diff --git a/CMakeLists.txt b/CMakeLists.txt
index cc4660f..b6df272 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -16,3 +16,4 @@ add_subdirectory(src)
 add_subdirectory(3rdparty/gtest)
 add_subdirectory(test)
 add_subdirectory(demo/chat)
+add_subdirectory(demo/msg_que)
diff --git a/demo/chat/main.cpp b/demo/chat/main.cpp
index 53e1cbc..ec9c3be 100755
--- a/demo/chat/main.cpp
+++ b/demo/chat/main.cpp
@@ -1,3 +1,4 @@
+
 #include <iostream>
 #include <string>
 #include <thread>
@@ -8,51 +9,54 @@
 
 namespace {
 
-char name__[] = "ipc-chat";
-char quit__[] = "q";
-char id__  [] = "c";
+constexpr char const name__[] = "ipc-chat";
+constexpr char const quit__[] = "q";
+constexpr char const id__  [] = "c";
 
-std::size_t calc_unique_id() {
+inline std::size_t calc_unique_id() {
     static ipc::shm::handle g_shm { "__CHAT_ACC_STORAGE__", sizeof(std::atomic<std::size_t>) };
     return static_cast<std::atomic<std::size_t>*>(g_shm.get())->fetch_add(1, std::memory_order_relaxed);
 }
 
+ipc::channel sender__   { name__, ipc::sender   };
+ipc::channel receiver__ { name__, ipc::receiver };
+
 } // namespace
 
 int main() {
     std::string buf, id = id__ + std::to_string(calc_unique_id());
     std::regex  reg { "(c\\d+)> (.*)" };
 
-    ipc::channel cc { name__, ipc::sender };
-
     std::thread r {[&id, &reg] {
-        ipc::channel cc { name__, ipc::receiver };
         std::cout << id << " is ready." << std::endl;
         while (1) {
-            auto buf = cc.recv();
-            if (buf.empty()) continue;
+            ipc::buff_t buf = receiver__.recv();
+            if (buf.empty()) break; // quit
             std::string dat { buf.get<char const *>(), buf.size() - 1 };
             std::smatch mid;
             if (std::regex_match(dat, mid, reg)) {
                 if (mid.str(1) == id) {
                     if (mid.str(2) == quit__) {
-                        std::cout << "receiver quit..." << std::endl;
-                        return;
+                        break;
                     }
                     continue;
                 }
             }
             std::cout << dat << std::endl;
         }
+        std::cout << id << " receiver is quit..." << std::endl;
     }};
 
     for (/*int i = 1*/;; /*++i*/) {
         std::cin >> buf;
+        if (buf.empty() || (buf == quit__)) break;
 //        std::cout << "[" << i << "]" << std::endl;
-        cc.send(id + "> " + buf);
-        if (buf == quit__) break;
+        sender__.send(id + "> " + buf);
+        buf.clear();
     }
 
+    receiver__.disconnect();
     r.join();
+    std::cout << id << " sender is quit..." << std::endl;
     return 0;
 }
diff --git a/demo/msg_que/CMakeLists.txt b/demo/msg_que/CMakeLists.txt
new file mode 100644
index 0000000..cd9e302
--- /dev/null
+++ b/demo/msg_que/CMakeLists.txt
@@ -0,0 +1,11 @@
+project(msg_que)
+
+include_directories(
+    ${CMAKE_SOURCE_DIR}/3rdparty)
+
+file(GLOB SRC_FILES ./*.cpp)
+file(GLOB HEAD_FILES ./*.h)
+
+add_executable(${PROJECT_NAME} ${SRC_FILES} ${HEAD_FILES})
+
+target_link_libraries(${PROJECT_NAME} ipc)
diff --git a/demo/msg_que/main.cpp b/demo/msg_que/main.cpp
new file mode 100644
index 0000000..79b5433
--- /dev/null
+++ b/demo/msg_que/main.cpp
@@ -0,0 +1,124 @@
+
+#include <signal.h>
+
+#include <iostream>
+#include <string>
+#include <atomic>
+#include <thread>
+#include <chrono>
+#include <cstddef>
+
+#include "libipc/ipc.h"
+#include "capo/random.hpp"
+
+namespace {
+
+constexpr char const name__  [] = "ipc-msg-que";
+constexpr char const mode_s__[] = "s";
+constexpr char const mode_r__[] = "r";
+
+constexpr std::size_t const min_sz = 128;
+constexpr std::size_t const max_sz = 1024 * 16;
+
+std::atomic<bool> is_quit__{ false };
+std::atomic<std::size_t> size_per_1s__{ 0 };
+
+using msg_que_t = ipc::chan<ipc::relat::single, ipc::relat::single, ipc::trans::unicast>;
+
+msg_que_t que__{ name__ };
+ipc::byte_t buff__[max_sz];
+capo::random<> rand__{ min_sz, max_sz };
+
+inline std::string str_of_size(std::size_t sz) noexcept {
+    if (sz <= 1024) {
+        return std::to_string(sz) + " bytes";
+    }
+    if (sz <= 1024 * 1024) {
+        return std::to_string(sz / 1024) + " KB";
+    }
+    return std::to_string(sz / (1024 * 1024)) + " MB";
+}
+
+inline std::string speed_of(std::size_t sz) noexcept {
+    return str_of_size(sz) + "/s";
+}
+
+void do_counting() {
+    for (int i = 1; !is_quit__.load(std::memory_order_acquire); ++i) {
+        std::this_thread::sleep_for(std::chrono::milliseconds(100)); // 100 ms
+        if (i % 10) continue;
+        i = 0;
+        std::cout
+            << speed_of(size_per_1s__.load(std::memory_order_acquire))
+            << std::endl;
+        size_per_1s__.store(0, std::memory_order_release);
+    }
+}
+
+void do_send() {
+    std::cout 
+        << __func__ << ": start [" 
+        << str_of_size(min_sz) << " - " << str_of_size(max_sz) 
+        << "]...\n";
+    if (!que__.reconnect(ipc::sender)) {
+        std::cerr << __func__ << ": connect failed.\n";
+    }
+    else {
+        std::thread counting{ do_counting };
+        while (!is_quit__.load(std::memory_order_acquire)) {
+            std::size_t sz = static_cast<std::size_t>(rand__());
+            if (!que__.send(ipc::buff_t(buff__, sz))) {
+                std::cerr << __func__ << ": send failed.\n";
+                std::cout << __func__ << ": waiting for receiver...\n";
+                if (!que__.wait_for_recv(1)) {
+                    std::cerr << __func__ << ": wait receiver failed.\n";
+                    is_quit__.store(true, std::memory_order_release);
+                    break;
+                }
+            }
+            size_per_1s__.fetch_add(sz, std::memory_order_release);
+            std::this_thread::yield();
+        }
+        counting.join();
+    }
+    std::cout << __func__ << ": quit...\n";
+}
+
+void do_recv() {
+    std::cout
+        << __func__ << ": start ["
+        << str_of_size(min_sz) << " - " << str_of_size(max_sz)
+        << "]...\n";
+    if (!que__.reconnect(ipc::receiver)) {
+        std::cerr << __func__ << ": connect failed.\n";
+    }
+    else {
+        std::thread counting{ do_counting };
+        while (!is_quit__.load(std::memory_order_acquire)) {
+            auto msg = que__.recv();
+            if (msg.empty()) break;
+            size_per_1s__.fetch_add(msg.size(), std::memory_order_release);
+        }
+        counting.join();
+    }
+    std::cout << __func__ << ": quit...\n";
+}
+
+} // namespace
+
+int main(int argc, char ** argv) {
+    if (argc < 2) return 0;
+
+    ::signal(SIGINT, [](int) {
+        is_quit__.store(true, std::memory_order_release);
+        que__.disconnect();
+    });
+
+    if (std::string{ argv[1] } == mode_s__) {
+        do_send();
+    }
+    else if (std::string{ argv[1] } == mode_r__) {
+        do_recv();
+    }
+    return 0;
+}
diff --git a/include/libipc/ipc.h b/include/libipc/ipc.h
index 44a7135..ed50d8e 100755
--- a/include/libipc/ipc.h
+++ b/include/libipc/ipc.h
@@ -19,19 +19,21 @@ enum : unsigned {
 
 template <typename Flag>
 struct IPC_EXPORT chan_impl {
-    static handle_t connect   (char const * name, unsigned mode);
-    static void     disconnect(handle_t h);
+    static bool connect   (ipc::handle_t * ph, char const * name, unsigned mode);
+    static bool reconnect (ipc::handle_t * ph, unsigned mode);
+    static void disconnect(ipc::handle_t h);
+    static void destroy   (ipc::handle_t h);
 
-    static char const * name(handle_t h);
+    static char const * name(ipc::handle_t h);
 
-    static std::size_t recv_count(handle_t h);
-    static bool wait_for_recv(handle_t h, std::size_t r_count, std::size_t tm);
+    static std::size_t recv_count(ipc::handle_t h);
+    static bool wait_for_recv(ipc::handle_t h, std::size_t r_count, std::size_t tm);
 
-    static bool   send(handle_t h, void const * data, std::size_t size, std::size_t tm);
-    static buff_t recv(handle_t h, std::size_t tm);
+    static bool   send(ipc::handle_t h, void const * data, std::size_t size, std::size_t tm);
+    static buff_t recv(ipc::handle_t h, std::size_t tm);
 
-    static bool   try_send(handle_t h, void const * data, std::size_t size, std::size_t tm);
-    static buff_t try_recv(handle_t h);
+    static bool   try_send(ipc::handle_t h, void const * data, std::size_t size, std::size_t tm);
+    static buff_t try_recv(ipc::handle_t h);
 };
 
 template <typename Flag>
@@ -39,7 +41,7 @@ class chan_wrapper {
 private:
     using detail_t = chan_impl<Flag>;
 
-    handle_t h_    = nullptr;
+    ipc::handle_t h_    = nullptr;
     unsigned mode_ = ipc::sender;
 
 public:
@@ -54,7 +56,7 @@ public:
     }
 
     ~chan_wrapper() {
-        disconnect();
+        detail_t::destroy(h_);
     }
 
     void swap(chan_wrapper& rhs) noexcept {
@@ -70,7 +72,7 @@ public:
         return detail_t::name(h_);
     }
 
-    handle_t handle() const noexcept {
+    ipc::handle_t handle() const noexcept {
         return h_;
     }
 
@@ -89,14 +91,18 @@ public:
     bool connect(char const * name, unsigned mode = ipc::sender | ipc::receiver) {
         if (name == nullptr || name[0] == '\0') return false;
         this->disconnect();
-        h_ = detail_t::connect(name, mode_ = mode);
-        return valid();
+        return detail_t::connect(&h_, name, mode_ = mode);
+    }
+
+    bool reconnect(unsigned mode) {
+        if (!valid()) return false;
+        if (mode_ == mode) return true;
+        return detail_t::reconnect(&h_, mode_ = mode);
     }
 
     void disconnect() {
         if (!valid()) return;
         detail_t::disconnect(h_);
-        h_ = nullptr;
     }
 
     std::size_t recv_count() const {
@@ -111,13 +117,25 @@ public:
         return chan_wrapper(name).wait_for_recv(r_count, tm);
     }
 
-    bool send    (void        const * data, std::size_t size, std::size_t tm = default_timeout) { return detail_t::send(h_, data, size, tm)             ; }
-    bool send    (buff_t      const & buff                  , std::size_t tm = default_timeout) { return     this->send(buff.data(), buff.size(), tm)   ; }
-    bool send    (std::string const & str                   , std::size_t tm = default_timeout) { return     this->send(str.c_str(), str.size() + 1, tm); }
+    bool send(void const * data, std::size_t size, std::size_t tm = default_timeout) {
+        return detail_t::send(h_, data, size, tm);
+    }
+    bool send(buff_t const & buff, std::size_t tm = default_timeout) {
+        return this->send(buff.data(), buff.size(), tm);
+    }
+    bool send(std::string const & str, std::size_t tm = default_timeout) {
+        return this->send(str.c_str(), str.size() + 1, tm);
+    }
 
-    bool try_send(void        const * data, std::size_t size, std::size_t tm = default_timeout) { return detail_t::try_send(h_, data, size, tm)             ; }
-    bool try_send(buff_t      const & buff                  , std::size_t tm = default_timeout) { return     this->try_send(buff.data(), buff.size(), tm)   ; }
-    bool try_send(std::string const & str                   , std::size_t tm = default_timeout) { return     this->try_send(str.c_str(), str.size() + 1, tm); }
+    bool try_send(void const * data, std::size_t size, std::size_t tm = default_timeout) {
+        return detail_t::try_send(h_, data, size, tm);
+    }
+    bool try_send(buff_t const & buff, std::size_t tm = default_timeout) {
+        return this->try_send(buff.data(), buff.size(), tm);
+    }
+    bool try_send(std::string const & str, std::size_t tm = default_timeout) {
+        return this->try_send(str.c_str(), str.size() + 1, tm);
+    }
 
     buff_t recv(std::size_t tm = invalid_value) {
         return detail_t::recv(h_, tm);
@@ -128,8 +146,8 @@ public:
     }
 };
 
-template <typename Flag>
-using chan = chan_wrapper<Flag>;
+template <relat Rp, relat Rc, trans Ts>
+using chan = chan_wrapper<ipc::wr<Rp, Rc, Ts>>;
 
 /*
  * class route
@@ -142,7 +160,7 @@ using chan = chan_wrapper<Flag>;
  * (one producer/writer to multi consumers/readers)
 */
 
-using route = chan<ipc::wr<relat::single, relat::multi, trans::broadcast>>;
+using route = chan<relat::single, relat::multi, trans::broadcast>;
 
 /*
  * class channel
@@ -152,6 +170,6 @@ using route = chan<ipc::wr<relat::single, relat::multi, trans::broadcast>>;
  * would receive your sent messages.
 */
 
-using channel = chan<ipc::wr<relat::multi, relat::multi, trans::broadcast>>;
+using channel = chan<relat::multi, relat::multi, trans::broadcast>;
 
 } // namespace ipc
diff --git a/include/libipc/rw_lock.h b/include/libipc/rw_lock.h
index 2a898b1..5757b23 100755
--- a/include/libipc/rw_lock.h
+++ b/include/libipc/rw_lock.h
@@ -77,11 +77,8 @@ inline void sleep(K& k, F&& f) {
     if (k < static_cast<K>(N)) {
         std::this_thread::yield();
     }
-    else if (std::forward<F>(f)()) {
-        return;
-    }
     else {
-        std::this_thread::sleep_for(std::chrono::milliseconds(1));
+        static_cast<void>(std::forward<F>(f)());
         return;
     }
     ++k;
@@ -89,7 +86,9 @@ inline void sleep(K& k, F&& f) {
 
 template <std::size_t N = 4096, typename K>
 inline void sleep(K& k) {
-    sleep<N>(k, [] { return false; });
+    sleep<N>(k, [] {
+        std::this_thread::sleep_for(std::chrono::milliseconds(1));
+    });
 }
 
 } // namespace ipc
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 2dccff1..4dfae8e 100755
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -19,6 +19,7 @@ aux_source_directory(${CMAKE_SOURCE_DIR}/src SRC_FILES)
 
 file(GLOB HEAD_FILES
   ${CMAKE_SOURCE_DIR}/include/libipc/*.h
+  ${CMAKE_SOURCE_DIR}/src/libipc/*.h
   ${CMAKE_SOURCE_DIR}/src/libipc/*.inc
   ${CMAKE_SOURCE_DIR}/src/libipc/circ/*.h
   ${CMAKE_SOURCE_DIR}/src/libipc/memory/*.h
diff --git a/src/ipc.cpp b/src/ipc.cpp
index e24cf6a..f2ddd37 100755
--- a/src/ipc.cpp
+++ b/src/ipc.cpp
@@ -8,6 +8,7 @@
 #include <string>
 #include <vector>
 #include <array>
+#include <cassert>
 
 #include "libipc/ipc.h"
 #include "libipc/def.h"
@@ -30,8 +31,6 @@
 
 namespace {
 
-using namespace ipc;
-
 using msg_id_t = std::uint32_t;
 using acc_t    = std::atomic<msg_id_t>;
 
@@ -64,54 +63,54 @@ struct msg_t : msg_t<0, AlignSize> {
 };
 
 template <typename T>
-buff_t make_cache(T& data, std::size_t size) {
-    auto ptr = mem::alloc(size);
+ipc::buff_t make_cache(T& data, std::size_t size) {
+    auto ptr = ipc::mem::alloc(size);
     std::memcpy(ptr, &data, (ipc::detail::min)(sizeof(data), size));
-    return { ptr, size, mem::free };
+    return { ptr, size, ipc::mem::free };
 }
 
 struct cache_t {
     std::size_t fill_;
-    buff_t      buff_;
+    ipc::buff_t buff_;
 
-    cache_t(std::size_t f, buff_t&& b)
+    cache_t(std::size_t f, ipc::buff_t && b)
         : fill_(f), buff_(std::move(b))
     {}
 
     void append(void const * data, std::size_t size) {
         if (fill_ >= buff_.size() || data == nullptr || size == 0) return;
         auto new_fill = (ipc::detail::min)(fill_ + size, buff_.size());
-        std::memcpy(static_cast<byte_t*>(buff_.data()) + fill_, data, new_fill - fill_);
+        std::memcpy(static_cast<ipc::byte_t*>(buff_.data()) + fill_, data, new_fill - fill_);
         fill_ = new_fill;
     }
 };
 
 auto cc_acc() {
-    static shm::handle acc_h("__CA_CONN__", sizeof(acc_t));
+    static ipc::shm::handle acc_h("__CA_CONN__", sizeof(acc_t));
     return static_cast<acc_t*>(acc_h.get());
 }
 
 auto& cls_storages() {
     struct cls_t {
-        shm::handle id_info_;
-        std::array<shm::handle, id_pool<>::max_count> mems_;
+        ipc::shm::handle id_info_;
+        std::array<ipc::shm::handle, ipc::id_pool<>::max_count> mems_;
     };
     static ipc::unordered_map<std::size_t, cls_t> cls_s;
     return cls_s;
 }
 
 auto& cls_lock() {
-    static spin_lock cls_l;
+    static ipc::spin_lock cls_l;
     return cls_l;
 }
 
 struct cls_info_t {
-    id_pool<> pool_;
-    spin_lock lock_;
+    ipc::id_pool<> pool_;
+    ipc::spin_lock lock_;
 };
 
 constexpr std::size_t calc_cls_size(std::size_t size) noexcept {
-    return (((size - 1) / large_msg_limit) + 1) * large_msg_limit;
+    return (((size - 1) / ipc::large_msg_limit) + 1) * ipc::large_msg_limit;
 }
 
 auto& cls_storage(std::size_t cls_size) {
@@ -135,8 +134,8 @@ cls_info_t* cls_storage_info(const char* func, T& cls_shm, std::size_t cls_size)
 }
 
 template <typename T>
-byte_t* cls_storage_mem(const char* func, T& cls_shm, std::size_t cls_size, std::size_t id) {
-    if (id == invalid_value) {
+ipc::byte_t* cls_storage_mem(const char* func, T& cls_shm, std::size_t cls_size, std::size_t id) {
+    if (id == ipc::invalid_value) {
         return nullptr;
     }
     if (!cls_shm.mems_[id].valid() &&
@@ -147,7 +146,7 @@ byte_t* cls_storage_mem(const char* func, T& cls_shm, std::size_t cls_size, std:
         return nullptr;
     }
 
-    byte_t* ptr = static_cast<byte_t*>(cls_shm.mems_[id].get());
+    auto ptr = static_cast<ipc::byte_t *>(cls_shm.mems_[id].get());
     if (ptr == nullptr) {
         ipc::error("[%s] cls_shm.mems_[id].get failed: id = %zd, cls_size = %zd\n", func, id, cls_size);
         return nullptr;
@@ -190,7 +189,7 @@ void* find_storage(std::size_t id, std::size_t size) {
 }
 
 void recycle_storage(std::size_t id, std::size_t size) {
-    if (id == invalid_value) {
+    if (id == ipc::invalid_value) {
         ipc::error("[recycle_storage] id is invalid: id = %zd, size = %zd\n", id, size);
         return;
     }
@@ -202,7 +201,7 @@ void recycle_storage(std::size_t id, std::size_t size) {
         ipc::error("[recycle_storage] should find storage first: id = %zd, cls_size = %zd\n", id, cls_size);
         return;
     }
-    byte_t* ptr = static_cast<byte_t*>(cls_shm.mems_[id].get());
+    auto ptr = static_cast<ipc::byte_t*>(cls_shm.mems_[id].get());
     if (ptr == nullptr) {
         ipc::error("[recycle_storage] cls_shm.mems_[id].get failed: id = %zd, cls_size = %zd\n", id, cls_size);
         return;
@@ -221,7 +220,7 @@ void recycle_storage(std::size_t id, std::size_t size) {
 }
 
 void clear_storage(std::size_t id, std::size_t size) {
-    if (id == invalid_value) {
+    if (id == ipc::invalid_value) {
         ipc::error("[clear_storage] id is invalid: id = %zd, size = %zd\n", id, size);
         return;
     }
@@ -254,8 +253,8 @@ struct conn_info_head {
 
     ipc::string name_;
     msg_id_t    cc_id_; // connection-info id
-    waiter      cc_waiter_, wt_waiter_, rd_waiter_;
-    shm::handle acc_h_;
+    ipc::waiter cc_waiter_, wt_waiter_, rd_waiter_;
+    ipc::shm::handle acc_h_;
 
     /*
      * <Remarks> thread_local may have some bugs.
@@ -268,7 +267,7 @@ struct conn_info_head {
      * - https://developercommunity.visualstudio.com/content/problem/124121/thread-local-variables-fail-to-be-initialized-when.html
      * - https://software.intel.com/en-us/forums/intel-c-compiler/topic/684827
     */
-    tls::pointer<ipc::unordered_map<msg_id_t, cache_t>> recv_cache_;
+    ipc::tls::pointer<ipc::unordered_map<msg_id_t, cache_t>> recv_cache_;
 
     conn_info_head(char const * name)
         : name_     (name)
@@ -279,6 +278,12 @@ struct conn_info_head {
         , acc_h_    (("__AC_CONN__" + name_).c_str(), sizeof(acc_t)) {
     }
 
+    void quit_waiting() {
+        cc_waiter_.quit_waiting();
+        wt_waiter_.quit_waiting();
+        rd_waiter_.quit_waiting();
+    }
+
     auto acc() {
         return static_cast<acc_t*>(acc_h_.get());
     }
@@ -295,10 +300,9 @@ bool wait_for(W& waiter, F&& pred, std::size_t tm) {
         bool loop = true, ret = true;
         ipc::sleep(k, [&k, &loop, &ret, &waiter, &pred, tm] {
             ret = waiter.wait_if([&loop, &pred] {
-                return loop = pred();
-            }, tm);
+                    return loop = pred();
+                }, tm);
             k = 0;
-            return true;
         });
         if (!ret ) return false; // timeout or fail
         if (!loop) break;
@@ -307,7 +311,7 @@ bool wait_for(W& waiter, F&& pred, std::size_t tm) {
 }
 
 template <typename Policy,
-          std::size_t DataSize  = data_length,
+          std::size_t DataSize  = ipc::data_length,
           std::size_t AlignSize = (ipc::detail::min)(DataSize, alignof(std::max_align_t))>
 struct queue_generator {
 
@@ -341,35 +345,54 @@ constexpr static queue_t* queue_of(ipc::handle_t h) {
 
 /* API implementations */
 
-static ipc::handle_t connect(char const * name, bool start) {
-    auto h = mem::alloc<conn_info_t>(name);
-    auto que = queue_of(h);
-    if (que == nullptr) {
-        return nullptr;
-    }
-    if (start) {
-        if (que->connect()) { // wouldn't connect twice
-            info_of(h)->cc_waiter_.broadcast();
-        }
-    }
-    return h;
-}
-
 static void disconnect(ipc::handle_t h) {
     auto que = queue_of(h);
     if (que == nullptr) {
         return;
     }
-    if (que->disconnect()) {
-        info_of(h)->cc_waiter_.broadcast();
+    bool dis = que->disconnect();
+    info_of(h)->quit_waiting();
+    if (dis) {
+        info_of(h)->recv_cache().clear();
     }
-    mem::free(info_of(h));
+}
+
+static bool reconnect(ipc::handle_t * ph, bool start) {
+    assert(ph != nullptr);
+    assert(*ph != nullptr);
+    auto que = queue_of(*ph);
+    if (que == nullptr) {
+        return false;
+    }
+    if (start) {
+        if (que->connect()) { // wouldn't connect twice
+            info_of(*ph)->cc_waiter_.broadcast();
+        }
+    }
+    // start == false
+    else if (que->connected()) {
+        disconnect(*ph);
+    }
+    return true;
+}
+
+static bool connect(ipc::handle_t * ph, char const * name, bool start) {
+    assert(ph != nullptr);
+    if (*ph == nullptr) {
+        *ph = ipc::mem::alloc<conn_info_t>(name);
+    }
+    return reconnect(ph, start);
+}
+
+static void destroy(ipc::handle_t h) {
+    disconnect(h);
+    ipc::mem::free(info_of(h));
 }
 
 static std::size_t recv_count(ipc::handle_t h) {
     auto que = queue_of(h);
     if (que == nullptr) {
-        return invalid_value;
+        return ipc::invalid_value;
     }
     return que->conn_count();
 }
@@ -411,30 +434,31 @@ static bool send(F&& gen_push, ipc::handle_t h, void const * data, std::size_t s
     }
     auto msg_id   = acc->fetch_add(1, std::memory_order_relaxed);
     auto try_push = std::forward<F>(gen_push)(info_of(h), que, msg_id);
-    if (size > large_msg_limit) {
+    if (size > ipc::large_msg_limit) {
         auto   dat = apply_storage(que->conn_count(), size);
         void * buf = dat.second;
         if (buf != nullptr) {
             std::memcpy(buf, data, size);
             return try_push(static_cast<std::int32_t>(size) - 
-                            static_cast<std::int32_t>(data_length), &(dat.first), 0);
+                            static_cast<std::int32_t>(ipc::data_length), &(dat.first), 0);
         }
         // try using message fragment
         // ipc::log("fail: shm::handle for big message. msg_id: %zd, size: %zd\n", msg_id, size);
     }
     // push message fragment
     std::int32_t offset = 0;
-    for (int i = 0; i < static_cast<int>(size / data_length); ++i, offset += data_length) {
-        if (!try_push(static_cast<std::int32_t>(size) - offset - static_cast<std::int32_t>(data_length),
-                      static_cast<byte_t const *>(data) + offset, data_length)) {
+    for (int i = 0; i < static_cast<int>(size / ipc::data_length); ++i, offset += ipc::data_length) {
+        if (!try_push(static_cast<std::int32_t>(size) - offset - static_cast<std::int32_t>(ipc::data_length),
+                      static_cast<ipc::byte_t const *>(data) + offset, ipc::data_length)) {
             return false;
         }
     }
     // if remain > 0, this is the last message fragment
     std::int32_t remain = static_cast<std::int32_t>(size) - offset;
     if (remain > 0) {
-        if (!try_push(remain - static_cast<std::int32_t>(data_length),
-                      static_cast<byte_t const *>(data) + offset, static_cast<std::size_t>(remain))) {
+        if (!try_push(remain - static_cast<std::int32_t>(ipc::data_length),
+                      static_cast<ipc::byte_t const *>(data) + offset, 
+                      static_cast<std::size_t>(remain))) {
             return false;
         }
     }
@@ -451,8 +475,9 @@ static bool send(ipc::handle_t h, void const * data, std::size_t size, std::size
                 if (!que->force_push([](void* p) {
                         auto tmp_msg = static_cast<typename queue_t::value_t*>(p);
                         if (tmp_msg->storage_) {
-                            clear_storage(*reinterpret_cast<std::size_t*>(&tmp_msg->data_), 
-                                        static_cast<std::int32_t>(data_length) + tmp_msg->remain_);
+                            clear_storage(
+                                *reinterpret_cast<std::size_t*>(&tmp_msg->data_), 
+                                static_cast<std::int32_t>(ipc::data_length) + tmp_msg->remain_);
                         }
                         return true;
                     }, info->cc_id_, msg_id, remain, data, size)) {
@@ -479,20 +504,22 @@ static bool try_send(ipc::handle_t h, void const * data, std::size_t size, std::
     }, h, data, size);
 }
 
-static buff_t recv(ipc::handle_t h, std::size_t tm) {
+static ipc::buff_t recv(ipc::handle_t h, std::size_t tm) {
     auto que = queue_of(h);
     if (que == nullptr) {
         ipc::error("fail: recv, queue_of(h) == nullptr\n");
         return {};
     }
-    if (que->connect()) { // wouldn't connect twice
-        info_of(h)->cc_waiter_.broadcast();
+    if (!que->connected()) {
+        // hasn't connected yet, just return.
+        return {};
     }
     auto& rc = info_of(h)->recv_cache();
     while (1) {
         // pop a new message
         typename queue_t::value_t msg;
         if (!wait_for(info_of(h)->rd_waiter_, [que, &msg] { return !que->pop(msg); }, tm)) {
+            // pop failed, just return.
             return {};
         }
         info_of(h)->wt_waiter_.broadcast();
@@ -500,18 +527,18 @@ static buff_t recv(ipc::handle_t h, std::size_t tm) {
             continue; // ignore message to self
         }
         // msg.remain_ may minus & abs(msg.remain_) < data_length
-        std::size_t remain = static_cast<std::int32_t>(data_length) + msg.remain_;
+        std::size_t remain = static_cast<std::int32_t>(ipc::data_length) + msg.remain_;
         // find cache with msg.id_
         auto cac_it = rc.find(msg.id_);
         if (cac_it == rc.end()) {
-            if (remain <= data_length) {
+            if (remain <= ipc::data_length) {
                 return make_cache(msg.data_, remain);
             }
             if (msg.storage_) {
                 std::size_t buf_id = *reinterpret_cast<std::size_t*>(&msg.data_);
                 void      * buf    = find_storage(buf_id, remain);
                 if (buf != nullptr) {
-                    return buff_t { buf, remain, [](void* ptr, std::size_t size) {
+                    return ipc::buff_t { buf, remain, [](void* ptr, std::size_t size) {
                         recycle_storage(reinterpret_cast<std::size_t>(ptr) - 1, size);
                     }, reinterpret_cast<void*>(buf_id + 1) };
                 }
@@ -529,7 +556,7 @@ static buff_t recv(ipc::handle_t h, std::size_t tm) {
                 for (auto id : need_del) rc.erase(id);
             }
             // cache the first message fragment
-            rc.emplace(msg.id_, cache_t { data_length, make_cache(msg.data_, remain) });
+            rc.emplace(msg.id_, cache_t { ipc::data_length, make_cache(msg.data_, remain) });
         }
         // has cached before this message
         else {
@@ -543,27 +570,32 @@ static buff_t recv(ipc::handle_t h, std::size_t tm) {
                 return buff;
             }
             // there are remain datas after this message
-            cac.append(&(msg.data_), data_length);
+            cac.append(&(msg.data_), ipc::data_length);
         }
     }
 }
 
-static buff_t try_recv(ipc::handle_t h) {
+static ipc::buff_t try_recv(ipc::handle_t h) {
     return recv(h, 0);
 }
 
 }; // detail_impl<Policy>
 
 template <typename Flag>
-using policy_t = policy::choose<circ::elem_array, Flag>;
+using policy_t = ipc::policy::choose<ipc::circ::elem_array, Flag>;
 
 } // internal-linkage
 
 namespace ipc {
 
 template <typename Flag>
-ipc::handle_t chan_impl<Flag>::connect(char const * name, unsigned mode) {
-    return detail_impl<policy_t<Flag>>::connect(name, mode & receiver);
+bool chan_impl<Flag>::connect(ipc::handle_t * ph, char const * name, unsigned mode) {
+    return detail_impl<policy_t<Flag>>::connect(ph, name, mode & receiver);
+}
+
+template <typename Flag>
+bool chan_impl<Flag>::reconnect(ipc::handle_t * ph, unsigned mode) {
+    return detail_impl<policy_t<Flag>>::reconnect(ph, mode & receiver);
 }
 
 template <typename Flag>
@@ -571,6 +603,11 @@ void chan_impl<Flag>::disconnect(ipc::handle_t h) {
     detail_impl<policy_t<Flag>>::disconnect(h);
 }
 
+template <typename Flag>
+void chan_impl<Flag>::destroy(ipc::handle_t h) {
+    detail_impl<policy_t<Flag>>::destroy(h);
+}
+
 template <typename Flag>
 char const * chan_impl<Flag>::name(ipc::handle_t h) {
     auto info = detail_impl<policy_t<Flag>>::info_of(h);
diff --git a/src/libipc/platform/waiter_linux.h b/src/libipc/platform/waiter_linux.h
index f118478..25bed4f 100755
--- a/src/libipc/platform/waiter_linux.h
+++ b/src/libipc/platform/waiter_linux.h
@@ -9,8 +9,11 @@
 
 #include <atomic>
 #include <tuple>
+#include <utility>
+#include <cassert>
 
 #include "libipc/def.h"
+#include "libipc/waiter_helper.h"
 
 #include "libipc/utility/log.h"
 #include "libipc/platform/detail.h"
@@ -176,7 +179,7 @@ public:
         return SEM_FAILED;
     }
 
-    static handle_t open(char const* name, long count) {
+    static handle_t open(char const * name, long count) {
         handle_t sem = ::sem_open(name, O_CREAT, 0666, count);
         if (sem == SEM_FAILED) {
             ipc::error("fail sem_open[%d]: %s\n", errno, name);
@@ -199,13 +202,19 @@ public:
         IPC_SEMAPHORE_FUNC_(sem_close, h);
     }
 
-    static bool destroy(char const* name) {
+    static bool destroy(char const * name) {
         IPC_SEMAPHORE_FUNC_(sem_unlink, name);
     }
 
-    static bool post(handle_t h) {
+    static bool post(handle_t h, long count) {
         if (h == invalid()) return false;
-        IPC_SEMAPHORE_FUNC_(sem_post, h);
+        auto spost = [](handle_t h) {
+            IPC_SEMAPHORE_FUNC_(sem_post, h);
+        };
+        for (long i = 0; i < count; ++i) {
+            if (!spost(h)) return false;
+        }
+        return true;
     }
 
     static bool wait(handle_t h, std::size_t tm = invalid_value) {
@@ -233,19 +242,63 @@ public:
 #pragma pop_macro("IPC_SEMAPHORE_FUNC_")
 };
 
-class waiter_helper {
-    mutex lock_;
-
-    std::atomic<unsigned> waiting_ { 0 };
-    long counter_ = 0;
-
+class waiter_holder {
 public:
-    using handle_t = std::tuple<ipc::string, sem_helper::handle_t, sem_helper::handle_t>;
+    using handle_t = std::tuple<
+        ipc::string, 
+        sem_helper::handle_t /* sema */, 
+        sem_helper::handle_t /* handshake */>;
 
     static handle_t invalid() noexcept {
-        return std::make_tuple(ipc::string{}, sem_helper::invalid(), sem_helper::invalid());
+        return std::make_tuple(
+            ipc::string{}, 
+            sem_helper::invalid(), 
+            sem_helper::invalid());
     }
 
+private:
+    using wait_flags   = waiter_helper::wait_flags;
+    using wait_counter = waiter_helper::wait_counter;
+
+    mutex lock_;
+    wait_counter cnt_;
+
+    struct contrl {
+        waiter_holder * me_;
+        wait_flags * flags_;
+        handle_t const & h_;
+
+        wait_flags & flags() noexcept {
+            assert(flags_ != nullptr);
+            return *flags_;
+        }
+
+        wait_counter & counter() noexcept {
+            return me_->cnt_;
+        }
+
+        auto get_lock() {
+            return ipc::detail::unique_lock(me_->lock_);
+        }
+
+        bool sema_wait(std::size_t tm) {
+            return sem_helper::wait(std::get<1>(h_), tm);
+        }
+
+        bool sema_post(long count) {
+            return sem_helper::post(std::get<1>(h_), count);
+        }
+
+        bool handshake_wait(std::size_t tm) {
+            return sem_helper::wait(std::get<2>(h_), tm);
+        }
+
+        bool handshake_post(long count) {
+            return sem_helper::post(std::get<2>(h_), count);
+        }
+    };
+
+public:
     handle_t open_h(ipc::string && name) {
         auto sem = sem_helper::open(("__WAITER_HELPER_SEM__" + name).c_str(), 0);
         if (sem == sem_helper::invalid()) {
@@ -278,63 +331,45 @@ public:
     }
 
     template <typename F>
-    bool wait_if(handle_t const & h, F&& pred, std::size_t tm = invalid_value) {
-        waiting_.fetch_add(1, std::memory_order_release);
-        {
-            IPC_UNUSED_ auto guard = ipc::detail::unique_lock(lock_);
-            if (!std::forward<F>(pred)()) return true;
-            ++ counter_;
-        }
-        bool ret = sem_helper::wait(std::get<1>(h), tm);
-        waiting_.fetch_sub(1, std::memory_order_release);
-        ret = sem_helper::post(std::get<2>(h)) && ret;
-        return ret;
+    bool wait_if(handle_t const & h, wait_flags * flags, F&& pred, std::size_t tm = invalid_value) {
+        assert(flags != nullptr);
+        contrl ctrl { this, flags, h };
+
+        class non_mutex {
+        public:
+            void lock  () noexcept {}
+            void unlock() noexcept {}
+        } nm;
+
+        return waiter_helper::wait_if(ctrl, nm, std::forward<F>(pred), tm);
     }
 
     bool notify(handle_t const & h) {
-        std::atomic_thread_fence(std::memory_order_acq_rel);
-        if (waiting_.load(std::memory_order_relaxed) == 0) {
-            return true;
-        }
-        bool ret = true;
-        IPC_UNUSED_ auto guard = ipc::detail::unique_lock(lock_);
-        if (counter_ > 0) {
-            ret = sem_helper::post(std::get<1>(h));
-            -- counter_;
-            ret = ret && sem_helper::wait(std::get<2>(h), default_timeout);
-        }
-        return ret;
+        contrl ctrl { this, nullptr, h };
+        return waiter_helper::notify(ctrl);
     }
 
     bool broadcast(handle_t const & h) {
-        std::atomic_thread_fence(std::memory_order_acq_rel);
-        if (waiting_.load(std::memory_order_relaxed) == 0) {
-            return true;
-        }
-        bool ret = true;
-        IPC_UNUSED_ auto guard = ipc::detail::unique_lock(lock_);
-        if (counter_ > 0) {
-            for (long i = 0; i < counter_; ++i) {
-                ret = ret && sem_helper::post(std::get<1>(h));
-            }
-            do {
-                -- counter_;
-                ret = ret && sem_helper::wait(std::get<2>(h), default_timeout);
-            } while (counter_ > 0);
-        }
-        return ret;
+        contrl ctrl { this, nullptr, h };
+        return waiter_helper::broadcast(ctrl);
+    }
+
+    bool quit_waiting(handle_t const & h, wait_flags * flags) {
+        assert(flags != nullptr);
+        contrl ctrl { this, flags, h };
+        return waiter_helper::quit_waiting(ctrl);
     }
 };
 
 class waiter {
-    waiter_helper helper_;
+    waiter_holder helper_;
     std::atomic<unsigned> opened_ { 0 };
 
 public:
-    using handle_t = waiter_helper::handle_t;
+    using handle_t = waiter_holder::handle_t;
 
     static handle_t invalid() noexcept {
-        return waiter_helper::invalid();
+        return waiter_holder::invalid();
     }
 
     handle_t open(char const * name) {
@@ -357,19 +392,24 @@ public:
     }
 
     template <typename F>
-    bool wait_if(handle_t h, F&& pred, std::size_t tm = invalid_value) {
+    bool wait_if(handle_t h, waiter_helper::wait_flags * flags, F && pred, std::size_t tm = invalid_value) {
         if (h == invalid()) return false;
-        return helper_.wait_if(h, std::forward<F>(pred), tm);
+        return helper_.wait_if(h, flags, std::forward<F>(pred), tm);
     }
 
-    void notify(handle_t h) {
-        if (h == invalid()) return;
-        helper_.notify(h);
+    bool notify(handle_t h) {
+        if (h == invalid()) return false;
+        return helper_.notify(h);
     }
 
-    void broadcast(handle_t h) {
-        if (h == invalid()) return;
-        helper_.broadcast(h);
+    bool broadcast(handle_t h) {
+        if (h == invalid()) return false;
+        return helper_.broadcast(h);
+    }
+
+    bool quit_waiting(handle_t h, waiter_helper::wait_flags * flags) {
+        if (h == invalid()) return false;
+        return helper_.quit_waiting(h, flags);
     }
 };
 
diff --git a/src/libipc/platform/waiter_win.h b/src/libipc/platform/waiter_win.h
index ca1f86e..4f3d080 100755
--- a/src/libipc/platform/waiter_win.h
+++ b/src/libipc/platform/waiter_win.h
@@ -3,11 +3,14 @@
 #include <Windows.h>
 
 #include <atomic>
-#include <tuple>
+#include <utility>
+#include <limits>
+#include <cassert>
 
 #include "libipc/rw_lock.h"
 #include "libipc/pool_alloc.h"
 #include "libipc/shm.h"
+#include "libipc/waiter_helper.h"
 
 #include "libipc/utility/log.h"
 #include "libipc/platform/to_tchar.h"
@@ -42,8 +45,9 @@ public:
         switch ((ret = ::WaitForSingleObject(h_, ms))) {
         case WAIT_OBJECT_0:
             return true;
-        case WAIT_ABANDONED:
         case WAIT_TIMEOUT:
+            return false;
+        case WAIT_ABANDONED:
         default:
             ipc::error("fail WaitForSingleObject[%lu]: 0x%08X\n", ::GetLastError(), ret);
             return false;
@@ -73,15 +77,51 @@ public:
 };
 
 class condition {
+    using wait_flags   = waiter_helper::wait_flags;
+    using wait_counter = waiter_helper::wait_counter;
+
     mutex     lock_;
     semaphore sema_, handshake_;
+    wait_counter * cnt_ = nullptr;
 
-    std::atomic<unsigned> * waiting_ = nullptr;
-    long                  * counter_ = nullptr;
+    struct contrl {
+        condition * me_;
+        wait_flags * flags_;
+
+        wait_flags & flags() noexcept {
+            assert(flags_ != nullptr);
+            return *flags_;
+        }
+
+        wait_counter & counter() noexcept {
+            assert(me_->cnt_ != nullptr);
+            return *(me_->cnt_);
+        }
+
+        auto get_lock() {
+            return ipc::detail::unique_lock(me_->lock_);
+        }
+
+        bool sema_wait(std::size_t tm) {
+            return me_->sema_.wait(tm);
+        }
+
+        bool sema_post(long count) {
+            return me_->sema_.post(count);
+        }
+
+        bool handshake_wait(std::size_t tm) {
+            return me_->handshake_.wait(tm);
+        }
+
+        bool handshake_post(long count) {
+            return me_->handshake_.post(count);
+        }
+    };
 
 public:
     friend bool operator==(condition const & c1, condition const & c2) {
-        return (c1.waiting_ == c2.waiting_) && (c1.counter_ == c2.counter_);
+        return c1.cnt_ == c2.cnt_;
     }
 
     friend bool operator!=(condition const & c1, condition const & c2) {
@@ -94,12 +134,11 @@ public:
         mutex    ::remove((ipc::string{ "__COND_MTX__" } + name).c_str());
     }
 
-    bool open(ipc::string const & name, std::atomic<unsigned> * waiting, long * counter) {
+    bool open(ipc::string const & name, wait_counter * cnt) {
         if (lock_     .open("__COND_MTX__" + name) &&
             sema_     .open("__COND_SEM__" + name) &&
             handshake_.open("__COND_HAN__" + name)) {
-            waiting_ = waiting;
-            counter_ = counter;
+            cnt_ = cnt;
             return true;
         }
         return false;
@@ -112,58 +151,31 @@ public:
     }
 
     template <typename Mutex, typename F>
-    bool wait_if(Mutex& mtx, F&& pred, std::size_t tm = invalid_value) {
-        waiting_->fetch_add(1, std::memory_order_release);
-        {
-            IPC_UNUSED_ auto guard = ipc::detail::unique_lock(lock_);
-            if (!std::forward<F>(pred)()) return true;
-            ++ *counter_;
-        }
-        mtx.unlock();
-        bool ret = sema_.wait(tm);
-        waiting_->fetch_sub(1, std::memory_order_release);
-        ret = handshake_.post() && ret;
-        mtx.lock();
-        return ret;
+    bool wait_if(Mutex & mtx, wait_flags * flags, F && pred, std::size_t tm = invalid_value) {
+        assert(flags != nullptr);
+        contrl ctrl { this, flags };
+        return waiter_helper::wait_if(ctrl, mtx, std::forward<F>(pred), tm);
     }
 
     bool notify() {
-        std::atomic_thread_fence(std::memory_order_acq_rel);
-        if (waiting_->load(std::memory_order_relaxed) == 0) {
-            return true;
-        }
-        bool ret = true;
-        IPC_UNUSED_ auto guard = ipc::detail::unique_lock(lock_);
-        if (*counter_ > 0) {
-            ret = sema_.post();
-            -- *counter_;
-            ret = ret && handshake_.wait(default_timeout);
-        }
-        return ret;
+        contrl ctrl { this, nullptr };
+        return waiter_helper::notify(ctrl);
     }
 
     bool broadcast() {
-        std::atomic_thread_fence(std::memory_order_acq_rel);
-        if (waiting_->load(std::memory_order_relaxed) == 0) {
-            return true;
-        }
-        bool ret = true;
-        IPC_UNUSED_ auto guard = ipc::detail::unique_lock(lock_);
-        if (*counter_ > 0) {
-            ret = sema_.post(*counter_);
-            do {
-                -- *counter_;
-                ret = ret && handshake_.wait(default_timeout);
-            } while (*counter_ > 0);
-        }
-        return ret;
+        contrl ctrl { this, nullptr };
+        return waiter_helper::broadcast(ctrl);
+    }
+
+    bool quit_waiting(wait_flags * flags) {
+        assert(flags != nullptr);
+        contrl ctrl { this, flags };
+        return waiter_helper::quit_waiting(ctrl);
     }
 };
 
 class waiter {
-
-    std::atomic<unsigned> waiting_ { 0 };
-    long                  counter_ = 0;
+    waiter_helper::wait_counter cnt_;
 
 public:
     using handle_t = condition;
@@ -177,7 +189,7 @@ public:
             return invalid();
         }
         condition cond;
-        if (cond.open(name, &waiting_, &counter_)) {
+        if (cond.open(name, &cnt_)) {
             return cond;
         }
         return invalid();
@@ -189,7 +201,7 @@ public:
     }
 
     template <typename F>
-    bool wait_if(handle_t& h, F&& pred, std::size_t tm = invalid_value) {
+    bool wait_if(handle_t& h, waiter_helper::wait_flags * flags, F&& pred, std::size_t tm = invalid_value) {
         if (h == invalid()) return false;
 
         class non_mutex {
@@ -198,17 +210,22 @@ public:
             void unlock() noexcept {}
         } nm;
 
-        return h.wait_if(nm, std::forward<F>(pred), tm);
+        return h.wait_if(nm, flags, std::forward<F>(pred), tm);
     }
 
-    void notify(handle_t& h) {
-        if (h == invalid()) return;
-        h.notify();
+    bool notify(handle_t& h) {
+        if (h == invalid()) return false;
+        return h.notify();
     }
 
-    void broadcast(handle_t& h) {
-        if (h == invalid()) return;
-        h.broadcast();
+    bool broadcast(handle_t& h) {
+        if (h == invalid()) return false;
+        return h.broadcast();
+    }
+
+    bool quit_waiting(handle_t& h, waiter_helper::wait_flags * flags) {
+        if (h == invalid()) return false;
+        return h.quit_waiting(flags);
     }
 };
 
diff --git a/src/libipc/platform/waiter_wrapper.h b/src/libipc/platform/waiter_wrapper.h
index 4638c84..553d2e1 100755
--- a/src/libipc/platform/waiter_wrapper.h
+++ b/src/libipc/platform/waiter_wrapper.h
@@ -21,35 +21,39 @@ using mutex_impl     = ipc::detail::mutex;
 using semaphore_impl = ipc::detail::semaphore;
 
 class condition_impl : public ipc::detail::condition {
+    using base_t = ipc::detail::condition;
 
-    ipc::shm::handle wait_h_, cnt_h_;
+    ipc::shm::handle cnt_h_;
+    waiter_helper::wait_flags flags_;
 
 public:
     static void remove(char const * name) {
-        ipc::detail::condition::remove(name);
+        base_t::remove(name);
         ipc::string n = name;
         ipc::shm::remove((n + "__COND_CNT__" ).c_str());
         ipc::shm::remove((n + "__COND_WAIT__").c_str());
     }
 
-    bool open(ipc::string const & name) {
-        if (wait_h_.acquire((name + "__COND_WAIT__").c_str(), sizeof(std::atomic<unsigned>)) &&
-            cnt_h_ .acquire((name + "__COND_CNT__" ).c_str(), sizeof(long))) {
-            return ipc::detail::condition::open(name,
-                                                static_cast<std::atomic<unsigned> *>(wait_h_.get()),
-                                                static_cast<long *>(cnt_h_.get()));
+    bool open(char const * name) {
+        if (cnt_h_ .acquire(
+                (ipc::string { name } + "__COND_CNT__" ).c_str(), 
+                sizeof(waiter_helper::wait_counter))) {
+            flags_.is_closed_.store(false, std::memory_order_release);
+            return base_t::open(name, 
+                static_cast<waiter_helper::wait_counter *>(cnt_h_.get()));
         }
         return false;
     }
 
     void close() {
-        ipc::detail::condition::close();
-        cnt_h_ .release();
-        wait_h_.release();
+        flags_.is_closed_.store(true, std::memory_order_release);
+        base_t::quit_waiting(&flags_);
+        base_t::close();
+        cnt_h_.release();
     }
 
     bool wait(mutex_impl& mtx, std::size_t tm = invalid_value) {
-        return ipc::detail::condition::wait_if(mtx, [] { return true; }, tm);
+        return base_t::wait_if(mtx, &flags_, [] { return true; }, tm);
     }
 };
 
@@ -165,17 +169,11 @@ public:
     }
 
     bool wait(std::size_t tm = invalid_value) {
-        if (h_ == sem_helper::invalid()) return false;
         return sem_helper::wait(h_, tm);
     }
 
     bool post(long count) {
-        if (h_ == sem_helper::invalid()) return false;
-        bool ret = true;
-        for (long i = 0; i < count; ++i) {
-            ret = ret && sem_helper::post(h_);
-        }
-        return ret;
+        return sem_helper::post(h_, count);
     }
 };
 
@@ -194,6 +192,7 @@ public:
 private:
     waiter_t* w_ = nullptr;
     waiter_t::handle_t h_ = waiter_t::invalid();
+    waiter_helper::wait_flags flags_;
 
 public:
     waiter_wrapper() = default;
@@ -218,20 +217,27 @@ public:
     bool open(char const * name) {
         if (w_ == nullptr) return false;
         close();
+        flags_.is_closed_.store(false, std::memory_order_release);
         h_ = w_->open(name);
         return valid();
     }
 
     void close() {
         if (!valid()) return;
+        flags_.is_closed_.store(true, std::memory_order_release);
+        quit_waiting();
         w_->close(h_);
         h_ = waiter_t::invalid();
     }
 
+    void quit_waiting() {
+        w_->quit_waiting(h_, &flags_);
+    }
+
     template <typename F>
-    bool wait_if(F&& pred, std::size_t tm = invalid_value) {
+    bool wait_if(F && pred, std::size_t tm = invalid_value) {
         if (!valid()) return false;
-        return w_->wait_if(h_, std::forward<F>(pred), tm);
+        return w_->wait_if(h_, &flags_, std::forward<F>(pred), tm);
     }
 
     bool notify() {
diff --git a/src/libipc/utility/log.h b/src/libipc/utility/log.h
index f09b385..bb1dcea 100755
--- a/src/libipc/utility/log.h
+++ b/src/libipc/utility/log.h
@@ -7,8 +7,8 @@ namespace ipc {
 namespace detail {
 
 template <typename O>
-void print(O out, char const * fmt) {
-    std::fprintf(out, "%s", fmt);
+void print(O out, char const * str) {
+    std::fprintf(out, "%s", str);
 }
 
 template <typename O, typename P1, typename... P>
@@ -27,8 +27,8 @@ void log(char const * fmt, P1&& p1, P&&... params) {
     ipc::detail::print(stdout, fmt, std::forward<P1>(p1), std::forward<P>(params)...);
 }
 
-inline void error(char const * fmt) {
-    ipc::detail::print(stderr, fmt);
+inline void error(char const * str) {
+    ipc::detail::print(stderr, str);
 }
 
 template <typename P1, typename... P>
diff --git a/src/libipc/utility/scope_guard.h b/src/libipc/utility/scope_guard.h
new file mode 100644
index 0000000..9f42149
--- /dev/null
+++ b/src/libipc/utility/scope_guard.h
@@ -0,0 +1,64 @@
+#pragma once
+
+#include <utility>      // std::forward, std::move
+#include <algorithm>    // std::swap
+#include <type_traits>  // std::decay
+
+namespace ipc {
+
+////////////////////////////////////////////////////////////////
+/// Execute guard function when the enclosing scope exits
+////////////////////////////////////////////////////////////////
+
+template <typename F>
+class scope_guard {
+    F destructor_;
+    mutable bool dismiss_;
+
+public:
+    template <typename D>
+    scope_guard(D && destructor)
+        : destructor_(std::forward<D>(destructor))
+        , dismiss_(false) {
+    }
+
+    scope_guard(scope_guard&& rhs)
+        : destructor_(std::move(rhs.destructor_))
+        , dismiss_(true) /* dismiss rhs */ {
+        std::swap(dismiss_, rhs.dismiss_);
+    }
+
+    ~scope_guard() {
+        try { do_exit(); }
+        /**
+         * In the realm of exceptions, it is fundamental that you can do nothing
+         * if your "undo/recover" action fails.
+        */
+        catch (...) { /* Do nothing */ }
+    }
+
+    void swap(scope_guard & rhs) {
+        std::swap(destructor_, rhs.destructor_);
+        std::swap(dismiss_   , rhs.dismiss_);
+    }
+
+    void dismiss() const noexcept {
+        dismiss_ = true;
+    }
+
+    void do_exit() {
+        if (!dismiss_) {
+            dismiss_ = true;
+            destructor_();
+        }
+    }
+};
+
+template <typename D>
+constexpr auto guard(D && destructor) noexcept {
+    return scope_guard<std::decay_t<D>> {
+        std::forward<D>(destructor)
+    };
+}
+
+} // namespace ipc
\ No newline at end of file
diff --git a/src/libipc/waiter_helper.h b/src/libipc/waiter_helper.h
new file mode 100644
index 0000000..46b03a3
--- /dev/null
+++ b/src/libipc/waiter_helper.h
@@ -0,0 +1,129 @@
+#pragma once
+
+#include <atomic>
+#include <limits>
+#include <utility>
+
+#include "libipc/def.h"
+#include "libipc/utility/scope_guard.h"
+
+namespace ipc {
+namespace detail {
+
+class waiter_helper {
+
+    enum : unsigned {
+        destruct_mask = (std::numeric_limits<unsigned>::max)() >> 1,
+        destruct_flag = ~destruct_mask
+    };
+
+public:
+    struct wait_counter {
+        std::atomic<unsigned> waiting_ { 0 };
+        long counter_ = 0;
+    };
+
+    struct wait_flags {
+        std::atomic<bool> is_waiting_ { false };
+        std::atomic<bool> is_closed_  { true  };
+    };
+
+    template <typename Mutex, typename Ctrl, typename F>
+    static bool wait_if(Ctrl & ctrl, Mutex & mtx, F && pred, std::size_t tm) {
+        auto & flags = ctrl.flags();
+        if (flags.is_closed_.load(std::memory_order_acquire)) {
+            return false;
+        }
+
+        auto & counter = ctrl.counter();
+        counter.waiting_.fetch_add(1, std::memory_order_release);
+        flags.is_waiting_.store(true, std::memory_order_relaxed);
+        auto finally = ipc::guard([&counter, &flags] {
+            counter.waiting_.fetch_sub(1, std::memory_order_release);
+            flags.is_waiting_.store(false, std::memory_order_relaxed);
+        });
+        {
+            IPC_UNUSED_ auto guard = ctrl.get_lock();
+            if (!std::forward<F>(pred)()) return true;
+            counter.counter_ += 1;
+        }
+        mtx.unlock();
+
+        bool ret = false;
+        do {
+            bool is_waiting = flags.is_waiting_.load(std::memory_order_relaxed);
+            bool is_closed  = flags.is_closed_ .load(std::memory_order_acquire);
+            if (!is_waiting || is_closed) {
+                ret = false;
+                break;
+            }
+            ret = ctrl.sema_wait(tm);
+        } while (counter.waiting_.load(std::memory_order_acquire) & destruct_flag);
+        finally.do_exit();
+        ret = ctrl.handshake_post(1) && ret;
+
+        mtx.lock();
+        return ret;
+    }
+
+    template <typename Ctrl>
+    static bool notify(Ctrl & ctrl) {
+        auto & counter = ctrl.counter();
+        if ((counter.waiting_.load(std::memory_order_acquire) & destruct_mask) == 0) {
+            return true;
+        }
+        bool ret = true;
+        IPC_UNUSED_ auto guard = ctrl.get_lock();
+        if (counter.counter_ > 0) {
+            ret = ctrl.sema_post(1);
+            counter.counter_ -= 1;
+            ret = ret && ctrl.handshake_wait(default_timeout);
+        }
+        return ret;
+    }
+
+    template <typename Ctrl>
+    static bool broadcast(Ctrl & ctrl) {
+        auto & counter = ctrl.counter();
+        if ((counter.waiting_.load(std::memory_order_acquire) & destruct_mask) == 0) {
+            return true;
+        }
+        bool ret = true;
+        IPC_UNUSED_ auto guard = ctrl.get_lock();
+        if (counter.counter_ > 0) {
+            ret = ctrl.sema_post(counter.counter_);
+            do {
+                counter.counter_ -= 1;
+                ret = ret && ctrl.handshake_wait(default_timeout);
+            } while (counter.counter_ > 0);
+        }
+        return ret;
+    }
+
+    template <typename Ctrl>
+    static bool quit_waiting(Ctrl & ctrl) {
+        auto & flags = ctrl.flags();
+        if (!flags.is_waiting_.exchange(false, std::memory_order_release)) {
+            return true;
+        }
+        auto & counter = ctrl.counter();
+        if ((counter.waiting_.load(std::memory_order_acquire) & destruct_mask) == 0) {
+            return true;
+        }
+        bool ret = true;
+        IPC_UNUSED_ auto guard = ctrl.get_lock();
+        counter.waiting_.fetch_or(destruct_flag, std::memory_order_relaxed);
+        IPC_UNUSED_ auto finally = ipc::guard([&counter] {
+            counter.waiting_.fetch_and(destruct_mask, std::memory_order_relaxed);
+        });
+        if (counter.counter_ > 0) {
+            ret = ctrl.sema_post(counter.counter_);
+            counter.counter_ -= 1;
+            ret = ret && ctrl.handshake_wait(default_timeout);
+        }
+        return ret;
+    }
+};
+
+} // namespace detail
+} // namespace ipc
diff --git a/test/test_ipc.cpp b/test/test_ipc.cpp
index 6221802..faae13c 100755
--- a/test/test_ipc.cpp
+++ b/test/test_ipc.cpp
@@ -52,7 +52,7 @@ public:
 
 template <relat Rp, relat Rc, trans Ts>
 void test_basic(char const * name) {
-    using que_t = chan<wr<Rp, Rc, Ts>>;
+    using que_t = chan<Rp, Rc, Ts>;
     rand_buf test1, test2;
 
     que_t que1 { name };
@@ -69,7 +69,7 @@ void test_basic(char const * name) {
 
 template <relat Rp, relat Rc, trans Ts>
 void test_sr(char const * name, int size, int s_cnt, int r_cnt) {
-    using que_t = chan<wr<Rp, Rc, Ts>>;
+    using que_t = chan<Rp, Rc, Ts>;
 
     ipc_ut::sender().start(static_cast<std::size_t>(s_cnt));
     ipc_ut::reader().start(static_cast<std::size_t>(r_cnt));