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| -rw-r--r-- | src/tools/clippy/src/docs/future_not_send.txt | 29 |
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diff --git a/src/tools/clippy/src/docs/future_not_send.txt b/src/tools/clippy/src/docs/future_not_send.txt new file mode 100644 index 000000000..0aa048d27 --- /dev/null +++ b/src/tools/clippy/src/docs/future_not_send.txt @@ -0,0 +1,29 @@ +### What it does +This lint requires Future implementations returned from +functions and methods to implement the `Send` marker trait. It is mostly +used by library authors (public and internal) that target an audience where +multithreaded executors are likely to be used for running these Futures. + +### Why is this bad? +A Future implementation captures some state that it +needs to eventually produce its final value. When targeting a multithreaded +executor (which is the norm on non-embedded devices) this means that this +state may need to be transported to other threads, in other words the +whole Future needs to implement the `Send` marker trait. If it does not, +then the resulting Future cannot be submitted to a thread pool in the +end user’s code. + +Especially for generic functions it can be confusing to leave the +discovery of this problem to the end user: the reported error location +will be far from its cause and can in many cases not even be fixed without +modifying the library where the offending Future implementation is +produced. + +### Example +``` +async fn not_send(bytes: std::rc::Rc<[u8]>) {} +``` +Use instead: +``` +async fn is_send(bytes: std::sync::Arc<[u8]>) {} +```
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