rust-update: handle SIGINT from long-running update threads The current code does not respond to ^C until after the Rust bit is finished doing its work. This is expected, since Rust holds the GIL for the duration of the call and does not call `PyErr_CheckSignals`. Freeing the GIL to do our work does not really improve anything since the Rust threads are still going, and the only way of cancelling a thread is by making it cooperate. So we do the following: - remember the SIGINT handler in hg-cpython and reset it after the call into core (see inline comment in `update.rs` about this) - make all update threads watch for a global `AtomicBool` being `true`, and if so stop their work - reset the global bool and exit early (i.e. before writing the dirstate) - raise SIGINT from `hg-cpython` if update returns `InterruptReceived`

pub type ExitCode = i32;

/// Successful exit
pub const OK: ExitCode = 0;

/// Generic abort
pub const ABORT: ExitCode = 255;

// Abort when there is a config related error
pub const CONFIG_ERROR_ABORT: ExitCode = 30;

/// Indicates that the operation might work if retried in a different state.
/// Examples: Unresolved merge conflicts, unfinished operations
pub const STATE_ERROR: ExitCode = 20;

// Abort when there is an error while parsing config
pub const CONFIG_PARSE_ERROR_ABORT: ExitCode = 10;

/// Generic something completed but did not succeed
pub const UNSUCCESSFUL: ExitCode = 1;

/// Command or feature not implemented by rhg
pub const UNIMPLEMENTED: ExitCode = 252;

/// The fallback path is not valid
pub const INVALID_FALLBACK: ExitCode = 253;