Index: tests/concurrent/.expect/clib.txt
===================================================================
--- tests/concurrent/.expect/clib.txt	(revision bb6620274a509c003557406a0e5bf61a36ffc572)
+++ tests/concurrent/.expect/clib.txt	(revision bb6620274a509c003557406a0e5bf61a36ffc572)
@@ -0,0 +1,21 @@
+Done
+Done
+Done
+Done
+Done
+Done
+Done
+Done
+Done
+Done
+Done
+Done
+Done
+Done
+Done
+Done
+Done
+Done
+Done
+Done
+Done Unparker
Index: tests/concurrent/clib.c
===================================================================
--- tests/concurrent/clib.c	(revision bb6620274a509c003557406a0e5bf61a36ffc572)
+++ tests/concurrent/clib.c	(revision bb6620274a509c003557406a0e5bf61a36ffc572)
@@ -0,0 +1,67 @@
+#include <clib/cfathread.h>
+
+#include <stdio.h>
+#include <stdlib.h>
+
+thread_local struct drand48_data buffer = { 0 };
+int myrand() {
+	long int result;
+	lrand48_r(&buffer, &result);
+	return result;
+}
+
+
+enum Constants { blocked_size = 20 };
+cfathread_t volatile blocked[blocked_size];
+
+void Worker( cfathread_t this ) {
+	for(int i = 0; i < 1000; i++) {
+		int idx = myrand() % blocked_size;
+		if(blocked[idx]) {
+			cfathread_t thrd = __atomic_exchange_n(&blocked[idx], NULL, __ATOMIC_SEQ_CST);
+			cfathread_unpark( thrd );
+		} else {
+			cfathread_t thrd = __atomic_exchange_n(&blocked[idx], this, __ATOMIC_SEQ_CST);
+			cfathread_unpark( thrd );
+			cfathread_park();
+		}
+	}
+	printf("Done\n");
+}
+
+volatile bool stop;
+void Unparker( cfathread_t this ) {
+	while(!stop) {
+		int idx = myrand() % blocked_size;
+		cfathread_t thrd = __atomic_exchange_n(&blocked[idx], NULL, __ATOMIC_SEQ_CST);
+		cfathread_unpark( thrd );
+		int r = myrand() % 20;
+		for( int i = 0; i < r; i++ ) {
+			cfathread_yield();
+		}
+	}
+	printf("Done Unparker\n");
+}
+
+
+int main() {
+	stop = false;
+	for(int i = 0; i < blocked_size; i++) {
+		blocked[i] = NULL;
+	}
+
+	cfathread_setproccnt( 4 );
+	cfathread_t u = cfathread_create( Unparker );
+	{
+		cfathread_t t[20];
+		for(int i = 0; i < 20; i++) {
+			t[i] = cfathread_create( Worker );
+		}
+		for(int i = 0; i < 20; i++) {
+			cfathread_join( t[i] );
+		}
+	}
+	stop = true;
+	cfathread_join(u);
+	cfathread_setproccnt( 1 );
+}