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//! Сooperative multitasking module //! //! With the fiber module, you can: //! - create, run and manage [fibers](struct.Fiber.html), //! - use a synchronization mechanism for fibers, similar to “condition variables” and similar to operating-system //! functions such as `pthread_cond_wait()` plus `pthread_cond_signal()`. //! //! See also: //! - [Threads, fibers and yields](https://www.tarantool.io/en/doc/latest/book/box/atomic/#threads-fibers-and-yields) //! - [Lua reference: Module fiber](https://www.tarantool.io/en/doc/latest/reference/reference_lua/fiber/) //! - [C API reference: Module fiber](https://www.tarantool.io/en/doc/latest/dev_guide/reference_capi/fiber/) use std::ffi::CString; use std::marker::PhantomData; use std::os::raw::c_void; use va_list::VaList; use crate::error::{Error, TarantoolError}; /// A fiber is a set of instructions which are executed with cooperative multitasking. /// /// Fibers managed by the fiber module are associated with a user-supplied function called the fiber function. /// /// A fiber has three possible states: **running**, **suspended** or **dead**. /// When a fiber is started with [fiber.start()](struct.Fiber.html#method.start), it is **running**. /// When a fiber is created with [Fiber::new()](struct.Fiber.html#method.new) (and has not been started yet) or yields control /// with [sleep()](fn.sleep.html), it is **suspended**. /// When a fiber ends (because the fiber function ends), it is **dead**. /// /// A runaway fiber can be stopped with [fiber.cancel()](struct.Fiber.html#method.cancel). /// However, [fiber.cancel()](struct.Fiber.html#method.cancel) is advisory — it works only if the runaway fiber calls /// [is_cancelled()](fn.is_cancelled.html) occasionally. In practice, a runaway fiber can only become unresponsive if it /// does many computations and does not check whether it has been cancelled. /// /// The other potential problem comes from fibers which never get scheduled, because they are not subscribed to any events, /// or because no relevant events occur. Such morphing fibers can be killed with [fiber.cancel()](struct.Fiber.html#method.cancel) /// at any time, since [fiber.cancel()](struct.Fiber.html#method.cancel) sends an asynchronous wakeup event to the fiber, /// and [is_cancelled()](fn.is_cancelled.html) is checked whenever such a wakeup event occurs. /// /// Example: /// ```rust /// use tarantool_module::fiber::Fiber; /// let mut fiber = Fiber::new("test_fiber", &mut |_| { /// println!("I'm a fiber"); /// 0 /// }); /// fiber.start(()); /// println!("Fiber started") /// ``` /// /// ```text /// I'm a fiber /// Fiber started /// ``` pub struct Fiber<'a, T: 'a> { inner: *mut ffi::Fiber, callback: *mut c_void, phantom: PhantomData<&'a T>, } impl<'a, T> Fiber<'a, T> { /// Create a new fiber. /// /// Takes a fiber from fiber cache, if it's not empty. Can fail only if there is not enough memory for /// the fiber structure or fiber stack. /// /// The created fiber automatically returns itself to the fiber cache when its `main` function /// completes. The initial fiber state is **suspended**. /// /// Ordinarily [Fiber::new()](#method.new) is used in conjunction with [fiber.set_joinable()](#method.set_joinable) /// and [fiber.join()](#method.join) /// /// - `name` - string with fiber name /// - `callback` - function for run inside fiber /// /// See also: [fiber.start()](#method.start) pub fn new<F>(name: &str, callback: &mut F) -> Self where F: FnMut(Box<T>) -> i32, { let (callback_ptr, trampoline) = unsafe { unpack_callback(callback) }; Self { inner: unsafe { ffi::fiber_new(CString::new(name).unwrap().as_ptr(), trampoline) }, callback: callback_ptr, phantom: PhantomData, } } /// Create a new fiber with defined attributes. /// /// Can fail only if there is not enough memory for the fiber structure or fiber stack. /// /// The created fiber automatically returns itself to the fiber cache if has default stack size /// when its `main` function completes. The initial fiber state is **suspended**. /// /// - `name` - string with fiber name /// - `fiber_attr` - fiber attributes /// - `callback` - function for run inside fiber /// /// See also: [fiber.start()](#method.start) pub fn new_with_attr<F>(name: &str, attr: &FiberAttr, callback: &mut F) -> Self where F: FnMut(Box<T>) -> i32, { let (callback_ptr, trampoline) = unsafe { unpack_callback(callback) }; Self { inner: unsafe { ffi::fiber_new_ex(CString::new(name).unwrap().as_ptr(), attr.inner, trampoline) }, callback: callback_ptr, phantom: PhantomData, } } /// Start execution of created fiber. /// /// - `arg` - argument to start the fiber with /// /// See also: [fiber.new()](#method.new) pub fn start(&mut self, arg: T) { unsafe { ffi::fiber_start(self.inner, self.callback, Box::into_raw(Box::<T>::new(arg))); } } /// Interrupt a synchronous wait of a fiber. pub fn wakeup(&self) { unsafe { ffi::fiber_wakeup(self.inner) } } /// Wait until the fiber is dead and then move its execution status to the caller. /// /// “Join” a joinable fiber. That is, let the fiber’s function run and wait until the fiber’s status is **dead** /// (normally a status becomes **dead** when the function execution finishes). Joining will cause a yield, /// therefore, if the fiber is currently in a **suspended** state, execution of its fiber function will resume. /// /// This kind of waiting is more convenient than going into a loop and periodically checking the status; /// however, it works only if the fiber was created with [fiber.new()](#method.new) and was made joinable with /// [fiber.set_joinable()](#method.set_joinable). /// /// The fiber must not be detached (See also: [fiber.set_joinable()](#method.set_joinable)). /// /// Return: fiber function return code pub fn join(&self) -> i32 { unsafe { ffi::fiber_join(self.inner) } } /// Set fiber to be joinable (false by default). /// /// - `is_joinable` - status to set pub fn set_joinable(&mut self, is_joinable: bool) { unsafe { ffi::fiber_set_joinable(self.inner, is_joinable) } } /// Cancel a fiber. (set `FIBER_IS_CANCELLED` flag) /// /// Running and suspended fibers can be cancelled. After a fiber has been cancelled, attempts to operate on it will /// cause error: the fiber is dead. But a dead fiber can still report its id and status. /// Possible errors: cancel is not permitted for the specified fiber object. /// /// If target fiber's flag `FIBER_IS_CANCELLABLE` set, then it would be woken up (maybe prematurely). /// Then current fiber yields until the target fiber is dead (or is woken up by /// [fiber.wakeup()](#method.wakeup)). pub fn cancel(&mut self) { unsafe { ffi::fiber_cancel(self.inner) } } } /// Make it possible or not possible to wakeup the current /// fiber immediately when it's cancelled. /// /// - `is_cancellable` - status to set /// /// Returns previous state. pub fn set_cancellable(is_cancellable: bool) -> bool { unsafe { ffi::fiber_set_cancellable(is_cancellable) } } /// Check current fiber for cancellation (it must be checked manually). pub fn is_cancelled() -> bool { unsafe { ffi::fiber_is_cancelled() } } /// Put the current fiber to sleep for at least `time` seconds. /// /// Yield control to the scheduler and sleep for the specified number of seconds. /// Only the current fiber can be made to sleep. /// /// - `time` - time to sleep /// /// > **Note:** this is a cancellation point (See also: [is_cancelled()](fn.is_cancelled.html)) pub fn sleep(time: f64) { unsafe { ffi::fiber_sleep(time) } } /// Report loop begin time as double (cheap). pub fn time() -> f64 { unsafe { ffi::fiber_time() } } /// Report loop begin time as 64-bit int. pub fn time64() -> u64 { unsafe { ffi::fiber_time64() } } /// Report loop begin time as double (cheap). Uses monotonic clock. pub fn clock() -> f64 { unsafe { ffi::fiber_clock() } } /// Report loop begin time as 64-bit int. Uses monotonic clock. pub fn clock64() -> u64 { unsafe { ffi::fiber_clock64() } } /// Yield control to the scheduler. /// /// Return control to another fiber and wait until it'll be woken. Equivalent to `fiber.sleep(0)`. /// /// See also: [Fiber::wakeup()](struct.Fiber.html#method.wakeup) pub fn fiber_yield() { unsafe { ffi::fiber_yield() } } /// Reschedule fiber to end of event loop cycle. pub fn reschedule() { unsafe { ffi::fiber_reschedule() } } /// Fiber attributes container pub struct FiberAttr { inner: *mut ffi::FiberAttr, } impl FiberAttr { /// Create a new fiber attribute container and initialize it with default parameters. /// Can be used for many fibers creation, corresponding fibers will not take ownership. /// /// This is safe to drop `FiberAttr` value when fibers created with this attribute still exist. pub fn new() -> Self { FiberAttr { inner: unsafe { ffi::fiber_attr_new() }, } } /// Get stack size from the fiber attribute. /// /// Returns: stack size pub fn stack_size(&self) -> usize { unsafe { ffi::fiber_attr_getstacksize(self.inner) } } ///Set stack size for the fiber attribute. /// /// - `stack_size` - stack size for new fibers pub fn set_stack_size(&mut self, stack_size: usize) -> Result<(), Error> { if unsafe { ffi::fiber_attr_setstacksize(self.inner, stack_size) } < 0 { Err(TarantoolError::last().into()) } else { Ok(()) } } } impl Drop for FiberAttr { fn drop(&mut self) { unsafe { ffi::fiber_attr_delete(self.inner) } } } /// Conditional variable for cooperative multitasking (fibers). /// /// A cond (short for "condition variable") is a synchronization primitive /// that allow fibers to yield until some predicate is satisfied. Fiber /// conditions have two basic operations - `wait()` and `signal()`. [cond.wait()](#method.wait) /// suspends execution of fiber (i.e. yields) until [cond.signal()](#method.signal) is called. /// /// Example: /// /// ```rust /// use tarantool_module::fiber::Cond; /// let cond = fiber.cond(); /// cond.wait(); /// ``` /// /// The job will hang because [cond.wait()](#method.wait) – will go to sleep until the condition variable changes. /// /// ```rust /// // Call from another fiber: /// cond.signal(); /// ``` /// /// The waiting stopped, and the [cond.wait()](#method.wait) function returned true. /// /// This example depended on the use of a global conditional variable with the arbitrary name cond. /// In real life, programmers would make sure to use different conditional variable names for different applications. /// /// Unlike `pthread_cond`, [Cond]() doesn't require mutex/latch wrapping. pub struct Cond { inner: *mut ffi::FiberCond, } /// - call [Cond::new()](#method.new) to create a named condition variable, which will be called `cond` for examples in this section. /// - call [cond.wait()](#method.wait) to make a fiber wait for a signal via a condition variable. /// - call [cond.signal()](#method.signal) to send a signal to wake up a single fiber that has executed [cond.wait()](#method.wait). /// - call [cond.broadcast()](#method.broadcast) to send a signal to all fibers that have executed [cond.wait()](#method.wait). impl Cond { /// Instantiate a new fiber cond object. pub fn new() -> Self { Cond { inner: unsafe { ffi::fiber_cond_new() }, } } /// Wake one fiber waiting for the cond. /// Does nothing if no one is waiting. Does not yield. pub fn signal(&self) { unsafe { ffi::fiber_cond_signal(self.inner) } } /// Wake up all fibers waiting for the cond. /// Does not yield. pub fn broadcast(&self) { unsafe { ffi::fiber_cond_broadcast(self.inner) } } /// Suspend the execution of the current fiber (i.e. yield) until [signal()](#method.signal) is called. /// /// Like pthread_cond, FiberCond can issue spurious wake ups caused by explicit /// [Fiber::wakeup()](struct.Fiber.html#method.wakeup) or [Fiber::cancel()](struct.Fiber.html#method.cancel) /// calls. It is highly recommended to wrap calls to this function into a loop /// and check an actual predicate and `fiber_testcancel()` on every iteration. /// /// - `timeout` - timeout in seconds /// /// Returns: /// - `true` on [signal()](#method.signal) call or a spurious wake up. /// - `false` on timeout, diag is set to `TimedOut` pub fn wait_timeout(&self, timeout: f64) -> bool { !(unsafe { ffi::fiber_cond_wait_timeout(self.inner, timeout) } < 0) } /// Shortcut for [wait_timeout()](#method.wait_timeout). pub fn wait(&self) -> bool { !(unsafe { ffi::fiber_cond_wait(self.inner) } < 0) } } impl Drop for Cond { fn drop(&mut self) { unsafe { ffi::fiber_cond_delete(self.inner) } } } /// A lock for cooperative multitasking environment pub struct Latch { inner: *mut ffi::Latch, } impl Latch { /// Allocate and initialize the new latch. pub fn new() -> Self { Latch { inner: unsafe { ffi::box_latch_new() }, } } /// Lock a latch. Waits indefinitely until the current fiber can gain access to the latch. pub fn lock(&self) -> LatchGuard { unsafe { ffi::box_latch_lock(self.inner) }; LatchGuard { latch: self } } /// Try to lock a latch. Return immediately if the latch is locked. /// /// Returns: /// - `Some` - success /// - `None` - the latch is locked. pub fn try_lock(&self) -> Option<LatchGuard> { if unsafe { ffi::box_latch_trylock(self.inner) } == 0 { Some(LatchGuard { latch: self }) } else { None } } } impl Drop for Latch { fn drop(&mut self) { unsafe { ffi::box_latch_delete(self.inner) } } } /// An RAII implementation of a "scoped lock" of a latch. When this structure is dropped (falls out of scope), /// the lock will be unlocked. pub struct LatchGuard<'a> { latch: &'a Latch, } impl<'a> Drop for LatchGuard<'a> { fn drop(&mut self) { unsafe { ffi::box_latch_unlock(self.latch.inner) } } } pub(crate) unsafe fn unpack_callback<F, T>(callback: &mut F) -> (*mut c_void, ffi::FiberFunc) where F: FnMut(Box<T>) -> i32, { unsafe extern "C" fn trampoline<F, T>(mut args: VaList) -> i32 where F: FnMut(Box<T>) -> i32, { let closure: &mut F = &mut *(args.get::<*const c_void>() as *mut F); let arg = Box::from_raw(args.get::<*const c_void>() as *mut T); (*closure)(arg) } (callback as *mut F as *mut c_void, Some(trampoline::<F, T>)) } mod ffi { use std::os::raw::{c_char, c_int}; use va_list::VaList; #[repr(C)] pub struct Fiber { _unused: [u8; 0], } pub type FiberFunc = Option<unsafe extern "C" fn(VaList) -> c_int>; extern "C" { pub fn fiber_new(name: *const c_char, f: FiberFunc) -> *mut Fiber; pub fn fiber_new_ex( name: *const c_char, fiber_attr: *const FiberAttr, f: FiberFunc, ) -> *mut Fiber; pub fn fiber_yield(); pub fn fiber_start(callee: *mut Fiber, ...); pub fn fiber_wakeup(f: *mut Fiber); pub fn fiber_cancel(f: *mut Fiber); pub fn fiber_set_cancellable(yesno: bool) -> bool; pub fn fiber_set_joinable(fiber: *mut Fiber, yesno: bool); pub fn fiber_join(f: *mut Fiber) -> c_int; pub fn fiber_sleep(s: f64); pub fn fiber_is_cancelled() -> bool; pub fn fiber_time() -> f64; pub fn fiber_time64() -> u64; pub fn fiber_clock() -> f64; pub fn fiber_clock64() -> u64; pub fn fiber_reschedule(); } #[repr(C)] pub struct FiberAttr { _unused: [u8; 0], } extern "C" { pub fn fiber_attr_new() -> *mut FiberAttr; pub fn fiber_attr_delete(fiber_attr: *mut FiberAttr); pub fn fiber_attr_setstacksize(fiber_attr: *mut FiberAttr, stack_size: usize) -> c_int; pub fn fiber_attr_getstacksize(fiber_attr: *mut FiberAttr) -> usize; } #[repr(C)] pub struct FiberCond { _unused: [u8; 0], } extern "C" { pub fn fiber_cond_new() -> *mut FiberCond; pub fn fiber_cond_delete(cond: *mut FiberCond); pub fn fiber_cond_signal(cond: *mut FiberCond); pub fn fiber_cond_broadcast(cond: *mut FiberCond); pub fn fiber_cond_wait_timeout(cond: *mut FiberCond, timeout: f64) -> c_int; pub fn fiber_cond_wait(cond: *mut FiberCond) -> c_int; } #[repr(C)] pub struct Latch { _unused: [u8; 0], } extern "C" { pub fn box_latch_new() -> *mut Latch; pub fn box_latch_delete(latch: *mut Latch); pub fn box_latch_lock(latch: *mut Latch); pub fn box_latch_trylock(latch: *mut Latch) -> c_int; pub fn box_latch_unlock(latch: *mut Latch); } }