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Code Issues Releases Wiki Activity

Clarify use of Arc in shared state (#221)

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This commit is contained in:
Mark Lodato
2021-04-05 19:41:26 -04:00
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parent a808293221
commit 1069dfa177
3 changed files with 28 additions and 8 deletions
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10
content/docs/extractors.md
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@ -99,11 +99,15 @@ Here is an example of a handler that stores the number of processed requests:
{{< include-example example="request-handlers" file="main.rs" section="data" >}}
Although this handler will work, `self.0` will be different depending on the number of threads and
number of requests processed per thread. A proper implementation would use `web::Data` and `AtomicUsize`.
Although this handler will work, `data.count` will only count the number of requests
handled *by each thread*. To count the number of total requests across all threads,
one should use `Arc` and [atomics][atomics].
{{< include-example example="request-handlers" file="handlers_arc.rs" section="arc" >}}
> **Note**, if you want the *entire* state to be shared across all threads, use
> `web::Data` and `app_data` as described in [Shared Mutable State][shared_mutable_state].
> Be careful with synchronization primitives like `Mutex` or `RwLock`. The `actix-web` framework
> handles requests asynchronously. By blocking thread execution, all concurrent
> request handling processes would block. If you need to share or update some state
@ -119,3 +123,5 @@ number of requests processed per thread. A proper implementation would use `web:
[bytesexample]: https://docs.rs/actix-web/3/actix_web/trait.FromRequest.html#example-4
[payloadexample]: https://docs.rs/actix-web/3/actix_web/web/struct.Payload.html
[actix]: https://actix.github.io/actix/actix/
[atomics]: https://doc.rust-lang.org/std/sync/atomic/
[shared_mutable_state]: ../application#shared-mutable-state