clean up PeriodicTask so I can eventually use it with a scheduler

src/PeriodicTask.h

@@ -1,8 +1,40 @@
 #pragma once
 
-#include <cstdint>
-
 #include "lock.h"
+#include <cstdint>
+#include <unordered_set>
+
+class PeriodicTask;
+
+/**
+ * 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.
+    meshtastic::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;
 
 /**
  * A base class for tasks that want their doTask() method invoked periodically
@@ -13,26 +45,33 @@
  */
 class PeriodicTask
 {
+    friend class PeriodicScheduler;
+
     uint32_t lastMsec = 0;
     uint32_t period = 1; // call soon after creation
 
-    // Protects the above variables.
-    meshtastic::Lock lock;
-
   public:
-    virtual ~PeriodicTask() {}
+    virtual ~PeriodicTask() { periodicScheduler.unschedule(this); }
 
+    /**
+     * Constructor (will schedule with the global PeriodicScheduler)
+     */
     PeriodicTask(uint32_t initialPeriod = 1);
 
-    /// call this from loop
-    virtual void loop();
+    /** MUST be be called once at startup (but after threading is running - i.e. not from a constructor)
+     */
+    void setup();
 
-    /// Set a new period in msecs (can be called from doTask or elsewhere and the scheduler will cope)
-    void setPeriod(uint32_t p)
-    {
-        meshtastic::LockGuard lg(&lock);
-        period = p;
-    }
+    /**
+     * Set a new period in msecs (can be called from doTask or elsewhere and the scheduler will cope)
+     * While zero this task is disabled and will not run
+     */
+    void setPeriod(uint32_t p) { period = p; }
+
+    /**
+     * Syntatic sugar for suspending tasks
+     */
+    void disable() { setPeriod(0); }
 
   protected:
     virtual void doTask() = 0;