fixes

src/concurrency/PeriodicScheduler.h

@@ -0,0 +1,40 @@
+#pragma once
+
+#include "Lock.h"
+#include <cstdint>
+#include <unordered_set>
+
+namespace concurrency {
+
+class PeriodicTask;
+
+/**
+ * @brief Runs all PeriodicTasks in the system. Currently called from main loop() 
+ *        but eventually should be its own thread blocked on a freertos timer.
+ */
+class PeriodicScheduler
+{
+    friend class PeriodicTask;
+
+    /**
+     * This really should be some form of heap, and when the period gets changed on a task it should get
+     * rescheduled in that heap.  Currently it is just a dumb array and everytime we run loop() we check
+     * _every_ tasks.  If it was a heap we'd only have to check the first task.
+     */
+    std::unordered_set<PeriodicTask *> tasks;
+
+    // Protects the above variables.
+    Lock lock;
+
+  public:
+    /// Run any next tasks which are due for execution
+    void loop();
+
+  private:
+    void schedule(PeriodicTask *t);
+    void unschedule(PeriodicTask *t);
+};
+
+extern PeriodicScheduler periodicScheduler;
+
+} // namespace concurrency