diff --git a/runtime/include/sandbox.h b/runtime/include/sandbox.h
index 51c44d4..e274494 100644
--- a/runtime/include/sandbox.h
+++ b/runtime/include/sandbox.h
@@ -57,6 +57,7 @@ struct sandbox {
 	i32 retval;
 
 	struct io_handle handles[SBOX_MAX_OPEN];
+	struct sockaddr client; //client requesting connection!
 
 	char *read_buf;
 	ssize_t read_len, read_size;
@@ -69,7 +70,7 @@ struct sandbox {
 DEQUE_PROTOTYPE(sandbox, struct sandbox *);
 
 // a runtime resource, malloc on this!
-struct sandbox *sandbox_alloc(struct module *mod, char *args);
+struct sandbox *sandbox_alloc(struct module *mod, char *args, const struct sockaddr *addr);
 // should free stack and heap resources.. also any I/O handles.
 void sandbox_free(struct sandbox *sbox);
 
@@ -138,6 +139,7 @@ void *sandbox_run_func(void *data);
 struct sandbox *sandbox_schedule(void);
 void sandbox_block(void);
 void sandbox_wakeup(sandbox_t *sb);
+void sandbox_response(struct sandbox *sb);
 
 // should be the entry-point for each sandbox so it can do per-sandbox mem/etc init.
 // should have been called with stack allocated and sandbox_current() set!
diff --git a/runtime/include/types.h b/runtime/include/types.h
index 94cebd7..a1bc6b8 100644
--- a/runtime/include/types.h
+++ b/runtime/include/types.h
@@ -132,4 +132,6 @@ typedef enum {
 #define SBOX_NCORES (NCORES > 1 ? NCORES - 1 : NCORES)  // number of sandboxing threads
 #define SBOX_MAX_REQS (1<<19) //random!
 
+#define SBOX_RESP_STRSZ 32
+
 #endif /* SFRT_TYPES_H */
diff --git a/runtime/include/util.h b/runtime/include/util.h
index fd60138..265c109 100644
--- a/runtime/include/util.h
+++ b/runtime/include/util.h
@@ -5,8 +5,8 @@
 #include <module.h>
 
 /* perhaps move it to module.h or sandbox.h? */
-struct sandbox *util_parse_sandbox_string_custom(struct module *m, char *str);
-struct sandbox *util_parse_sandbox_string_json(struct module *m, char *str);
+struct sandbox *util_parse_sandbox_string_custom(struct module *m, char *str, const struct sockaddr *addr);
+struct sandbox *util_parse_sandbox_string_json(struct module *m, char *str, const struct sockaddr *addr);
 int util_parse_modules_file_json(char *filename);
 int util_parse_modules_file_custom(char *filename);
 
diff --git a/runtime/src/main.c b/runtime/src/main.c
index 5c7839a..c0e7003 100644
--- a/runtime/src/main.c
+++ b/runtime/src/main.c
@@ -107,7 +107,7 @@ main(int argc, char* argv[])
 	/* in current dir! */
 	struct module *m = module_alloc(argv[1], argv[1], 0, 0, 0, 0, 0, 0);
 	assert(m);
-	struct sandbox *s = sandbox_alloc(m, argv[1]);
+	struct sandbox *s = sandbox_alloc(m, argv[1], NULL);
 
 	exit(0);
 #endif
diff --git a/runtime/src/memory/64bit_nix.c b/runtime/src/memory/64bit_nix.c
index ba28790..1995364 100644
--- a/runtime/src/memory/64bit_nix.c
+++ b/runtime/src/memory/64bit_nix.c
@@ -38,8 +38,9 @@ free_linear_memory(void *base, u32 bound, u32 max)
 	struct sandbox *curr = sandbox_current();
 
 	assert(base && bound);
+
 	// cannot free currently executing sandbox's memory
-	assert(base != curr->linear_start || base != sandbox_lmbase);
+	assert(curr == NULL || base != curr->linear_start || base != sandbox_lmbase);
 
 	int ret = munmap(base, MAX_LINEAR_MEM);
 	if (ret) perror("munmap");
diff --git a/runtime/src/module.c b/runtime/src/module.c
index 6f0c9ba..5511366 100644
--- a/runtime/src/module.c
+++ b/runtime/src/module.c
@@ -39,8 +39,8 @@ module_on_recv(uv_udp_t *h, ssize_t nr, const uv_buf_t *rcvbuf, const struct soc
 
 	debuglog("MC:%s, %s\n", h->data, rcvbuf->base);
 	// invoke a function!
-	struct sandbox *s = util_parse_sandbox_string_json((struct module *)(h->data), rcvbuf->base);
-	//struct sandbox *s = util_parse_sandbox_string_custom((struct module *)(h->data), rcvbuf->base);
+	struct sandbox *s = util_parse_sandbox_string_json((struct module *)(h->data), rcvbuf->base, addr);
+	//struct sandbox *s = util_parse_sandbox_string_custom((struct module *)(h->data), rcvbuf->base, addr);
 	assert(s);
 
 done:
diff --git a/runtime/src/runtime.c b/runtime/src/runtime.c
index 2c34735..f231f18 100644
--- a/runtime/src/runtime.c
+++ b/runtime/src/runtime.c
@@ -12,9 +12,9 @@
 struct deque_sandbox *glb_dq;
 pthread_mutex_t glbq_mtx = PTHREAD_MUTEX_INITIALIZER;
 
-// per-thread (per-core) run and wait queues.. (using doubly-linked-lists)
+// per-thread (per-core) run and completion queue.. (using doubly-linked-lists)
 __thread static struct ps_list_head runq;
-__thread static struct ps_list_head waitq;
+__thread static struct ps_list_head endq;
 
 // current sandbox that is active..
 __thread sandbox_t *current_sandbox = NULL;
@@ -92,9 +92,24 @@ sandbox_schedule(void)
 	return s;
 }
 
+static inline void
+sandbox_local_free(unsigned int n)
+{
+	int i = 0;
+
+	while (i < n) {
+		i ++;
+		struct sandbox *s = ps_list_head_first_d(&endq, struct sandbox);
+		if (!s) break;
+		ps_list_rem_d(s);
+		sandbox_free(s);
+	}
+}
+
 struct sandbox *
 sandbox_schedule_uvio(void)
 {
+	sandbox_local_free(1);
 	if (!in_callback) sandbox_io_nowait();
 
 	assert(sandbox_current() == NULL);
@@ -154,13 +169,20 @@ sandbox_local_stop(struct sandbox *s)
 	ps_list_rem_d(s);
 }
 
+static inline void
+sandbox_local_end(struct sandbox *s)
+{
+	assert(ps_list_singleton_d(s));
+	ps_list_head_append_d(&endq, s);
+}
+
 void *
 sandbox_run_func(void *data)
 {
 	arch_context_init(&base_context, 0, 0);
 
 	ps_list_head_init(&runq);
-	ps_list_head_init(&waitq);
+	ps_list_head_init(&endq);
 	softint_off = 0;
 	next_context = NULL;
 #ifndef PREEMPT_DISABLE
@@ -207,13 +229,13 @@ sandbox_exit(void)
 	assert(curr);
 
 	fprintf(stderr, "(%d,%lu) %s: %p, %s exit\n", sched_getcpu(), pthread_self(), __func__, curr, curr->mod->name);
-	//printf("%s: disable\n", __func__);
 	softint_disable();
 	sandbox_local_stop(curr);
 	curr->state = SANDBOX_RETURNED;
-	// TODO: free resources here? or only from main?
+	// free resources from "main function execution", as stack still in use. 
+	sandbox_local_end(curr);
+	sandbox_response(curr);
 	struct sandbox *n = sandbox_schedule();
-        //printf("%s: enable\n", __func__);
 	softint_enable();
 	sandbox_switch(n);
 #else
diff --git a/runtime/src/sandbox.c b/runtime/src/sandbox.c
index c40e7f5..a208e70 100644
--- a/runtime/src/sandbox.c
+++ b/runtime/src/sandbox.c
@@ -68,7 +68,7 @@ sandbox_entry(void)
 }
 
 struct sandbox *
-sandbox_alloc(struct module *mod, char *args)
+sandbox_alloc(struct module *mod, char *args, const struct sockaddr *addr)
 {
 	if (!module_is_valid(mod)) return NULL;
 
@@ -91,6 +91,7 @@ sandbox_alloc(struct module *mod, char *args)
 	}
 	for (int i = 0; i < SBOX_MAX_OPEN; i++) sb->handles[i].fd = -1;
 	ps_list_init_d(sb);
+	if (addr) memcpy(&sb->client, addr, sizeof(struct sockaddr));
 
 	arch_context_init(&sb->ctxt, (reg_t)sandbox_entry, (reg_t)(sb->stack_start + sb->stack_size));
 	sandbox_run(sb);
@@ -98,20 +99,40 @@ sandbox_alloc(struct module *mod, char *args)
 	return sb;
 }
 
+void
+sandbox_response(struct sandbox *sb)
+{
+        // send response.
+#ifndef STANDALONE
+        int sock = -1;
+        char resp[SBOX_RESP_STRSZ] = { 0 };
+        int ret = uv_fileno((uv_handle_t *)&sb->mod->udpsrv, &sock);
+        assert(ret == 0);
+	// sends return value only for now!
+        sprintf(resp, "%d", sb->retval);
+	// using system call here because uv_udp_t is in the "module listener thread"'s loop, cannot access here. also dnot want to mess with cross-core/cross-thread uv loop states or structures.
+        ret = sendto(sock, resp, strlen(resp), 0, &sb->client, sizeof(struct sockaddr));
+        assert(ret == strlen(resp));
+#endif
+}
+
 void
 sandbox_free(struct sandbox *sb)
 {
+	int ret;
+
 	// you have to context switch away to free a sandbox.
 	if (!sb || sb == sandbox_current()) return;
 
 	// again sandbox should be done and waiting for the parent.
 	// TODO: this needs to be enhanced. you may be killing a sandbox when its in any other execution states.
 	if (sb->state != SANDBOX_RETURNED) return;
+
 	module_release(sb->mod);
 
 	free(sb->args);
 	// remove stack! and also heap!
-	int ret = munmap(sb->stack_start, sb->stack_size);
+	ret = munmap(sb->stack_start, sb->stack_size);
 	if (ret) perror("munmap");
 
 	// depending on the memory type
diff --git a/runtime/src/util.c b/runtime/src/util.c
index 797272d..d2bb687 100644
--- a/runtime/src/util.c
+++ b/runtime/src/util.c
@@ -152,7 +152,7 @@ parse_sandbox_file_custom(char *filename)
 			assert(0);
 		}
 
-		sb = sandbox_alloc(mod, args);
+		sb = sandbox_alloc(mod, args, NULL);
 		assert(sb);
 		total_boxes++;
 
@@ -168,7 +168,7 @@ next:
 
 
 struct sandbox *
-util_parse_sandbox_string_json(struct module *mod, char *str)
+util_parse_sandbox_string_json(struct module *mod, char *str, const struct sockaddr *addr)
 {
 	jsmn_parser sp;
 	jsmntok_t tk[JSON_ELE_MAX];
@@ -202,7 +202,7 @@ util_parse_sandbox_string_json(struct module *mod, char *str)
 				*(args + ((k - 1) * MOD_ARG_MAX_SZ) + g->end - g->start) = '\0';
 			}
 
-			struct sandbox *sb = sandbox_alloc(mod, args);
+			struct sandbox *sb = sandbox_alloc(mod, args, addr);
 			assert(sb);
 
 			return sb;
@@ -215,7 +215,7 @@ util_parse_sandbox_string_json(struct module *mod, char *str)
 }
 
 struct sandbox *
-util_parse_sandbox_string_custom(struct module *mod, char *str)
+util_parse_sandbox_string_custom(struct module *mod, char *str, const struct sockaddr *addr)
 {
 	char *tok = NULL, *src = str;
 
@@ -238,7 +238,7 @@ util_parse_sandbox_string_custom(struct module *mod, char *str)
 		assert(ntoks < MOD_MAX_ARGS);
 	}
 
-	struct sandbox *sb = sandbox_alloc(mod, args);
+	struct sandbox *sb = sandbox_alloc(mod, args, addr);
 	assert(sb);
 
 	return sb; 
diff --git a/runtime/tools/udpclient/Makefile b/runtime/tools/udpclient/Makefile
index ed447f5..22cee3f 100644
--- a/runtime/tools/udpclient/Makefile
+++ b/runtime/tools/udpclient/Makefile
@@ -1,6 +1,6 @@
 udp: udpclient.c
 	@echo "Compiling udpclient"
-	@gcc udpclient.c -o ../../bin/udpclient
+	@gcc udpclient.c -o ../../bin/udpclient -lpthread
 
 clean:
 	@echo "Cleaning up udpclient"
diff --git a/runtime/tools/udpclient/udpclient.c b/runtime/tools/udpclient/udpclient.c
index 9eb9cc8..f115053 100644
--- a/runtime/tools/udpclient/udpclient.c
+++ b/runtime/tools/udpclient/udpclient.c
@@ -10,12 +10,20 @@
 #include <malloc.h>
 #include <stdlib.h>
 #include <unistd.h>
+#include <pthread.h>
 
 #include <sys/time.h>
 #include <signal.h>
 #include <time.h>
 
 #define MSG_MAX 1024
+#define STR_MAX 32
+
+struct request {
+	char ip[32];
+	char port[32];
+	char msg[MSG_MAX];
+};
 
 static char *
 remove_spaces(char *str)
@@ -28,6 +36,41 @@ remove_spaces(char *str)
         return str;
 }
 
+void *
+send_fn(void *d)
+{
+	struct request *r = (struct request *)d;
+
+	char resp[STR_MAX] = { 0 };
+	int fd = -1;
+	struct sockaddr_in sa;
+
+	sa.sin_family      = AF_INET;
+	sa.sin_port        = htons(atoi(r->port));
+	sa.sin_addr.s_addr = inet_addr(r->ip);
+	if ((fd = socket(PF_INET, SOCK_DGRAM, 0)) == -1) {
+		perror("Establishing socket");
+		return NULL;
+	}
+
+	if (sendto(fd, r->msg, strlen(r->msg), 0, (struct sockaddr*)&sa, sizeof(sa)) < 0 &&
+			errno != EINTR) {
+		perror("sendto");
+		return NULL;
+	}
+
+	//todo: select rcv from!
+	int sa_len = sizeof(sa);
+	if (recvfrom(fd, resp, STR_MAX, 0, (struct sockaddr *)&sa, &sa_len) < 0) {
+		perror("recvfrom");
+	}
+	printf("Done[%s]!\n", resp);
+	close(fd);
+	free(r);
+
+	return NULL;
+}
+
 int main(int argc, char *argv[])
 {
 
@@ -47,10 +90,8 @@ int main(int argc, char *argv[])
 
 		char line[MSG_MAX] = { 0 };
 		while (fgets(line, MSG_MAX, f) != NULL) {
-			int fd = -1;
-			struct sockaddr_in sa;
 			char *msg = NULL, *tok, *src = line;
-			char ip[32] = { 0 }, port[32] = { 0 };
+			char ip[STR_MAX] = { 0 }, port[STR_MAX] = { 0 };
 			src = remove_spaces(src);
 
 			if (src[0] == ';') goto next;
@@ -67,32 +108,22 @@ int main(int argc, char *argv[])
 				printf("Exiting!\n");
 				exit(0);
 			} else if (i == 1) {
+				pthread_t t;
 				printf("Proceeding!\n");
+				struct request *r = (struct request *)malloc(sizeof(struct request));
+				strncpy(r->ip, ip, STR_MAX);
+				strncpy(r->port, port, STR_MAX);
+				strncpy(r->msg, msg, MSG_MAX);
+				pthread_create(&t, NULL, send_fn, r);
 			} else {
 				printf("Skipping!\n");
 				goto next;
 			}
 
-			sa.sin_family      = AF_INET;
-			sa.sin_port        = htons(atoi(port));
-			sa.sin_addr.s_addr = inet_addr(ip);
-			if ((fd = socket(PF_INET, SOCK_DGRAM, 0)) == -1) {
-				perror("Establishing socket");
-				return -1;
-			}
-
-			if (sendto(fd, msg, strlen(msg), 0, (struct sockaddr*)&sa, sizeof(sa)) < 0 &&
-					errno != EINTR) {
-				perror("sendto");
-				return -1;
-			}
-			printf("Done!\n");
 next:
 			memset(line, 0, MSG_MAX);
 			fflush(stdin);
 			fflush(stdout);
-
-			if (fd >= 0) close(fd);
 		}
 	}