diff --git a/httpd.c b/httpd.c
index c5e8ae3..cb386e7 100644
--- a/httpd.c
+++ b/httpd.c
@@ -95,7 +95,8 @@ void stop_serve(int dummy) {
 	ERR_remove_state(0);
 	ERR_free_strings();
 #endif
-	close(server_sock);
+	if(server_sock != -1)
+		close(server_sock);
 	sigprocmask(SIG_UNBLOCK, &mask, NULL); 
 }
 int main(int argc, char* argv[])
@@ -130,23 +131,28 @@ int main(int argc, char* argv[])
 	LOG("httpd running on port %d\n", port);
 	// default to 4 workers
 	antd_scheduler_init(&scheduler, config()->n_workers);
-    set_nonblock(server_sock);
-	int stat = 0;
-	struct timespec ts_sleep;
+	// use blocking server_sock
+	// make the scheduler wait for event on another thread
+	// this allow to ged rid of high cpu usage on
+	// endless loop without doing anything
+    // set_nonblock(server_sock);
+	pthread_t scheduler_th;
+	if (pthread_create(&scheduler_th, NULL,(void *(*)(void *))antd_wait, (void*)&scheduler) != 0)
+	{
+		perror("pthread_create: cannot create worker\n");
+		stop_serve(0);
+		exit(1);
+	}
+	else
+	{
+		// reclaim data when exit
+		pthread_detach(scheduler_th);
+	}
 	while (scheduler.status)
 	{
-		stat = antd_task_schedule(&scheduler);
 		client_sock = accept(server_sock,(struct sockaddr *)&client_name,&client_name_len);
 		if (client_sock == -1)
 		{
-			if(!stat)
-			{
-				// sleep for 500usec if 
-				// there is nothing todo
-            	ts_sleep.tv_sec = 0;
-            	ts_sleep.tv_nsec = 500000;
-            	nanosleep(&ts_sleep, NULL);
-			}
 			continue;
 		}
 		antd_client_t* client = (antd_client_t*)malloc(sizeof(antd_client_t));
diff --git a/libs/scheduler.c b/libs/scheduler.c
index a8c6e91..97bc7cc 100644
--- a/libs/scheduler.c
+++ b/libs/scheduler.c
@@ -22,13 +22,20 @@ static void enqueue(antd_task_queue_t* q, antd_task_t* task)
 static void stop(antd_scheduler_t* scheduler)
 {
     scheduler->status = 0;
+    // unlock all idle workers if any
     for (int i = 0; i < scheduler->n_workers; i++)
-        pthread_join(scheduler->workers[i], NULL);
+        sem_post(&scheduler->worker_sem);
+    sem_post(&scheduler->scheduler_sem);
+    for (int i = 0; i < scheduler->n_workers; i++)
+        if(scheduler->workers[i].id != -1)
+            pthread_join(scheduler->workers[i].tid, NULL);
     if(scheduler->workers) free(scheduler->workers);
     // destroy all the mutex
     pthread_mutex_destroy(&scheduler->scheduler_lock);
     pthread_mutex_destroy(&scheduler->worker_lock);
     pthread_mutex_destroy(&scheduler->pending_lock);
+    sem_destroy(&scheduler->scheduler_sem);
+    sem_destroy(&scheduler->worker_sem);
 }
 
 static antd_task_item_t dequeue(antd_task_queue_t* q)
@@ -108,8 +115,9 @@ static void destroy_queue(antd_task_queue_t q)
         free(curr);
     }
 }
-static void work(antd_scheduler_t* scheduler)
+static void work(antd_worker_t* worker)
 {
+    antd_scheduler_t* scheduler = (antd_scheduler_t*) worker->manager;
     while(scheduler->status)
     {
         antd_task_item_t it;
@@ -118,16 +126,18 @@ static void work(antd_scheduler_t* scheduler)
         pthread_mutex_unlock(&scheduler->worker_lock);
         // execute the task
         //LOG("task executed by worker %d\n", worker->pid);
-        // no task to execute, just sleep for 500usec
+        // no task to execute, just sleep wait
         if(!it)
         {
-            struct timespec ts_sleep;
-            ts_sleep.tv_sec = 0;
-            ts_sleep.tv_nsec = 500000;
-            nanosleep(&ts_sleep, NULL);
-            continue;
+            //LOG("Worker %d goes to idle state\n", worker->id);
+            sem_wait(&scheduler->worker_sem);
         }
-        antd_execute_task(scheduler, it);
+        else
+        {
+            //LOG("task executed by worker %d\n", worker->id);
+            antd_execute_task(scheduler, it);
+        }
+        
     }
 }
 
@@ -142,7 +152,18 @@ void antd_scheduler_init(antd_scheduler_t* scheduler, int n)
     scheduler->status = 1;
     scheduler->workers_queue = NULL;
     scheduler->pending_task = 0 ;
-    // init lock
+    // init semaphore
+    if (sem_init(&scheduler->scheduler_sem, 0, 0) == -1)
+    {
+        LOG("Cannot init semaphore for scheduler\n");
+        exit(-1);
+    }
+    if (sem_init(&scheduler->worker_sem, 0, 0) == -1)
+    {
+        LOG("Cannot init semaphore for workers\n");
+        exit(-1);
+    }
+    // init lock 
     pthread_mutex_init(&scheduler->scheduler_lock,NULL);
     pthread_mutex_init(&scheduler->worker_lock, NULL);
     pthread_mutex_init(&scheduler->pending_lock, NULL);
@@ -150,7 +171,7 @@ void antd_scheduler_init(antd_scheduler_t* scheduler, int n)
     // create scheduler.workers
     if(n > 0)
     {
-        scheduler->workers = (pthread_t*)malloc(n*(sizeof(pthread_t)));
+        scheduler->workers = (antd_worker_t*)malloc(n*(sizeof(antd_worker_t)));
         if(!scheduler->workers)
         {
             LOG("Cannot allocate memory for worker\n");
@@ -158,10 +179,16 @@ void antd_scheduler_init(antd_scheduler_t* scheduler, int n)
         }
         for(int i = 0; i < scheduler->n_workers;i++)
         {
-            if (pthread_create(&scheduler->workers[i], NULL,(void *(*)(void *))work, (void*)scheduler) != 0)
+            scheduler->workers[i].id = -1;
+            scheduler->workers[i].manager = (void*)scheduler;
+            if (pthread_create(&scheduler->workers[i].tid, NULL,(void *(*)(void *))work, (void*)&scheduler->workers[i]) != 0)
             {
                 perror("pthread_create: cannot create worker\n");
             }
+            else
+            {
+                scheduler->workers[i].id = i;
+            }
         }
     }
     LOG("Antd scheduler initialized with %d worker\n", scheduler->n_workers);
@@ -211,6 +238,8 @@ void antd_add_task(antd_scheduler_t* scheduler, antd_task_t* task)
     pthread_mutex_lock(&scheduler->pending_lock);
     scheduler->pending_task++;
     pthread_mutex_unlock(&scheduler->pending_lock);
+    // wake up the scheduler if idle
+    sem_post(&scheduler->scheduler_sem);
 }
 
 
@@ -283,7 +312,7 @@ int antd_task_schedule(antd_scheduler_t* scheduler)
         return 0;
     }
     // has the task now
-    // check the type of tas
+    // check the type of task
     if(it->task->type == LIGHT || scheduler->n_workers <= 0)
     {
         // do it by myself
@@ -296,7 +325,22 @@ int antd_task_schedule(antd_scheduler_t* scheduler)
         pthread_mutex_lock(&scheduler->worker_lock);
         enqueue(&scheduler->workers_queue, it->task);
         pthread_mutex_unlock(&scheduler->worker_lock);
+        // wake up idle worker
+        sem_post(&scheduler->worker_sem);
         free(it);
     }
     return 1;
+}
+void antd_wait(antd_scheduler_t* scheduler)
+{
+    int stat;
+    while(scheduler->status)
+    {
+        stat = antd_task_schedule(scheduler);
+        if(!stat)
+        {
+            // no task found, go to idle state
+            sem_wait(&scheduler->scheduler_sem);
+        }
+    }
 }
\ No newline at end of file
diff --git a/libs/scheduler.h b/libs/scheduler.h
index 349c1f2..4b3cc55 100644
--- a/libs/scheduler.h
+++ b/libs/scheduler.h
@@ -3,6 +3,7 @@
 
 #include "utils.h"
 #include <pthread.h>
+#include <semaphore.h>
 
 #define N_PRIORITY 10
 #define NORMAL_PRIORITY ((int)((N_PRIORITY - 1) / 2))
@@ -52,13 +53,24 @@ typedef struct __task_item_t{
 typedef antd_task_item_t antd_task_queue_t;
 
 typedef struct {
+    int id;
+    pthread_t tid;
+    void* manager;
+} antd_worker_t;
+
+typedef struct {
+    // data lock
     pthread_mutex_t scheduler_lock;
     pthread_mutex_t worker_lock;
     pthread_mutex_t pending_lock;
+    // event handle
+    sem_t scheduler_sem;
+    sem_t worker_sem;
+    // worker and data
     antd_task_queue_t task_queue[N_PRIORITY];
     antd_task_queue_t workers_queue;
     uint8_t status; // 0 stop, 1 working
-    pthread_t* workers;
+    antd_worker_t* workers;
     int n_workers;
     int pending_task;
 } antd_scheduler_t;
@@ -93,4 +105,8 @@ int antd_scheduler_busy(antd_scheduler_t*);
     schedule a task
 */
 int antd_task_schedule(antd_scheduler_t*);
+/*
+wait for event
+*/
+void antd_wait(antd_scheduler_t*);
 #endif
\ No newline at end of file