Friendlier error messages for re-entrancy failures #66
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Currently, if code tries to re-acquire a lock it already holds, it correctly panics but with an unhelpful error message about Shuttle's internals. Instead, let's provide a nicer error message about why the calling code is buggy. This came up while trying out the super neat example from a [fasterthanlime blog post], which Shuttle has no trouble finding the deadlock in, but wasn't giving a helpful error message for. [fasterthanlime blog post]: https://fasterthanli.me/articles/a-rust-match-made-in-hell
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Neat example and usability improvement!
One thing I was thinking about is whether it makes sense to have a feature in Shuttle that does precise on-the-fly deadlock detection. Right now there might be a deadlock among some tasks early on in an execution, but we need to wait until the end of the execution to detect it. It might be helpful for debugging to stop the execution right when the deadlock happens.
The nice thing about the current check is that it is completely generic. What I'm proposing would require knowledge about the synchronization primitives (e.g., a combined resource allocation graph for both Mutex and RwLock).
| if *writer == me { | ||
| panic!("deadlock! task {:?} tried to acquire a RwLock it already holds", me); | ||
| } |
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nit: Should be an RwLock, like in the doc. Same below.
I bet we could get some of the same effect by just having the ability to print a stacktrace of all the deadlocked threads. I'll open a separate issue for that. |
Currently, if code tries to re-acquire a lock it already holds, it
correctly panics but with an unhelpful error message about Shuttle's
internals. Instead, let's provide a nicer error message about why the
calling code is buggy.
This came up while trying out the super neat example from a
fasterthanlime blog post, which Shuttle has no trouble finding the
deadlock in, but wasn't giving a helpful error message for.
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