diff --git a/demo/chat/main.cpp b/demo/chat/main.cpp
index 715dd0d..d3fc0ac 100755
--- a/demo/chat/main.cpp
+++ b/demo/chat/main.cpp
@@ -26,10 +26,6 @@ ipc::channel receiver__ { name__, ipc::receiver };
 } // namespace
 
 int main() {
-    ::signal(SIGINT, [](int) {
-        receiver__.disconnect();
-    });
-
     std::string buf, id = id__ + std::to_string(calc_unique_id());
     std::regex  reg { "(c\\d+)> (.*)" };
 
@@ -58,6 +54,7 @@ int main() {
         if (buf.empty() || (buf == quit__)) break;
 //        std::cout << "[" << i << "]" << std::endl;
         sender__.send(id + "> " + buf);
+        buf.clear();
     }
 
     receiver__.disconnect();
diff --git a/src/ipc.cpp b/src/ipc.cpp
index 71c0a1c..379799a 100755
--- a/src/ipc.cpp
+++ b/src/ipc.cpp
@@ -280,10 +280,10 @@ struct conn_info_head {
         , acc_h_    (("__AC_CONN__" + name_).c_str(), sizeof(acc_t)) {
     }
 
-    void enable(bool e) {
-        cc_waiter_.set_enabled(e);
-        wt_waiter_.set_enabled(e);
-        rd_waiter_.set_enabled(e);
+    void quit_waiting() {
+        cc_waiter_.quit_waiting();
+        wt_waiter_.quit_waiting();
+        rd_waiter_.quit_waiting();
     }
 
     auto acc() {
@@ -356,7 +356,6 @@ static bool connect(handle_t * ph, char const * name, bool start) {
     if (que == nullptr) {
         return false;
     }
-    info_of(*ph)->enable(true);
     if (start) {
         if (que->connect()) { // wouldn't connect twice
             info_of(*ph)->cc_waiter_.broadcast();
@@ -371,7 +370,7 @@ static void disconnect(ipc::handle_t h) {
         return;
     }
     bool dis = que->disconnect();
-    info_of(h)->enable(false);
+    info_of(h)->quit_waiting();
     if (dis) {
         info_of(h)->recv_cache().clear();
     }
diff --git a/src/libipc/platform/waiter_linux.h b/src/libipc/platform/waiter_linux.h
index 0fe0ed2..d8ff4ef 100755
--- a/src/libipc/platform/waiter_linux.h
+++ b/src/libipc/platform/waiter_linux.h
@@ -10,8 +10,10 @@
 #include <atomic>
 #include <tuple>
 #include <utility>
+#include <cassert>
 
 #include "libipc/def.h"
+#include "libipc/waiter_helper.h"
 
 #include "libipc/utility/log.h"
 #include "libipc/utility/scope_guard.h"
@@ -178,7 +180,7 @@ 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);
@@ -201,13 +203,19 @@ 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) {
@@ -235,23 +243,61 @@ public:
 #pragma pop_macro("IPC_SEMAPHORE_FUNC_")
 };
 
-class waiter_helper {
+class waiter_holder {
+public:
+    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());
+    }
+
+private:
     mutex lock_;
+    waiter_helper::wait_counter cnt_;
 
-    std::atomic<unsigned> waiting_ { 0 };
-    long counter_ = 0;
+    struct contrl {
+        waiter_holder * me_;
+        waiter_helper::wait_flags * flags_;
+        handle_t const & h_;
 
-    enum : unsigned {
-        destruct_mask = (std::numeric_limits<unsigned>::max)() >> 1,
-        destruct_flag = ~destruct_mask
+        waiter_helper::wait_flags & flags() noexcept {
+            assert(flags_ != nullptr);
+            return *flags_;
+        }
+
+        waiter_helper::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:
-    using handle_t = std::tuple<ipc::string, sem_helper::handle_t, sem_helper::handle_t>;
-
-    static handle_t invalid() noexcept {
-        return std::make_tuple(ipc::string{}, sem_helper::invalid(), sem_helper::invalid());
-    }
+    using wait_flags = waiter_helper::wait_flags;
 
     handle_t open_h(ipc::string && name) {
         auto sem = sem_helper::open(("__WAITER_HELPER_SEM__" + name).c_str(), 0);
@@ -285,95 +331,38 @@ public:
     }
 
     template <typename F>
-    bool wait_if(handle_t const & h, std::atomic<bool> const & enabled, F&& pred, std::size_t tm = invalid_value) {
-        if (!enabled.load(std::memory_order_acquire)) {
-            return false;
-        }
-        waiting_.fetch_add(1, std::memory_order_release);
-        auto finally = ipc::guard([this] {
-            waiting_.fetch_sub(1, std::memory_order_release);
-        });
-        {
-            IPC_UNUSED_ auto guard = ipc::detail::unique_lock(lock_);
-            if (!std::forward<F>(pred)()) return true;
-            ++ counter_;
-        }
-        bool ret = false;
-        do {
-            if (!enabled.load(std::memory_order_acquire)) {
-                break;
-            }
-            ret = sem_helper::wait(std::get<1>(h), tm);
-        } while (waiting_.load(std::memory_order_acquire) & destruct_flag);
-        finally.do_exit();
-        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 };
+        return waiter_helper::wait_if(ctrl, mtx, std::forward<F>(pred), tm);
     }
 
     bool notify(handle_t const & h) {
-        if ((waiting_.load(std::memory_order_acquire) & destruct_mask) == 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) {
-        if ((waiting_.load(std::memory_order_acquire) & destruct_mask) == 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 emit_destruction(handle_t const & h) {
-        if ((waiting_.load(std::memory_order_acquire) & destruct_mask) == 0) {
-            return true;
-        }
-        bool ret = true;
-        IPC_UNUSED_ auto guard = ipc::detail::unique_lock(lock_);
-        waiting_.fetch_or(destruct_flag, std::memory_order_relaxed);
-        IPC_UNUSED_ auto finally = ipc::guard([this] {
-            waiting_.fetch_and(destruct_mask, std::memory_order_relaxed);
-        });
-        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;
+    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) {
@@ -396,9 +385,9 @@ public:
     }
 
     template <typename F>
-    bool wait_if(handle_t h, std::atomic<bool> const & enabled, F && pred, std::size_t tm = invalid_value) {
+    bool wait_if(handle_t h, waiter_holder::wait_flags * flags, F && pred, std::size_t tm = invalid_value) {
         if (h == invalid()) return false;
-        return helper_.wait_if(h, enabled, std::forward<F>(pred), tm);
+        return helper_.wait_if(h, flags, std::forward<F>(pred), tm);
     }
 
     bool notify(handle_t h) {
@@ -411,9 +400,9 @@ public:
         return helper_.broadcast(h);
     }
 
-    bool emit_destruction(handle_t h) {
+    bool quit_waiting(handle_t h, waiter_holder::wait_flags * flags) {
         if (h == invalid()) return false;
-        return helper_.emit_destruction(h);
+        return helper_.quit_waiting(h, flags);
     }
 };
 
diff --git a/src/libipc/platform/waiter_win.h b/src/libipc/platform/waiter_win.h
index 0782510..155cadb 100755
--- a/src/libipc/platform/waiter_win.h
+++ b/src/libipc/platform/waiter_win.h
@@ -5,10 +5,12 @@
 #include <atomic>
 #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/utility/scope_guard.h"
@@ -44,8 +46,9 @@ 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;
@@ -77,18 +80,48 @@ public:
 class condition {
     mutex     lock_;
     semaphore sema_, handshake_;
+    waiter_helper::wait_counter * cnt_ = nullptr;
 
-    std::atomic<unsigned> * waiting_ = nullptr;
-    long                  * counter_ = nullptr;
+    struct contrl {
+        condition * me_;
+        waiter_helper::wait_flags * flags_;
 
-    enum : unsigned {
-        destruct_mask = (std::numeric_limits<unsigned>::max)() >> 1,
-        destruct_flag = ~destruct_mask
+        waiter_helper::wait_flags & flags() noexcept {
+            assert(flags_ != nullptr);
+            return *flags_;
+        }
+
+        waiter_helper::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:
+    using wait_flags = waiter_helper::wait_flags;
+
     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) {
@@ -101,12 +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, waiter_helper::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;
@@ -119,88 +151,31 @@ public:
     }
 
     template <typename Mutex, typename F>
-    bool wait_if(Mutex & mtx, std::atomic<bool> const & enabled, F && pred, std::size_t tm = invalid_value) {
-        if (!enabled.load(std::memory_order_acquire)) {
-            return false;
-        }
-        waiting_->fetch_add(1, std::memory_order_release);
-        auto finally = ipc::guard([this] {
-            waiting_->fetch_sub(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 = false;
-        do {
-            if (!enabled.load(std::memory_order_acquire)) {
-                break;
-            }
-            ret = sema_.wait(tm);
-        } while (waiting_->load(std::memory_order_acquire) & destruct_flag);
-        finally.do_exit();
-        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() {
-        if ((waiting_->load(std::memory_order_acquire) & destruct_mask) == 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() {
-        if ((waiting_->load(std::memory_order_acquire) & destruct_mask) == 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 emit_destruction() {
-        if ((waiting_->load(std::memory_order_acquire) & destruct_mask) == 0) {
-            return true;
-        }
-        bool ret = true;
-        IPC_UNUSED_ auto guard = ipc::detail::unique_lock(lock_);
-        waiting_->fetch_or(destruct_flag, std::memory_order_relaxed);
-        IPC_UNUSED_ auto finally = ipc::guard([this] {
-            waiting_->fetch_and(destruct_mask, std::memory_order_relaxed);
-        });
-        if (*counter_ > 0) {
-            ret = sema_.post(*counter_);
-            do {
-                -- *counter_;
-                ret = ret && handshake_.wait(default_timeout);
-            } while (*counter_ > 0);
-        }
-        return ret;
+    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;
@@ -214,7 +189,7 @@ public:
             return invalid();
         }
         condition cond;
-        if (cond.open(name, &waiting_, &counter_)) {
+        if (cond.open(name, &cnt_)) {
             return cond;
         }
         return invalid();
@@ -226,7 +201,7 @@ public:
     }
 
     template <typename F>
-    bool wait_if(handle_t& h, std::atomic<bool> const & enabled, F&& pred, std::size_t tm = invalid_value) {
+    bool wait_if(handle_t& h, handle_t::wait_flags * flags, F&& pred, std::size_t tm = invalid_value) {
         if (h == invalid()) return false;
 
         class non_mutex {
@@ -235,7 +210,7 @@ public:
             void unlock() noexcept {}
         } nm;
 
-        return h.wait_if(nm, enabled, std::forward<F>(pred), tm);
+        return h.wait_if(nm, flags, std::forward<F>(pred), tm);
     }
 
     bool notify(handle_t& h) {
@@ -248,9 +223,9 @@ public:
         return h.broadcast();
     }
 
-    bool emit_destruction(handle_t& h) {
+    bool quit_waiting(handle_t& h, handle_t::wait_flags * flags) {
         if (h == invalid()) return false;
-        return h.emit_destruction();
+        return h.quit_waiting(flags);
     }
 };
 
diff --git a/src/libipc/platform/waiter_wrapper.h b/src/libipc/platform/waiter_wrapper.h
index 4c30094..bbb9902 100755
--- a/src/libipc/platform/waiter_wrapper.h
+++ b/src/libipc/platform/waiter_wrapper.h
@@ -21,39 +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_;
-    std::atomic<bool> enabled_ { false };
+    ipc::shm::handle cnt_h_;
+    base_t::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))) {
-            enabled_.store(true, std::memory_order_release);
-            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() {
-        enabled_.store(false, std::memory_order_release);
-        ipc::detail::condition::emit_destruction();
-        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, enabled_, [] { return true; }, tm);
+        return base_t::wait_if(mtx, &flags_, [] { return true; }, tm);
     }
 };
 
@@ -169,17 +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);
     }
 };
 
@@ -198,7 +192,7 @@ public:
 private:
     waiter_t* w_ = nullptr;
     waiter_t::handle_t h_ = waiter_t::invalid();
-    std::atomic<bool> enabled_ { true };
+    waiter_t::handle_t::wait_flags flags_;
 
 public:
     waiter_wrapper() = default;
@@ -223,27 +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 set_enabled(bool e) {
-        if (enabled_.exchange(e, std::memory_order_acq_rel) == e) {
-            return;
-        }
-        if (!e) w_->emit_destruction(h_);
+    void quit_waiting() {
+        w_->quit_waiting(h_, &flags_);
     }
 
     template <typename F>
     bool wait_if(F && pred, std::size_t tm = invalid_value) {
         if (!valid()) return false;
-        return w_->wait_if(h_, enabled_, std::forward<F>(pred), tm);
+        return w_->wait_if(h_, &flags_, std::forward<F>(pred), tm);
     }
 
     bool notify() {
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