PolledTimeout Class for wrapping millis() loops (WIP) (#5198)

* PolledTimeout Class for wrapping millis() loops

* Add yield policies, improve reset, add host tests

* Fix copyright, comments

* adjust host tests for better time precision

* add fuzzyness to timing tests for CI jitter

* add blink example with polledTimeout

* improve namespace and type naming, add copyright, comments

* fix astyle

cores/esp8266/PolledTimeout.h

@@ -0,0 +1,126 @@
+#ifndef __POLLEDTIMING_H__
+#define __POLLEDTIMING_H__
+
+
+/*
+ PolledTimeout.h - Encapsulation of a polled Timeout
+ 
+ Copyright (c) 2018 Daniel Salazar. All rights reserved.
+ This file is part of the esp8266 core for Arduino environment.
+
+ This library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ This library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with this library; if not, write to the Free Software
+ Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ */
+
+
+
+namespace esp8266
+{
+
+
+namespace polledTimeout
+{
+
+namespace YieldPolicy
+{
+
+struct DoNothing
+{
+  static void execute() {}
+};
+
+struct YieldOrSkip
+{
+  static void execute() {delay(0);}
+};
+
+} //YieldPolicy
+
+
+template <bool PeriodicT, typename YieldPolicyT = YieldPolicy::DoNothing>  
+class timeoutTemplate
+{
+public:
+  using timeType = decltype(millis());
+  
+  timeoutTemplate(timeType timeout) 
+    : _timeout(timeout), _start(millis())  
+  {} 
+
+  bool expired()
+  {
+    YieldPolicyT::execute(); //in case of DoNothing: gets optimized away
+    if(PeriodicT)           //in case of false: gets optimized away
+      return expiredRetrigger();
+    return expiredOneShot();
+  }
+  
+  operator bool()
+  {
+    return expired(); 
+  }
+  
+  void reset(timeType newTimeout)
+  {
+    _timeout = newTimeout;
+    reset();
+  }
+
+  void reset()
+  {
+    _start = millis(); 
+  }
+  
+protected:
+  bool checkExpired(timeType t) const
+  {
+    return (t - _start) >=  _timeout;
+  }
+  
+  bool expiredRetrigger()
+  {
+    timeType current = millis();
+    if(checkExpired(current))
+    {
+      unsigned long n = (current - _start) / _timeout; //how many _timeouts periods have elapsed, will usually be 1 (current - _start >= _timeout)
+      _start += n  * _timeout;
+      return true;
+    }
+    return false;
+  }
+  
+  bool expiredOneShot() const
+  {
+    return checkExpired(millis());
+  }
+  
+  timeType _timeout;
+  timeType _start;
+};
+
+using oneShot = polledTimeout::timeoutTemplate<false>;
+using periodic = polledTimeout::timeoutTemplate<true>;
+
+} //polledTimeout
+
+
+/* A 1-shot timeout that auto-yields when in CONT can be built as follows:
+ * using oneShotYield = esp8266::polledTimeout::timeoutTemplate<false, esp8266::polledTimeout::YieldPolicy::YieldOrSkip>;
+ *
+ * Other policies can be implemented by the user, e.g.: simple yield that panics in SYS, and the polledTimeout types built as needed as shown above, without modifying this file.
+ */
+
+}//esp8266
+
+#endif