--- old/src/os/posix/vm/os_posix.hpp	2015-06-15 21:33:24.396125571 +0200
+++ new/src/os/posix/vm/os_posix.hpp	2015-06-15 21:33:24.248120600 +0200
@@ -89,4 +89,12 @@
   sigjmp_buf _jmpbuf;
 };
 
+class PosixSemaphore : public Semaphore {
+ public:
+  PosixSemaphore(uint value = 0) : Semaphore(value) {}
+
+  bool trywait();
+  bool timedwait(struct timespec ts);
+};
+
 #endif // OS_POSIX_VM_OS_POSIX_HPP