diff --git a/src/bthread/bthread.h b/src/bthread/bthread.h
index 008beffadc..e0d95892c7 100644
--- a/src/bthread/bthread.h
+++ b/src/bthread/bthread.h
@@ -249,6 +249,7 @@ extern int bthread_cond_timedwait(
 
 // Initialize read-write lock `rwlock' using attributes `attr', or use
 // the default values if later is nullptr.
+// NOTE: attr is not used in the current implementation.
 extern int bthread_rwlock_init(bthread_rwlock_t* __restrict rwlock,
                                const bthread_rwlockattr_t* __restrict attr);
 
@@ -281,20 +282,20 @@ extern int bthread_rwlock_unlock(bthread_rwlock_t* rwlock);
 // ---------------------------------------------------
 // Functions for handling read-write lock attributes.
 // ---------------------------------------------------
+// TODO: Implement these APIs. bthread_rwlock_init() currently ignores attr.
 
 // Initialize attribute object `attr' with default values.
-extern int bthread_rwlockattr_init(bthread_rwlockattr_t* attr);
+// extern int bthread_rwlockattr_init(bthread_rwlockattr_t* attr);
 
 // Destroy attribute object `attr'.
-extern int bthread_rwlockattr_destroy(bthread_rwlockattr_t* attr);
+// extern int bthread_rwlockattr_destroy(bthread_rwlockattr_t* attr);
 
 // Return current setting of reader/writer preference.
-extern int bthread_rwlockattr_getkind_np(const bthread_rwlockattr_t* attr,
-                                         int* pref);
+// extern int bthread_rwlockattr_getkind_np(const bthread_rwlockattr_t* attr,
+//                                          int* pref);
 
 // Set reader/write preference.
-extern int bthread_rwlockattr_setkind_np(bthread_rwlockattr_t* attr,
-                                         int pref);
+// extern int bthread_rwlockattr_setkind_np(bthread_rwlockattr_t* attr, int pref);
 
 // -------------------------------------------
 // Functions for handling semaphore.
@@ -343,18 +344,18 @@ extern int bthread_sem_post(bthread_sem_t* sem);
 // Return 0 on success, errno otherwise.
 extern int bthread_sem_post_n(bthread_sem_t* sem, size_t n);
 
-
 // ----------------------------------------------------------------------
 // Functions for handling barrier which is a new feature in 1003.1j-2000.
 // ----------------------------------------------------------------------
+// TODO: Implement bthread barrier.
 
-extern int bthread_barrier_init(bthread_barrier_t* __restrict barrier,
-                                const bthread_barrierattr_t* __restrict attr,
-                                unsigned count);
+// extern int bthread_barrier_init(bthread_barrier_t* __restrict barrier,
+//                                 const bthread_barrierattr_t* __restrict attr,
+//                                 unsigned count);
 
-extern int bthread_barrier_destroy(bthread_barrier_t* barrier);
+// extern int bthread_barrier_destroy(bthread_barrier_t* barrier);
 
-extern int bthread_barrier_wait(bthread_barrier_t* barrier);
+// extern int bthread_barrier_wait(bthread_barrier_t* barrier);
 
 // ---------------------------------------------------------------------
 // Functions for handling thread-specific data. 
diff --git a/src/bthread/types.h b/src/bthread/types.h
index 1fb7a5d0cb..14411e5e06 100644
--- a/src/bthread/types.h
+++ b/src/bthread/types.h
@@ -247,15 +247,18 @@ typedef struct bthread_rwlock_t {
     unsigned* lock_word;
 } bthread_rwlock_t;
 
+// Kept for ABI compatibility with bthread_rwlock_init(). Pass nullptr
+// for the default. See TODO on bthread_rwlockattr_* in bthread.h.
 typedef struct {
 } bthread_rwlockattr_t;
 
-typedef struct {
-    unsigned int count;
-} bthread_barrier_t;
-
-typedef struct {
-} bthread_barrierattr_t;
+// TODO: Implement bthread barrier.
+// typedef struct {
+//     unsigned int count;
+// } bthread_barrier_t;
+//
+// typedef struct {
+// } bthread_barrierattr_t;
 
 #if defined(__cplusplus)
 class bthread_once_t;