fix (client): fix race condition in process.subscribe that made the client crash #702
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…g it from the subscriptionNotifiers object. Also added a regression test.
VAX-1006 Possible race condition in `process.subscribe()`
We sometimes are encountering an issue in the subscribe call. The subscription notifier doesn't have the subscription id after the client.subscribe() is finished. While debugging we noticed that when this happens it's because the subscription data message is received before client.subscribe() finishes. So when trying to read the promise from the subscription notifiers it's undefined. The subscribe function This is what triggers the websocket communication that can end up deleting the subscriptionId before finishing. Here is where we get the undefined exception. Here is where the subscription is being removed. Would it make sense to check after client.subscribe() if the subscription exists? Or is that something that shouldn't happen? When everything works fine, during client.subscribe() WebSocket only receives SatSubsResp. And after that the rest of the subscription messages are received (SatSubsDataBegin, ..., SatSubsDataEnd). When it fails this messages are received while the client.subscribe() is running. |
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This PR fixes the race condition described in #426.
The problem was that
process.subscribewas creating a promise, storing it, making an async call, fetching the promise and returning it. But, depending on the order in which messages are received from Electric, the async call may resolve after the subscription was already delivered and hence the promise had already been deleted. The fix consists of storing the promise in a local variable insideprocess.subscribesuch that it doesn't need to fetch the promise after the async call.