diff --git a/src/pool/fifo.c b/src/pool/fifo.c
index 0f85fcda..7f852123 100644
--- a/src/pool/fifo.c
+++ b/src/pool/fifo.c
@@ -32,6 +32,9 @@ struct data {
     size_t num_threads;
     ABTI_thread *p_head;
     ABTI_thread *p_tail;
+    /* If the pool is empty, pop() accesses only is_empty so that pop() does not
+     * slow down a push operation. */
+    ABTD_atomic_int is_empty; /* Whether the pool is empty or not. */
 };
 typedef struct data data_t;
 
@@ -40,6 +43,28 @@ static inline data_t *pool_get_data_ptr(void *p_data)
     return (data_t *)p_data;
 }
 
+ABTU_ret_err static inline int spinlock_acquire_if_not_empty(data_t *p_data)
+{
+    if (ABTD_atomic_acquire_load_int(&p_data->is_empty)) {
+        /* The pool is empty.  Lock is not taken. */
+        return 1;
+    }
+    while (ABTD_spinlock_try_acquire(&p_data->mutex)) {
+        /* Lock acquisition failed.  Check the size. */
+        while (1) {
+            if (ABTD_atomic_acquire_load_int(&p_data->is_empty)) {
+                /* The pool becomes empty.  Lock is not taken. */
+                return 1;
+            } else if (!ABTD_spinlock_is_locked(&p_data->mutex)) {
+                /* Lock seems released.  Let's try to take a lock again. */
+                break;
+            }
+        }
+    }
+    /* Lock is acquired. */
+    return 0;
+}
+
 /* Obtain the FIFO pool definition according to the access type */
 ABTU_ret_err int ABTI_pool_get_fifo_def(ABT_pool_access access,
                                         ABTI_pool_def *p_def)
@@ -105,6 +130,7 @@ static int pool_init(ABT_pool pool, ABT_pool_config config)
     p_data->num_threads = 0;
     p_data->p_head = NULL;
     p_data->p_tail = NULL;
+    ABTD_atomic_relaxed_store_int(&p_data->is_empty, 1);
 
     p_pool->data = p_data;
 
@@ -141,6 +167,8 @@ static void pool_push_shared(ABT_pool pool, ABT_unit unit)
         p_thread->p_next = p_thread;
         p_data->p_head = p_thread;
         p_data->p_tail = p_thread;
+        p_data->num_threads = 1;
+        ABTD_atomic_release_store_int(&p_data->is_empty, 0);
     } else {
         ABTI_thread *p_head = p_data->p_head;
         ABTI_thread *p_tail = p_data->p_tail;
@@ -149,8 +177,8 @@ static void pool_push_shared(ABT_pool pool, ABT_unit unit)
         p_thread->p_prev = p_tail;
         p_thread->p_next = p_head;
         p_data->p_tail = p_thread;
+        p_data->num_threads++;
     }
-    p_data->num_threads++;
 
     ABTD_atomic_release_store_int(&p_thread->is_in_pool, 1);
     ABTD_spinlock_release(&p_data->mutex);
@@ -167,6 +195,8 @@ static void pool_push_private(ABT_pool pool, ABT_unit unit)
         p_thread->p_next = p_thread;
         p_data->p_head = p_thread;
         p_data->p_tail = p_thread;
+        p_data->num_threads = 1;
+        ABTD_atomic_release_store_int(&p_data->is_empty, 0);
     } else {
         ABTI_thread *p_head = p_data->p_head;
         ABTI_thread *p_tail = p_data->p_tail;
@@ -175,8 +205,8 @@ static void pool_push_private(ABT_pool pool, ABT_unit unit)
         p_thread->p_prev = p_tail;
         p_thread->p_next = p_head;
         p_data->p_tail = p_thread;
+        p_data->num_threads++;
     }
-    p_data->num_threads++;
 
     ABTD_atomic_release_store_int(&p_thread->is_in_pool, 1);
 }
@@ -186,120 +216,125 @@ static ABT_unit pool_pop_wait(ABT_pool pool, double time_secs)
     ABTI_pool *p_pool = ABTI_pool_get_ptr(pool);
     data_t *p_data = pool_get_data_ptr(p_pool->data);
     ABTI_thread *p_thread = NULL;
-    ABT_unit h_unit = ABT_UNIT_NULL;
 
     double time_start = 0.0;
 
-    do {
-        ABTD_spinlock_acquire(&p_data->mutex);
-        if (p_data->num_threads > 0) {
-            p_thread = p_data->p_head;
-            if (p_data->num_threads == 1) {
-                p_data->p_head = NULL;
-                p_data->p_tail = NULL;
-            } else {
-                p_thread->p_prev->p_next = p_thread->p_next;
-                p_thread->p_next->p_prev = p_thread->p_prev;
-                p_data->p_head = p_thread->p_next;
+    while (1) {
+        if (spinlock_acquire_if_not_empty(p_data) == 0) {
+            ABT_unit h_unit = ABT_UNIT_NULL;
+            if (p_data->num_threads > 0) {
+                p_thread = p_data->p_head;
+                if (p_data->num_threads == 1) {
+                    p_data->p_head = NULL;
+                    p_data->p_tail = NULL;
+                    p_data->num_threads = 0;
+                    ABTD_atomic_release_store_int(&p_data->is_empty, 1);
+                } else {
+                    p_thread->p_prev->p_next = p_thread->p_next;
+                    p_thread->p_next->p_prev = p_thread->p_prev;
+                    p_data->p_head = p_thread->p_next;
+                    p_data->num_threads--;
+                }
+
+                p_thread->p_prev = NULL;
+                p_thread->p_next = NULL;
+                ABTD_atomic_release_store_int(&p_thread->is_in_pool, 0);
+
+                h_unit = (ABT_unit)p_thread;
             }
-            p_data->num_threads--;
-
-            p_thread->p_prev = NULL;
-            p_thread->p_next = NULL;
-            ABTD_atomic_release_store_int(&p_thread->is_in_pool, 0);
-
-            h_unit = (ABT_unit)p_thread;
             ABTD_spinlock_release(&p_data->mutex);
+            if (h_unit != ABT_UNIT_NULL)
+                return h_unit;
+        }
+        if (time_start == 0.0) {
+            time_start = ABTI_get_wtime();
         } else {
-            ABTD_spinlock_release(&p_data->mutex);
-            if (time_start == 0.0) {
-                time_start = ABTI_get_wtime();
-            } else {
-                double elapsed = ABTI_get_wtime() - time_start;
-                if (elapsed > time_secs)
-                    break;
+            double elapsed = ABTI_get_wtime() - time_start;
+            if (elapsed > time_secs)
+                return ABT_UNIT_NULL;
+        }
+        /* Sleep. */
+        const int sleep_nsecs = 100;
+        struct timespec ts = { 0, sleep_nsecs };
+        nanosleep(&ts, NULL);
+    }
+}
+
+static ABT_unit pool_pop_timedwait(ABT_pool pool, double abstime_secs)
+{
+    ABTI_pool *p_pool = ABTI_pool_get_ptr(pool);
+    data_t *p_data = pool_get_data_ptr(p_pool->data);
+    ABTI_thread *p_thread = NULL;
+
+    while (1) {
+        if (spinlock_acquire_if_not_empty(p_data) == 0) {
+            ABT_unit h_unit = ABT_UNIT_NULL;
+            if (p_data->num_threads > 0) {
+                p_thread = p_data->p_head;
+                if (p_data->num_threads == 1) {
+                    p_data->p_head = NULL;
+                    p_data->p_tail = NULL;
+                    p_data->num_threads = 0;
+                    ABTD_atomic_release_store_int(&p_data->is_empty, 1);
+                } else {
+                    p_thread->p_prev->p_next = p_thread->p_next;
+                    p_thread->p_next->p_prev = p_thread->p_prev;
+                    p_data->p_head = p_thread->p_next;
+                    p_data->num_threads--;
+                }
+
+                p_thread->p_prev = NULL;
+                p_thread->p_next = NULL;
+                ABTD_atomic_release_store_int(&p_thread->is_in_pool, 0);
+
+                h_unit = (ABT_unit)p_thread;
             }
-            /* Sleep. */
-            const int sleep_nsecs = 100;
-            struct timespec ts = { 0, sleep_nsecs };
-            nanosleep(&ts, NULL);
+            ABTD_spinlock_release(&p_data->mutex);
+            if (h_unit != ABT_UNIT_NULL)
+                return h_unit;
         }
-    } while (h_unit == ABT_UNIT_NULL);
+        const int sleep_nsecs = 100;
+        struct timespec ts = { 0, sleep_nsecs };
+        nanosleep(&ts, NULL);
 
-    return h_unit;
+        if (ABTI_get_wtime() > abstime_secs)
+            return ABT_UNIT_NULL;
+    }
 }
 
-static ABT_unit pool_pop_timedwait(ABT_pool pool, double abstime_secs)
+static ABT_unit pool_pop_shared(ABT_pool pool)
 {
     ABTI_pool *p_pool = ABTI_pool_get_ptr(pool);
     data_t *p_data = pool_get_data_ptr(p_pool->data);
     ABTI_thread *p_thread = NULL;
-    ABT_unit h_unit = ABT_UNIT_NULL;
 
-    do {
-        ABTD_spinlock_acquire(&p_data->mutex);
+    if (spinlock_acquire_if_not_empty(p_data) == 0) {
+        ABT_unit h_unit = ABT_UNIT_NULL;
         if (p_data->num_threads > 0) {
             p_thread = p_data->p_head;
             if (p_data->num_threads == 1) {
                 p_data->p_head = NULL;
                 p_data->p_tail = NULL;
+                p_data->num_threads = 0;
+                ABTD_atomic_release_store_int(&p_data->is_empty, 1);
             } else {
                 p_thread->p_prev->p_next = p_thread->p_next;
                 p_thread->p_next->p_prev = p_thread->p_prev;
                 p_data->p_head = p_thread->p_next;
+                p_data->num_threads--;
             }
-            p_data->num_threads--;
 
             p_thread->p_prev = NULL;
             p_thread->p_next = NULL;
             ABTD_atomic_release_store_int(&p_thread->is_in_pool, 0);
 
             h_unit = (ABT_unit)p_thread;
-            ABTD_spinlock_release(&p_data->mutex);
-        } else {
-            ABTD_spinlock_release(&p_data->mutex);
-            /* Sleep. */
-            const int sleep_nsecs = 100;
-            struct timespec ts = { 0, sleep_nsecs };
-            nanosleep(&ts, NULL);
-
-            if (ABTI_get_wtime() > abstime_secs)
-                break;
-        }
-    } while (h_unit == ABT_UNIT_NULL);
-
-    return h_unit;
-}
-
-static ABT_unit pool_pop_shared(ABT_pool pool)
-{
-    ABTI_pool *p_pool = ABTI_pool_get_ptr(pool);
-    data_t *p_data = pool_get_data_ptr(p_pool->data);
-    ABTI_thread *p_thread = NULL;
-    ABT_unit h_unit = ABT_UNIT_NULL;
-
-    ABTD_spinlock_acquire(&p_data->mutex);
-    if (p_data->num_threads > 0) {
-        p_thread = p_data->p_head;
-        if (p_data->num_threads == 1) {
-            p_data->p_head = NULL;
-            p_data->p_tail = NULL;
-        } else {
-            p_thread->p_prev->p_next = p_thread->p_next;
-            p_thread->p_next->p_prev = p_thread->p_prev;
-            p_data->p_head = p_thread->p_next;
         }
-        p_data->num_threads--;
-
-        p_thread->p_prev = NULL;
-        p_thread->p_next = NULL;
-        ABTD_atomic_release_store_int(&p_thread->is_in_pool, 0);
-
-        h_unit = (ABT_unit)p_thread;
+        ABTD_spinlock_release(&p_data->mutex);
+        return h_unit;
+    } else {
+        return ABT_UNIT_NULL;
     }
-    ABTD_spinlock_release(&p_data->mutex);
-
-    return h_unit;
 }
 
 static ABT_unit pool_pop_private(ABT_pool pool)
@@ -307,19 +342,21 @@ static ABT_unit pool_pop_private(ABT_pool pool)
     ABTI_pool *p_pool = ABTI_pool_get_ptr(pool);
     data_t *p_data = pool_get_data_ptr(p_pool->data);
     ABTI_thread *p_thread = NULL;
-    ABT_unit h_unit = ABT_UNIT_NULL;
 
+    ABT_unit h_unit = ABT_UNIT_NULL;
     if (p_data->num_threads > 0) {
         p_thread = p_data->p_head;
         if (p_data->num_threads == 1) {
             p_data->p_head = NULL;
             p_data->p_tail = NULL;
+            p_data->num_threads = 0;
+            ABTD_atomic_relaxed_store_int(&p_data->is_empty, 1);
         } else {
             p_thread->p_prev->p_next = p_thread->p_next;
             p_thread->p_next->p_prev = p_thread->p_prev;
             p_data->p_head = p_thread->p_next;
+            p_data->num_threads--;
         }
-        p_data->num_threads--;
 
         p_thread->p_prev = NULL;
         p_thread->p_next = NULL;
@@ -327,7 +364,6 @@ static ABT_unit pool_pop_private(ABT_pool pool)
 
         h_unit = (ABT_unit)p_thread;
     }
-
     return h_unit;
 }
 
@@ -345,6 +381,8 @@ static int pool_remove_shared(ABT_pool pool, ABT_unit unit)
     if (p_data->num_threads == 1) {
         p_data->p_head = NULL;
         p_data->p_tail = NULL;
+        p_data->num_threads = 0;
+        ABTD_atomic_release_store_int(&p_data->is_empty, 1);
     } else {
         p_thread->p_prev->p_next = p_thread->p_next;
         p_thread->p_next->p_prev = p_thread->p_prev;
@@ -353,8 +391,8 @@ static int pool_remove_shared(ABT_pool pool, ABT_unit unit)
         } else if (p_thread == p_data->p_tail) {
             p_data->p_tail = p_thread->p_prev;
         }
+        p_data->num_threads--;
     }
-    p_data->num_threads--;
 
     ABTD_atomic_release_store_int(&p_thread->is_in_pool, 0);
     ABTD_spinlock_release(&p_data->mutex);
@@ -378,6 +416,8 @@ static int pool_remove_private(ABT_pool pool, ABT_unit unit)
     if (p_data->num_threads == 1) {
         p_data->p_head = NULL;
         p_data->p_tail = NULL;
+        p_data->num_threads = 0;
+        ABTD_atomic_relaxed_store_int(&p_data->is_empty, 1);
     } else {
         p_thread->p_prev->p_next = p_thread->p_next;
         p_thread->p_next->p_prev = p_thread->p_prev;
@@ -386,8 +426,8 @@ static int pool_remove_private(ABT_pool pool, ABT_unit unit)
         } else if (p_thread == p_data->p_tail) {
             p_data->p_tail = p_thread->p_prev;
         }
+        p_data->num_threads--;
     }
-    p_data->num_threads--;
 
     ABTD_atomic_release_store_int(&p_thread->is_in_pool, 0);
     p_thread->p_prev = NULL;
diff --git a/src/pool/fifo_wait.c b/src/pool/fifo_wait.c
index 7fd62c65..99b4acff 100644
--- a/src/pool/fifo_wait.c
+++ b/src/pool/fifo_wait.c
@@ -28,6 +28,7 @@ struct data {
     size_t num_threads;
     ABTI_thread *p_head;
     ABTI_thread *p_tail;
+    ABTD_atomic_int is_empty; /* Whether the pool is empty or not. */
 };
 typedef struct data data_t;
 
@@ -84,6 +85,7 @@ static int pool_init(ABT_pool pool, ABT_pool_config config)
     p_data->num_threads = 0;
     p_data->p_head = NULL;
     p_data->p_tail = NULL;
+    ABTD_atomic_relaxed_store_int(&p_data->is_empty, 1);
 
     p_pool->data = p_data;
 
@@ -122,6 +124,8 @@ static void pool_push(ABT_pool pool, ABT_unit unit)
         p_thread->p_next = p_thread;
         p_data->p_head = p_thread;
         p_data->p_tail = p_thread;
+        p_data->num_threads = 1;
+        ABTD_atomic_release_store_int(&p_data->is_empty, 0);
     } else {
         ABTI_thread *p_head = p_data->p_head;
         ABTI_thread *p_tail = p_data->p_tail;
@@ -130,8 +134,8 @@ static void pool_push(ABT_pool pool, ABT_unit unit)
         p_thread->p_prev = p_tail;
         p_thread->p_next = p_head;
         p_data->p_tail = p_thread;
+        p_data->num_threads++;
     }
-    p_data->num_threads++;
 
     ABTD_atomic_release_store_int(&p_thread->is_in_pool, 1);
     pthread_cond_signal(&p_data->cond);
@@ -179,12 +183,14 @@ static ABT_unit pool_pop_wait(ABT_pool pool, double time_secs)
         if (p_data->num_threads == 1) {
             p_data->p_head = NULL;
             p_data->p_tail = NULL;
+            p_data->num_threads = 0;
+            ABTD_atomic_release_store_int(&p_data->is_empty, 1);
         } else {
             p_thread->p_prev->p_next = p_thread->p_next;
             p_thread->p_next->p_prev = p_thread->p_prev;
             p_data->p_head = p_thread->p_next;
+            p_data->num_threads--;
         }
-        p_data->num_threads--;
 
         p_thread->p_prev = NULL;
         p_thread->p_next = NULL;
@@ -224,12 +230,14 @@ static ABT_unit pool_pop_timedwait(ABT_pool pool, double abstime_secs)
         if (p_data->num_threads == 1) {
             p_data->p_head = NULL;
             p_data->p_tail = NULL;
+            p_data->num_threads = 0;
+            ABTD_atomic_release_store_int(&p_data->is_empty, 1);
         } else {
             p_thread->p_prev->p_next = p_thread->p_next;
             p_thread->p_next->p_prev = p_thread->p_prev;
             p_data->p_head = p_thread->p_next;
+            p_data->num_threads--;
         }
-        p_data->num_threads--;
 
         p_thread->p_prev = NULL;
         p_thread->p_next = NULL;
@@ -247,30 +255,35 @@ static ABT_unit pool_pop(ABT_pool pool)
     ABTI_pool *p_pool = ABTI_pool_get_ptr(pool);
     data_t *p_data = pool_get_data_ptr(p_pool->data);
     ABTI_thread *p_thread = NULL;
-    ABT_unit h_unit = ABT_UNIT_NULL;
 
-    pthread_mutex_lock(&p_data->mutex);
-    if (p_data->num_threads > 0) {
-        p_thread = p_data->p_head;
-        if (p_data->num_threads == 1) {
-            p_data->p_head = NULL;
-            p_data->p_tail = NULL;
-        } else {
-            p_thread->p_prev->p_next = p_thread->p_next;
-            p_thread->p_next->p_prev = p_thread->p_prev;
-            p_data->p_head = p_thread->p_next;
+    if (ABTD_atomic_acquire_load_int(&p_data->is_empty) == 0) {
+        ABT_unit h_unit = ABT_UNIT_NULL;
+        pthread_mutex_lock(&p_data->mutex);
+        if (p_data->num_threads > 0) {
+            p_thread = p_data->p_head;
+            if (p_data->num_threads == 1) {
+                p_data->p_head = NULL;
+                p_data->p_tail = NULL;
+                p_data->num_threads = 0;
+                ABTD_atomic_release_store_int(&p_data->is_empty, 1);
+            } else {
+                p_thread->p_prev->p_next = p_thread->p_next;
+                p_thread->p_next->p_prev = p_thread->p_prev;
+                p_data->p_head = p_thread->p_next;
+                p_data->num_threads--;
+            }
+
+            p_thread->p_prev = NULL;
+            p_thread->p_next = NULL;
+            ABTD_atomic_release_store_int(&p_thread->is_in_pool, 0);
+
+            h_unit = (ABT_unit)p_thread;
         }
-        p_data->num_threads--;
-
-        p_thread->p_prev = NULL;
-        p_thread->p_next = NULL;
-        ABTD_atomic_release_store_int(&p_thread->is_in_pool, 0);
-
-        h_unit = (ABT_unit)p_thread;
+        pthread_mutex_unlock(&p_data->mutex);
+        return h_unit;
+    } else {
+        return ABT_UNIT_NULL;
     }
-    pthread_mutex_unlock(&p_data->mutex);
-
-    return h_unit;
 }
 
 static int pool_remove(ABT_pool pool, ABT_unit unit)
@@ -287,6 +300,8 @@ static int pool_remove(ABT_pool pool, ABT_unit unit)
     if (p_data->num_threads == 1) {
         p_data->p_head = NULL;
         p_data->p_tail = NULL;
+        p_data->num_threads = 0;
+        ABTD_atomic_release_store_int(&p_data->is_empty, 1);
     } else {
         p_thread->p_prev->p_next = p_thread->p_next;
         p_thread->p_next->p_prev = p_thread->p_prev;
@@ -295,8 +310,8 @@ static int pool_remove(ABT_pool pool, ABT_unit unit)
         } else if (p_thread == p_data->p_tail) {
             p_data->p_tail = p_thread->p_prev;
         }
+        p_data->num_threads--;
     }
-    p_data->num_threads--;
 
     ABTD_atomic_release_store_int(&p_thread->is_in_pool, 0);
     pthread_mutex_unlock(&p_data->mutex);