apache / apache/pulsar-client-node
Interruptible Reader.readNext()?
- Lingua principale
- C++
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Descrizione
Hi,
I have a use case where I expose a Pulsar topic over HTTP via Server-Sent Events. Basically, when a client connects over HTTP, I do this:
```js
const reader = await client.createReader({
topic: request.params.topic,
startMessageId: request.headers['last-event-id'] ?
Pulsar.MessageId.deserialize(Buffer.from(request.headers['last-event-id'], 'base64')) :
Pulsar.MessageId.earliest()
});
```
Then I use a loop that reads messages as they come and sends them to the client:
```js
while (!clientGoneAway) {
let message;
message = await reader.readNext();
reply.raw.write(formatServerSentEvent(
message.getMessageId().serialize().toString('base64'),
message.getData().toString('utf-8')
));
}
```
Additionally, the server detects the `close` event on the HTTP requests, closes the reader and prevents further iteration:
```js
request.raw.once('close', async function() {
clientGoneAway = true;
await reader.close();
reply.raw.end();
})
```
(`request.raw` and `reply.raw` are Node.js req and res objects, respectively - they're just wrapped like this in Fastify.js)
Now, my problem is that even if I call `reader.close()`, the `reader.readNext();` never resolves nor rejects. It's not just a Promise problem - it seems like it's keeping a thread busy, because then all other operations hang: things like `fs.createReadStream`, as well as creating new readers, hang forever until I completely restart the Node.js process.
I know I can use a timeout with `reader.readNext(timeoutMS)`, but this has 2 major disadvantages:
* It turns the reader into a kind of poller
* It still does not vacate the thread - so it's possible to trivially saturate the thread pool by creating more readers than the pool size within the timeout period (so for example 4 readers in 1 second, when using a timeout of 1000 ms)
Is there any way to have the reader immediately abort all reads when closed?
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Direzione di ricerca
Inizia dai punti di ingresso di Reader API utilizzati da reader.readNext() e reader.close(), quindi riproduci il caso di chiusura durante la lettura con il client Node.js. Verifica se la chiusura del reader interrompe una lettura in sospeso e controlla il comportamento asincrono correlato. Il lavoro è completato quando una lettura bloccata viene risolta o rifiutata tempestivamente dopo la chiusura senza impedire altre operazioni Node.js.
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Valutazione
- Stack tecnologico
- javascript, node.js
- Ambito
- backend
- Tipo di issue
- Bug
- Difficoltà
- 4/5
- Tempo stimato
- 3-5 giorni
- Stato di attività
- Ferma
- Chiarezza
- Abbastanza chiara
- Idoneità per principianti
- 38/100