diff --git a/src/api/algo.cpp b/src/api/algo.cpp
index b310183a..aa0bb9ab 100644
--- a/src/api/algo.cpp
+++ b/src/api/algo.cpp
@@ -48,11 +48,10 @@ auto Algo::hash(const pjs::Value &value) -> size_t {
 //
 
 Cache::Options::Options(pjs::Object *options) {
-  thread_local static pjs::ConstStr str_size("size"), str_ttl("ttl");
-  Value(options, str_size)
+  Value(options, "size")
     .get(size)
     .check_nullable();
-  Value(options, str_ttl)
+  Value(options, "ttl")
     .get_seconds(ttl)
     .check_nullable();
 }
@@ -507,6 +506,100 @@ void Quota::Counter::finalize() {
   });
 }
 
+//
+// SharedMap
+//
+
+SharedMap::SharedMap(pjs::Str *name)
+  : m_map(Map::get(name->str()))
+{
+}
+
+auto SharedMap::size() -> size_t {
+  return m_map->size();
+}
+
+void SharedMap::clear() {
+  m_map->clear();
+}
+
+bool SharedMap::erase(pjs::Str *key) {
+  return m_map->erase(key->data());
+}
+
+bool SharedMap::has(pjs::Str *key) {
+  return m_map->has(key->data());
+}
+
+bool SharedMap::get(pjs::Str *key, pjs::Value &value) {
+  pjs::SharedValue sv;
+  if (m_map->get(key->data(), sv)) {
+    sv.to_value(value);
+    return true;
+  } else {
+    return false;
+  }
+}
+
+void SharedMap::set(pjs::Str *key, const pjs::Value &value) {
+  pjs::SharedValue sv(value);
+  m_map->set(key->data(), sv);
+}
+
+//
+// SharedMap::Map
+//
+
+std::map<std::string, SharedMap::Map*> SharedMap::Map::m_maps;
+std::mutex SharedMap::Map::m_maps_mutex;
+
+auto SharedMap::Map::get(const std::string &name) -> Map* {
+  std::lock_guard<std::mutex> lock(m_maps_mutex);
+  auto &p = m_maps[name];
+  if (!p) {
+    p = new Map;
+    p->retain();
+  }
+  return p;
+}
+
+auto SharedMap::Map::size() -> size_t {
+  std::lock_guard<std::mutex> lock(m_mutex);
+  return m_map.size();
+}
+
+void SharedMap::Map::clear() {
+  std::lock_guard<std::mutex> lock(m_mutex);
+  m_map.clear();
+}
+
+bool SharedMap::Map::erase(pjs::Str::CharData *key) {
+  std::lock_guard<std::mutex> lock(m_mutex);
+  auto i = m_map.find(key);
+  if (i == m_map.end()) return false;
+  m_map.erase(i);
+  return true;
+}
+
+bool SharedMap::Map::has(pjs::Str::CharData *key) {
+  std::lock_guard<std::mutex> lock(m_mutex);
+  auto i = m_map.find(key);
+  return i != m_map.end();
+}
+
+bool SharedMap::Map::get(pjs::Str::CharData *key, pjs::SharedValue &value) {
+  std::lock_guard<std::mutex> lock(m_mutex);
+  auto i = m_map.find(key);
+  if (i == m_map.end()) return false;
+  value = i->second;
+  return true;
+}
+
+void SharedMap::Map::set(pjs::Str::CharData *key, const pjs::SharedValue &value) {
+  std::lock_guard<std::mutex> lock(m_mutex);
+  m_map[key] = value;
+}
+
 //
 // URLRouter
 //
@@ -1469,8 +1562,16 @@ template<> void ClassDef<Cache>::init() {
   ctor([](Context &ctx) -> Object* {
     Function *allocate = nullptr, *free = nullptr;
     Object *options = nullptr;
-    if (!ctx.arguments(0, &allocate, &free, &options)) return nullptr;
-    return Cache::make(options, allocate, free);
+    if (
+      ctx.try_arguments(2, &allocate, &free, &options) ||
+      ctx.try_arguments(1, &allocate, &options) ||
+      ctx.try_arguments(0, &options)
+    ) {
+      return Cache::make(options, allocate, free);
+    } else {
+      ctx.error_argument_type(0, "a function or an object");
+      return nullptr;
+    }
   });
 
   method("get", [](Context &ctx, Object *obj, Value &ret) {
@@ -1555,6 +1656,54 @@ template<> void ClassDef<Constructor<Quota>>::init() {
   ctor();
 }
 
+//
+// SharedMap
+//
+
+template<> void ClassDef<SharedMap>::init() {
+  ctor([](Context &ctx) -> Object * {
+    Str *name;
+    if (!ctx.arguments(1, &name)) return nullptr;
+    return SharedMap::make(name);
+  });
+
+  accessor("size", [](Object *obj, Value &ret) { ret.set((int)obj->as<SharedMap>()->size()); });
+
+  method("clear", [](Context &ctx, Object *obj, Value &ret) {
+    obj->as<SharedMap>()->clear();
+  });
+
+  method("delete", [](Context &ctx, Object *obj, Value &ret) {
+    Str *key;
+    if (!ctx.arguments(1, &key)) return;
+    ret.set(obj->as<SharedMap>()->erase(key));
+  });
+
+  method("has", [](Context &ctx, Object *obj, Value &ret) {
+    Str *key;
+    if (!ctx.arguments(1, &key)) return;
+    ret.set(obj->as<SharedMap>()->has(key));
+  });
+
+  method("get", [](Context &ctx, Object *obj, Value &ret) {
+    Str *key;
+    if (!ctx.arguments(1, &key)) return;
+    if (!obj->as<SharedMap>()->get(key, ret)) ret = Value::undefined;
+  });
+
+  method("set", [](Context &ctx, Object *obj, Value &ret) {
+    Str *key;
+    Value value;
+    if (!ctx.arguments(2, &key, &value)) return;
+    obj->as<SharedMap>()->set(key, value);
+  });
+}
+
+template<> void ClassDef<Constructor<SharedMap>>::init() {
+  super<Function>();
+  ctor();
+}
+
 //
 // URLRouter
 //
@@ -1882,6 +2031,7 @@ template<> void ClassDef<Algo>::init() {
   ctor();
   variable("Cache", class_of<Constructor<Cache>>());
   variable("Quota", class_of<Constructor<Quota>>());
+  variable("SharedMap", class_of<Constructor<SharedMap>>());
   variable("URLRouter", class_of<Constructor<URLRouter>>());
   variable("LoadBalancer", class_of<Constructor<LoadBalancer>>());
   variable("HashingLoadBalancer", class_of<Constructor<HashingLoadBalancer>>());
diff --git a/src/api/algo.hpp b/src/api/algo.hpp
index a54ecfb5..78c2fa34 100644
--- a/src/api/algo.hpp
+++ b/src/api/algo.hpp
@@ -217,6 +217,64 @@ class Quota : public pjs::ObjectTemplate<Quota> {
   friend class pjs::ObjectTemplate<Quota>;
 };
 
+//
+// SharedMap
+//
+
+class SharedMap : public pjs::ObjectTemplate<SharedMap> {
+public:
+  SharedMap(pjs::Str *name);
+
+  auto size() -> size_t;
+  void clear();
+  bool erase(pjs::Str *key);
+  bool has(pjs::Str *key);
+  bool get(pjs::Str *key, pjs::Value &value);
+  void set(pjs::Str *key, const pjs::Value &value);
+
+private:
+
+  //
+  // SharedMap::Map
+  //
+
+  class Map : public pjs::RefCountMT<Map> {
+  public:
+    static auto get(const std::string &name) -> Map*;
+
+    auto size() -> size_t;
+    void clear();
+    bool erase(pjs::Str::CharData *key);
+    bool has(pjs::Str::CharData *key);
+    bool get(pjs::Str::CharData *key, pjs::SharedValue &value);
+    void set(pjs::Str::CharData *key, const pjs::SharedValue &value);
+
+  private:
+    typedef pjs::Ref<pjs::Str::CharData> Key;
+
+    struct Hash {
+      size_t operator()(const Key &k) const {
+        std::hash<std::string> h;
+        return h(k->str());
+      }
+    };
+
+    struct EqualTo {
+      bool operator()(const Key &a, const Key &b) const {
+        return a->str() == b->str();
+      }
+    };
+
+    std::unordered_map<Key, pjs::SharedValue, Hash, EqualTo> m_map;
+    std::mutex m_mutex;
+
+    static std::map<std::string, Map*> m_maps;
+    static std::mutex m_maps_mutex;
+  };
+
+  pjs::Ref<Map> m_map;
+};
+
 //
 // ResourcePool
 //
diff --git a/src/pjs/types.cpp b/src/pjs/types.cpp
index d03139b1..7b216556 100644
--- a/src/pjs/types.cpp
+++ b/src/pjs/types.cpp
@@ -878,7 +878,17 @@ void SharedValue::to_value(Value &v) const {
   }
 }
 
-void SharedValue::from_value(const Value &v) {
+void SharedValue::assign(const SharedValue &v) {
+  switch (m_t = v.m_t) {
+    case Value::Type::Boolean: m_v.b = v.m_v.b; break;
+    case Value::Type::Number: m_v.n = v.m_v.n; break;
+    case Value::Type::String: m_v.s = v.m_v.s->retain(); break;
+    case Value::Type::Object: if (auto o = m_v.o = v.m_v.o) o->retain(); break;
+    default: break;
+  }
+}
+
+void SharedValue::assign(const Value &v) {
   switch (m_t = v.type()) {
     case Value::Type::Boolean: m_v.b = v.b(); break;
     case Value::Type::Number: m_v.n = v.n(); break;
@@ -930,8 +940,9 @@ auto SharedObject::to_object() -> Object* {
     for (auto i = 0, n = b->length; i < n; i++) {
       const auto &e = b->entries[i];
       if (e.k) {
+        Ref<Str> k(Str::make(e.k));
         Value v; e.v.to_value(v);
-        obj->set(Str::make(e.k), v);
+        obj->set(k, v);
       }
     }
   }
diff --git a/src/pjs/types.hpp b/src/pjs/types.hpp
index 25896d99..83a2bc14 100644
--- a/src/pjs/types.hpp
+++ b/src/pjs/types.hpp
@@ -1913,10 +1913,12 @@ inline auto Value::value_of() const -> double {
 class SharedValue {
 public:
   SharedValue() : m_t(Value::Type::Empty) {}
-  SharedValue(const Value &v) { from_value(v); }
+  SharedValue(const SharedValue &v) { assign(v); }
+  SharedValue(const Value &v) { assign(v); }
   ~SharedValue() { release(); }
 
-  auto operator=(const Value &v) -> SharedValue& { release(); from_value(v); return *this; }
+  auto operator=(const SharedValue &v) -> SharedValue& { release(); assign(v); return *this; }
+  auto operator=(const Value &v) -> SharedValue& { release(); assign(v); return *this; }
   void to_value(Value &v) const;
 
 private:
@@ -1928,7 +1930,8 @@ class SharedValue {
     SharedObject* o;
   } m_v;
 
-  void from_value(const Value &v);
+  void assign(const SharedValue &v);
+  void assign(const Value &v);
   void release();
 };
 
diff --git a/src/thread.hpp b/src/thread.hpp
index 00c8937b..63131686 100644
--- a/src/thread.hpp
+++ b/src/thread.hpp
@@ -30,8 +30,6 @@
 
 namespace pipy {
 
-class WorkerThread;
-
 //
 // Thread
 //