diff --git a/include/pocketpy/common/threads.h b/include/pocketpy/common/threads.h
index a84731bd..4be7458b 100644
--- a/include/pocketpy/common/threads.h
+++ b/include/pocketpy/common/threads.h
@@ -44,10 +44,12 @@ void c11_cond__broadcast(c11_cond_t* cond);
 
 typedef void (*c11_thrdpool_func_t)(void* arg);
 
+
 typedef struct c11_thrdpool_tasks {
     c11_thrdpool_func_t func;
     void** args;
     int length;
+    int sync_val;
     atomic_int current_index;
     atomic_int completed_count;
 } c11_thrdpool_tasks;
@@ -56,8 +58,6 @@ typedef struct c11_thrdpool_worker {
     c11_mutex_t* p_mutex;
     c11_cond_t* p_cond;
     c11_thrdpool_tasks* p_tasks;
-
-    bool should_exit;
     c11_thrd_t thread;
 } c11_thrdpool_worker;
 
@@ -66,8 +66,8 @@ typedef struct c11_thrdpool {
     c11_thrdpool_worker* workers;
     atomic_bool is_busy;
     
-    c11_mutex_t workers_mutex;
-    c11_cond_t workers_cond;
+    c11_mutex_t workers_mutex[2];
+    c11_cond_t workers_cond[2];
     c11_thrdpool_tasks tasks;
 } c11_thrdpool;
 
diff --git a/src/common/threads.c b/src/common/threads.c
index 95bfc4c5..2b1e2a73 100644
--- a/src/common/threads.c
+++ b/src/common/threads.c
@@ -71,23 +71,30 @@ void c11_cond__broadcast(c11_cond_t* cond) { cnd_broadcast(cond); }
 
 #endif
 
+static bool _thrdpool_worker_sync(c11_mutex_t* p_mutex,
+                                  c11_cond_t* p_cond,
+                                  int* p_sync_val,
+                                  int expected_sync_val) {
+    int index = (int)expected_sync_val;
+    c11_mutex__lock(p_mutex + index);
+    while(true) {
+        c11_cond__wait(p_cond + index, p_mutex + index);
+        if(*p_sync_val == -1) return false;
+        if(*p_sync_val == expected_sync_val) break;
+    }
+    c11_mutex__unlock(p_mutex + index);
+    return true;
+}
+
 static c11_thrd_retval_t _thrdpool_worker(void* arg) {
     c11_thrdpool_worker* p_worker = (c11_thrdpool_worker*)arg;
+    c11_thrdpool_tasks* p_tasks = p_worker->p_tasks;
 
     while(true) {
-        // wait for tasks
-        c11_mutex__lock(p_worker->p_mutex);
-        while(!p_worker->p_tasks && !p_worker->should_exit) {
-            c11_cond__wait(p_worker->p_cond, p_worker->p_mutex);
-        }
-        if(p_worker->should_exit) {
-            c11_mutex__unlock(p_worker->p_mutex);
+        if(!_thrdpool_worker_sync(p_worker->p_mutex, p_worker->p_cond, &p_tasks->sync_val, 0)) {
             break;
         }
 
-        c11_thrdpool_tasks* p_tasks = p_worker->p_tasks;
-        c11_mutex__unlock(p_worker->p_mutex);
-
         // execute tasks
         while(true) {
             int arg_index = atomic_fetch_add(&p_tasks->current_index, 1);
@@ -96,12 +103,13 @@ static c11_thrd_retval_t _thrdpool_worker(void* arg) {
                 p_tasks->func(arg);
                 atomic_fetch_add(&p_tasks->completed_count, 1);
             } else {
-                c11_mutex__lock(p_worker->p_mutex);
-                p_worker->p_tasks = NULL;
-                c11_mutex__unlock(p_worker->p_mutex);
                 break;
             }
         }
+
+        if(!_thrdpool_worker_sync(p_worker->p_mutex, p_worker->p_cond, &p_tasks->sync_val, 1)) {
+            break;
+        }
     }
     return 0;
 }
@@ -111,28 +119,30 @@ void c11_thrdpool__ctor(c11_thrdpool* pool, int length) {
     pool->workers = PK_MALLOC(sizeof(c11_thrdpool_worker) * length);
     atomic_store(&pool->is_busy, false);
 
-    c11_mutex__ctor(&pool->workers_mutex);
-    c11_cond__ctor(&pool->workers_cond);
+    c11_mutex__ctor(&pool->workers_mutex[0]);
+    c11_mutex__ctor(&pool->workers_mutex[1]);
+    c11_cond__ctor(&pool->workers_cond[0]);
+    c11_cond__ctor(&pool->workers_cond[1]);
 
     for(int i = 0; i < length; i++) {
         c11_thrdpool_worker* p_worker = &pool->workers[i];
-
-        p_worker->p_mutex = &pool->workers_mutex;
-        p_worker->p_cond = &pool->workers_cond;
+        p_worker->p_mutex = pool->workers_mutex;
+        p_worker->p_cond = pool->workers_cond;
         p_worker->p_tasks = &pool->tasks;
-        p_worker->should_exit = false;
-
         bool ok = c11_thrd__create(&p_worker->thread, _thrdpool_worker, p_worker);
         c11__rtassert(ok);
     }
 }
 
 void c11_thrdpool__dtor(c11_thrdpool* pool) {
-    for(int i = 0; i < pool->length; i++) {
-        c11_thrdpool_worker* p_worker = &pool->workers[i];
-        atomic_store(&p_worker->should_exit, true);
-    }
-    c11_cond__broadcast(&pool->workers_cond);
+    c11_mutex__lock(&pool->workers_mutex[0]);
+    c11_mutex__lock(&pool->workers_mutex[1]);
+    pool->tasks.sync_val = -1;
+    c11_mutex__unlock(&pool->workers_mutex[1]);
+    c11_mutex__unlock(&pool->workers_mutex[0]);
+    
+    c11_cond__broadcast(&pool->workers_cond[0]);
+    c11_cond__broadcast(&pool->workers_cond[1]);
 
     for(int i = 0; i < pool->length; i++) {
         c11_thrdpool_worker* p_worker = &pool->workers[i];
@@ -140,8 +150,10 @@ void c11_thrdpool__dtor(c11_thrdpool* pool) {
     }
 
     PK_FREE(pool->workers);
-    c11_mutex__dtor(&pool->workers_mutex);
-    c11_cond__dtor(&pool->workers_cond);
+    c11_mutex__dtor(&pool->workers_mutex[0]);
+    c11_mutex__dtor(&pool->workers_mutex[1]);
+    c11_cond__dtor(&pool->workers_cond[0]);
+    c11_cond__dtor(&pool->workers_cond[1]);
 }
 
 void c11_thrdpool__map(c11_thrdpool* pool, c11_thrdpool_func_t func, void** args, int num_tasks) {
@@ -152,19 +164,25 @@ void c11_thrdpool__map(c11_thrdpool* pool, c11_thrdpool_func_t func, void** args
         c11_thrd__yield();
     }
     // assign tasks
-    c11_mutex__lock(&pool->workers_mutex);
+    c11_mutex__lock(&pool->workers_mutex[0]);
     pool->tasks.func = func;
     pool->tasks.args = args;
     pool->tasks.length = num_tasks;
+    pool->tasks.sync_val = 0;
     atomic_store(&pool->tasks.current_index, 0);
     atomic_store(&pool->tasks.completed_count, 0);
-    // wake up all workers
-    c11_cond__broadcast(&pool->workers_cond);
-    c11_mutex__unlock(&pool->workers_mutex);
+    c11_cond__broadcast(&pool->workers_cond[0]);
+    c11_mutex__unlock(&pool->workers_mutex[0]);
     // wait for complete
     while(atomic_load(&pool->tasks.completed_count) < num_tasks) {
         c11_thrd__yield();
     }
+    // notify workers to proceed
+    c11_mutex__lock(&pool->workers_mutex[1]);
+    pool->tasks.sync_val = 1;
+    c11_cond__broadcast(&pool->workers_cond[1]);
+    c11_mutex__unlock(&pool->workers_mutex[1]);
+    // mark as not busy
     atomic_store(&pool->is_busy, false);
 }