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//! # Clone only when it's necessary //! //! This library provides an efficient way to clone values in a rayon thread pool, but only once //! per thread. It cuts down on computation time for potentially expensive cloning operations. //! //! //! # Examples //! //! ``` //! use rayon_tlsctx::ThreadLocalCtx; //! use rayon::iter::*; //! //! const NUM_COPIES: usize = 16; //! //! let mut buf: Vec<u16> = (0..!0).collect(); //! //! // Create a thread local context with value 0. //! let ctx = ThreadLocalCtx::new(|| { //! // Simulate expensive operation. //! // Since we are building unlocked context, //! // the sleeps will occur concurrently. //! std::thread::sleep_ms(200); //! 0 //! }); //! //! let pool = rayon::ThreadPoolBuilder::new().num_threads(64).build().unwrap(); //! //! // Run inside a custom thread pool. //! pool.install(|| { //! // Sum the buffer `NUM_COPIES` times and accumulate the results //! // into the threaded pool of counts. Note that the counts may be //! // Unevenly distributed. //! (0..NUM_COPIES) //! .into_par_iter() //! .flat_map(|_| buf.par_iter()) //! .for_each(|i| { //! let mut cnt = unsafe { ctx.get() }; //! *cnt += *i as usize; //! }); //! }); //! //! //! let buf_sum = buf.into_iter().fold(0, |acc, i| acc + i as usize); //! //! // What matters is that the final sum matches the expected value. //! assert_eq!(ctx.into_iter().sum::<usize>(), buf_sum * NUM_COPIES); //! ``` use std::cell::Cell; use std::iter::FilterMap; use std::ops::{Deref, DerefMut}; use std::sync::Mutex; /// A thread local storage container for Rayon jobs /// /// This context can be used to efficiently clone `inner`, only when it's necessary. pub struct ThreadLocalCtx<T, F> { inner: F, init_mutex: Mutex<Vec<(Option<T>, bool)>>, cloned: Cell<*mut (Option<T>, bool)>, } unsafe impl<T, F: Send + Sync> Sync for ThreadLocalCtx<T, F> {} unsafe impl<T, F: Send + Sync> Send for ThreadLocalCtx<T, F> {} impl<T, F: Fn() -> T> ThreadLocalCtx<T, F> { /// Create a new `TlsCtx` /// /// # Examples /// /// Creating a thread-local byte buffer: /// ``` /// use rayon_tlsctx::ThreadLocalCtx; /// let ctx = ThreadLocalCtx::new(Vec::<u8>::new); /// ``` pub fn new(inner: F) -> Self { Self { inner, //: Mutex::new(inner), init_mutex: Mutex::new(vec![]), cloned: Cell::new(std::ptr::null_mut()), } } /// Create a new `TlsCtx`. /// /// This context utilises a lock for cloning values, making it usable for non-sync types. /// /// Cloning an initialised buffer for each thread: /// ``` /// use rayon_tlsctx::ThreadLocalCtx; /// use rayon::iter::*; /// use std::cell::Cell; /// # use rand::prelude::*; /// # let mut rng = rand::thread_rng(); /// /// let mut buf: Vec<u16> = (0..!0).collect(); /// buf.shuffle(&mut rng); /// /// let buf = (buf, Cell::new(0)); /// /// // Must use new_locked, because cloning a cell across threads is not allowed /// let ctx = ThreadLocalCtx::new_locked(move || buf.clone()); /// /// (0..16).into_par_iter().for_each(|_| unsafe { ctx.get(); }); /// ``` pub fn new_locked(inner: F) -> ThreadLocalCtx<T, impl Fn() -> T> { let locked_inner = Mutex::new(inner); let inner = move || (locked_inner.lock().unwrap())(); ThreadLocalCtx { inner, init_mutex: Mutex::new(vec![]), cloned: Cell::new(std::ptr::null_mut()), } } /// Get a thread local context reference with dynamically checked borrow rules /// /// # Safety /// /// Only one thread pool at a given time should use this scope. The thread pool size can not /// grow midway through. /// /// # Panics /// /// If called from outside of a Rayon thread pool, or when the reference is already being /// borrowed. /// /// # Examples /// /// ``` /// use rayon_tlsctx::ThreadLocalCtx; /// use rayon::iter::*; /// /// const NUM_COPIES: usize = 16; /// /// let mut buf: Vec<u16> = (0..!0).collect(); /// /// // Create a thread local context with value 0. /// let ctx = ThreadLocalCtx::new(|| 0); /// /// // Sum the buffer `NUM_COPIES` times and accumulate the results /// // into the threaded pool of counts. Note that the counts may be /// // Unevenly distributed. /// (0..NUM_COPIES) /// .into_par_iter() /// .flat_map(|_| buf.par_iter()) /// .for_each(|i| { /// let mut cnt = unsafe { ctx.get() }; /// *cnt += *i as usize; /// }); /// /// let buf_sum = buf.into_iter().fold(0, |acc, i| acc + i as usize); /// /// // What matters is that the final sum matches the expected value. /// assert_eq!(ctx.into_iter().sum::<usize>(), buf_sum * NUM_COPIES); /// ``` pub unsafe fn get<'a>(&'a self) -> ThreadLocalMut<'a, T, F> { if self.cloned.get().is_null() { let mut data = self.init_mutex.lock().unwrap(); if self.cloned.get().is_null() { *data = (0..rayon::current_num_threads()) .map(|_| (None, false)) .collect(); self.cloned.set(data.as_mut_ptr()); } } let tid = rayon::current_thread_index().unwrap(); match &mut *self.cloned.get().add(tid) { (_, true) => panic!("Already borrowed the value on thread {}!", tid), (Some(val), b) => { *b = true; ThreadLocalMut { val, parent: self, tid, } } (val, b) => { *b = true; let cloned = (self.inner)(); *val = Some(cloned); ThreadLocalMut { val: val.as_mut().unwrap(), parent: self, tid, } } } } } /// Consume the context and retrieve all created items. impl<T, F> IntoIterator for ThreadLocalCtx<T, F> { type Item = T; type IntoIter = FilterMap<std::vec::IntoIter<(Option<T>, bool)>, fn((Option<T>, bool)) -> Option<T>>; fn into_iter(self) -> Self::IntoIter { self.init_mutex .into_inner() .unwrap() .into_iter() .filter_map(|(i, _)| i) } } /// Borrowed thread local variable. /// /// This structure tracks borrow rules at runtime, it may be necessary to manually /// drop the object, if multiple rayon loops are involved. pub struct ThreadLocalMut<'a, T, F> { val: &'a mut T, parent: &'a ThreadLocalCtx<T, F>, tid: usize, } impl<'a, T, F> Deref for ThreadLocalMut<'a, T, F> { type Target = T; fn deref(&self) -> &T { self.val } } impl<'a, T, F> DerefMut for ThreadLocalMut<'a, T, F> { fn deref_mut(&mut self) -> &mut T { self.val } } impl<'a, T, F> Drop for ThreadLocalMut<'a, T, F> { fn drop(&mut self) { unsafe { (*self.parent.cloned.get().add(self.tid)).1 = false; } } }