diff --git a/demo/msg_que/main.cpp b/demo/msg_que/main.cpp
index ea60f39..5635101 100644
--- a/demo/msg_que/main.cpp
+++ b/demo/msg_que/main.cpp
@@ -23,7 +23,7 @@ constexpr std::size_t const max_sz = 1024 * 16;
 std::atomic<bool> is_quit__{ false };
 std::atomic<std::size_t> size_counter__{ 0 };
 
-using msg_que_t = ipc::chan<ipc::relat::single, ipc::relat::single, ipc::trans::unicast>;
+using msg_que_t = ipc::chan<ipc::relat::single, ipc::relat::multi, ipc::trans::broadcast>;
 
 msg_que_t que__{ name__ };
 ipc::byte_t buff__[max_sz];
diff --git a/include/libipc/def.h b/include/libipc/def.h
index 9be5206..2b80b81 100755
--- a/include/libipc/def.h
+++ b/include/libipc/def.h
@@ -29,7 +29,7 @@ enum : std::size_t {
     invalid_value   = (std::numeric_limits<std::size_t>::max)(),
     data_length     = 64,
     large_msg_limit = data_length,
-    large_msg_align = 512,
+    large_msg_align = 1024,
     large_msg_cache = 32,
     default_timeout = 100 // ms
 };
diff --git a/src/ipc.cpp b/src/ipc.cpp
index 8b18dde..dcf60b3 100755
--- a/src/ipc.cpp
+++ b/src/ipc.cpp
@@ -20,6 +20,7 @@
 
 #include "libipc/utility/log.h"
 #include "libipc/utility/id_pool.h"
+#include "libipc/utility/scope_guard.h"
 #include "libipc/utility/utility.h"
 
 #include "libipc/memory/resource.h"
@@ -39,7 +40,7 @@ struct msg_t;
 
 template <std::size_t AlignSize>
 struct msg_t<0, AlignSize> {
-    msg_id_t     conn_;
+    msg_id_t     cc_id_;
     msg_id_t     id_;
     std::int32_t remain_;
     bool         storage_;
@@ -50,15 +51,16 @@ struct msg_t : msg_t<0, AlignSize> {
     std::aligned_storage_t<DataSize, AlignSize> data_ {};
 
     msg_t() = default;
-    msg_t(msg_id_t c, msg_id_t i, std::int32_t r, void const * d, std::size_t s)
-        : msg_t<0, AlignSize> { c, i, r, (d == nullptr) || (s == 0) } {
+    msg_t(msg_id_t cc_id, msg_id_t id, std::int32_t remain, void const * data, std::size_t size)
+        : msg_t<0, AlignSize> {cc_id, id, remain, (data == nullptr) || (size == 0)} {
         if (this->storage_) {
-            if (d != nullptr) {
+            if (data != nullptr) {
                 // copy storage-id
-                *reinterpret_cast<std::size_t*>(&data_) = *static_cast<std::size_t const *>(d);
+                *reinterpret_cast<ipc::storage_id_t*>(&data_) =
+                     *static_cast<ipc::storage_id_t const *>(data);
             }
         }
-        else std::memcpy(&data_, d, s);
+        else std::memcpy(&data_, data, size);
     }
 };
 
@@ -90,26 +92,46 @@ auto cc_acc() {
     return static_cast<acc_t*>(acc_h.get());
 }
 
+IPC_CONSTEXPR_ std::size_t align_chunk_size(std::size_t size) noexcept {
+    return (((size - 1) / ipc::large_msg_align) + 1) * ipc::large_msg_align;
+}
+
+IPC_CONSTEXPR_ std::size_t calc_chunk_size(std::size_t size) noexcept {
+    return ipc::make_align(alignof(std::max_align_t), align_chunk_size(
+           ipc::make_align(alignof(std::max_align_t), sizeof(std::atomic<ipc::circ::cc_t>)) + size));
+}
+
+struct chunk_t {
+    std::atomic<ipc::circ::cc_t> &conns() noexcept {
+        return *reinterpret_cast<std::atomic<ipc::circ::cc_t> *>(this);
+    }
+
+    void *data() noexcept {
+        return reinterpret_cast<ipc::byte_t *>(this)
+             + ipc::make_align(alignof(std::max_align_t), sizeof(std::atomic<ipc::circ::cc_t>));
+    }
+};
+
 struct chunk_info_t {
     ipc::id_pool<> pool_;
     ipc::spin_lock lock_;
 
-    IPC_CONSTEXPR_ static std::size_t chunks_elem_size(std::size_t chunk_size) noexcept {
-        return ipc::make_align(alignof(std::max_align_t), chunk_size + sizeof(acc_t));
-    }
-
     IPC_CONSTEXPR_ static std::size_t chunks_mem_size(std::size_t chunk_size) noexcept {
-        return ipc::id_pool<>::max_count * chunks_elem_size(chunk_size);
+        return ipc::id_pool<>::max_count * chunk_size;
     }
 
-    ipc::byte_t *at(std::size_t chunk_size, std::size_t id) noexcept {
-        if (id == ipc::invalid_value) return nullptr;
-        return reinterpret_cast<ipc::byte_t *>(this + 1) + (chunks_elem_size(chunk_size) * id);
+    ipc::byte_t *chunks_mem() noexcept {
+        return reinterpret_cast<ipc::byte_t *>(this + 1);
+    }
+
+    chunk_t *at(std::size_t chunk_size, ipc::storage_id_t id) noexcept {
+        if (id < 0) return nullptr;
+        return reinterpret_cast<chunk_t *>(chunks_mem() + (chunk_size * id));
     }
 };
 
 auto& chunk_storages() {
-    class chunk_t {
+    class chunk_handle_t {
         ipc::shm::handle handle_;
 
     public:
@@ -128,31 +150,29 @@ auto& chunk_storages() {
             return info;
         }
     };
-    static ipc::unordered_map<std::size_t, chunk_t> chunk_s;
-    return chunk_s;
+    static ipc::map<std::size_t, chunk_handle_t> chunk_hs;
+    return chunk_hs;
 }
 
-auto& chunk_lock() {
-    static ipc::spin_lock chunk_l;
-    return chunk_l;
+chunk_info_t *chunk_storage_info(std::size_t chunk_size) {
+    auto &storages = chunk_storages();
+    std::decay_t<decltype(storages)>::iterator it;
+    {
+        static ipc::rw_lock lock;
+        IPC_UNUSED_ std::shared_lock<ipc::rw_lock> guard {lock};
+        if ((it = storages.find(chunk_size)) == storages.end()) {
+            using chunk_handle_t = std::decay_t<decltype(storages)>::value_type::second_type;
+            guard.unlock();
+            IPC_UNUSED_ std::lock_guard<ipc::rw_lock> guard {lock};
+            it = storages.emplace(chunk_size, chunk_handle_t{}).first;
+        }
+    }
+    return it->second.get_info(chunk_size);
 }
 
-constexpr std::size_t calc_chunk_size(std::size_t size) noexcept {
-    return ( ((size - 1) / ipc::large_msg_align) + 1 ) * ipc::large_msg_align;
-}
-
-auto& chunk_storage(std::size_t chunk_size) {
-    IPC_UNUSED_ auto guard = ipc::detail::unique_lock(chunk_lock());
-    return chunk_storages()[chunk_size];
-}
-
-std::pair<std::size_t, void*> apply_storage(std::size_t conn_count, std::size_t size) {
-    if (conn_count == 0) return {};
-
+std::pair<ipc::storage_id_t, void*> acquire_storage(std::size_t size, ipc::circ::cc_t conns) {
     std::size_t chunk_size = calc_chunk_size(size);
-    auto &      chunk_shm  = chunk_storage(chunk_size);
-
-    auto info = chunk_shm.get_info(chunk_size);
+    auto info = chunk_storage_info(chunk_size);
     if (info == nullptr) return {};
 
     info->lock_.lock();
@@ -161,90 +181,92 @@ std::pair<std::size_t, void*> apply_storage(std::size_t conn_count, std::size_t
     auto id = info->pool_.acquire();
     info->lock_.unlock();
 
-    auto ptr = info->at(chunk_size, id);
-    if (ptr == nullptr) return {};
-    reinterpret_cast<acc_t*>(ptr + chunk_size)->store(static_cast<msg_id_t>(conn_count), std::memory_order_release);
-    return { id, ptr };
+    auto chunk = info->at(chunk_size, id);
+    if (chunk == nullptr) return {};
+    chunk->conns().store(conns, std::memory_order_relaxed);
+    return { id, chunk->data() };
 }
 
-void *find_storage(std::size_t id, std::size_t size) {
-    if (id == ipc::invalid_value) {
-        ipc::error("[find_storage] id is invalid: id = %zd, size = %zd\n", id, size);
+void *find_storage(ipc::storage_id_t id, std::size_t size) {
+    if (id < 0) {
+        ipc::error("[find_storage] id is invalid: id = %ld, size = %zd\n", (long)id, size);
         return nullptr;
     }
-
     std::size_t chunk_size = calc_chunk_size(size);
-    auto &      chunk_shm  = chunk_storage(chunk_size);
-
-    auto info = chunk_shm.get_info(chunk_size);
+    auto info = chunk_storage_info(chunk_size);
     if (info == nullptr) return nullptr;
-
-    auto ptr = info->at(chunk_size, id);
-    if (ptr == nullptr) return nullptr;
-    if (reinterpret_cast<acc_t*>(ptr + chunk_size)->load(std::memory_order_acquire) == 0) {
-        ipc::error("[find_storage] cc test failed: id = %zd, chunk_size = %zd\n", id, chunk_size);
-        return nullptr;
-    }
-    return ptr;
+    return info->at(chunk_size, id)->data();
 }
 
-void recycle_storage(std::size_t id, std::size_t size) {
-    if (id == ipc::invalid_value) {
-        ipc::error("[recycle_storage] id is invalid: id = %zd, size = %zd\n", id, size);
+void release_storage(ipc::storage_id_t id, std::size_t size) {
+    if (id < 0) {
+        ipc::error("[release_storage] id is invalid: id = %ld, size = %zd\n", (long)id, size);
         return;
     }
-
     std::size_t chunk_size = calc_chunk_size(size);
-    auto &      chunk_shm  = chunk_storage(chunk_size);
-
-    auto info = chunk_shm.get_info(chunk_size);
+    auto info = chunk_storage_info(chunk_size);
     if (info == nullptr) return;
-
-    auto ptr = info->at(chunk_size, id);
-    if (ptr == nullptr) {
-        ipc::error("[recycle_storage] chunk_shm.mems[%zd] failed: chunk_size = %zd\n", id, chunk_size);
-        return;
-    }
-    if (reinterpret_cast<acc_t*>(ptr + chunk_size)->fetch_sub(1, std::memory_order_acq_rel) > 1) {
-        // not the last receiver, just return
-        return;
-    }
-
     info->lock_.lock();
     info->pool_.release(id);
     info->lock_.unlock();
 }
 
-void clear_storage(std::size_t id, std::size_t size) {
-    if (id == ipc::invalid_value) {
-        ipc::error("[clear_storage] id is invalid: id = %zd, size = %zd\n", id, size);
-        return;
-    }
+template <ipc::relat Rp, ipc::relat Rc>
+bool sub_rc(ipc::wr<Rp, Rc, ipc::trans::unicast>, 
+            std::atomic<ipc::circ::cc_t> &/*conns*/, ipc::circ::cc_t /*curr_conns*/, ipc::circ::cc_t /*conn_id*/) noexcept {
+    return true;
+}
 
-    std::size_t chunk_size = calc_chunk_size(size);
-    auto &      chunk_shm  = chunk_storage(chunk_size);
-
-    auto info = chunk_shm.get_info(chunk_size);
-    if (info == nullptr) return;
-
-    auto ptr = info->at(chunk_size, id);
-    if (ptr == nullptr) return;
-
-    auto cc_flag = reinterpret_cast<acc_t*>(ptr + chunk_size);
+template <ipc::relat Rp, ipc::relat Rc>
+bool sub_rc(ipc::wr<Rp, Rc, ipc::trans::broadcast>, 
+            std::atomic<ipc::circ::cc_t> &conns, ipc::circ::cc_t curr_conns, ipc::circ::cc_t conn_id) noexcept {
+    auto last_conns = curr_conns & ~conn_id;
     for (unsigned k = 0;;) {
-        auto cc_curr = cc_flag->load(std::memory_order_acquire);
-        if (cc_curr == 0) return; // means this id has been cleared
-        if (cc_flag->compare_exchange_weak(cc_curr, 0, std::memory_order_release)) {
-            break;
+        auto chunk_conns  = conns.load(std::memory_order_acquire);
+        if (conns.compare_exchange_weak(chunk_conns, chunk_conns & last_conns, std::memory_order_release)) {
+            return (chunk_conns & last_conns) == 0;
         }
         ipc::yield(k);
     }
+}
 
+template <typename Flag>
+void recycle_storage(ipc::storage_id_t id, std::size_t size, ipc::circ::cc_t curr_conns, ipc::circ::cc_t conn_id) {
+    if (id < 0) {
+        ipc::error("[recycle_storage] id is invalid: id = %ld, size = %zd\n", (long)id, size);
+        return;
+    }
+    std::size_t chunk_size = calc_chunk_size(size);
+    auto info = chunk_storage_info(chunk_size);
+    if (info == nullptr) return;
+
+    auto chunk = info->at(chunk_size, id);
+    if (chunk == nullptr) return;
+
+    if (!sub_rc(Flag{}, chunk->conns(), curr_conns, conn_id)) {
+        return;
+    }
     info->lock_.lock();
     info->pool_.release(id);
     info->lock_.unlock();
 }
 
+template <typename MsgT>
+bool clear_message(void* p) {
+    auto msg = static_cast<MsgT*>(p);
+    if (msg->storage_) {
+        std::int32_t r_size = static_cast<std::int32_t>(ipc::data_length) + msg->remain_;
+        if (r_size <= 0) {
+            ipc::error("[clear_message] invalid msg size: %d\n", (int)r_size);
+            return true;
+        }
+        release_storage(
+            *reinterpret_cast<ipc::storage_id_t*>(&msg->data_),
+            static_cast<std::size_t>(r_size));
+    }
+    return true;
+}
+
 struct conn_info_head {
 
     ipc::string name_;
@@ -324,8 +346,10 @@ struct queue_generator {
 template <typename Policy>
 struct detail_impl {
 
-using queue_t     = typename queue_generator<Policy>::queue_t;
-using conn_info_t = typename queue_generator<Policy>::conn_info_t;
+using policy_t    = Policy;
+using flag_t      = typename policy_t::flag_t;
+using queue_t     = typename queue_generator<policy_t>::queue_t;
+using conn_info_t = typename queue_generator<policy_t>::conn_info_t;
 
 constexpr static conn_info_t* info_of(ipc::handle_t h) noexcept {
     return static_cast<conn_info_t*>(h);
@@ -419,7 +443,8 @@ static bool send(F&& gen_push, ipc::handle_t h, void const * data, std::size_t s
         ipc::error("fail: send, que->ready_sending() == false\n");
         return false;
     }
-    if (que->elems()->connections(std::memory_order_relaxed) == 0) {
+    ipc::circ::cc_t conns = que->elems()->connections(std::memory_order_relaxed);
+    if (conns == 0) {
         ipc::error("fail: send, there is no receiver on this connection.\n");
         return false;
     }
@@ -432,7 +457,7 @@ 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 > ipc::large_msg_limit) {
-        auto   dat = apply_storage(que->conn_count(), size);
+        auto   dat = acquire_storage(size, conns);
         void * buf = dat.second;
         if (buf != nullptr) {
             std::memcpy(buf, data, size);
@@ -440,11 +465,11 @@ static bool send(F&& gen_push, ipc::handle_t h, void const * data, std::size_t s
                             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);
+        //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 / ipc::data_length); ++i, offset += ipc::data_length) {
+    for (std::int32_t i = 0; i < static_cast<std::int32_t>(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;
@@ -466,18 +491,14 @@ static bool send(ipc::handle_t h, void const * data, std::size_t size, std::size
     return send([tm](auto info, auto que, auto msg_id) {
         return [tm, info, que, msg_id](std::int32_t remain, void const * data, std::size_t size) {
             if (!wait_for(info->wt_waiter_, [&] {
-                    return !que->push(info->cc_id_, msg_id, remain, data, size);
+                    return !que->push(
+                        [](void*) { return true; },
+                        info->cc_id_, msg_id, remain, data, size);
                 }, tm)) {
                 ipc::log("force_push: msg_id = %zd, remain = %d, size = %zd\n", msg_id, remain, 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>(ipc::data_length) + tmp_msg->remain_);
-                        }
-                        return true;
-                    }, info->cc_id_, msg_id, remain, data, size)) {
+                if (!que->force_push(
+                        clear_message<typename queue_t::value_t>,
+                        info->cc_id_, msg_id, remain, data, size)) {
                     return false;
                 }
             }
@@ -491,7 +512,9 @@ static bool try_send(ipc::handle_t h, void const * data, std::size_t size, std::
     return send([tm](auto info, auto que, auto msg_id) {
         return [tm, info, que, msg_id](std::int32_t remain, void const * data, std::size_t size) {
             if (!wait_for(info->wt_waiter_, [&] {
-                    return !que->push(info->cc_id_, msg_id, remain, data, size);
+                    return !que->push(
+                        [](void*) { return true; },
+                        info->cc_id_, msg_id, remain, data, size);
                 }, tm)) {
                 return false;
             }
@@ -512,34 +535,60 @@ static ipc::buff_t recv(ipc::handle_t h, std::size_t tm) {
         return {};
     }
     auto& rc = info_of(h)->recv_cache();
-    while (1) {
+    for (;;) {
         // 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)) {
+        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();
-        if ((info_of(h)->acc() != nullptr) && (msg.conn_ == info_of(h)->cc_id_)) {
+        if ((info_of(h)->acc() != nullptr) && (msg.cc_id_ == info_of(h)->cc_id_)) {
             continue; // ignore message to self
         }
         // msg.remain_ may minus & abs(msg.remain_) < data_length
-        std::size_t remain = static_cast<std::int32_t>(ipc::data_length) + msg.remain_;
+        std::int32_t r_size = static_cast<std::int32_t>(ipc::data_length) + msg.remain_;
+        if (r_size <= 0) {
+            ipc::error("fail: recv, r_size = %d\n", (int)r_size);
+            return {};
+        }
+        std::size_t msg_size = static_cast<std::size_t>(r_size);
+        // large message
+        if (msg.storage_) {
+            ipc::storage_id_t buf_id = *reinterpret_cast<ipc::storage_id_t*>(&msg.data_);
+            void* buf = find_storage(buf_id, msg_size);
+            if (buf != nullptr) {
+                struct recycle_t {
+                    ipc::storage_id_t storage_id;
+                    ipc::circ::cc_t   curr_conns;
+                    ipc::circ::cc_t   conn_id;
+                } *r_info = ipc::mem::alloc<recycle_t>(recycle_t{
+                    buf_id, que->elems()->connections(std::memory_order_relaxed), que->connected_id()
+                });
+                if (r_info == nullptr) {
+                    ipc::log("fail: ipc::mem::alloc<recycle_t>.\n");
+                    return ipc::buff_t{buf, msg_size}; // no recycle
+                } else {
+                    return ipc::buff_t{buf, msg_size, [](void* p_info, std::size_t size) {
+                        auto r_info = static_cast<recycle_t *>(p_info);
+                        IPC_UNUSED_ auto finally = ipc::guard([r_info] {
+                            ipc::mem::free(r_info);
+                        });
+                        recycle_storage<flag_t>(r_info->storage_id, size, r_info->curr_conns, r_info->conn_id);
+                    }, r_info};
+                }
+            } else {
+                ipc::log("fail: shm::handle for large message. msg_id: %zd, buf_id: %zd, size: %zd\n", msg.id_, buf_id, msg_size);
+                continue;
+            }
+        }
         // find cache with msg.id_
         auto cac_it = rc.find(msg.id_);
         if (cac_it == rc.end()) {
-            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 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) };
-                }
-                else ipc::log("fail: shm::handle for big message. msg_id: %zd, buf_id: %zd, size: %zd\n", msg.id_, buf_id, remain);
+            if (msg_size <= ipc::data_length) {
+                return make_cache(msg.data_, msg_size);
             }
             // gc
             if (rc.size() > 1024) {
@@ -553,14 +602,14 @@ static ipc::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 { ipc::data_length, make_cache(msg.data_, remain) });
+            rc.emplace(msg.id_, cache_t { ipc::data_length, make_cache(msg.data_, msg_size) });
         }
         // has cached before this message
         else {
             auto& cac = cac_it->second;
             // this is the last message fragment
             if (msg.remain_ <= 0) {
-                cac.append(&(msg.data_), remain);
+                cac.append(&(msg.data_), msg_size);
                 // finish this message, erase it from cache
                 auto buff = std::move(cac.buff_);
                 rc.erase(cac_it);
diff --git a/src/libipc/circ/elem_array.h b/src/libipc/circ/elem_array.h
index 74f031a..0b21f48 100755
--- a/src/libipc/circ/elem_array.h
+++ b/src/libipc/circ/elem_array.h
@@ -130,10 +130,10 @@ public:
         return head_.force_push(que, std::forward<F>(f), block_);
     }
 
-    template <typename Q, typename F>
-    bool pop(Q* que, cursor_t* cur, F&& f) {
+    template <typename Q, typename F, typename R>
+    bool pop(Q* que, cursor_t* cur, F&& f, R&& out) {
         if (cur == nullptr) return false;
-        return head_.pop(que, *cur, std::forward<F>(f), block_);
+        return head_.pop(que, *cur, std::forward<F>(f), std::forward<R>(out), block_);
     }
 };
 
diff --git a/src/libipc/circ/elem_def.h b/src/libipc/circ/elem_def.h
index f2379e2..4003948 100755
--- a/src/libipc/circ/elem_def.h
+++ b/src/libipc/circ/elem_def.h
@@ -16,7 +16,7 @@ namespace circ {
 using u1_t = ipc::uint_t<8>;
 using u2_t = ipc::uint_t<32>;
 
-/** only supports max 32 connections */
+/** only supports max 32 connections in broadcast mode */
 using cc_t = u2_t;
 
 constexpr u1_t index_of(u2_t c) noexcept {
diff --git a/src/libipc/memory/resource.h b/src/libipc/memory/resource.h
index 1084e64..063e8dc 100755
--- a/src/libipc/memory/resource.h
+++ b/src/libipc/memory/resource.h
@@ -5,6 +5,7 @@
 #include <utility>
 #include <functional>
 #include <unordered_map>
+#include <map>
 #include <string>
 #include <cstdio>
 
@@ -49,6 +50,11 @@ using unordered_map = std::unordered_map<
     Key, T, std::hash<Key>, std::equal_to<Key>, ipc::mem::allocator<std::pair<const Key, T>>
 >;
 
+template <typename Key, typename T>
+using map = std::map<
+    Key, T, std::less<Key>, ipc::mem::allocator<std::pair<const Key, T>>
+>;
+
 template <typename Char>
 using basic_string = std::basic_string<
     Char, std::char_traits<Char>, ipc::mem::allocator<Char>
diff --git a/src/libipc/platform/detail.h b/src/libipc/platform/detail.h
index fbf539a..141de6e 100755
--- a/src/libipc/platform/detail.h
+++ b/src/libipc/platform/detail.h
@@ -111,5 +111,17 @@ constexpr const T& (min)(const T& a, const T& b) {
 
 #endif/*__cplusplus < 201703L*/
 
+template <typename T, typename U>
+auto horrible_cast(U rhs) noexcept
+    -> typename std::enable_if<std::is_trivially_copyable<T>::value
+                            && std::is_trivially_copyable<U>::value, T>::type {
+    union {
+        T t;
+        U u;
+    } r = {};
+    r.u = rhs;
+    return r.t;
+}
+
 } // namespace detail
 } // namespace ipc
diff --git a/src/libipc/policy.h b/src/libipc/policy.h
index d2ad313..8959607 100755
--- a/src/libipc/policy.h
+++ b/src/libipc/policy.h
@@ -15,8 +15,10 @@ struct choose;
 
 template <typename Flag>
 struct choose<circ::elem_array, Flag> {
+    using flag_t = Flag;
+
     template <std::size_t DataSize, std::size_t AlignSize>
-    using elems_t = circ::elem_array<ipc::prod_cons_impl<Flag>, DataSize, AlignSize>;
+    using elems_t = circ::elem_array<ipc::prod_cons_impl<flag_t>, DataSize, AlignSize>;
 };
 
 } // namespace policy
diff --git a/src/libipc/prod_cons.h b/src/libipc/prod_cons.h
index d5684fa..28d99bd 100755
--- a/src/libipc/prod_cons.h
+++ b/src/libipc/prod_cons.h
@@ -58,13 +58,14 @@ struct prod_cons_impl<wr<relat::single, relat::single, trans::unicast>> {
         return false;
     }
 
-    template <typename W, typename F, typename E>
-    bool pop(W* /*wrapper*/, circ::u2_t& /*cur*/, F&& f, E* elems) {
+    template <typename W, typename F, typename R, typename E>
+    bool pop(W* /*wrapper*/, circ::u2_t& /*cur*/, F&& f, R&& out, E* elems) {
         auto cur_rd = circ::index_of(rd_.load(std::memory_order_relaxed));
         if (cur_rd == circ::index_of(wt_.load(std::memory_order_acquire))) {
             return false; // empty
         }
         std::forward<F>(f)(&(elems[cur_rd].data_));
+        std::forward<R>(out)(true);
         rd_.fetch_add(1, std::memory_order_release);
         return true;
     }
@@ -80,8 +81,9 @@ struct prod_cons_impl<wr<relat::single, relat::multi , trans::unicast>>
         return false;
     }
 
-    template <typename W, typename F, template <std::size_t, std::size_t> class E, std::size_t DS, std::size_t AS>
-    bool pop(W* /*wrapper*/, circ::u2_t& /*cur*/, F&& f, E<DS, AS>* elems) {
+    template <typename W, typename F, typename R, 
+              template <std::size_t, std::size_t> class E, std::size_t DS, std::size_t AS>
+    bool pop(W* /*wrapper*/, circ::u2_t& /*cur*/, F&& f, R&& out, E<DS, AS>* elems) {
         byte_t buff[DS];
         for (unsigned k = 0;;) {
             auto cur_rd = rd_.load(std::memory_order_relaxed);
@@ -92,6 +94,7 @@ struct prod_cons_impl<wr<relat::single, relat::multi , trans::unicast>>
             std::memcpy(buff, &(elems[circ::index_of(cur_rd)].data_), sizeof(buff));
             if (rd_.compare_exchange_weak(cur_rd, cur_rd + 1, std::memory_order_release)) {
                 std::forward<F>(f)(buff);
+                std::forward<R>(out)(true);
                 return true;
             }
             ipc::yield(k);
@@ -156,8 +159,9 @@ struct prod_cons_impl<wr<relat::multi , relat::multi, trans::unicast>>
         return false;
     }
 
-    template <typename W, typename F, template <std::size_t, std::size_t> class E, std::size_t DS, std::size_t AS>
-    bool pop(W* /*wrapper*/, circ::u2_t& /*cur*/, F&& f, E<DS, AS>* elems) {
+    template <typename W, typename F, typename R, 
+              template <std::size_t, std::size_t> class E, std::size_t DS, std::size_t AS>
+    bool pop(W* /*wrapper*/, circ::u2_t& /*cur*/, F&& f, R&& out, E<DS, AS>* elems) {
         byte_t buff[DS];
         for (unsigned k = 0;;) {
             auto cur_rd = rd_.load(std::memory_order_relaxed);
@@ -179,6 +183,7 @@ struct prod_cons_impl<wr<relat::multi , relat::multi, trans::unicast>>
                 std::memcpy(buff, &(elems[circ::index_of(cur_rd)].data_), sizeof(buff));
                 if (rd_.compare_exchange_weak(cur_rd, cur_rd + 1, std::memory_order_release)) {
                     std::forward<F>(f)(buff);
+                    std::forward<R>(out)(true);
                     return true;
                 }
                 ipc::yield(k);
@@ -263,20 +268,20 @@ struct prod_cons_impl<wr<relat::single, relat::multi, trans::broadcast>> {
         return true;
     }
 
-    template <typename W, typename F, typename E>
-    bool pop(W* wrapper, circ::u2_t& cur, F&& f, E* elems) {
+    template <typename W, typename F, typename R, typename E>
+    bool pop(W* wrapper, circ::u2_t& cur, F&& f, R&& out, E* elems) {
         if (cur == cursor()) return false; // acquire
         auto* el = elems + circ::index_of(cur++);
         std::forward<F>(f)(&(el->data_));
         for (unsigned k = 0;;) {
             auto cur_rc = el->rc_.load(std::memory_order_acquire);
-            circ::cc_t rem_cc = cur_rc & ep_mask;
-            if (rem_cc == 0) {
+            if ((cur_rc & ep_mask) == 0) {
+                std::forward<R>(out)(true);
                 return true;
             }
-            if (el->rc_.compare_exchange_weak(cur_rc,
-                        cur_rc & ~static_cast<rc_t>(wrapper->connected_id()),
-                        std::memory_order_release)) {
+            auto nxt_rc = cur_rc & ~static_cast<rc_t>(wrapper->connected_id());
+            if (el->rc_.compare_exchange_weak(cur_rc, nxt_rc, std::memory_order_release)) {
+                std::forward<R>(out)((nxt_rc & ep_mask) == 0);
                 return true;
             }
             ipc::yield(k);
@@ -395,8 +400,8 @@ struct prod_cons_impl<wr<relat::multi, relat::multi, trans::broadcast>> {
         return true;
     }
 
-    template <typename W, typename F, typename E, std::size_t N>
-    bool pop(W* wrapper, circ::u2_t& cur, F&& f, E(& elems)[N]) {
+    template <typename W, typename F, typename R, typename E, std::size_t N>
+    bool pop(W* wrapper, circ::u2_t& cur, F&& f, R&& out, E(& elems)[N]) {
         auto* el = elems + circ::index_of(cur);
         auto cur_fl = el->f_ct_.load(std::memory_order_acquire);
         if (cur_fl != ~static_cast<flag_t>(cur)) {
@@ -406,17 +411,18 @@ struct prod_cons_impl<wr<relat::multi, relat::multi, trans::broadcast>> {
         std::forward<F>(f)(&(el->data_));
         for (unsigned k = 0;;) {
             auto cur_rc = el->rc_.load(std::memory_order_acquire);
-            circ::cc_t rem_cc = cur_rc & rc_mask;
-            if (rem_cc == 0) {
+            if ((cur_rc & rc_mask) == 0) {
+                std::forward<R>(out)(true);
                 el->f_ct_.store(cur + N - 1, std::memory_order_release);
                 return true;
             }
-            if ((rem_cc & ~wrapper->connected_id()) == 0) {
+            auto nxt_rc = inc_rc(cur_rc) & ~static_cast<rc_t>(wrapper->connected_id());
+            bool last_one = false;
+            if ((last_one = (nxt_rc & rc_mask) == 0)) {
                 el->f_ct_.store(cur + N - 1, std::memory_order_release);
             }
-            if (el->rc_.compare_exchange_weak(cur_rc,
-                        inc_rc(cur_rc) & ~static_cast<rc_t>(wrapper->connected_id()),
-                        std::memory_order_release)) {
+            if (el->rc_.compare_exchange_weak(cur_rc, nxt_rc, std::memory_order_release)) {
+                std::forward<R>(out)(last_one);
                 return true;
             }
             ipc::yield(k);
diff --git a/src/libipc/queue.h b/src/libipc/queue.h
index f04febf..1a782a9 100755
--- a/src/libipc/queue.h
+++ b/src/libipc/queue.h
@@ -155,11 +155,11 @@ public:
         return !valid() || (cursor_ == elems_->cursor());
     }
 
-    template <typename T, typename... P>
-    bool push(P&&... params) {
+    template <typename T, typename F, typename... P>
+    bool push(F&& prep, P&&... params) {
         if (elems_ == nullptr) return false;
         return elems_->push(this, [&](void* p) {
-            ::new (p) T(std::forward<P>(params)...);
+            if (prep(p)) ::new (p) T(std::forward<P>(params)...);
         });
     }
 
@@ -171,14 +171,14 @@ public:
         });
     }
 
-    template <typename T>
-    bool pop(T& item) {
+    template <typename T, typename F>
+    bool pop(T& item, F&& out) {
         if (elems_ == nullptr) {
             return false;
         }
         return elems_->pop(this, &(this->cursor_), [&item](void* p) {
             ::new (&item) T(std::move(*static_cast<T*>(p)));
-        });
+        }, std::forward<F>(out));
     }
 };
 
@@ -204,7 +204,12 @@ public:
     }
 
     bool pop(T& item) {
-        return base_t::pop(item);
+        return base_t::pop(item, [](bool) {});
+    }
+
+    template <typename F>
+    bool pop(T& item, F&& out) {
+        return base_t::pop(item, std::forward<F>(out));
     }
 };
 
diff --git a/src/libipc/utility/id_pool.h b/src/libipc/utility/id_pool.h
index 7207aa9..24d32e4 100755
--- a/src/libipc/utility/id_pool.h
+++ b/src/libipc/utility/id_pool.h
@@ -2,13 +2,15 @@
 
 #include <type_traits>  // std::aligned_storage_t
 #include <cstring>      // std::memcmp
+#include <cstdint>
 
 #include "libipc/def.h"
-
 #include "libipc/platform/detail.h"
 
 namespace ipc {
 
+using storage_id_t = std::int32_t;
+
 template <std::size_t DataSize, std::size_t AlignSize>
 struct id_type;
 
@@ -16,7 +18,7 @@ template <std::size_t AlignSize>
 struct id_type<0, AlignSize> {
     uint_t<8> id_;
 
-    id_type& operator=(std::size_t val) {
+    id_type& operator=(storage_id_t val) {
         id_ = static_cast<uint_t<8>>(val);
         return (*this);
     }
@@ -57,7 +59,7 @@ public:
     }
 
     void init() {
-        for (std::size_t i = 0; i < max_count;) {
+        for (storage_id_t i = 0; i < max_count;) {
             i = next_[i] = (i + 1);
         }
     }
@@ -71,22 +73,22 @@ public:
         return cursor_ == max_count;
     }
 
-    std::size_t acquire() {
-        if (empty()) return invalid_value;
-        std::size_t id = cursor_;
+    storage_id_t acquire() {
+        if (empty()) return -1;
+        storage_id_t id = cursor_;
         cursor_ = next_[id]; // point to next
         return id;
     }
 
-    bool release(std::size_t id) {
-        if (id == invalid_value) return false;
+    bool release(storage_id_t id) {
+        if (id < 0) return false;
         next_[id] = cursor_;
         cursor_ = static_cast<uint_t<8>>(id); // put it back
         return true;
     }
 
-    void       * at(std::size_t id)       { return &(next_[id].data_); }
-    void const * at(std::size_t id) const { return &(next_[id].data_); }
+    void       * at(storage_id_t id)       { return &(next_[id].data_); }
+    void const * at(storage_id_t id) const { return &(next_[id].data_); }
 };
 
 template <typename T>
@@ -94,8 +96,8 @@ class obj_pool : public id_pool<sizeof(T), alignof(T)> {
     using base_t = id_pool<sizeof(T), alignof(T)>;
 
 public:
-    T       * at(std::size_t id)       { return reinterpret_cast<T       *>(base_t::at(id)); }
-    T const * at(std::size_t id) const { return reinterpret_cast<T const *>(base_t::at(id)); }
+    T       * at(storage_id_t id)       { return reinterpret_cast<T       *>(base_t::at(id)); }
+    T const * at(storage_id_t id) const { return reinterpret_cast<T const *>(base_t::at(id)); }
 };
 
 } // namespace ipc
diff --git a/test/test_ipc.cpp b/test/test_ipc.cpp
index faae13c..16c076c 100755
--- a/test/test_ipc.cpp
+++ b/test/test_ipc.cpp
@@ -1,6 +1,8 @@
 
 #include <vector>
 #include <iostream>
+#include <mutex>
+#include <atomic>
 #include <cstring>
 
 #include "libipc/ipc.h"
@@ -16,15 +18,28 @@ using namespace ipc;
 
 namespace {
 
+constexpr int LoopCount = 10000;
+constexpr int MultiMax  = 8;
+
+struct msg_head {
+    int id_;
+};
+
 class rand_buf : public buffer {
 public:
     rand_buf() {
-        int size = capo::random<>{1, 65536}();
+        int size = capo::random<>{sizeof(msg_head), 65536}();
         *this = buffer(new char[size], size, [](void * p, std::size_t) {
             delete [] static_cast<char *>(p);
         });
     }
 
+    rand_buf(msg_head const &msg) {
+        *this = buffer(new msg_head{msg}, sizeof(msg), [](void * p, std::size_t) {
+            delete static_cast<msg_head *>(p);
+        });
+    }
+
     rand_buf(rand_buf &&) = default;
     rand_buf(rand_buf const & rhs) {
         if (rhs.empty()) return;
@@ -40,11 +55,11 @@ public:
     }
 
     void set_id(int k) noexcept {
-        *get<char *>() = static_cast<char>(k);
+        get<msg_head *>()->id_ = k;
     }
 
     int get_id() const noexcept {
-        return static_cast<int>(*get<char *>());
+        return get<msg_head *>()->id_;
     }
 
     using buffer::operator=;
@@ -60,64 +75,79 @@ void test_basic(char const * name) {
     EXPECT_FALSE(que1.try_send(test2));
 
     que_t que2 { que1.name(), ipc::receiver };
-    EXPECT_TRUE(que1.send(test1));
-    EXPECT_TRUE(que1.try_send(test2));
+    ASSERT_TRUE(que1.send(test1));
+    ASSERT_TRUE(que1.try_send(test2));
 
     EXPECT_EQ(que2.recv(), test1);
     EXPECT_EQ(que2.recv(), test2);
 }
 
-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<Rp, Rc, Ts>;
+class data_set {
+    std::vector<rand_buf> datas_;
 
+public:
+    data_set() {
+        datas_.resize(LoopCount);
+        for (int i = 0; i < LoopCount; ++i) {
+            datas_[i].set_id(i);
+        }
+    }
+
+    std::vector<rand_buf> const &get() const noexcept {
+        return datas_;
+    }
+} const data_set__;
+
+template <relat Rp, relat Rc, trans Ts, typename Que = chan<Rp, Rc, Ts>>
+void test_sr(char const * name, int s_cnt, int r_cnt) {
     ipc_ut::sender().start(static_cast<std::size_t>(s_cnt));
     ipc_ut::reader().start(static_cast<std::size_t>(r_cnt));
+
+    std::atomic_thread_fence(std::memory_order_seq_cst);
     ipc_ut::test_stopwatch sw;
-    std::vector<rand_buf> tests(size);
 
     for (int k = 0; k < s_cnt; ++k) {
-        ipc_ut::sender() << [name, &tests, &sw, r_cnt, k] {
-            que_t que1 { name };
-            EXPECT_TRUE(que1.wait_for_recv(r_cnt));
+        ipc_ut::sender() << [name, &sw, r_cnt, k] {
+            Que que { name, ipc::sender };
+            EXPECT_TRUE(que.wait_for_recv(r_cnt));
             sw.start();
-            for (auto & buf : tests) {
-                rand_buf data { buf };
-                data.set_id(k);
-                EXPECT_TRUE(que1.send(data));
+            for (int i = 0; i < (int)data_set__.get().size(); ++i) {
+                EXPECT_TRUE(que.send(data_set__.get()[i]));
             }
         };
     }
 
     for (int k = 0; k < r_cnt; ++k) {
-        ipc_ut::reader() << [name, &tests, s_cnt] {
-            que_t que2 { name, ipc::receiver };
-            std::vector<int> cursors(s_cnt);
+        ipc_ut::reader() << [name] {
+            Que que { name, ipc::receiver };
             for (;;) {
-                rand_buf got { que2.recv() };
+                rand_buf got { que.recv() };
                 ASSERT_FALSE(got.empty());
-                int & cur = cursors.at(got.get_id());
-                ASSERT_TRUE((cur >= 0) && (cur < static_cast<int>(tests.size())));
-                rand_buf buf { tests.at(cur++) };
-                buf.set_id(got.get_id());
-                EXPECT_EQ(got, buf);
-                int n = 0;
-                for (; n < static_cast<int>(cursors.size()); ++n) {
-                    if (cursors[n] < static_cast<int>(tests.size())) break;
+                int i = got.get_id();
+                if (i == -1) {
+                    return;
+                }
+                ASSERT_TRUE((i >= 0) && (i < (int)data_set__.get().size()));
+                auto const &data_set = data_set__.get()[i];
+                if (data_set != got) {
+                    printf("data_set__.get()[%d] != got, size = %zd/%zd\n", 
+                            i, data_set.size(), got.size());
+                    EXPECT_TRUE(false);
                 }
-                if (n == static_cast<int>(cursors.size())) break;
             }
         };
     }
 
     ipc_ut::sender().wait_for_done();
+    Que que { name };
+    EXPECT_TRUE(que.wait_for_recv(r_cnt));
+    for (int k = 0; k < r_cnt; ++k) {
+        que.send(rand_buf{msg_head{-1}});
+    }
     ipc_ut::reader().wait_for_done();
-    sw.print_elapsed<std::chrono::microseconds>(s_cnt, r_cnt, size, name);
+    sw.print_elapsed<std::chrono::microseconds>(s_cnt, r_cnt, (int)data_set__.get().size(), name);
 }
 
-constexpr int LoopCount = 10000;
-constexpr int MultiMax  = 8;
-
 } // internal-linkage
 
 TEST(IPC, basic) {
@@ -129,22 +159,26 @@ TEST(IPC, basic) {
 }
 
 TEST(IPC, 1v1) {
-    test_sr<relat::single, relat::single, trans::unicast  >("ssu", LoopCount, 1, 1);
-    test_sr<relat::single, relat::multi , trans::unicast  >("smu", LoopCount, 1, 1);
-    test_sr<relat::multi , relat::multi , trans::unicast  >("mmu", LoopCount, 1, 1);
-    test_sr<relat::single, relat::multi , trans::broadcast>("smb", LoopCount, 1, 1);
-    test_sr<relat::multi , relat::multi , trans::broadcast>("mmb", LoopCount, 1, 1);
+    test_sr<relat::single, relat::single, trans::unicast  >("ssu", 1, 1);
+    test_sr<relat::single, relat::multi , trans::unicast  >("smu", 1, 1);
+    test_sr<relat::multi , relat::multi , trans::unicast  >("mmu", 1, 1);
+    test_sr<relat::single, relat::multi , trans::broadcast>("smb", 1, 1);
+    test_sr<relat::multi , relat::multi , trans::broadcast>("mmb", 1, 1);
 }
 
 TEST(IPC, 1vN) {
-    test_sr<relat::single, relat::multi , trans::broadcast>("smb", LoopCount, 1, MultiMax);
-    test_sr<relat::multi , relat::multi , trans::broadcast>("mmb", LoopCount, 1, MultiMax);
+    //test_sr<relat::single, relat::multi , trans::unicast  >("smu", 1, MultiMax);
+    //test_sr<relat::multi , relat::multi , trans::unicast  >("mmu", 1, MultiMax);
+    test_sr<relat::single, relat::multi , trans::broadcast>("smb", 1, MultiMax);
+    test_sr<relat::multi , relat::multi , trans::broadcast>("mmb", 1, MultiMax);
 }
 
 TEST(IPC, Nv1) {
-    test_sr<relat::multi , relat::multi , trans::broadcast>("mmb", LoopCount, MultiMax, 1);
+    //test_sr<relat::multi , relat::multi , trans::unicast  >("mmu", MultiMax, 1);
+    test_sr<relat::multi , relat::multi , trans::broadcast>("mmb", MultiMax, 1);
 }
 
 TEST(IPC, NvN) {
-    test_sr<relat::multi , relat::multi , trans::broadcast>("mmb", LoopCount, MultiMax, MultiMax);
+    //test_sr<relat::multi , relat::multi , trans::unicast  >("mmu", MultiMax, MultiMax);
+    test_sr<relat::multi , relat::multi , trans::broadcast>("mmb", MultiMax, MultiMax);
 }
diff --git a/test/test_queue.cpp b/test/test_queue.cpp
index c1114ef..a59b3a7 100755
--- a/test/test_queue.cpp
+++ b/test/test_queue.cpp
@@ -44,7 +44,7 @@ constexpr int ThreadMax = 8;
 
 template <typename Que>
 void push(Que & que, int p, int d) {
-    for (int n = 0; !que.push(p, d); ++n) {
+    for (int n = 0; !que.push([](void*) { return true; }, p, d); ++n) {
         ASSERT_NE(n, PushRetry);
         std::this_thread::yield();
     }
diff --git a/test/thread_pool.h b/test/thread_pool.h
index a7d2b28..03b7e8f 100755
--- a/test/thread_pool.h
+++ b/test/thread_pool.h
@@ -9,6 +9,8 @@
 #include <cstddef>            // std::size_t
 #include <cassert>            // assert
 
+#include "capo/scope_guard.hpp"
+
 namespace ipc_ut {
 
 class thread_pool final {
@@ -32,6 +34,9 @@ class thread_pool final {
         if (pool->quit_) return;
         if (pool->jobs_.empty()) {
           pool->waiting_cnt_ += 1;
+          CAPO_SCOPE_GUARD_ = [pool] {
+              pool->waiting_cnt_ -= 1;
+          };
 
           if (pool->waiting_cnt_ == pool->workers_.size()) {
             pool->cv_empty_.notify_all();
@@ -41,8 +46,6 @@ class thread_pool final {
             pool->cv_jobs_.wait(guard);
             if (pool->quit_) return;
           } while (pool->jobs_.empty());
-
-          pool->waiting_cnt_ -= 1;
         }
         assert(!pool->jobs_.empty());
         job = std::move(pool->jobs_.front());
@@ -71,6 +74,7 @@ public:
   }
 
   void start(std::size_t n) {
+    std::unique_lock<std::mutex> guard { lock_ };
     if (n <= workers_.size()) return;
     for (std::size_t i = workers_.size(); i < n; ++i) {
       workers_.push_back(std::thread { &thread_pool::proc, this });