Wakeup delayed scheduling (#6485)

* Fix for scheduling recurrent functions while inside scheduled function

* Check that fn are valid. Invoking invalid functions throws otherwise.

* Added wakeup token to scheduler. Toggling the token value breaks a scheduled function

out from a delayed execution and makes it run on the next scheduler iteration.

* Timer reset reliability fix.

* Shrink interrupts-locked regions.

Add check for periodic yield to scheduled functions run-loop.

* Ordered, more predictable, scheduling. Before, it had different ordering compared to

FastScheduler as well as sequential calls from loop().

* Optional, for the paranoid: revert changes to (non-recurrent) schedule_function() / run_scheduled_functions().

* Comment

* Adapt one-line ifs to general style in same source file.

* Fix wakeupToken handling - don't respond to toggle, but to different value

vs. that at registering function with scheduler.

* Reword comment.

* Putting aside std::atomic concerns, use a callback for scheduler alarming.

In the future, async future's .then() might take advantage of this direction.

* Drop atomic include, align function type syntax.

* Reduce flash use.

* Prefer const ref over call by value plus std::move().

cores/esp8266/Schedule.cpp

@@ -24,16 +24,18 @@ struct recurrent_fn_t
     recurrent_fn_t* mNext = nullptr;
     mRecFuncT mFunc;
     esp8266::polledTimeout::periodicFastUs callNow;
-    recurrent_fn_t (esp8266::polledTimeout::periodicFastUs interval): callNow(interval) { }
+    std::function<bool(void)> alarm = nullptr;
+    recurrent_fn_t(esp8266::polledTimeout::periodicFastUs interval) : callNow(interval) { }
 };
 
-static recurrent_fn_t* rFirst = nullptr; // fifo not needed
+static recurrent_fn_t* rFirst = nullptr;
+static recurrent_fn_t* rLast = nullptr;
 
 // Returns a pointer to an unused sched_fn_t,
 // or if none are available allocates a new one,
 // or nullptr if limit is reached
 IRAM_ATTR // called from ISR
-static scheduled_fn_t* get_fn_unsafe ()
+static scheduled_fn_t* get_fn_unsafe()
 {
     scheduled_fn_t* result = nullptr;
     // try to get an item from unused items list
@@ -52,7 +54,7 @@ static scheduled_fn_t* get_fn_unsafe ()
     return result;
 }
 
-static void recycle_fn_unsafe (scheduled_fn_t* fn)
+static void recycle_fn_unsafe(scheduled_fn_t* fn)
 {
     fn->mFunc = nullptr; // special overload in c++ std lib
     fn->mNext = sUnused;
@@ -60,8 +62,11 @@ static void recycle_fn_unsafe (scheduled_fn_t* fn)
 }
 
 IRAM_ATTR // (not only) called from ISR
-bool schedule_function (const std::function<void(void)>& fn)
+bool schedule_function(const std::function<void(void)>& fn)
 {
+    if (!fn)
+        return false;
+
     esp8266::InterruptLock lockAllInterruptsInThisScope;
 
     scheduled_fn_t* item = get_fn_unsafe();
@@ -80,27 +85,37 @@ bool schedule_function (const std::function<void(void)>& fn)
     return true;
 }
 
-bool schedule_recurrent_function_us (const std::function<bool(void)>& fn, uint32_t repeat_us)
+bool schedule_recurrent_function_us(const std::function<bool(void)>& fn,
+    uint32_t repeat_us, const std::function<bool(void)>& alarm)
 {
     assert(repeat_us < decltype(recurrent_fn_t::callNow)::neverExpires); //~26800000us (26.8s)
 
-    esp8266::InterruptLock lockAllInterruptsInThisScope;
+    if (!fn)
+        return false;
 
     recurrent_fn_t* item = new (std::nothrow) recurrent_fn_t(repeat_us);
     if (!item)
         return false;
 
     item->mFunc = fn;
+    item->alarm = alarm;
 
-    if (rFirst)
-        item->mNext = rFirst;
+    esp8266::InterruptLock lockAllInterruptsInThisScope;
 
-    rFirst = item;
+    if (rLast)
+    {
+        rLast->mNext = item;
+    }
+    else
+    {
+        rFirst = item;
+    }
+    rLast = item;
 
     return true;
 }
 
-void run_scheduled_functions ()
+void run_scheduled_functions()
 {
     esp8266::polledTimeout::periodicFastMs yieldNow(100); // yield every 100ms
 
@@ -128,15 +143,18 @@ void run_scheduled_functions ()
     }
 }
 
-void run_scheduled_recurrent_functions ()
+void run_scheduled_recurrent_functions()
 {
+    esp8266::polledTimeout::periodicFastMs yieldNow(100); // yield every 100ms
+
     // Note to the reader:
     // There is no exposed API to remove a scheduled function:
     // Scheduled functions are removed only from this function, and
     // its purpose is that it is never called from an interrupt
     // (always on cont stack).
 
-    if (!rFirst)
+    auto current = rFirst;
+    if (!current)
         return;
 
     static bool fence = false;
@@ -153,26 +171,35 @@ void run_scheduled_recurrent_functions ()
     }
 
     recurrent_fn_t* prev = nullptr;
-    recurrent_fn_t* current = rFirst;
+    // prevent scheduling of new functions during this run
+    auto stop = rLast;
 
-    while (current)
+    bool done;
+    do
     {
-        if (current->callNow && !current->mFunc())
+        done = current == stop;
+        const bool wakeup = current->alarm && current->alarm();
+        bool callNow = current->callNow;
+
+        if ((wakeup || callNow) && !current->mFunc())
         {
             // remove function from stack
             esp8266::InterruptLock lockAllInterruptsInThisScope;
 
             auto to_ditch = current;
 
+            // removing rLast
+            if (rLast == current)
+                rLast = prev;
+
+            current = current->mNext;
             if (prev)
             {
-                current = current->mNext;
                 prev->mNext = current;
             }
             else
             {
-                rFirst = rFirst->mNext;
-                current = rFirst;
+                rFirst = current;
             }
 
             delete(to_ditch);
@@ -182,7 +209,15 @@ void run_scheduled_recurrent_functions ()
             prev = current;
             current = current->mNext;
         }
-    }
+
+        if (yieldNow)
+        {
+            // because scheduled functions might last too long for watchdog etc,
+            // this is yield() in cont stack:
+            esp_schedule();
+            cont_yield(g_pcont);
+        }
+    } while (current && !done);
 
     fence = false;
 }

cores/esp8266/Schedule.h

@@ -10,7 +10,7 @@
 // in user stack (called CONT stack) without the common restrictions from
 // system context.  Details are below.
 
-// The purpose of recurrent scheduled function is to independantly execute
+// The purpose of recurrent scheduled function is to independently execute
 // user code in CONT stack on a regular basis.
 // It has been introduced with ethernet service in mind, it can also be used
 // for all libraries in the need of a regular `libdaemon_handlestuff()`.
@@ -58,14 +58,14 @@ void run_scheduled_functions();
 //   functions.  However a user function returning false will cancel itself.
 // * Long running operations or yield() or delay() are not allowed in the
 //   recurrent function.
-// * A recurrent function currently must not schedule another recurrent
-//   functions.
-
-bool schedule_recurrent_function_us (const std::function<bool(void)>& fn, uint32_t repeat_us);
+// * If alarm is used, anytime during scheduling when it returns true,
+//   any remaining delay from repeat_us is disregarded, and fn is executed.
+bool schedule_recurrent_function_us(const std::function<bool(void)>& fn,
+    uint32_t repeat_us, const std::function<bool(void)>& alarm = nullptr);
 
 // Test recurrence and run recurrent scheduled functions.
 // (internally called at every `yield()` and `loop()`)
 
-void run_scheduled_recurrent_functions ();
+void run_scheduled_recurrent_functions();
 
 #endif // ESP_SCHEDULE_H