Merge pull request #1125 from smallrye/doc/emitOn-warning

Warning about potential multi-threading issues when not using emitOn properly
smallrye · Nov 21, 2022 · fd46bdd · fd46bdd
2 parents 60ba371 + 3b165d2
commit fd46bdd
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diff --git a/documentation/docs/guides/emission-threads.md b/documentation/docs/guides/emission-threads.md
@@ -23,4 +23,9 @@ Just pass the _executor_ you want to use.
 
 !!! note
 
-    You cannot pass a specific thread, but you can implement a simple `Executor` dispatching on that specific thread, or use a _single threaded executor_.
+    You cannot pass a specific thread, but you can implement a simple `Executor` dispatching on that specific thread, or use a _single threaded executor_.
+
+!!! warning
+
+    Be careful as this operator can lead to concurrency problems with non thread-safe objects such as CDI request-scoped beans.
+    It might also break reactive-streams semantics with items being emitted concurrently.
diff --git a/documentation/docs/guides/emit-on-vs-run-subscription-on.md b/documentation/docs/guides/emit-on-vs-run-subscription-on.md
@@ -34,6 +34,11 @@ sequenceDiagram
     Note right of O: On executor thread
 ```
 
+!!! warning
+
+    Be careful as this operator can lead to concurrency problems with non thread-safe objects such as CDI request-scoped beans.
+    It might also break reactive-streams semantics with items being emitted concurrently.
+
 ## The case of runSubscriptionOn
 
 `runSubscriptionOn` applies to the subscription process.

diff --git a/documentation/docs/guides/imperative-to-reactive.md b/documentation/docs/guides/imperative-to-reactive.md
@@ -60,4 +60,9 @@ While `runSubscriptionOn` runs the subscription on the given executor, `emitOn`
 
 `emitOn` is also available on `Uni`.
 
+!!! warning
+
+    Be careful as this operator can lead to concurrency problems with non thread-safe objects such as CDI request-scoped beans.
+    It might also break reactive-streams semantics with items being emitted concurrently.
+
 
diff --git a/implementation/src/main/java/io/smallrye/mutiny/Multi.java b/implementation/src/main/java/io/smallrye/mutiny/Multi.java
@@ -215,6 +215,10 @@ default <O> O stage(Function<Multi<T>, O> stage) {
      * threading context to switch to a thread from the given executor. Same behavior for failure and completion.
      * <p>
      * Note that the subscriber is guaranteed to never be called concurrently.
+     * <p>
+     * <strong>Be careful as this operator can lead to concurrency problems with non thread-safe objects such as
+     * CDI request-scoped beans.
+     * It might also break reactive-streams semantics with items being emitted concurrently.</strong>
      *
      * @param executor the executor to use, must not be {@code null}
      * @return a new {@link Multi}

diff --git a/implementation/src/main/java/io/smallrye/mutiny/Uni.java b/implementation/src/main/java/io/smallrye/mutiny/Uni.java
@@ -317,6 +317,9 @@ default UniAwait<T> awaitUsing(Context context) {
      * <p>
      * Instead of receiving the {@code item} event on the thread firing the event, this method influences the
      * threading context to switch to a thread from the given executor.
+     * <p>
+     * <strong>Be careful as this operator can lead to concurrency problems with non thread-safe objects such as
+     * CDI request-scoped beans.</strong>
      *
      * @param executor the executor to use, must not be {@code null}
      * @return a new {@link Uni}