copying condition-class branch over from my 2012 repo
diff --git a/aos/common/condition.h b/aos/common/condition.h
new file mode 100644
index 0000000..c527f34
--- /dev/null
+++ b/aos/common/condition.h
@@ -0,0 +1,62 @@
+#ifndef AOS_COMMON_CONDITION_H_
+#define AOS_COMMON_CONDITION_H_
+
+#ifdef __VXWORKS__
+#include <semLib.h>
+#endif
+
+#include "aos/aos_core.h"
+#include "aos/common/mutex.h"
+
+namespace aos {
+
+// A condition variable (IPC mechanism where 1 process/task can notify all
+// others that are waiting for something to happen).
+// There are implementations for both the atom and the cRIO.
+// They both LOG(FATAL) if anything weird happens.
+//
+// A condition is either set or unset, and multiple processes/tasks can wait on
+// one for it to be set.
+class Condition {
+ public:
+ // Creates an unset condition.
+ Condition();
+#ifdef __VXWORKS__
+ // Will not make sure that it is either set or unset.
+ ~Condition();
+#endif
+ // Waits for the condition to be set. Will return true immediately if it is
+ // already set.
+ // Returns false if returning before a confirmed condition set, although doing
+ // anything very useful with the return value is difficult because the
+ // condition may have been set (and possibly even unset again) between the
+ // time when the system call to block returned and this function returns.
+ bool Wait();
+ // Waits for the next Set(), regardless of whether or not the condition is
+ // currently set.
+ // Same return value as Wait().
+ bool WaitNext();
+
+ // Sets the condition. Any processes/tasks that are currently Wait()ing will
+ // continue.
+ // All implementations will wake all waiting processes/tasks at once so that
+ // the highest priority one(s) will run before others like usual.
+ void Set();
+ // Unsets the condition.
+ void Unset();
+
+ private:
+#ifdef __VXWORKS__
+ // Always empty. Used to make tasks wait and then gets flushed to unblock all
+ // of them.
+ SEM_ID wait_;
+ // Whether or not the conditon is set.
+ bool set_;
+#else
+ mutex impl_;
+#endif
+};
+
+} // namespace aos
+
+#endif // AOS_COMMON_CONDITION_H_