add circuitpython code

1 files changed, 53 insertions, 0 deletions

diff --git a/circuitpython/extmod/uasyncio/lock.py b/circuitpython/extmod/uasyncio/lock.py
new file mode 100644
index 0000000..bddca29
--- /dev/null
+++ b/circuitpython/extmod/uasyncio/lock.py
@@ -0,0 +1,53 @@
+# MicroPython uasyncio module
+# MIT license; Copyright (c) 2019-2020 Damien P. George
+
+from . import core
+
+# Lock class for primitive mutex capability
+class Lock:
+    def __init__(self):
+        # The state can take the following values:
+        # - 0: unlocked
+        # - 1: locked
+        # - <Task>: unlocked but this task has been scheduled to acquire the lock next
+        self.state = 0
+        # Queue of Tasks waiting to acquire this Lock
+        self.waiting = core.TaskQueue()
+
+    def locked(self):
+        return self.state == 1
+
+    def release(self):
+        if self.state != 1:
+            raise RuntimeError("Lock not acquired")
+        if self.waiting.peek():
+            # Task(s) waiting on lock, schedule next Task
+            self.state = self.waiting.pop_head()
+            core._task_queue.push_head(self.state)
+        else:
+            # No Task waiting so unlock
+            self.state = 0
+
+    async def acquire(self):
+        if self.state != 0:
+            # Lock unavailable, put the calling Task on the waiting queue
+            self.waiting.push_head(core.cur_task)
+            # Set calling task's data to the lock's queue so it can be removed if needed
+            core.cur_task.data = self.waiting
+            try:
+                yield
+            except core.CancelledError as er:
+                if self.state == core.cur_task:
+                    # Cancelled while pending on resume, schedule next waiting Task
+                    self.state = 1
+                    self.release()
+                raise er
+        # Lock available, set it as locked
+        self.state = 1
+        return True
+
+    async def __aenter__(self):
+        return await self.acquire()
+
+    async def __aexit__(self, exc_type, exc, tb):
+        return self.release()