Index: libcfa/src/concurrency/io.cfa
===================================================================
--- libcfa/src/concurrency/io.cfa	(revision 1860885bf96eb1e05136e94b1b36893ab6369f93)
+++ libcfa/src/concurrency/io.cfa	(revision 9f5a71eb57274fa2ef0c856174e9628d92d8f703)
@@ -408,8 +408,12 @@
 // I/O Arbiter
 //=============================================================================================
-	static inline void block(__outstanding_io_queue & queue, __outstanding_io & item) {
+	static inline bool enqueue(__outstanding_io_queue & queue, __outstanding_io & item) {
+		bool was_empty;
+
 		// Lock the list, it's not thread safe
 		lock( queue.lock __cfaabi_dbg_ctx2 );
 		{
+			was_empty = empty(queue.queue);
+
 			// Add our request to the list
 			add( queue.queue, item );
@@ -420,5 +424,5 @@
 		unlock( queue.lock );
 
-		wait( item.sem );
+		return was_empty;
 	}
 
@@ -438,5 +442,7 @@
 		pa.want = want;
 
-		block(this.pending, (__outstanding_io&)pa);
+		enqueue(this.pending, (__outstanding_io&)pa);
+
+		wait( pa.sem );
 
 		return pa.ctx;
@@ -491,5 +497,14 @@
 		ei.lazy = lazy;
 
-		block(ctx->ext_sq, (__outstanding_io&)ei);
+		bool we = enqueue(ctx->ext_sq, (__outstanding_io&)ei);
+
+		ctx->proc->io.pending = true;
+
+		if( we ) {
+			sigval_t value = { PREEMPT_IO };
+			pthread_sigqueue(ctx->proc->kernel_thread, SIGUSR1, value);
+		}
+
+		wait( ei.sem );
 
 		__cfadbg_print_safe(io, "Kernel I/O : %u submitted from arbiter\n", have);