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Document how error is received from worker transport #1548

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merged 7 commits into from Sep 5, 2022
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Document how error is received from worker transport #1548

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e155de3
document how error is received from worker transport
TommyDew42 Sep 3, 2022
94dc201
add a link to nodejs worker thread doc
TommyDew42 Sep 4, 2022
87e6732
improve doc based on review
TommyDew42 Sep 5, 2022
2ba6eb3
ops, missed a few places
TommyDew42 Sep 5, 2022
763e0ea
Update docs/transports.md
TommyDew42 Sep 5, 2022
72fec9a
add a line between sentences
TommyDew42 Sep 5, 2022
e70e756
Merge branch 'error-message-from-worker-doc' of github.com:TommyDew42…
TommyDew42 Sep 5, 2022
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18 changes: 9 additions & 9 deletions docs/transports.md
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Expand Up @@ -889,16 +889,16 @@ For full documentation of command line switches read the [README](https://github
[pino-pretty]: https://github.com/pinojs/pino-pretty

<a id="communication-between-pino-and-transport"></a>
## Communication between pino and transport
Here we discuss some technical details of how pino communicates with its [worker threads](https://nodejs.org/api/worker_threads.html).
## Communication between Pino and Transports
Here we discuss some technical details of how Pino communicates with its [worker threads](https://nodejs.org/api/worker_threads.html).

pino uses [`thread-stream`](https://github.com/pinojs/thread-stream) to create a stream for transports.
When we create a stream with `thread-stream`, `thread-stream` spawns a [worker](https://github.com/pinojs/thread-stream/blob/f19ac8dbd602837d2851e17fbc7dfc5bbc51083f/index.js#L50-L60) (an independent JS execution thread).
Pino uses [`thread-stream`](https://github.com/pinojs/thread-stream) to create a stream for transports.
When we create a stream with `thread-stream`, `thread-stream` spawns a [worker](https://github.com/pinojs/thread-stream/blob/f19ac8dbd602837d2851e17fbc7dfc5bbc51083f/index.js#L50-L60) (an independent JavaScript execution thread).


### Error message
How is error message propagated from a transport worker to pino?
Say we have a transport with an error listener:
### Error messages
How are error messages propagated from a transport worker to Pino?
Let's assume we have a transport with an error listener:
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```js
// index.js
const transport = pino.transport({
Expand All @@ -911,5 +911,5 @@ transport.on('error', err => {

const log = pino(transport)
```
When our worker emits an error event, the worker has listeners for it: [error](https://github.com/pinojs/thread-stream/blob/f19ac8dbd602837d2851e17fbc7dfc5bbc51083f/lib/worker.js#L59-L70) and [unhandledRejection](https://github.com/pinojs/thread-stream/blob/f19ac8dbd602837d2851e17fbc7dfc5bbc51083f/lib/worker.js#L135-L141). These listeners send the error message to the main thread where pino is in.
When pino receives the error message, it further [emit](https://github.com/pinojs/thread-stream/blob/f19ac8dbd602837d2851e17fbc7dfc5bbc51083f/index.js#L349) the error message. Finally the error message arrives at our index.js and caught by our error listener.
When our worker emits an error event, the worker has listeners for it: [error](https://github.com/pinojs/thread-stream/blob/f19ac8dbd602837d2851e17fbc7dfc5bbc51083f/lib/worker.js#L59-L70) and [unhandledRejection](https://github.com/pinojs/thread-stream/blob/f19ac8dbd602837d2851e17fbc7dfc5bbc51083f/lib/worker.js#L135-L141). These listeners send the error message to the main thread where pino is present.
When Pino receives the error message, it further [emits](https://github.com/pinojs/thread-stream/blob/f19ac8dbd602837d2851e17fbc7dfc5bbc51083f/index.js#L349) the error message. Finally the error message arrives at our `index.js` and is caught by our error listener.
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When our worker emits an error event, the worker has listeners for it: [error](https://github.com/pinojs/thread-stream/blob/f19ac8dbd602837d2851e17fbc7dfc5bbc51083f/lib/worker.js#L59-L70) and [unhandledRejection](https://github.com/pinojs/thread-stream/blob/f19ac8dbd602837d2851e17fbc7dfc5bbc51083f/lib/worker.js#L135-L141). These listeners send the error message to the main thread where pino is present.
When Pino receives the error message, it further [emits](https://github.com/pinojs/thread-stream/blob/f19ac8dbd602837d2851e17fbc7dfc5bbc51083f/index.js#L349) the error message. Finally the error message arrives at our `index.js` and is caught by our error listener.
When our worker emits an error event, the worker has listeners for it: [error](https://github.com/pinojs/thread-stream/blob/f19ac8dbd602837d2851e17fbc7dfc5bbc51083f/lib/worker.js#L59-L70) and [unhandledRejection](https://github.com/pinojs/thread-stream/blob/f19ac8dbd602837d2851e17fbc7dfc5bbc51083f/lib/worker.js#L135-L141). These listeners send the error message to the main thread where pino is present.
When Pino receives the error message, it further [emits](https://github.com/pinojs/thread-stream/blob/f19ac8dbd602837d2851e17fbc7dfc5bbc51083f/index.js#L349) the error message. Finally, the error message arrives at our `index.js` and is caught by our error listener.