// Copyright 2018-2021 the Deno authors. All rights reserved. MIT license.
// Think of Resources as File Descriptors. They are integers that are allocated
// by the privileged side of Deno which refer to various rust objects that need
// to be persisted between various ops. For example, network sockets are
// resources. Resources may or may not correspond to a real operating system
// file descriptor (hence the different name).
use std::any::type_name;
use std::any::Any;
use std::any::TypeId;
use std::borrow::Cow;
use std::collections::BTreeMap;
use std::iter::Iterator;
use std::rc::Rc;
/// All objects that can be store in the resource table should implement the
/// `Resource` trait.
pub trait Resource: Any + 'static {
/// Returns a string representation of the resource which is made available
/// to JavaScript code through `op_resources`. The default implementation
/// returns the Rust type name, but specific resource types may override this
/// trait method.
fn name(&self) -> Cow<str> {
type_name::<Self>().into()
}
/// Resources may implement the `close()` trait method if they need to do
/// resource specific clean-ups, such as cancelling pending futures, after a
/// resource has been removed from the resource table.
fn close(self: Rc<Self>) {}
}
impl dyn Resource {
#[inline(always)]
fn is<T: Resource>(&self) -> bool {
self.type_id() == TypeId::of::<T>()
}
#[inline(always)]
#[allow(clippy::needless_lifetimes)]
pub fn downcast_rc<'a, T: Resource>(self: &'a Rc<Self>) -> Option<&'a Rc<T>> {
if self.is::<T>() {
let ptr = self as *const Rc<_> as *const Rc<T>;
Some(unsafe { &*ptr })
} else {
None
}
}
}
/// A `ResourceId` is an integer value referencing a resource. It could be
/// considered to be the Deno equivalent of a `file descriptor` in POSIX like
/// operating systems. Elsewhere in the code base it is commonly abbreviated
/// to `rid`.
// TODO: use `u64` instead?
pub type ResourceId = u32;
/// Map-like data structure storing Deno's resources (equivalent to file
/// descriptors).
///
/// Provides basic methods for element access. A resource can be of any type.
/// Different types of resources can be stored in the same map, and provided
/// with a name for description.
///
/// Each resource is identified through a _resource ID (rid)_, which acts as
/// the key in the map.
#[derive(Default)]
pub struct ResourceTable {
index: BTreeMap<ResourceId, Rc<dyn Resource>>,
next_rid: ResourceId,
}
impl ResourceTable {
/// Inserts resource into the resource table, which takes ownership of it.
///
/// The resource type is erased at runtime and must be statically known
/// when retrieving it through `get()`.
///
/// Returns a unique resource ID, which acts as a key for this resource.
pub fn add<T: Resource>(&mut self, resource: T) -> ResourceId {
self.add_rc(Rc::new(resource))
}
/// Inserts a `Rc`-wrapped resource into the resource table.
///
/// The resource type is erased at runtime and must be statically known
/// when retrieving it through `get()`.
///
/// Returns a unique resource ID, which acts as a key for this resource.
pub fn add_rc<T: Resource>(&mut self, resource: Rc<T>) -> ResourceId {
let resource = resource as Rc<dyn Resource>;
let rid = self.next_rid;
let removed_resource = self.index.insert(rid, resource);
assert!(removed_resource.is_none());
self.next_rid += 1;
rid
}
/// Returns true if any resource with the given `rid` exists.
pub fn has(&self, rid: ResourceId) -> bool {
self.index.contains_key(&rid)
}
/// Returns a reference counted pointer to the resource of type `T` with the
/// given `rid`. If `rid` is not present or has a type different than `T`,
/// this function returns `None`.
pub fn get<T: Resource>(&self, rid: ResourceId) -> Option<Rc<T>> {
self
.index
.get(&rid)
.and_then(|rc| rc.downcast_rc::<T>())
.map(Clone::clone)
}
pub fn get_any(&self, rid: ResourceId) -> Option<Rc<dyn Resource>> {
self.index.get(&rid).map(Clone::clone)
}
/// Removes a resource of type `T` from the resource table and returns it.
/// If a resource with the given `rid` exists but its type does not match `T`,
/// it is not removed from the resource table. Note that the resource's
/// `close()` method is *not* called.
pub fn take<T: Resource>(&mut self, rid: ResourceId) -> Option<Rc<T>> {
let resource = self.get::<T>(rid)?;
self.index.remove(&rid);
Some(resource)
}
/// Removes a resource from the resource table and returns it. Note that the
/// resource's `close()` method is *not* called.
pub fn take_any(&mut self, rid: ResourceId) -> Option<Rc<dyn Resource>> {
self.index.remove(&rid)
}
/// Removes the resource with the given `rid` from the resource table. If the
/// only reference to this resource existed in the resource table, this will
/// cause the resource to be dropped. However, since resources are reference
/// counted, therefore pending ops are not automatically cancelled. A resource
/// may implement the `close()` method to perform clean-ups such as canceling
/// ops.
pub fn close(&mut self, rid: ResourceId) -> Option<()> {
self.index.remove(&rid).map(|resource| resource.close())
}
/// Returns an iterator that yields a `(id, name)` pair for every resource
/// that's currently in the resource table. This can be used for debugging
/// purposes or to implement the `op_resources` op. Note that the order in
/// which items appear is not specified.
///
/// # Example
///
/// ```
/// # use deno_core::ResourceTable;
/// # let resource_table = ResourceTable::default();
/// let resource_names = resource_table.names().collect::<Vec<_>>();
/// ```
pub fn names(&self) -> impl Iterator<Item = (ResourceId, Cow<str>)> {
self
.index
.iter()
.map(|(&id, resource)| (id, resource.name()))
}
}