diff --git a/src/circ_queue.h b/src/circ_queue.h
index 8ae737c..e510760 100644
--- a/src/circ_queue.h
+++ b/src/circ_queue.h
@@ -7,17 +7,15 @@
 #include <utility>
 #include <limits>
 #include <algorithm>
-#include <thread>
 
 namespace ipc {
 
 struct circ_queue_head {
-    using u8_t = std::atomic<std::uint8_t>;
-    using ms_t = std::atomic<std::size_t>; // message head
+    using ui_t = std::atomic<std::uint16_t>;
+    using el_t = std::atomic<std::size_t>; // element head
 
-    ms_t mc_ { 0 }; // message counter
-    u8_t cc_ { 0 }; // connection counter
-    u8_t cr_ { 0 }; // write cursor
+    ui_t cc_ { 0 }; // connection counter
+    ui_t cr_ { 0 }; // write cursor
 };
 
 template <std::size_t Size>
@@ -29,33 +27,36 @@ public:
         block_size = Size - head_size,
         elem_max   = std::numeric_limits<std::uint8_t>::max(),
         elem_size  = (Size / (elem_max + 1)),
-        msg_size   = elem_size - sizeof(ms_t)
+        data_size  = elem_size - sizeof(el_t)
     };
 
     static_assert(Size > head_size        , "Size must > head_size");
     static_assert(elem_size >= head_size  , "elem_size must >= head_size");
-    static_assert(elem_size > sizeof(ms_t), "elem_size must > sizeof(ms_t)");
+    static_assert(elem_size > sizeof(el_t), "elem_size must > sizeof(el_t)");
     static_assert(Size % elem_size == 0   , "Size must be multiple of elem_size");
 
 private:
     struct elem_t {
-        ms_t head_;
-        std::uint8_t msg_[msg_size];
+        el_t head_;
+        std::uint8_t data_[data_size];
     };
 
     elem_t* elem_start(void) {
         return reinterpret_cast<elem_t*>(this) + 1;
     }
 
-    static void next(u8_t& i) {
-        if (++i == elem_max) i.store(0, std::memory_order_release);
+    static std::uint8_t id(std::uint16_t i) {
+        return i & 0x00ff;
     }
 
     std::uint8_t block_[block_size];
 
 public:
-    static void next(std::uint8_t& i) {
-        if (++i == elem_max) i = 0;
+    static std::uint16_t next(std::uint16_t i) {
+        if (id(++i) == elem_max) {
+            return ++i;
+        }
+        else return i;
     }
 
     circ_queue(void) {
@@ -81,7 +82,7 @@ public:
     }
 
     void* acquire(void) {
-        auto st = elem_start() + cr_.load(std::memory_order_relaxed);
+        auto st = elem_start() + id(cr_.load(std::memory_order_relaxed));
         do {
             // check remain count of consumers
             if (!st->head_.load(std::memory_order_acquire)) {
@@ -89,30 +90,24 @@ public:
                 break;
             }
         } while(1);
-        return st->msg_;
+        return st->data_;
     }
 
     void commit(void) {
-        next(cr_);
-        mc_.fetch_add(1, std::memory_order_release);
+        cr_.store(next(cr_.load(std::memory_order_relaxed)), std::memory_order_release);
     }
 
-    std::uint8_t cursor(void) const {
+    std::uint16_t cursor(void) const {
         return cr_.load(std::memory_order_acquire);
     }
 
-    constexpr std::size_t begin(void) const {
-        return 0;
+    void* get(std::uint16_t index) {
+        return (elem_start() + id(index))->data_;
     }
 
-    std::size_t end(void) const {
-        return mc_.load(std::memory_order_acquire);
-    }
-
-    void* get(std::uint8_t index) {
-        auto st = elem_start() + index;
+    void commit(std::uint16_t index) {
+        auto st = elem_start() + id(index);
         st->head_.fetch_sub(1, std::memory_order_release);
-        return st->msg_;
     }
 };
 
diff --git a/test/test_circ_queue.cpp b/test/test_circ_queue.cpp
index f4d31ec..dbdba49 100644
--- a/test/test_circ_queue.cpp
+++ b/test/test_circ_queue.cpp
@@ -3,6 +3,8 @@
 #include <type_traits>
 #include <memory>
 #include <new>
+#include <vector>
+#include <thread>
 
 #include "circ_queue.h"
 #include "test.h"
@@ -46,14 +48,15 @@ void Unit::test_producer(void) {
             auto disconn = [](cq_t* cq) { cq->disconnect(); };
             std::unique_ptr<cq_t, decltype(disconn)> guard(cq__, disconn);
 
-            auto it = cq__->begin();
             int i = 0;
             do {
-                while (it != cq__->end()) {
+                while (cur != cq__->cursor()) {
                     int d = *static_cast<const int*>(cq__->get(cur));
+                    cq__->commit(cur);
                     if (d < 0) return;
-                    QCOMPARE(d, i);
-                    ++i; ++it; cq__->next(cur);
+                    cur = cq__->next(cur);
+                    QCOMPARE(i, d);
+                    ++i;
                 }
             } while(1);
         }};
@@ -63,7 +66,7 @@ void Unit::test_producer(void) {
         std::this_thread::yield();
     }
     capo::stopwatch<> sw;
-    constexpr static int loops = 267/*1000000*/;
+    constexpr static int loops = 1000000;
 
     std::cout << "start producer..." << std::endl;
     sw.start();