NUL-terminated...
     dependencies.insert(std::make_pair(id, loader.loadEmpty(
-        id, kj::str("(unknown type used by ", nodeName , ")", '\0').begin(), expectedKind)));
+        id, kj::str("(unknown type used by ", nodeName , ")"), expectedKind)));
   }
 
 #undef VALIDATE_SCHEMA
@@ -423,7 +450,7 @@ public:
 
   bool shouldReplace(const schema::Node::Reader& existingNode,
                      const schema::Node::Reader& replacement,
-                     bool replacementIsNative) {
+                     bool preferReplacementIfEquivalent) {
     KJ_CONTEXT("checking compatibility with previously-loaded node of the same id",
                existingNode.getDisplayName());
 
@@ -434,9 +461,8 @@ public:
 
     checkCompatibility(existingNode, replacement);
 
-    // Prefer the newer schema.  If neither is newer, prefer native types, otherwise prefer the
-    // existing type.
-    return replacementIsNative ? compatibility != OLDER : compatibility == NEWER;
+    // Prefer the newer schema.
+    return preferReplacementIfEquivalent ? compatibility != OLDER : compatibility == NEWER;
   }
 
 private:
@@ -798,8 +824,7 @@ private:
     MallocMessageBuilder builder(kj::arrayPtr(scratch, sizeof(scratch)));
     auto node = builder.initRoot<schema::Node>();
     node.setId(structTypeId);
-    // TODO(cleanup):  str() really needs to return something NUL-terminated...
-    node.setDisplayName(kj::str("(unknown type used in ", nodeName, ")", '\0').begin());
+    node.setDisplayName(kj::str("(unknown type used in ", nodeName, ")"));
     auto structNode = node.getBody().initStructNode();
 
     switch (type.getBody().which()) {
@@ -864,7 +889,7 @@ private:
     member.setCodeOrder(0);
     member.getBody().initFieldMember().setType(type);
 
-    loader.load(node);
+    loader.load(node, true);
   }
 
   bool canUpgradeToData(const schema::Type::Reader& type) {
@@ -959,7 +984,7 @@ private:
 
 // =======================================================================================
 
-_::RawSchema* SchemaLoader::Impl::load(const schema::Node::Reader& reader) {
+_::RawSchema* SchemaLoader::Impl::load(const schema::Node::Reader& reader, bool isPlaceholder) {
   // Make a copy of the node which can be used unchecked.
   size_t size = reader.totalSizeInWords() + 1;
   kj::ArrayPtr<word> validated = arena.allocateArray<word>(size);
@@ -979,68 +1004,110 @@ _::RawSchema* SchemaLoader::Impl::load(const schema::Node::Reader& reader) {
 
   // Check if we already have a schema for this ID.
   _::RawSchema*& slot = schemas[validatedReader.getId()];
+  bool shouldReplace;
   if (slot == nullptr) {
     // Nope, allocate a new RawSchema.
     slot = &arena.allocate<_::RawSchema>();
+    slot->id = validatedReader.getId();
+    slot->canCastTo = nullptr;
+    shouldReplace = true;
   } else {
     // Yes, check if it is compatible and figure out which schema is newer.
+
+    if (slot->lazyInitializer == nullptr) {
+      // The existing slot is not a placeholder, so whether we overwrite it or not, we cannot
+      // end up with a placeholder.
+      isPlaceholder = false;
+    }
+
     auto existing = readMessageUnchecked<schema::Node>(slot->encodedNode);
     CompatibilityChecker checker(*this);
-    if (!checker.shouldReplace(existing, validatedReader, false)) {
-      // The new schema does not appear to be any newer than the existing one, so keep the existing.
-      return slot;
-    }
+
+    // Prefer to replace the existing schema if the existing schema is a placeholder.  Otherwise,
+    // prefer to keep the existing schema.
+    shouldReplace = checker.shouldReplace(
+        existing, validatedReader, slot->lazyInitializer != nullptr);
   }
 
-  // Initialize the RawSchema.
-  slot->encodedNode = validated.begin();
-  slot->dependencies = validator.makeDependencyArray(&slot->dependencyCount);
-  slot->membersByName = validator.makeMemberInfoArray(&slot->memberCount);
+  if (shouldReplace) {
+    // Initialize the RawSchema.
+    slot->encodedNode = validated.begin();
+    slot->dependencies = validator.makeDependencyArray(&slot->dependencyCount);
+    slot->membersByName = validator.makeMemberInfoArray(&slot->memberCount);
+  }
+
+  if (isPlaceholder) {
+    slot->lazyInitializer = &initializer;
+  } else {
+    // If this schema is not newly-allocated, it may already be in the wild, specifically in the
+    // dependency list of other schemas.  Once the initializer is null, it is live, so we must do
+    // a release-store here.
+    __atomic_store_n(&slot->lazyInitializer, nullptr, __ATOMIC_RELEASE);
+  }
 
   return slot;
 }
 
 _::RawSchema* SchemaLoader::Impl::loadNative(const _::RawSchema* nativeSchema) {
-  auto reader = readMessageUnchecked<schema::Node>(nativeSchema->encodedNode);
-  _::RawSchema*& slot = schemas[reader.getId()];
+  _::RawSchema*& slot = schemas[nativeSchema->id];
+  bool shouldReplace;
   if (slot == nullptr) {
     slot = &arena.allocate<_::RawSchema>();
+    shouldReplace = true;
   } else if (slot->canCastTo != nullptr) {
+    // Already loaded natively, or we're currently in the process of loading natively and there
+    // was a dependency cycle.
     KJ_REQUIRE(slot->canCastTo == nativeSchema,
         "two different compiled-in type have the same type ID",
-        reader.getId(), reader.getDisplayName(),
+        nativeSchema->id,
+        readMessageUnchecked<schema::Node>(nativeSchema->encodedNode).getDisplayName(),
         readMessageUnchecked<schema::Node>(slot->canCastTo->encodedNode).getDisplayName());
-    // Already loaded.
     return slot;
   } else {
     auto existing = readMessageUnchecked<schema::Node>(slot->encodedNode);
     auto native = readMessageUnchecked<schema::Node>(nativeSchema->encodedNode);
     CompatibilityChecker checker(*this);
-    if (!checker.shouldReplace(existing, native, true)) {
-      // The existing schema is newer, so just make sure the dependencies are loaded.
-      slot->canCastTo = nativeSchema;
-      for (uint i = 0; i < nativeSchema->dependencyCount; i++) {
-        loadNative(nativeSchema->dependencies[i]);
-      }
-      return slot;
-    }
+    shouldReplace = checker.shouldReplace(existing, native, true);
   }
 
-  // Set the slot to a copy of the native schema.
-  *slot = *nativeSchema;
+  // Since we recurse below, the slot in the hash map could move around.  Copy out the pointer
+  // for subsequent use.
+  _::RawSchema* result = slot;
+
+  if (shouldReplace) {
+    // Set the schema to a copy of the native schema.
+    *kj::implicitCast<_::RawSchema*>(result) = *nativeSchema;
+
+    // Indicate that casting is safe.  Note that it's important to set this before recursively
+    // loading dependencies, so that cycles don't cause infinite loops!
+    result->canCastTo = nativeSchema;
+
+    // Except that we need to set the dependency list to point at other loader-owned RawSchemas.
+    kj::ArrayPtr<const _::RawSchema*> dependencies =
+        arena.allocateArray<const _::RawSchema*>(result->dependencyCount);
+    for (uint i = 0; i < nativeSchema->dependencyCount; i++) {
+      dependencies[i] = loadNative(nativeSchema->dependencies[i]);
+    }
+    result->dependencies = dependencies.begin();
+  } else {
+    // The existing schema is newer.
 
-  // Indicate that casting is safe.
-  slot->canCastTo = nativeSchema;
+    // Indicate that casting is safe.  Note that it's important to set this before recursively
+    // loading dependencies, so that cycles don't cause infinite loops!
+    result->canCastTo = nativeSchema;
 
-  // Except that we need to set the dependency list to point at other loader-owned RawSchemas.
-  kj::ArrayPtr<const _::RawSchema*> dependencies =
-      arena.allocateArray<const _::RawSchema*>(slot->dependencyCount);
-  for (uint i = 0; i < nativeSchema->dependencyCount; i++) {
-    dependencies[i] = loadNative(nativeSchema->dependencies[i]);
+    // Make sure the dependencies are loaded and compatible.
+    for (uint i = 0; i < nativeSchema->dependencyCount; i++) {
+      loadNative(nativeSchema->dependencies[i]);
+    }
   }
-  slot->dependencies = dependencies.begin();
 
-  return slot;
+  // If this schema is not newly-allocated, it may already be in the wild, specifically in the
+  // dependency list of other schemas.  Once the initializer is null, it is live, so we must do
+  // a release-store here.
+  __atomic_store_n(&result->lazyInitializer, nullptr, __ATOMIC_RELEASE);
+
+  return result;
 }
 
 _::RawSchema* SchemaLoader::Impl::loadEmpty(
@@ -1063,57 +1130,107 @@ _::RawSchema* SchemaLoader::Impl::loadEmpty(
       break;
   }
 
-  return load(node);
+  return load(node, true);
 }
 
-_::RawSchema* SchemaLoader::Impl::tryGet(uint64_t typeId) const {
+SchemaLoader::Impl::TryGetResult SchemaLoader::Impl::tryGet(uint64_t typeId) const {
   auto iter = schemas.find(typeId);
   if (iter == schemas.end()) {
-    return nullptr;
+    return {nullptr, initializer.getCallback()};
   } else {
-    return iter->second;
+    return {iter->second, initializer.getCallback()};
   }
 }
 
 kj::Array<Schema> SchemaLoader::Impl::getAllLoaded() const {
-  kj::Array<Schema> result = kj::heapArray<Schema>(schemas.size());
+  size_t count = 0;
+  for (auto& schema: schemas) {
+    if (schema.second->lazyInitializer == nullptr) ++count;
+  }
+
+  kj::Array<Schema> result = kj::heapArray<Schema>(count);
   size_t i = 0;
   for (auto& schema: schemas) {
-    result[i++] = Schema(schema.second);
+    if (schema.second->lazyInitializer == nullptr) result[i++] = Schema(schema.second);
   }
   return result;
 }
 
+void SchemaLoader::InitializerImpl::init(const _::RawSchema* schema) const {
+  KJ_IF_MAYBE(c, callback) {
+    c->load(loader, schema->id);
+  }
+
+  if (schema->lazyInitializer != nullptr) {
+    // The callback declined to load a schema.  We need to disable the initializer so that it
+    // doesn't get invoked again later, as we can no longer modify this schema once it is in use.
+
+    // Lock the loader for read to make sure no one is concurrently loading a replacement for this
+    // schema node.
+    auto lock = loader.impl.lockForRead();
+
+    // Get the mutable version of the schema.
+    _::RawSchema* mutableSchema = lock->get()->tryGet(schema->id).schema;
+    KJ_ASSERT(mutableSchema == schema,
+              "A schema not belonging to this loader used its initializer.");
+
+    // Disable the initializer.
+    __atomic_store_n(&mutableSchema->lazyInitializer, nullptr, __ATOMIC_RELEASE);
+  }
+}
+
 // =======================================================================================
 
-SchemaLoader::SchemaLoader(): impl(kj::heap<Impl>()) {}
+SchemaLoader::SchemaLoader(): impl(kj::heap<Impl>(*this)) {}
+SchemaLoader::SchemaLoader(const LazyLoadCallback& callback)
+    : impl(kj::heap<Impl>(*this, callback)) {}
 SchemaLoader::~SchemaLoader() noexcept(false) {}
 
 Schema SchemaLoader::get(uint64_t id) const {
-  _::RawSchema* raw = impl->tryGet(id);
-  KJ_REQUIRE(raw != nullptr, "no schema node loaded for id", id);
-  return Schema(raw);
+  KJ_IF_MAYBE(result, tryGet(id)) {
+    return *result;
+  } else {
+    KJ_FAIL_REQUIRE("no schema node loaded for id", id);
+  }
 }
 
 kj::Maybe<Schema> SchemaLoader::tryGet(uint64_t id) const {
-  _::RawSchema* raw = impl->tryGet(id);
-  if (raw == nullptr) {
-    return nullptr;
+  auto getResult = impl.lockForRead()->get()->tryGet(id);
+  if (getResult.schema == nullptr || getResult.schema->lazyInitializer != nullptr) {
+    KJ_IF_MAYBE(c, getResult.callback) {
+      c->load(*this, id);
+    }
+    getResult = impl.lockForRead()->get()->tryGet(id);
+  }
+  if (getResult.schema != nullptr && getResult.schema->lazyInitializer == nullptr) {
+    return Schema(getResult.schema);
   } else {
-    return Schema(raw);
+    return nullptr;
   }
 }
 
 Schema SchemaLoader::load(const schema::Node::Reader& reader) {
-  return Schema(impl->load(reader));
+  return Schema(impl.lock()->get()->load(reader, false));
+}
+
+Schema SchemaLoader::loadIfNew(const schema::Node::Reader& reader) const {
+  auto locked = impl.lock();
+  auto getResult = locked->get()->tryGet(reader.getId());
+  if (getResult.schema == nullptr || getResult.schema->lazyInitializer != nullptr) {
+    // Doesn't exist yet, or the existing schema is a placeholder and therefore has not yet been
+    // seen publicly.  Go ahead and load the incoming reader.
+    return Schema(locked->get()->load(reader, false));
+  } else {
+    return Schema(getResult.schema);
+  }
 }
 
 kj::Array<Schema> SchemaLoader::getAllLoaded() const {
-  return impl->getAllLoaded();
+  return impl.lockForRead()->get()->getAllLoaded();
 }
 
 void SchemaLoader::loadNative(const _::RawSchema* nativeSchema) {
-  impl->loadNative(nativeSchema);
+  impl.lock()->get()->loadNative(nativeSchema);
 }
 
 }  // namespace capnp

c++/src/capnp/schema-loader.h

@@ -26,12 +26,34 @@
 
 #include "schema.h"
 #include <kj/memory.h>
+#include <kj/mutex.h>
 
 namespace capnp {
 
 class SchemaLoader {
 public:
+  class LazyLoadCallback {
+  public:
+    virtual void load(const SchemaLoader& loader, uint64_t id) const = 0;
+    // Request that the schema node with the given ID be loaded into the given SchemaLoader.  If
+    // the callback is able to find a schema for this ID, it should invoke `loadIfNew()` on
+    // `loader` to load it.  If no such node exists, it should simply do nothing and return.
+    //
+    // The callback is allowed to load schema nodes other than the one requested, e.g. because it
+    // expects they will be needed soon.
+    //
+    // If the `SchemaLoader` is used from multiple threads, the callback must be thread-safe.
+    // In particular, it's possible for multiple threads to invoke `load()` with the same ID.
+    // If the callback performs a large amount of work to look up IDs, it should be sure to
+    // de-dup these requests.
+  };
+
   SchemaLoader();
+
+  SchemaLoader(const LazyLoadCallback& callback);
+  // Construct a SchemaLoader which will invoke the given callback when a schema node is requested
+  // that isn't already loaded.
+
   ~SchemaLoader() noexcept(false);
   KJ_DISALLOW_COPY(SchemaLoader);
 
@@ -79,6 +101,11 @@ public:
   // Also note that unknown types are not considered invalid.  Instead, the dynamic API returns
   // a DynamicValue with type UNKNOWN for these.
 
+  Schema loadIfNew(const schema::Node::Reader& reader) const;
+  // Like `load()` but does nothing if a schema with the same ID is already loaded.  In contrast,
+  // `load()` would attempt to compare the schemas and take the newer one.  `loadIfNew()` is safe
+  // to call even while concurrently using schemas from this loader.
+
   template <typename T>
   void loadCompiledTypeAndDependencies();
   // Load the schema for the given compiled-in type and all of its dependencies.
@@ -96,7 +123,8 @@ private:
   class Validator;
   class CompatibilityChecker;
   class Impl;
-  kj::Own<Impl> impl;
+  class InitializerImpl;
+  kj::MutexGuarded<kj::Own<Impl>> impl;
 
   void loadNative(const _::RawSchema* nativeSchema);
 };

c++/src/capnp/schema.c++

@@ -38,11 +38,12 @@ Schema Schema::getDependency(uint64_t id) const {
   while (lower < upper) {
     uint mid = (lower + upper) / 2;
 
-    Schema candidate(raw->dependencies[mid]);
+    const _::RawSchema* candidate = raw->dependencies[mid];
 
-    uint64_t candidateId = candidate.getProto().getId();
+    uint64_t candidateId = candidate->id;
     if (candidateId == id) {
-      return candidate;
+      candidate->ensureInitialized();
+      return Schema(candidate);
     } else if (candidateId < id) {
       lower = mid + 1;
     } else {

c++/src/capnp/schema.h

@@ -86,7 +86,10 @@ public:
 private:
   const _::RawSchema* raw;
 
-  inline explicit Schema(const _::RawSchema* raw): raw(raw) {}
+  inline explicit Schema(const _::RawSchema* raw): raw(raw) {
+    KJ_IREQUIRE(raw->lazyInitializer == nullptr,
+        "Must call ensureInitialized() on RawSchema before constructing Schema.");
+  }
 
   template <typename T> static inline Schema fromImpl() {
     return Schema(&_::rawSchema<T>());

c++/src/kj/mutex.c++

@@ -50,15 +50,15 @@ Mutex::~Mutex() {
   KJ_PTHREAD_CLEANUP(pthread_rwlock_destroy(&mutex));
 }
 
-void Mutex::lock() noexcept {
+void Mutex::lock() {
   KJ_PTHREAD_CALL(pthread_rwlock_wrlock(&mutex));
 }
 
-void Mutex::readLock() noexcept {
+void Mutex::readLock() {
   KJ_PTHREAD_CALL(pthread_rwlock_rdlock(&mutex));
 }
 
-void Mutex::unlock(bool lockedForRead) noexcept {
+void Mutex::unlock(bool lockedForRead) {
   KJ_PTHREAD_CALL(pthread_rwlock_unlock(&mutex));
 }
 

c++/src/kj/mutex.h

@@ -47,9 +47,9 @@ public:
   ~Mutex();
   KJ_DISALLOW_COPY(Mutex);
 
-  void lock() noexcept;
-  void readLock() noexcept;
-  void unlock(bool lockedForRead) noexcept;
+  void lock();
+  void readLock();
+  void unlock(bool lockedForRead);
 
 private:
   mutable pthread_rwlock_t mutex;

compiler/src/c++-source.mustache

@@ -69,8 +69,8 @@ static const ::capnp::_::RawSchema::MemberInfo m_{{schemaId}}[] = {
 {{/schemaMembersByName}}
 };
 const ::capnp::_::RawSchema s_{{schemaId}} = {
-  b_{{schemaId}}.words, d_{{schemaId}}, m_{{schemaId}},
-  {{schemaDependencyCount}}, {{schemaMemberCount}}, nullptr
+  0x{{schemaId}}, b_{{schemaId}}.words, d_{{schemaId}}, m_{{schemaId}},
+  {{schemaDependencyCount}}, {{schemaMemberCount}}, nullptr, nullptr
 };
 {{/typeSchema}}
 {{/fileTypes}}