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Take the DAP lock on the R thread to avoid deadlock #992

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Take the DAP lock on the R thread to avoid deadlock #992

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26 changes: 14 additions & 12 deletions crates/ark/src/dap/dap_server.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -446,19 +446,21 @@ impl<R: Read, W: Write> DapServer<R, W> {
}

fn collect_r_variables(&self, variables_reference: i64) -> Vec<RVariable> {
let state = self.state.lock().unwrap();
let variables_reference_to_r_object = &state.variables_reference_to_r_object;

let Some(object) = variables_reference_to_r_object.get(&variables_reference) else {
log::error!(
"Failed to locate R object for `variables_reference` {variables_reference}."
);
return Vec::new();
};
// Wait until we're in the `r_task()` to lock
// See https://github.com/posit-dev/positron/issues/5024
let state = self.state.clone();
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@DavisVaughan DavisVaughan Dec 16, 2025

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Suggested change
let state = self.state.clone();
let state = Arc::clone(&self.state);

Just so it's very clear this is a cheap clone. I had to go look it up myself to make sure.

This is a typical rust pattern i see with Arc


let variables = r_task(move || {
let state = state.lock().unwrap();
let variables_reference_to_r_object = &state.variables_reference_to_r_object;

let Some(object) = variables_reference_to_r_object.get(&variables_reference) else {
log::error!(
"Failed to locate R object for `variables_reference` {variables_reference}."
);
return Vec::new();
};

// Should be safe to run an r-task while paused in the debugger, tasks
// are still run while polling within the read console hook
let variables = r_task(|| {
let object = object.get();
object_variables(object.sexp)
});
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