Broadcasting Events in gRPC from Server to Clients

When creating applications involving multiple clients connecting to a server, it's often necessary to broadcast events to all connected clients. In gRPC, there are several approaches to achieve this.

One option to consider is using a long-polling approach. This involves having clients periodically poll the server for updates. When an event occurs, the server notifies all connected clients, triggering their polling calls to return with the new information.

To implement a long-polling approach in Python, consider the following code (a similar implementation is possible in other languages like Go):

# SERVER
class UpdaterServer(UpdaterServicer):
    def __init__(self):
        self.condition = threading.Condition()
        self.updates = []

    def post_update(self, update):
        with self.condition:
            self.updates.append(updates)
            self.condition.notify_all()

    def GetUpdates(self, req, context):
        with self.condition:
            while self.updates[req.last_received_update   1:] == []:
                self.condition.wait()
            new_updates = self.updates[req.last_received_update   1:]
            response = GetUpdatesResponse()
            for update in new_updates:
                response.updates.add().CopyFrom(update)
            response.update_index = req.last_received_update   len(new_updates)
            return response

# SEPARATE THREAD IN CLIENT
request = GetUpdatesRequest()
request.last_received_update = -1
while True:
    stub = UpdaterStub(channel)
    try:
        response = stub.GetUpdates(request, timeout=60*10)
        handle_updates(response.updates)
        request.last_received_update = response.update_index
    except grpc.FutureTimeoutError:
        pass

In this example:

• The post_update() method allows the clients to be notified about events.
• The server maintains a list of updates and notifies clients when a new update becomes available.
• The client polls the server periodically, waiting for updates.
• When events occur, the server triggers the client's polling calls to return with the updated information.

Using a long-polling approach ensures that all connected clients receive broadcast events and provides a reliable way to communicate updates to multiple parties.