diff --git a/moo/kernel/Process.moo b/moo/kernel/Process.moo
index b9dc5c9..a8d33f0 100644
--- a/moo/kernel/Process.moo
+++ b/moo/kernel/Process.moo
@@ -129,64 +129,6 @@ TODO: how to prohibit wait and signal???
 		^block ensure: [ self signal ]
 	}
 }
-
- 
-(*
- xxx := Semaphore new.
- xxx on: #signal do: [ ].
- 
- 
- ========= CASE 1 ====================
- sg := SemaphoreGroup with (xxx, yyy, zzz).
- System signal: xxx onInput: aaa.
- System signal: yyy onInput: bbb.
- System signal: zzz onOutput: ccc.
- 
- while (true)
- {
-	sem := sg wait.
-	if (sem == xxx)
-	{
-		
-	}
-	elsif (sem == yyy)
-	{
-	}
-	elsif (sem == zzz)
-	{
-	}.
- }
- 
- ============ CASE 2====================
- ### ASSOCIATE CALLBACK WITH SEMAPHORE.
- 
- sg := SemaphoreGroup with (xxx, yyy, zzz).
- 
- oldaction := xxx signalAction: [ ... ].  ### similar interface like unix system call signal()????   method signalAction: block {} , method signalAction { ^self.signalAction }
- yyy signalAction: [ ... ].
- zzz signalAction: [ ... ].
- 
- System signal: xxx onInput: aaa.
- System signal: yyy onInput: bbb.
- System signal: zzz onOutput: ccc.
- 
- 
- while (true)
- {
-	sem := sg wait. ### the action associated with the semaphore must get executed.  => wait may be a primitive. the primitive handler may return failure... if so, the actual primitive body can execute the action easily
- }
- 
- 
- Semaphore>>method wait 
- {
-	<primitive: #Semaphore_wait>
-	if (errorCode == NO ERROR)
-	{
-		self.signalAction value.  ## which is better???
-		self.sginalAction value: self.
-	}
- } 
-*)
  
 
 class SemaphoreGroup(Object)
diff --git a/moo/lib/exec.c b/moo/lib/exec.c
index f93a778..94fc28f 100644
--- a/moo/lib/exec.c
+++ b/moo/lib/exec.c
@@ -1354,14 +1354,14 @@ static void signal_io_semaphore (moo_t* moo, moo_ooi_t io_handle, moo_ooi_t mask
 
 		sem_io_index = moo->sem_io_map[io_handle];
 
-		sem = moo->sem_io_tuple[sem_io_index].sem[MOO_SEMAPHORE_IO_TYPE_INPUT];
-		if (sem && (mask & (MOO_SEMAPHORE_IO_MASK_INPUT | MOO_SEMAPHORE_IO_MASK_HANGUP | MOO_SEMAPHORE_IO_MASK_ERROR)))
+		sem = moo->sem_io_tuple[sem_io_index].sem[MOO_SEMAPHORE_IO_TYPE_OUTPUT];
+		if (sem && (mask & MOO_SEMAPHORE_IO_MASK_OUTPUT))
 		{
 			_signal_io_semaphore (moo, sem);
 		}
 
-		sem = moo->sem_io_tuple[sem_io_index].sem[MOO_SEMAPHORE_IO_TYPE_OUTPUT];
-		if (sem && (mask & MOO_SEMAPHORE_IO_MASK_OUTPUT))
+		sem = moo->sem_io_tuple[sem_io_index].sem[MOO_SEMAPHORE_IO_TYPE_INPUT];
+		if (sem && (mask & (MOO_SEMAPHORE_IO_MASK_INPUT | MOO_SEMAPHORE_IO_MASK_HANGUP | MOO_SEMAPHORE_IO_MASK_ERROR)))
 		{
 			_signal_io_semaphore (moo, sem);
 		}
diff --git a/moo/lib/main.c b/moo/lib/main.c
index e59982e..b3ff6d8 100644
--- a/moo/lib/main.c
+++ b/moo/lib/main.c
@@ -1022,6 +1022,12 @@ static int _mod_poll_fd (moo_t* moo, int fd, int event_mask)
 	MOO_ASSERT (moo, xtn->ep >= 0);
 	memset (&ev, 0, MOO_SIZEOF(ev));
 	ev.events = event_mask;
+	#if defined(USE_THREAD) && defined(EPOLLET)
+	/* epoll_wait may return again if the worker thread consumes events.
+	 * switch to level-trigger. */
+	/* TODO: verify if EPOLLLET is desired */
+	ev.events |= EPOLLET;
+	#endif
 	ev.data.fd = fd;
 	if (epoll_ctl (xtn->ep, EPOLL_CTL_MOD, fd, &ev) == -1)
 	{
@@ -1402,7 +1408,7 @@ static void* iothr_main (void* arg)
 			dvp.dp_nfds = MOO_COUNTOF(xtn->ev.buf);
 			n = ioctl (xtn->ep, DP_POLL, &dvp);
 		#elif defined(USE_EPOLL)
-			n = epoll_wait (xtn->ep, xtn->ev.buf, MOO_COUNTOF(xtn->ev.buf), 10000);
+			n = epoll_wait (xtn->ep, xtn->ev.buf, MOO_COUNTOF(xtn->ev.buf), 10000); /* TODO: make this timeout value in the io thread */
 		#elif defined(USE_POLL)
 			MUTEX_LOCK (&xtn->ev.reg.pmtx);
 			memcpy (xtn->ev.buf, xtn->ev.reg.ptr, xtn->ev.reg.len * MOO_SIZEOF(*xtn->ev.buf));