diff -urN rt_v42/img.c rt_v43/img.c
--- rt_v42/img.c	2018-05-29 21:41:28.000000000 +0900
+++ rt_v43/img.c	2018-05-30 21:34:32.000000000 +0900
@@ -122,15 +122,63 @@
 }
 
 static struct ut_cache_tbl cache_tbl = {
-	256, NULL, ut_cache_geti_int,
+	256, 0, NULL, ut_cache_geti_int,
 };
 
 struct img_col_cache_inf{
-	int w, h, frn;
+	int fn, w, h, frn;
 	double fps;
 	struct ut_cache_tbl img_tbl;
 };
 
+struct i_img{
+	int i;
+	unsigned char *img;
+};
+
+static struct img_col_cache_inf *
+get_inf(int fn)
+{
+	struct img_col_cache_inf *inf = ut_cache_get(&cache_tbl, &fn, sizeof(fn));
+	if(!inf){
+		int wh[2];
+
+		inf = malloc( sizeof(*inf) );
+		inf->fn = fn;
+		img_wh(fn, wh);
+		inf->w = wh[0];
+		inf->h = wh[1];
+		inf->frn = img_frn(fn);
+		inf->fps = img_fps(fn);
+
+		inf->img_tbl.n = 2; /* ! */
+		inf->img_tbl.chain_max_n = 1; /* ! */
+		inf->img_tbl.tbl = NULL;
+		inf->img_tbl.geti = ut_cache_geti_int;
+		ut_cache_alloc(&inf->img_tbl);
+
+		ut_cache_set(&cache_tbl, &inf->fn, sizeof(inf->fn), inf);
+	}
+	return inf;
+}
+
+static unsigned char *
+get_img(struct ut_cache_tbl *img_tbl, int i, int fn, double sec)
+{
+	struct i_img *del_v, *p = ut_cache_get(img_tbl, &i, sizeof(i));
+	if(!p){
+		p = malloc( sizeof(*p) );
+		p->i = i;
+		p->img = img_col_wh(fn, sec, NULL);
+		del_v = ut_cache_set(img_tbl, &p->i, sizeof(p->i), p);
+		if(del_v){
+			free(del_v->img);
+			free(del_v);
+		}
+	}
+	return p->img;
+}
+
 void
 rep_xy(int *px, int *py, int w, int h, int rep_x, int rep_y)
 {
@@ -145,11 +193,12 @@
 	*py = y;
 }
 
+pthread_mutex_t lock_inf = PTHREAD_MUTEX_INITIALIZER;
+pthread_mutex_t lock_img = PTHREAD_MUTEX_INITIALIZER;
+
 void
 img_col_cache(int fn, double sec, int x, int y, int *def_col, int rep_x, int rep_y, int *ret_col)
 {
-	void *k = &fn;
-	int ksz = sizeof(fn);
 	struct img_col_cache_inf *inf;
 	int i;
 	unsigned char *img;
@@ -158,24 +207,9 @@
 		ut_cache_alloc(&cache_tbl);
 	}
 
-	inf = ut_cache_get(&cache_tbl, k, ksz);
-	if(!inf){
-		int wh[2];
-
-		inf = malloc( sizeof(*inf) );
-		img_wh(fn, wh);
-		inf->w = wh[0];
-		inf->h = wh[1];
-		inf->frn = img_frn(fn);
-		inf->fps = img_fps(fn);
-
-		inf->img_tbl.n = inf->frn;
-		inf->img_tbl.tbl = NULL;
-		inf->img_tbl.geti = ut_cache_geti_int;
-		ut_cache_alloc(&inf->img_tbl);
-
-		ut_cache_set(&cache_tbl, k, ksz, inf);
-	}
+	pthread_mutex_lock(&lock_inf);
+	inf = get_inf(fn);
+	pthread_mutex_unlock(&lock_inf);
 
 	if(!in_wh(x, y, inf->w, inf->h)){
 		if(!rep_x && !rep_y){
@@ -189,11 +223,9 @@
 
 	i = (int)(inf->fps * sec) % inf->frn;
 
-	img = ut_cache_get(&inf->img_tbl, &i, sizeof(i));
-	if(!img){
-		img = img_col_wh(fn, sec, NULL);
-		ut_cache_set(&inf->img_tbl, &i, sizeof(i), img);
-	}
+	pthread_mutex_lock(&lock_img);
+	img = get_img(&inf->img_tbl, i, fn, sec);
+	pthread_mutex_unlock(&lock_img);
 	
 	i = (y * inf->w + x) * 3;
 	*ret_col++ = img[i++];
diff -urN rt_v42/ut.c rt_v43/ut.c
--- rt_v42/ut.c	2018-05-30 11:36:27.000000000 +0900
+++ rt_v43/ut.c	2018-05-30 20:09:11.000000000 +0900
@@ -108,9 +108,10 @@
 	return p ? p->v : NULL;
 }
 
-void
+void *
 ut_cache_set(struct ut_cache_tbl *t, void *k, int ksz, void *v)
 {
+	void *del_v = NULL;
 	int i = (*t->geti)(k, ksz) % t->n;
 	struct ut_cache *p = malloc( sizeof(*p) );
 	p->k = k;
@@ -118,17 +119,33 @@
 	p->v = v;
 	p->next = t->tbl[i];
 	t->tbl[i] = p;
+
+	if(t->chain_max_n > 0){
+		for(i=0; i<t->chain_max_n; i++){
+			if(!p){
+				break;
+			}
+			p = p->next;
+		}
+		if(p){ /* ! 1 */
+			del_v = ut_cache_del(t, p->k, p->ksz);
+		}
+	}
+	return del_v;
 }
 
-void
+void *
 ut_cache_del(struct ut_cache_tbl *t, void *k, int ksz)
 {
+	void *v = NULL;
 	struct ut_cache **pp = ut_cache_get_pptr(t, k, ksz);
 	if(pp){
 		struct ut_cache *p = *pp;
 		*pp = p->next;
+		v = p->v;
 		free(p);
 	}
+	return v;
 }
 
 void
@@ -140,7 +157,7 @@
 			struct ut_cache *p = t->tbl[i];
 			while(p){
 				struct ut_cache *n = p->next;
-				free(p);
+				free(p); /* ! p->v not free */
 				p = n;
 			}
 		}
diff -urN rt_v42/ut.h rt_v43/ut.h
--- rt_v42/ut.h	2018-05-30 11:35:55.000000000 +0900
+++ rt_v43/ut.h	2018-05-30 20:09:11.000000000 +0900
@@ -29,6 +29,7 @@
 
 struct ut_cache_tbl{
 	int n;
+	int chain_max_n; /* <= 0 : no limit */
 	struct ut_cache **tbl;
 	int (*geti)(void *k, int ksz);
 };
@@ -37,8 +38,8 @@
 struct ut_cache **ut_cache_get_pptr(struct ut_cache_tbl *t, void *k, int ksz);
 struct ut_cache *ut_cache_get_ptr(struct ut_cache_tbl *t, void *k, int ksz);
 void *ut_cache_get(struct ut_cache_tbl *t, void *k, int ksz);
-void ut_cache_set(struct ut_cache_tbl *t, void *k, int ksz, void *v);
-void ut_cache_del(struct ut_cache_tbl *t, void *k, int ksz);
+void *ut_cache_set(struct ut_cache_tbl *t, void *k, int ksz, void *v);
+void *ut_cache_del(struct ut_cache_tbl *t, void *k, int ksz);
 void ut_cache_free(struct ut_cache_tbl *t);
 
 int ut_cache_geti_int(void *k, int ksz);