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Broadcasting in gRPC: Server to Client Communication
When establishing a gRPC connection, it's often necessary to broadcast events or updates from the server to connected clients. To achieve this, various approaches can be employed.
Stream Observables
One common approach is to utilize server-side streams. Each connected client establishes its own stream with the server. However, subscribing to other server-client streams directly is not feasible.
Long-Polling
An alternative option is to implement a long-polling approach. This involves having clients continuously poll the server at regular intervals, checking for new updates. Upon receiving an update, the client will receive a response and wait for the next polling interval.
Example Implementation
Here's an example of how you might implement long-polling using gRPC:
Server-Side Code
<code class="python">import threading class UpdaterServer: 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:] return GetUpdatesResponse( updates=new_updates, update_index=req.last_received_update + len(new_updates), )</code>
Client-Side Code (Separate Thread)
<code class="python">from threading import Event def handle_updates(updates): pass event = Event() request = GetUpdatesRequest(last_received_update=-1) while not event.is_set(): try: stub = UpdaterStub(channel) response = stub.GetUpdates(request, timeout=60*10) handle_updates(response.updates) request.last_received_update = response.update_index except grpc.FutureTimeoutError: pass</code>
By implementing this approach, connected clients can retrieve updates from the server in a continuous fashion.
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