diff --git a/cos_c_sdk/cos_http_io.c b/cos_c_sdk/cos_http_io.c
index 3df997d..4dc5597 100644
--- a/cos_c_sdk/cos_http_io.c
+++ b/cos_c_sdk/cos_http_io.c
@@ -63,6 +63,27 @@ void request_release(CURL *request)
     }
 }
 
+void request_release2(cos_curl_http_transport_t* t)
+{
+    CURL* request = t->curl;
+    CURLcode code = t->curl_code;
+    apr_thread_mutex_lock(requestStackMutexG);
+
+    // If the request stack is full, destroy this one
+    // else put this one at the front of the request stack; we do this because
+    // we want the most-recently-used curl handle to be re-used on the next
+    // request, to maximize our chances of re-using a TCP connection before it
+    // times out
+    if (requestStackCountG == COS_REQUEST_STACK_SIZE || code != CURLE_OK) {
+        apr_thread_mutex_unlock(requestStackMutexG);
+        curl_easy_cleanup(request);
+    }
+    else {
+        requestStackG[requestStackCountG++] = request;
+        apr_thread_mutex_unlock(requestStackMutexG);
+    }
+}
+
 void cos_set_default_request_options(cos_http_request_options_t *op)
 {
     cos_default_http_request_options = op;
diff --git a/cos_c_sdk/cos_http_io.h b/cos_c_sdk/cos_http_io.h
index 8dc0407..c4bb306 100644
--- a/cos_c_sdk/cos_http_io.h
+++ b/cos_c_sdk/cos_http_io.h
@@ -18,6 +18,7 @@ static APR_INLINE const char *cos_http_controller_get_reason(cos_http_controller
 
 CURL *cos_request_get();
 void request_release(CURL *request);
+void request_release2(cos_curl_http_transport_t* t);
 
 int cos_http_io_initialize(const char *user_agent_info, int flag);
 void cos_http_io_deinitialize();
diff --git a/cos_c_sdk/cos_sys_define.h b/cos_c_sdk/cos_sys_define.h
index a7901bf..7184527 100644
--- a/cos_c_sdk/cos_sys_define.h
+++ b/cos_c_sdk/cos_sys_define.h
@@ -132,7 +132,7 @@ typedef apr_array_header_t cos_array_header_t;
 #define CR     (char) 13
 #define CRLF   "\x0d\x0a"
 
-#define COS_VERSION    "5.0.17"
+#define COS_VERSION    "5.0.18"
 #define COS_VER        "cos-sdk-c/" COS_VERSION
 
 #define COS_HTTP_PREFIX   "http://"
diff --git a/cos_c_sdk/cos_transport.c b/cos_c_sdk/cos_transport.c
index 6a0a50e..283985c 100644
--- a/cos_c_sdk/cos_transport.c
+++ b/cos_c_sdk/cos_transport.c
@@ -152,8 +152,8 @@ cos_http_transport_t *cos_curl_http_transport_create(cos_pool_t *p)
     cos_fstack_push(t->cleanup, t, func, 1);
     
     t->curl = cos_request_get();
-    func.func1 = (cos_func1_pt)request_release;
-    cos_fstack_push(t->cleanup, t->curl, func, 1);
+    func.func1 = (cos_func1_pt)request_release2;
+    cos_fstack_push(t->cleanup, t, func, 1);
 
     t->header_callback = cos_curl_default_header_callback;
     t->read_callback = cos_curl_default_read_callback;
@@ -487,7 +487,8 @@ int cos_curl_http_transport_perform(cos_http_transport_t *t_)
     code = curl_easy_perform(t->curl);
     t->controller->finish_time = apr_time_now();
     cos_move_transport_state(t, TRANS_STATE_DONE);
-
+    
+    t->curl_code = code;
     if ((code != CURLE_OK) && (t->controller->error_code == COSE_OK)) {
         ecode = cos_curl_code_to_status(code);
         if (ecode != COSE_OK) {
diff --git a/cos_c_sdk/cos_transport.h b/cos_c_sdk/cos_transport.h
index e29204d..682a933 100644
--- a/cos_c_sdk/cos_transport.h
+++ b/cos_c_sdk/cos_transport.h
@@ -144,6 +144,7 @@ struct cos_http_transport_s {
 struct cos_curl_http_transport_s {
     COS_HTTP_BASE_TRANSPORT_DEFINE
     CURL *curl;
+    CURLcode curl_code;
     char *url;
     struct curl_slist *headers;
     curl_read_callback header_callback;