eventloop: add a timer class

Signed-off-by:  Eric Callahan <arksine.code@gmail.com>

moonraker/eventloop.py

@@ -15,12 +15,14 @@ from typing import (
     Callable,
     Coroutine,
     Optional,
-    TypeVar
+    TypeVar,
+    Union
 )
 
 if TYPE_CHECKING:
     _T = TypeVar("_T")
     FlexCallback = Callable[..., Optional[Awaitable]]
+    TimerCallback = Callable[[float], Union[float, Awaitable[float]]]
 
 class EventLoop:
     TimeoutError = asyncio.TimeoutError
@@ -34,6 +36,8 @@ class EventLoop:
         self.remove_writer = self.aioloop.remove_writer
         self.get_loop_time = self.aioloop.time
         self.create_future = self.aioloop.create_future
+        self.create_task = self.aioloop.create_task
+        self.call_at = self.aioloop.call_at
 
     def register_callback(self,
                           callback: FlexCallback,
@@ -60,6 +64,9 @@ class EventLoop:
             return self.aioloop.call_later(
                 delay, functools.partial(callback, *args, **kwargs))
 
+    def register_timer(self, callback: TimerCallback):
+        return FlexTimer(self, callback)
+
     def _async_callback(self, callback: Callable[[], Coroutine]) -> None:
         # This wrapper delays creation of the coroutine object.  In the
         # event that a callback is cancelled this prevents "coroutine
@@ -81,3 +88,45 @@ class EventLoop:
 
     def close(self):
         self.aioloop.close()
+
+class FlexTimer:
+    def __init__(self,
+                 eventloop: EventLoop,
+                 callback: TimerCallback
+                 ) -> None:
+        self.eventloop = eventloop
+        self.callback = callback
+        self.timer_handle: Optional[asyncio.TimerHandle] = None
+        self.running: bool = False
+
+    def start(self, delay: float = 0.):
+        if self.running:
+            return
+        self.running = True
+        call_time = self.eventloop.get_loop_time() + delay
+        self.timer_handle = self.eventloop.call_at(
+            call_time, self._schedule_task)
+
+    def stop(self):
+        if not self.running:
+            return
+        self.running = False
+        if self.timer_handle is not None:
+            self.timer_handle.cancel()
+            self.timer_handle = None
+
+    def _schedule_task(self):
+        self.timer_handle = None
+        self.eventloop.create_task(self._call_wrapper())
+
+    def is_running(self) -> bool:
+        return self.running
+
+    async def _call_wrapper(self):
+        if not self.running:
+            return
+        ret = self.callback(self.eventloop.get_loop_time())
+        if isinstance(ret, Awaitable):
+            ret = await ret
+        if self.running:
+            self.timer_handle = self.eventloop.call_at(ret, self._schedule_task)