Common and Device:

- Implemented generic MutexQueues class
- Implemented sequentialization of operations in Device component to prevent data corruption and race conditions

src/common/tools/mutex_queues/MutexQueues.py

+# Copyright 2021-2023 H2020 TeraFlow (https://www.teraflow-h2020.eu/)
+#
+# 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.
+
+# MutexQueues:
+# ------------
+# This class enables to schedule and serialize operations concurrently issued
+# over a number of resources. For instance, when multiple components want to
+# configure devices through the Device component, configuration operations
+# have to be serialized to prevent data corruptions, and race conditions, etc.
+# Usage Example:
+#   class Servicer():
+#       def __init__(self):
+#           # init other stuff
+#           self.drivers = dict()
+#           self.mutex_queues = MutexQueues()
+#       
+#       def configure_device(self, device_uuid, settings):
+#           self.mutex_queues.wait_my_turn(device_uuid)
+#           driver = self.drivers.get(device_uuid)
+#           if driver is None:
+#               driver = Driver(device_uuid)
+#               self.drivers[device_uuid] = driver
+#           driver.configure(settings)
+#           self.mutex_queues.signal_done(device_uuid)
+
+import threading
+from queue import Queue
+from typing import Dict
+
+class MutexQueues:
+    def __init__(self) -> None:
+        # lock to protect dictionary updates
+        self.lock = threading.Lock()
+
+        # dictionaty of queues of mutexes: queue_name => queue[mutex]
+        # first mutex is the running one
+        self.mutex_queues : Dict[str, Queue[threading.Event]] = dict()
+    
+    def wait_my_turn(self, queue_name : str) -> None:
+        # create my mutex and enqueue it
+        mutex = threading.Event()
+        with self.lock:
+            queue : Queue = self.mutex_queues.setdefault(queue_name, Queue())
+            first_in_queue = (queue.qsize() == 0)
+            queue.put_nowait(mutex)
+
+        # if I'm the first in the queue upon addition, means there are no running tasks
+        # directly return without waiting
+        if first_in_queue: return
+
+        # otherwise, wait for my turn in the queue
+        mutex.wait()
+
+    def signal_done(self, queue_name : str) -> None:
+        # I'm done with my work
+        with self.lock:
+            queue : Queue = self.mutex_queues.setdefault(queue_name, Queue())
+            
+            # remove muself from the queue
+            queue.get_nowait()
+
+            # if there are no other tasks queued, return
+            if queue.qsize() == 0: return
+
+            # otherwise, signal the next task in the queue to start
+            next_mutex : threading.Event = queue.queue[0]
+            next_mutex.set()

src/common/tools/mutex_queues/__init__.py

+# Copyright 2021-2023 H2020 TeraFlow (https://www.teraflow-h2020.eu/)
+#
+# 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.
+

src/device/service/DeviceService.py

@@ -23,10 +23,15 @@ from .driver_api.DriverInstanceCache import DriverInstanceCache
 from .DeviceServiceServicerImpl import DeviceServiceServicerImpl
 from .MonitoringLoops import MonitoringLoops
 
+# Custom gRPC settings
+# Multiple clients might keep connections alive waiting for RPC methods to be executed.
+# Requests needs to be serialized to ensure correct device configurations
+GRPC_MAX_WORKERS = 200
+
 class DeviceService(GenericGrpcService):
     def __init__(self, driver_instance_cache : DriverInstanceCache, cls_name: str = __name__) -> None:
         port = get_service_port_grpc(ServiceNameEnum.DEVICE)
-        super().__init__(port, cls_name=cls_name)
+        super().__init__(port, max_workers=GRPC_MAX_WORKERS, cls_name=cls_name)
         database = Database(get_database_backend(backend=BackendEnum.INMEMORY))
         self.monitoring_loops = MonitoringLoops(database)
         self.device_servicer = DeviceServiceServicerImpl(database, driver_instance_cache, self.monitoring_loops)