Document that runWithClient must be called for every isolate (#1069)
diff --git a/pkgs/http/README.md b/pkgs/http/README.md
index 8ce106d..157a52f 100644
--- a/pkgs/http/README.md
+++ b/pkgs/http/README.md
@@ -255,7 +255,9 @@
If you depend on code that uses top-level functions (e.g. `http.post`) or
calls the [`Client()`][clientconstructor] constructor, then you can use
[`runWithClient`](runwithclient) to ensure that the correct
-`Client` is used.
+`Client` is used. When an [Isolate][isolate] is spawned, it does not inherit
+any variables from the calling Zone, so `runWithClient` needs to be used in
+each Isolate that uses `package:http`.
You can ensure that only the `Client` that you have explicitly configured is
used by defining `no_default_http_client=true` in the environment. This will
@@ -283,6 +285,7 @@
[fetchclient]: https://pub.dev/documentation/fetch_client/latest/fetch_client/FetchClient-class.html
[flutterhttpexample]: https://github.com/dart-lang/http/tree/master/pkgs/flutter_http_example
[ioclient]: https://pub.dev/documentation/http/latest/io_client/IOClient-class.html
+[isolate]: https://dart.dev/language/concurrency#how-isolates-work
[flutterstatemanagement]: https://docs.flutter.dev/data-and-backend/state-mgmt/options
[provider]: https://pub.dev/packages/provider
[runwithclient]: https://pub.dev/documentation/http/latest/http/runWithClient.html
