wasi_common/
table.rs

1use crate::{Error, ErrorExt};
2use std::any::Any;
3use std::collections::HashMap;
4use std::sync::{Arc, RwLock};
5
6/// The `Table` type is designed to map u32 handles to resources. The table is now part of the
7/// public interface to a `WasiCtx` - it is reference counted so that it can be shared beyond a
8/// `WasiCtx` with other WASI proposals (e.g. `wasi-crypto` and `wasi-nn`) to manage their
9/// resources. Elements in the `Table` are `Any` typed.
10///
11/// The `Table` type is intended to model how the Interface Types concept of Resources is shaping
12/// up. Right now it is just an approximation.
13pub struct Table(RwLock<Inner>);
14
15struct Inner {
16    map: HashMap<u32, Arc<dyn Any + Send + Sync>>,
17    next_key: u32,
18}
19
20impl Table {
21    /// Create an empty table. New insertions will begin at 3, above stdio.
22    pub fn new() -> Self {
23        Table(RwLock::new(Inner {
24            map: HashMap::new(),
25            next_key: 3, // 0, 1 and 2 are reserved for stdio
26        }))
27    }
28
29    /// Insert a resource at a certain index.
30    pub fn insert_at<T: Any + Send + Sync>(&self, key: u32, a: Arc<T>) {
31        self.0.write().unwrap().map.insert(key, a);
32    }
33
34    /// Insert a resource at the next available index.
35    pub fn push<T: Any + Send + Sync>(&self, a: Arc<T>) -> Result<u32, Error> {
36        let mut inner = self.0.write().unwrap();
37        // NOTE: The performance of this new key calculation could be very bad once keys wrap
38        // around.
39        if inner.map.len() == u32::MAX as usize {
40            return Err(Error::trap(anyhow::Error::msg("table has no free keys")));
41        }
42        loop {
43            let key = inner.next_key;
44            inner.next_key += 1;
45            if inner.map.contains_key(&key) {
46                continue;
47            }
48            inner.map.insert(key, a);
49            return Ok(key);
50        }
51    }
52
53    /// Check if the table has a resource at the given index.
54    pub fn contains_key(&self, key: u32) -> bool {
55        self.0.read().unwrap().map.contains_key(&key)
56    }
57
58    /// Check if the resource at a given index can be downcast to a given type.
59    /// Note: this will always fail if the resource is already borrowed.
60    pub fn is<T: Any + Sized>(&self, key: u32) -> bool {
61        if let Some(r) = self.0.read().unwrap().map.get(&key) {
62            r.is::<T>()
63        } else {
64            false
65        }
66    }
67
68    /// Get an Arc reference to a resource of a given type at a given index. Multiple
69    /// immutable references can be borrowed at any given time.
70    pub fn get<T: Any + Send + Sync + Sized>(&self, key: u32) -> Result<Arc<T>, Error> {
71        if let Some(r) = self.0.read().unwrap().map.get(&key).cloned() {
72            r.downcast::<T>()
73                .map_err(|_| Error::badf().context("element is a different type"))
74        } else {
75            Err(Error::badf().context("key not in table"))
76        }
77    }
78
79    /// Get a mutable reference to a resource of a given type at a given index.
80    /// Only one such reference can be borrowed at any given time.
81    pub fn get_mut<T: Any>(&mut self, key: u32) -> Result<&mut T, Error> {
82        let entry = match self.0.get_mut().unwrap().map.get_mut(&key) {
83            Some(entry) => entry,
84            None => return Err(Error::badf().context("key not in table")),
85        };
86        let entry = match Arc::get_mut(entry) {
87            Some(entry) => entry,
88            None => return Err(Error::badf().context("cannot mutably borrow shared file")),
89        };
90        entry
91            .downcast_mut::<T>()
92            .ok_or_else(|| Error::badf().context("element is a different type"))
93    }
94
95    /// Remove a resource at a given index from the table. Returns the resource
96    /// if it was present.
97    pub fn delete<T: Any + Send + Sync>(&self, key: u32) -> Option<Arc<T>> {
98        self.0
99            .write()
100            .unwrap()
101            .map
102            .remove(&key)
103            .map(|r| r.downcast::<T>().unwrap())
104    }
105
106    /// Remove a resource at a given index from the table. Returns the resource
107    /// if it was present.
108    pub fn renumber(&self, from: u32, to: u32) -> Result<(), Error> {
109        let map = &mut self.0.write().unwrap().map;
110        let from_entry = map.remove(&from).ok_or(Error::badf())?;
111        map.insert(to, from_entry);
112        Ok(())
113    }
114}
wasi_common/table.rs

wasi_common/
table.rs
