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use std::fmt;
use std::panic::{self, UnwindSafe};
/// A panic payload indicating that execution of a salsa query was cancelled.
///
/// This can occur for a few reasons:
/// *
/// *
/// *
#[derive(Debug)]
#[non_exhaustive]
pub enum Cancelled {
/// The query was operating but the local database execution has been cancelled.
Local,
/// The query was operating on revision R, but there is a pending write to move to revision R+1.
PendingWrite,
/// The query was blocked on another thread, and that thread panicked.
PropagatedPanic,
}
impl Cancelled {
#[cold]
pub(crate) fn throw(self) -> ! {
// We use resume and not panic here to avoid running the panic
// hook (that is, to avoid collecting and printing backtrace).
panic::resume_unwind(Box::new(self));
}
/// Runs `f`, and catches any salsa cancellation.
pub fn catch<F, T>(f: F) -> Result<T, Cancelled>
where
F: FnOnce() -> T + UnwindSafe,
{
match panic::catch_unwind(f) {
Ok(t) => Ok(t),
Err(payload) => match payload.downcast() {
Ok(cancelled) => Err(*cancelled),
Err(payload) => panic::resume_unwind(payload),
},
}
}
}
impl std::fmt::Display for Cancelled {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
let why = match self {
Cancelled::Local => "local cancellation request",
Cancelled::PendingWrite => "pending write",
Cancelled::PropagatedPanic => "propagated panic",
};
f.write_str("cancelled because of ")?;
f.write_str(why)
}
}
impl std::error::Error for Cancelled {}