Initial commit

[ta/config-manager.git] / cmframework / src / cmframework / server / cmeventletrwlock.py

diff --git a/cmframework/src/cmframework/server/cmeventletrwlock.py b/cmframework/src/cmframework/server/cmeventletrwlock.py
new file mode 100644 (file)
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+++ b/cmframework/src/cmframework/server/cmeventletrwlock.py
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+# Copyright 2019 Nokia
+
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+from __future__ import print_function
+from eventlet import greenthread, hubs
+
+
+class CMEventletRWLock(object):
+    def __init__(self):
+        self.counter = 0
+        self._read_waiters = set()
+        self._write_waiters = set()
+
+    def reader(self):
+        return self.Reader(self)
+
+    def writer(self):
+        return self.Writer(self)
+
+    class Base(object):
+        def __init__(self, parent):
+            self.parent = parent
+
+        def _acquire(self, waiters):
+            waiters.add(greenthread.getcurrent())
+
+            try:
+                while self.parent.counter != 0:
+                    hubs.get_hub().switch()
+            finally:
+                waiters.discard(greenthread.getcurrent())
+
+        def _exit(self):
+            for waiters, fn in (
+                    (self.parent._read_waiters, lambda x: x >= 0),
+                    (self.parent._write_waiters, lambda x: x == 0),
+            ):
+                if not waiters:
+                    continue
+
+                hubs.get_hub().schedule_call_global(
+                    0, self._release, waiters, fn,
+                )
+
+        def _release(self, waiters, fn):
+            if waiters and fn(self.parent.counter):
+                waiters.pop().switch()
+
+    class Reader(Base):
+        def __enter__(self):
+            if self.parent.counter < 0:
+                self._acquire(self.parent._read_waiters)
+            self.parent.counter += 1
+
+        def __exit__(self, *args, **kwargs):
+            self.parent.counter -= 1
+            self._exit()
+
+    class Writer(Base):
+        def __enter__(self):
+            if self.parent.counter != 0:
+                self._acquire(self.parent._write_waiters)
+            self.parent.counter -= 1
+
+        def __exit__(self, *args, **kwargs):
+            self.parent.counter += 1
+            self._exit()
+
+
+def main():
+    lock = CMEventletRWLock()
+    with lock.reader():
+        print('Got reader lock')
+
+    with lock.writer():
+        print('Got write lock')
+
+
+if __name__ == '__main__':
+    main()