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In Tokio, the futures for tasks are stored on the stack unless they are explicitly boxed, either by the user or auto-boxed by Tokio when they are especially large. Auto-boxing now also occurs in release mode (since #6826). Having very large futures can be problematic as it can cause a stack overflow. In some cases it might be desireable to have smaller futures, even if they are placed on the heap. This change adds the size of the future driving an async task or the function driving a blocking task to the tracing instrumentation. In the case of a future that is auto-boxed by Tokio, both the final size as well the original size before boxing is included. To do this, a new struct `SpawnMeta` gets passed down from where a future might get boxed to where the instrumentation is added. This contains the task name (optionally) and the original future or function size. If the `tokio_unstable` cfg flag and the `tracing` feature aren't both enabled, then this struct will be zero sized, which is a small improvement on the previous behavior of unconditionally passing down an `Option<&str>` for the name. This will make this information immediately available in Tokio Console, and will enable new lints which will warn users if they have large futures (just for async tasks). We have some tests under the `tracing-instrumentation` crate which test that the `size.bytes` and `original_size.bytes` fields are set correctly. The minimal version of `tracing` required for Tokio has been bumped from 0.1.25 to 0.1.29 to get the `Value` impl on `Option<T>`. Given that the current version is 0.1.40, this seems reasonable, especially given that Tracing's MSRV is still lower than Tokio's in the latest version.
tokio-util
Utilities for working with Tokio.
License
This project is licensed under the MIT license.
Contribution
Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in Tokio by you, shall be licensed as MIT, without any additional terms or conditions.