88 lines
2.8 KiB
Python
88 lines
2.8 KiB
Python
# SPDX-FileCopyrightText: 2019-2020 Damien P. George
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#
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# SPDX-License-Identifier: MIT
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#
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# MicroPython uasyncio module
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# MIT license; Copyright (c) 2019-2020 Damien P. George
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#
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# This code comes from MicroPython, and has not been run through black or pylint there.
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# Altering these files significantly would make merging difficult, so we will not use
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# pylint or black.
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# pylint: skip-file
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# fmt: off
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"""
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Locks
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=====
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"""
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from . import core
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# Lock class for primitive mutex capability
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class Lock:
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"""Create a new lock which can be used to coordinate tasks. Locks start in
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the unlocked state.
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In addition to the methods below, locks can be used in an ``async with``
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statement.
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"""
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def __init__(self):
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# The state can take the following values:
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# - 0: unlocked
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# - 1: locked
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# - <Task>: unlocked but this task has been scheduled to acquire the lock next
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self.state = 0
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# Queue of Tasks waiting to acquire this Lock
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self.waiting = core.TaskQueue()
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def locked(self):
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"""Returns ``True`` if the lock is locked, otherwise ``False``."""
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return self.state == 1
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def release(self):
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"""Release the lock. If any tasks are waiting on the lock then the next
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one in the queue is scheduled to run and the lock remains locked. Otherwise,
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no tasks are waiting and the lock becomes unlocked.
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"""
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if self.state != 1:
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raise RuntimeError("Lock not acquired")
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if self.waiting.peek():
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# Task(s) waiting on lock, schedule next Task
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self.state = self.waiting.pop_head()
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core._task_queue.push_head(self.state)
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else:
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# No Task waiting so unlock
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self.state = 0
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async def acquire(self):
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"""Wait for the lock to be in the unlocked state and then lock it in an
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atomic way. Only one task can acquire the lock at any one time.
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This is a coroutine.
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"""
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if self.state != 0:
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# Lock unavailable, put the calling Task on the waiting queue
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self.waiting.push_head(core.cur_task)
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# Set calling task's data to the lock's queue so it can be removed if needed
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core.cur_task.data = self.waiting
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try:
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await core._never()
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except core.CancelledError as er:
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if self.state == core.cur_task:
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# Cancelled while pending on resume, schedule next waiting Task
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self.state = 1
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self.release()
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raise er
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# Lock available, set it as locked
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self.state = 1
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return True
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async def __aenter__(self):
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return await self.acquire()
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async def __aexit__(self, exc_type, exc, tb):
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return self.release()
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