telltale-vm 4.0.0

Bytecode VM for choreographic session type protocols
Documentation 
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//! Backend abstraction for VM execution engines.
//!
//! Allows swapping cooperative and threaded backends behind a common API.

use cfg_if::cfg_if;

use crate::effect::EffectHandler;
use crate::loader::CodeImage;
use crate::session::SessionId;
use crate::vm::{ObsEvent, RunStatus, StepResult, VMError, VM};

/// Common VM backend interface.
pub trait VMBackend {
    /// Load a choreography into the backend, returning the session ID.
    ///
    /// # Errors
    ///
    /// Returns a `VMError` if limits are exceeded or the image is invalid.
    fn load_choreography(&mut self, image: &CodeImage) -> Result<SessionId, VMError>;

    /// Execute one scheduler round: advance up to `n` ready coroutines.
    ///
    /// # Errors
    ///
    /// Returns a `VMError` if any coroutine faults.
    fn step_round(&mut self, handler: &dyn EffectHandler, n: usize) -> Result<StepResult, VMError>;

    /// Run until completion or `max_rounds` is reached.
    ///
    /// # Errors
    ///
    /// Returns a `VMError` if any coroutine faults.
    fn run(&mut self, handler: &dyn EffectHandler, max_rounds: usize)
        -> Result<RunStatus, VMError>;

    /// Get the observable trace (cloned).
    #[must_use]
    fn trace(&self) -> Vec<ObsEvent>;
}

impl VMBackend for VM {
    fn load_choreography(&mut self, image: &CodeImage) -> Result<SessionId, VMError> {
        self.load_choreography(image)
    }

    fn step_round(&mut self, handler: &dyn EffectHandler, n: usize) -> Result<StepResult, VMError> {
        self.step_round(handler, n)
    }

    fn run(
        &mut self,
        handler: &dyn EffectHandler,
        max_rounds: usize,
    ) -> Result<RunStatus, VMError> {
        self.run_concurrent(handler, max_rounds, 1)
    }

    fn trace(&self) -> Vec<ObsEvent> {
        self.trace().to_vec()
    }
}

cfg_if! {
    if #[cfg(feature = "multi-thread")] {
        use crate::threaded::ThreadedVM;

        impl VMBackend for ThreadedVM {
            fn load_choreography(&mut self, image: &CodeImage) -> Result<SessionId, VMError> {
                self.load_choreography(image)
            }

            fn step_round(
                &mut self,
                handler: &dyn EffectHandler,
                n: usize,
            ) -> Result<StepResult, VMError> {
                self.step_round(handler, n)
            }

            fn run(
                &mut self,
                handler: &dyn EffectHandler,
                max_rounds: usize,
            ) -> Result<RunStatus, VMError> {
                self.run(handler, max_rounds)
            }

            fn trace(&self) -> Vec<ObsEvent> {
                self.trace().to_vec()
            }
        }
    }
}