diff --git a/display_bar.h b/display_bar.h
index c7fbddf..9488619 100644
--- a/display_bar.h
+++ b/display_bar.h
@@ -24,9 +24,13 @@ bool isatty_file(FILE * file);
 
 //After calling ready_progress_bar, you must use following functions on print.
 void myd_perror(const char * msg);
-//argument `line` is number of newline created by argument `msg`.
+/*argument `line` is number of newline created by argument `msg`.
+* thread-safe
+*/
 int myd_vfprintf(int line,FILE * f,const char * msg,va_list arg);
-//argument `line` is number of newline created by argument `msg`.
+/*argument `line` is number of newline created by argument `msg`.
+* thread-safe
+*/
 int myd_fprintf(int line,FILE * f,const char * msg, ...);
 
 
diff --git a/server.c b/server.c
index b7ca317..cad3836 100644
--- a/server.c
+++ b/server.c
@@ -250,6 +250,9 @@ int send_response(int sock,int fd, uint8_t * buf, size_t bufsize){
 #endif
     return 0;
 }
+/** print help message
+ * arg `n`: executable name
+ */
 const char * help(const char * n){
     const char * msg = "USASE : %s [Option] ...\n"
     "Options and arguments: \n"
@@ -259,7 +262,8 @@ const char * help(const char * n){
     printf(msg,n);
     return msg;
 }
-/** return 0 ok. otherwise invalid format*/
+/** parse arguments. 
+ * if return 0, success. otherwise arguments are invalid format.*/
 int parse_args(int argc,const char * argv[] , in_port_t * port){
     int pos = 1;
     const char * opt;
@@ -274,7 +278,7 @@ int parse_args(int argc,const char * argv[] , in_port_t * port){
                 const char * value = argv[pos++];
                 *port = atoi(value);
                 if (port == 0){ // either not number or zero 
-                    fprintf(stderr,"argument is either not number or zero\n");
+                    fprintf(stderr,"port argument is either not number or zero\n");
                     return 2;
                 }
             }
@@ -302,11 +306,10 @@ typedef struct SharedState{
     //empty if less than 0
     queue_struct(int,WORK_QUEUE_SIZE) socks;
     #ifdef USE_TRACE
-    queue_struct(struct timespec,WORK_QUEUE_SIZE) trace_timer;
+    queue_struct(struct timespec,WORK_QUEUE_SIZE) trace_timer;  //sock timer for TRACE
     #endif
-    pthread_mutex_t sock_mutex;
+    pthread_mutex_t sock_mutex;//mutex for queue
     pthread_cond_t ready;
-    //int progress[MAX_THREAD_NUMBER];
 } shared_state_t;
 
 void init_shared_state(shared_state_t * state) {
@@ -437,6 +440,7 @@ int main(int argc, const char *argv[]){
     int bufsize;
     int i = 0;
     in_port_t binding_port_number = SERVER_PORT;
+    //parse argument
     if (argc > 1){
         int d = parse_args(argc,argv,&binding_port_number);
         if(d != 0 ) return d;
@@ -446,6 +450,7 @@ int main(int argc, const char *argv[]){
     #ifdef USE_TRACE
     report_resolution();
     #endif
+    //create socket
     sock = socket(AF_INET,SOCK_STREAM,0);
     atexit(safe_exit);
     if(sock < 0){
@@ -460,6 +465,7 @@ int main(int argc, const char *argv[]){
     }
     bufsize = getBufferSizeFrom(sock);
 #ifndef USE_NO_QUEUE
+    //initialize shared_state and create worker thread.
     init_shared_state(&globalState);
     for (i = 0; i < MAX_THREAD_NUMBER; i++) {
         worker_argument_t * args = create_worker_argument(i,bufsize);
@@ -470,6 +476,7 @@ int main(int argc, const char *argv[]){
         pthread_create(&worker_threads[i],NULL,worker_proc,args);
     }
 #endif
+    //bind socket.
     addr.sin_addr.s_addr = htonl(INADDR_ANY); /*0.0.0.0 모든 네트워크 인터페이스에 묶임.*/
     addr.sin_family = AF_INET;
     addr.sin_port = htons(binding_port_number);
@@ -504,11 +511,11 @@ int main(int argc, const char *argv[]){
             if (queue_isfull(&globalState.socks)){
                 pthread_mutex_unlock(&globalState.sock_mutex);
     #ifdef _GNU_SOURCE
-                pthread_yield();
+                pthread_yield();//yield for other thread and process.
     #else
-                usleep(400);
+                usleep(400); //alternative for `pthread_yield`, but this could occur 'busy waiting' by implementation.
     #endif    
-                continue;
+                continue;//retry to enqueue `csock`.
             }
             else {
                 enqueue(&globalState.socks,csock);
diff --git a/socket_wrapper.h b/socket_wrapper.h
index e8fa0bd..1b34570 100644
--- a/socket_wrapper.h
+++ b/socket_wrapper.h
@@ -25,15 +25,11 @@ struct ReadOp{
 struct TransferResult{
     int16_t res;
     int16_t error_msg_size;
-    int64_t file_size; /**/
+    int64_t file_size;
     int32_t err_number; /*errno*/
 };
 #pragma pack(pop)
 
-#ifdef USE_GETADDRINFO
-
-#endif
-
 /**
  * find buffer size from sock
  * thread safe