Implement a heap based task scheduler

kmk/kmk_keyboard.py

@@ -1,19 +1,17 @@
 try:
-    from typing import Callable, Optional, Tuple
+    from typing import Callable, Optional
 except ImportError:
     pass
 
-from supervisor import ticks_ms
-
 from collections import namedtuple
 from keypad import Event as KeyEvent
 
 from kmk.consts import UnicodeMode
 from kmk.hid import BLEHID, USBHID, AbstractHID, HIDModes
 from kmk.keys import KC, Key
-from kmk.kmktime import ticks_add, ticks_diff
 from kmk.modules import Module
 from kmk.scanners.keypad import MatrixScanner
+from kmk.scheduler import Task, cancel_task, create_task, get_due_task
 from kmk.utils import Debug
 
 debug = Debug('kmk.keyboard')
@@ -266,60 +264,17 @@ class KMKKeyboard:
     def tap_key(self, keycode: Key) -> None:
         self.add_key(keycode)
         # On the next cycle, we'll remove the key.
-        self.set_timeout(False, lambda: self.remove_key(keycode))
+        self.set_timeout(0, lambda: self.remove_key(keycode))
 
-    def set_timeout(
-        self, after_ticks: int, callback: Callable[[None], None]
-    ) -> Tuple[int, int]:
-        # We allow passing False as an implicit "run this on the next process timeouts cycle"
-        if after_ticks is False:
-            after_ticks = 0
-
-        if after_ticks == 0 and self._processing_timeouts:
-            after_ticks += 1
-
-        timeout_key = ticks_add(ticks_ms(), after_ticks)
-
-        if timeout_key not in self._timeouts:
-            self._timeouts[timeout_key] = []
-
-        idx = len(self._timeouts[timeout_key])
-        self._timeouts[timeout_key].append(callback)
-
-        return (timeout_key, idx)
+    def set_timeout(self, after_ticks: int, callback: Callable[[None], None]) -> [Task]:
+        return create_task(callback, after_ms=after_ticks)
 
     def cancel_timeout(self, timeout_key: int) -> None:
-        try:
-            self._timeouts[timeout_key[0]][timeout_key[1]] = None
-        except (KeyError, IndexError):
-            if debug.enabled:
-                debug(f'no such timeout: {timeout_key}')
+        cancel_task(timeout_key)
 
     def _process_timeouts(self) -> None:
-        if not self._timeouts:
-            return
-
-        # Copy timeout keys to a temporary list to allow sorting.
-        # Prevent net timeouts set during handling from running on the current
-        # cycle by setting a flag `_processing_timeouts`.
-        current_time = ticks_ms()
-        timeout_keys = []
-        self._processing_timeouts = True
-
-        for k in self._timeouts.keys():
-            if ticks_diff(k, current_time) <= 0:
-                timeout_keys.append(k)
-
-        if timeout_keys and debug.enabled:
-            debug('processing timeouts')
-
-        for k in sorted(timeout_keys):
-            for callback in self._timeouts[k]:
-                if callback:
-                    callback()
-            del self._timeouts[k]
-
-        self._processing_timeouts = False
+        for task in get_due_task():
+            task()
 
     def _init_sanity_check(self) -> None:
         '''

kmk/scheduler.py

@@ -0,0 +1,67 @@
+'''
+Here we're abusing _asyncios TaskQueue to implement a very simple priority
+queue task scheduler.
+Despite documentation, Circuitpython doesn't usually ship with a min-heap
+module; it does however implement a pairing-heap for `TaskQueue` in native code.
+'''
+
+try:
+    from typing import Callable
+except ImportError:
+    pass
+
+from supervisor import ticks_ms
+
+from _asyncio import Task, TaskQueue
+
+from kmk.kmktime import ticks_add, ticks_diff
+
+_task_queue = TaskQueue()
+
+
+class PeriodicTaskMeta:
+    def __init__(self, func: Callable[[None], None], period: int) -> None:
+        self._task = Task(self.call)
+        self._coro = func
+        self.period = period
+
+    def call(self) -> None:
+        self._coro()
+        after_ms = ticks_add(self._task.ph_key, self.period)
+        _task_queue.push_sorted(self._task, after_ms)
+
+
+def create_task(
+    func: Callable[[None], None],
+    *,
+    after_ms: int = 0,
+    period_ms: int = 0,
+) -> [Task, PeriodicTaskMeta]:
+    if period_ms:
+        r = PeriodicTaskMeta(func, period_ms)
+        t = r._task
+    else:
+        t = r = Task(func)
+
+    if after_ms:
+        after_ms = ticks_add(ticks_ms(), after_ms)
+        _task_queue.push_sorted(t, after_ms)
+    else:
+        _task_queue.push_head(t)
+
+    return r
+
+
+def get_due_task() -> [Callable, None]:
+    while True:
+        t = _task_queue.peek()
+        if not t or ticks_diff(t.ph_key, ticks_ms()) > 0:
+            break
+        _task_queue.pop_head()
+        yield t.coro
+
+
+def cancel_task(t: [Task, PeriodicTaskMeta]) -> None:
+    if isinstance(t, PeriodicTaskMeta):
+        t = t._task
+    _task_queue.remove(t)

tests/keyboard_test.py

@@ -6,6 +6,7 @@ from kmk.keys import KC, ModifierKey
 from kmk.kmk_keyboard import KMKKeyboard
 from kmk.scanners import DiodeOrientation
 from kmk.scanners.digitalio import MatrixScanner
+from kmk.scheduler import _task_queue
 
 
 class DigitalInOut(Mock):
@@ -81,7 +82,7 @@ class KeyboardTest:
         timeout = time.time_ns() + 10 * 1_000_000_000
         while timeout > time.time_ns():
             self.do_main_loop()
-            if not self.keyboard._timeouts and not self.keyboard._resume_buffer:
+            if not _task_queue.peek() and not self.keyboard._resume_buffer:
                 break
         assert timeout > time.time_ns(), 'infinite loop detected'
 

tests/mocks.py

@@ -9,6 +9,10 @@ class KeyEvent:
         self.pressed = pressed
 
 
+def ticks_ms():
+    return (time.time_ns() // 1_000_000) % (1 << 29)
+
+
 def init_circuit_python_modules_mocks():
     sys.modules['usb_hid'] = Mock()
     sys.modules['digitalio'] = Mock()
@@ -26,4 +30,8 @@ def init_circuit_python_modules_mocks():
     sys.modules['micropython'].const = lambda x: x
 
     sys.modules['supervisor'] = Mock()
-    sys.modules['supervisor'].ticks_ms = lambda: time.time_ns() // 1_000_000
+    sys.modules['supervisor'].ticks_ms = ticks_ms
+
+    from . import task
+
+    sys.modules['_asyncio'] = task

tests/task.py

@@ -0,0 +1,196 @@
+# MicroPython uasyncio module
+# MIT license; Copyright (c) 2019-2020 Damien P. George
+
+# This file contains the core TaskQueue based on a pairing heap, and the core Task class.
+# They can optionally be replaced by C implementations.
+
+# This file is a modified version, based on the extmod in Circuitpython, for
+# unit testing in KMK only.
+
+from supervisor import ticks_ms
+
+from kmk.kmktime import ticks_diff
+
+cur_task = None
+__task_queue = None
+
+
+class CancelledError(BaseException):
+    pass
+
+
+# pairing-heap meld of 2 heaps; O(1)
+def ph_meld(h1, h2):
+    if h1 is None:
+        return h2
+    if h2 is None:
+        return h1
+    lt = ticks_diff(h1.ph_key, h2.ph_key) < 0
+    if lt:
+        if h1.ph_child is None:
+            h1.ph_child = h2
+        else:
+            h1.ph_child_last.ph_next = h2
+        h1.ph_child_last = h2
+        h2.ph_next = None
+        h2.ph_rightmost_parent = h1
+        return h1
+    else:
+        h1.ph_next = h2.ph_child
+        h2.ph_child = h1
+        if h1.ph_next is None:
+            h2.ph_child_last = h1
+            h1.ph_rightmost_parent = h2
+        return h2
+
+
+# pairing-heap pairing operation; amortised O(log N)
+def ph_pairing(child):
+    heap = None
+    while child is not None:
+        n1 = child
+        child = child.ph_next
+        n1.ph_next = None
+        if child is not None:
+            n2 = child
+            child = child.ph_next
+            n2.ph_next = None
+            n1 = ph_meld(n1, n2)
+        heap = ph_meld(heap, n1)
+    return heap
+
+
+# pairing-heap delete of a node; stable, amortised O(log N)
+def ph_delete(heap, node):
+    if node is heap:
+        child = heap.ph_child
+        node.ph_child = None
+        return ph_pairing(child)
+    # Find parent of node
+    parent = node
+    while parent.ph_next is not None:
+        parent = parent.ph_next
+    parent = parent.ph_rightmost_parent
+    if parent is None or parent.ph_child is None:
+        return heap
+    # Replace node with pairing of its children
+    if node is parent.ph_child and node.ph_child is None:
+        parent.ph_child = node.ph_next
+        node.ph_next = None
+        return heap
+    elif node is parent.ph_child:
+        child = node.ph_child
+        next = node.ph_next
+        node.ph_child = None
+        node.ph_next = None
+        node = ph_pairing(child)
+        parent.ph_child = node
+    else:
+        n = parent.ph_child
+        while node is not n.ph_next:
+            n = n.ph_next
+            if not n:
+                return heap
+        child = node.ph_child
+        next = node.ph_next
+        node.ph_child = None
+        node.ph_next = None
+        node = ph_pairing(child)
+        if node is None:
+            node = n
+        else:
+            n.ph_next = node
+    node.ph_next = next
+    if next is None:
+        node.ph_rightmost_parent = parent
+        parent.ph_child_last = node
+    return heap
+
+
+# TaskQueue class based on the above pairing-heap functions.
+class TaskQueue:
+    def __init__(self):
+        self.heap = None
+
+    def peek(self):
+        return self.heap
+
+    def push_sorted(self, v, key):
+        v.data = None
+        v.ph_key = key
+        v.ph_child = None
+        v.ph_next = None
+        self.heap = ph_meld(v, self.heap)
+
+    def push_head(self, v):
+        self.push_sorted(v, ticks_ms())
+
+    def pop_head(self):
+        v = self.heap
+        self.heap = ph_pairing(v.ph_child)
+        # v.ph_child = None
+        return v
+
+    def remove(self, v):
+        self.heap = ph_delete(self.heap, v)
+
+
+# Task class representing a coroutine, can be waited on and cancelled.
+class Task:
+    def __init__(self, coro, globals=None):
+        self.coro = coro  # Coroutine of this Task
+        self.data = None  # General data for queue it is waiting on
+        self.state = True  # None, False, True or a TaskQueue instance
+        self.ph_key = 0  # Pairing heap
+        self.ph_child = None  # Paring heap
+        self.ph_child_last = None  # Paring heap
+        self.ph_next = None  # Paring heap
+        self.ph_rightmost_parent = None  # Paring heap
+
+    def __await__(self):
+        if not self.state:
+            # Task finished, signal that is has been await'ed on.
+            self.state = False
+        elif self.state is True:
+            # Allocated head of linked list of Tasks waiting on completion of this task.
+            self.state = TaskQueue()
+        return self
+
+    def __next__(self):
+        if not self.state:
+            if self.data is None:
+                # Task finished but has already been sent to the loop's exception handler.
+                raise StopIteration
+            else:
+                # Task finished, raise return value to caller so it can continue.
+                raise self.data
+        else:
+            # Put calling task on waiting queue.
+            self.state.push_head(cur_task)
+            # Set calling task's data to this task that it waits on, to double-link it.
+            cur_task.data = self
+
+    def done(self):
+        return not self.state
+
+    def cancel(self):
+        # Check if task is already finished.
+        if not self.state:
+            return False
+        # Can't cancel self (not supported yet).
+        if self is cur_task:
+            raise RuntimeError("can't cancel self")
+        # If Task waits on another task then forward the cancel to the one it's waiting on.
+        while isinstance(self.data, Task):
+            self = self.data
+        # Reschedule Task as a cancelled task.
+        if hasattr(self.data, 'remove'):
+            # Not on the main running queue, remove the task from the queue it's on.
+            self.data.remove(self)
+            __task_queue.push_head(self)
+        elif ticks_diff(self.ph_key, ticks_ms()) > 0:
+            # On the main running queue but scheduled in the future, so bring it forward to now.
+            __task_queue.remove(self)
+            __task_queue.push_head(self)
+        self.data = CancelledError
+        return True