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//! Stack abstraction for lightweight processes //! //! This abstraction allows us to execute lifecycle callbacks when //! a process transites from one state to another. //! //! If we want to make an analogy, stack abstraction is similar to actor lifecycle abstractions //! in frameworks like Akka, but tailored version for Rust environment. use super::proc_state::*; use std::fmt::{self, Debug, Formatter}; use std::sync::atomic::{AtomicUsize, Ordering}; use std::sync::{Arc, Mutex}; /// Stack abstraction for lightweight processes /// /// # Example /// /// ```rust /// use lightproc::proc_stack::ProcStack; /// use lightproc::proc_state::EmptyProcState; /// /// ProcStack::default() /// .with_before_start(|s: &mut EmptyProcState| { println!("Before start"); }) /// .with_after_complete(|s: &mut EmptyProcState| { println!("After complete"); }) /// .with_after_panic(|s: &mut EmptyProcState| { println!("After panic"); }); /// ``` pub struct ProcStack { /// Process ID for the Lightweight Process /// /// Can be used to identify specific processes during any executor, reactor implementations. pub pid: AtomicUsize, pub(crate) state: ProcState, /// Before start callback /// /// This callback is called before we start to inner future of the process pub(crate) before_start: Option<Arc<dyn Fn(ProcState) + Send + Sync>>, /// After complete callback /// /// This callback is called after future resolved to it's output. /// Mind that, even panic occurs this callback will get executed. /// /// Eventually all panics are coming from an Error output. pub(crate) after_complete: Option<Arc<dyn Fn(ProcState) + Send + Sync>>, /// After panic callback /// /// This callback is only called when a panic has been occurred. /// Mind that [ProcHandle](proc_handle/struct.ProcHandle.html) is not using this pub(crate) after_panic: Option<Arc<dyn Fn(ProcState) + Send + Sync>>, } impl ProcStack { /// Adds pid for the process which is going to take this stack /// /// # Example /// /// ```rust /// use lightproc::proc_stack::ProcStack; /// /// ProcStack::default() /// .with_pid(1); /// ``` pub fn with_pid(mut self, pid: usize) -> Self { self.pid = AtomicUsize::new(pid); self } /// Adds state for the process which is going to be embedded into this stack. /// /// # Example /// /// ```rust /// use lightproc::proc_stack::ProcStack; /// /// pub struct GlobalState { /// pub amount: usize /// } /// /// ProcStack::default() /// .with_pid(1) /// .with_state(GlobalState { amount: 1 }); /// ``` pub fn with_state<S>(mut self, state: S) -> Self where S: State + 'static, { self.state = Arc::new(Mutex::new(state)); self } /// Adds a callback that will be executed before polling inner future to the stack /// /// ```rust /// use lightproc::proc_stack::{ProcStack}; /// use lightproc::proc_state::EmptyProcState; /// /// ProcStack::default() /// .with_before_start(|s: &mut EmptyProcState| { println!("Before start"); }); /// ``` pub fn with_before_start<C, S>(mut self, callback: C) -> Self where S: State, C: Fn(&mut S) + Send + Sync + 'static, { self.before_start = Some(self.wrap_callback(callback)); self } /// Adds a callback that will be executed after inner future resolves to an output to the stack /// /// ```rust /// use lightproc::proc_stack::ProcStack; /// use lightproc::proc_state::EmptyProcState; /// /// ProcStack::default() /// .with_after_complete(|s: &mut EmptyProcState| { println!("After complete"); }); /// ``` pub fn with_after_complete<C, S>(mut self, callback: C) -> Self where S: State, C: Fn(&mut S) + Send + Sync + 'static, { self.after_complete = Some(self.wrap_callback(callback)); self } /// Adds a callback that will be executed after inner future panics to the stack /// /// ```rust /// use lightproc::proc_stack::ProcStack; /// use lightproc::proc_state::EmptyProcState; /// /// ProcStack::default() /// .with_after_panic(|s: &mut EmptyProcState| { println!("After panic"); }); /// ``` pub fn with_after_panic<C, S>(mut self, callback: C) -> Self where S: State, C: Fn(&mut S) + Send + Sync + 'static, { self.after_panic = Some(self.wrap_callback(callback)); self } /// Utility function to get_pid for the implementation of executors. /// /// ```rust /// use lightproc::proc_stack::ProcStack; /// /// let proc = ProcStack::default().with_pid(123); /// /// assert_eq!(proc.get_pid(), 123); /// ``` pub fn get_pid(&self) -> usize { self.pid.load(Ordering::Acquire) } /// Get the state which is embedded into this [ProcStack]. /// /// ```rust /// use lightproc::proc_stack::ProcStack; /// /// #[derive(Copy, Clone)] /// pub struct GlobalState { /// pub amount: usize /// } /// /// let mut proc = ProcStack::default().with_pid(123) /// .with_state(GlobalState { amount: 0} ); /// /// let state = proc.get_state::<GlobalState>(); /// ``` pub fn get_state<S>(&self) -> S where S: State + Copy + 'static, { let state = self.state.clone(); let s = unsafe { &*(&state as *const ProcState as *const Arc<Mutex<S>>) }; *s.lock().unwrap() } /// Wraps the callback to the with given trait boundaries of the state. /// /// Why there is unsafe? /// * Given state is taken as dyn State we don't know the size. But rest assured it is sized. /// * Executor of the callback should know what exactly coming up from state. That said it can even pass dynamically sized trait too, we can't constrain that. /// * Cast it to the correct type and trust the boundaries which was already ensured at the method signature. /// * Synchronization can't revolve around the unsafe. because we lock the dynamic state right after the cast. fn wrap_callback<C, S>(&self, callback: C) -> Arc<dyn Fn(ProcState) + Send + Sync> where S: State + 'static, C: Fn(&mut S) + Send + Sync + 'static, { let wrapped = move |s: ProcState| { let x = unsafe { &*(&s as *const ProcState as *const Arc<Mutex<S>>) }; let mut mg = x.lock().unwrap(); callback(&mut *mg); }; Arc::new(wrapped) } } /// /// Default implementation for the ProcStack impl Default for ProcStack { fn default() -> Self { ProcStack { pid: AtomicUsize::new(0xDEAD_BEEF), state: Arc::new(Mutex::new(EmptyState)), before_start: None, after_complete: None, after_panic: None, } } } impl Debug for ProcStack { fn fmt(&self, fmt: &mut Formatter) -> fmt::Result { fmt.debug_struct("ProcStack") .field("pid", &self.pid.load(Ordering::SeqCst)) .field("state", &self.state) .field("before_start", &self.before_start.is_some()) .field("after_complete", &self.after_complete.is_some()) .field("after_panic", &self.after_panic.is_some()) .finish() } } impl Clone for ProcStack { fn clone(&self) -> Self { ProcStack { pid: AtomicUsize::new(self.pid.load(Ordering::Acquire)), state: self.state.clone(), before_start: self.before_start.clone(), after_complete: self.after_complete.clone(), after_panic: self.after_panic.clone(), } } }