wayland_commons/
filter.rs

1//! Filter
2
3use std::{cell::RefCell, collections::VecDeque, rc::Rc};
4
5/// Holder of global dispatch-related data
6///
7/// This struct serves as a dynamic container for the dispatch-time
8/// global data that you gave to the dispatch method, and is given as
9/// input to all your callbacks. It allows you to share global state
10/// between your filters.
11///
12/// The main method of interest is the `get` method, which allows you to
13/// access a `&mut _` reference to the global data itself. The other methods
14/// are mostly used internally by the crate.
15pub struct DispatchData<'a> {
16    data: &'a mut dyn std::any::Any,
17}
18
19impl<'a> std::fmt::Debug for DispatchData<'a> {
20    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
21        f.write_str("DispatchData { ... }")
22    }
23}
24
25impl<'a> DispatchData<'a> {
26    /// Access the dispatch data knowing its type
27    ///
28    /// Will return `None` if the provided type is not the correct
29    /// inner type.
30    pub fn get<T: std::any::Any>(&mut self) -> Option<&mut T> {
31        self.data.downcast_mut()
32    }
33
34    /// Wrap a mutable reference
35    ///
36    /// This creates a new `DispatchData` from a mutable reference
37    pub fn wrap<T: std::any::Any>(data: &'a mut T) -> DispatchData<'a> {
38        DispatchData { data }
39    }
40
41    /// Reborrows this `DispatchData` to create a new one with the same content
42    ///
43    /// This is a quick and cheap way to propagate the `DispatchData` down a
44    /// callback stack by value. It is basically a noop only there to ease
45    /// work with the borrow checker.
46    pub fn reborrow(&mut self) -> DispatchData {
47        DispatchData { data: &mut *self.data }
48    }
49}
50
51struct Inner<E, F: ?Sized> {
52    pending: RefCell<VecDeque<E>>,
53    cb: RefCell<F>,
54}
55
56type DynInner<E> = Inner<E, dyn FnMut(E, &Filter<E>, DispatchData<'_>)>;
57
58/// An event filter
59///
60/// Can be used in wayland-client and wayland-server to aggregate
61/// messages from different objects into the same closure.
62///
63/// You need to provide it a closure of type `FnMut(E, &Filter<E>)`,
64/// which will be called any time a message is sent to the filter
65/// via the `send(..)` method. Your closure also receives a handle
66/// to the filter as argument, so that you can use it from within
67/// the callback (to assign new wayland objects to this filter for
68/// example).
69///
70/// The `Filter` can be cloned, and all clones send messages to the
71/// same closure. However it is not threadsafe.
72pub struct Filter<E> {
73    inner: Rc<DynInner<E>>,
74}
75
76impl<E: std::fmt::Debug> std::fmt::Debug for Filter<E> {
77    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
78        f.debug_struct("Filter").field("pending", &self.inner.pending).finish()
79    }
80}
81
82impl<E> Clone for Filter<E> {
83    fn clone(&self) -> Filter<E> {
84        Filter { inner: self.inner.clone() }
85    }
86}
87
88impl<E> Filter<E> {
89    /// Create a new filter from given closure
90    pub fn new<F: FnMut(E, &Filter<E>, DispatchData<'_>) + 'static>(f: F) -> Filter<E> {
91        Filter {
92            inner: Rc::new(Inner { pending: RefCell::new(VecDeque::new()), cb: RefCell::new(f) }),
93        }
94    }
95
96    /// Send a message to this filter
97    pub fn send(&self, evt: E, mut data: DispatchData) {
98        // gracefully handle reentrancy
99        if let Ok(mut guard) = self.inner.cb.try_borrow_mut() {
100            (&mut *guard)(evt, self, data.reborrow());
101            // process all events that might have been enqueued by the cb
102            while let Some(evt) = self.inner.pending.borrow_mut().pop_front() {
103                (&mut *guard)(evt, self, data.reborrow());
104            }
105        } else {
106            self.inner.pending.borrow_mut().push_back(evt);
107        }
108    }
109}
wayland_commons/filter.rs

wayland_commons/
filter.rs
