Kernel/LibC: Implement simple futex

userspace/libraries/LibC/include/sys/futex.h

@@ -0,0 +1,45 @@
+#ifndef _SYS_FUTEX_H
+#define _SYS_FUTEX_H 1
+
+#include <sys/cdefs.h>
+
+__BEGIN_DECLS
+
+#include <stdint.h>
+#include <time.h>
+
+#define FUTEX_WAIT     0
+#define FUTEX_WAKE     1
+#define FUTEX_PRIVATE  0x10
+#define FUTEX_REALTIME 0x20
+
+#define FUTEX_WAIT_PRIVATE (FUTEX_WAIT | FUTEX_PRIVATE)
+#define FUTEX_WAKE_PRIVATE (FUTEX_WAKE | FUTEX_PRIVATE)
+
+// op is one of FUTEX_WAIT or FUTEX_WAKE optionally or'ed with FUTEX_PRIVATE and/or FUTEX_REALTIME
+//
+// FUTEX_WAIT
+//   put current thread to sleep until *addr != value or until timeout occurs
+//   timeout is specified as a absolute time or NULL for indefinite wait
+//
+// FUTEX_WAKE
+//   signals waiting futexes to recheck *addr. at most value threads are woken up
+//
+// FUTEX_PRIVATE
+//   limit futex wait/wake events to the current process
+//
+// FUTEX_REALTIME
+//   abstime corresponds to CLOCK_REALTIME instead of the default CLOCK_MONOTONIC
+//
+// ERRORS
+//   ETIMEDOUT timeout occured
+//   EINVAL    addr is not aligned on 4 byte boundary
+//   ENOSYS    op contains unrecognized value
+//   EINTR     function was interrupted
+//   ENOMEM    not enough memory to allocate futex object
+//   EAGAIN    *addr != value before thread was put to sleep
+int futex(int op, const uint32_t* addr, uint32_t value, const struct timespec* abstime);
+
+__END_DECLS
+
+#endif

userspace/libraries/LibC/include/sys/syscall.h

@@ -109,6 +109,7 @@ __BEGIN_DECLS
 	O(SYS_EPOLL_PWAIT2,		epoll_pwait2)	\
 	O(SYS_FLOCK,			flock)			\
 	O(SYS_GET_NPROCESSOR,	get_nprocessor)	\
+	O(SYS_FUTEX,			futex)			\
 
 enum Syscall
 {