Struct sharded_slab::Slab
source · pub struct Slab<T, C: Config = DefaultConfig> { /* private fields */ }
Expand description
A sharded slab.
See the crate-level documentation for details on using this type.
Implementations§
source§impl<T, C: Config> Slab<T, C>
impl<T, C: Config> Slab<T, C>
sourcepub const USED_BITS: usize = C::USED_BITS
pub const USED_BITS: usize = C::USED_BITS
The number of bits in each index which are used by the slab.
If other data is packed into the usize
indices returned by
Slab::insert
, user code is free to use any bits higher than the
USED_BITS
-th bit freely.
This is determined by the Config
type that configures the slab’s
parameters. By default, all bits are used; this can be changed by
overriding the Config::RESERVED_BITS
constant.
sourcepub fn insert(&self, value: T) -> Option<usize>
pub fn insert(&self, value: T) -> Option<usize>
Inserts a value into the slab, returning the integer index at which that value was inserted. This index can then be used to access the entry.
If this function returns None
, then the shard for the current thread
is full and no items can be added until some are removed, or the maximum
number of shards has been reached.
Examples
let slab = Slab::new();
let key = slab.insert("hello world").unwrap();
assert_eq!(slab.get(key).unwrap(), "hello world");
sourcepub fn vacant_entry(&self) -> Option<VacantEntry<'_, T, C>>
pub fn vacant_entry(&self) -> Option<VacantEntry<'_, T, C>>
Return a handle to a vacant entry allowing for further manipulation.
This function is useful when creating values that must contain their
slab index. The returned VacantEntry
reserves a slot in the slab and
is able to return the index of the entry.
Examples
let mut slab = Slab::new();
let hello = {
let entry = slab.vacant_entry().unwrap();
let key = entry.key();
entry.insert((key, "hello"));
key
};
assert_eq!(hello, slab.get(hello).unwrap().0);
assert_eq!("hello", slab.get(hello).unwrap().1);
sourcepub fn remove(&self, idx: usize) -> bool
pub fn remove(&self, idx: usize) -> bool
Remove the value at the given index in the slab, returning true
if a
value was removed.
Unlike take
, this method does not block the current thread until
the value can be removed. Instead, if another thread is currently
accessing that value, this marks it to be removed by that thread when it
finishes accessing the value.
Examples
let slab = sharded_slab::Slab::new();
let key = slab.insert("hello world").unwrap();
// Remove the item from the slab.
assert!(slab.remove(key));
// Now, the slot is empty.
assert!(!slab.contains(key));
use std::sync::Arc;
let slab = Arc::new(sharded_slab::Slab::new());
let key = slab.insert("hello world").unwrap();
let slab2 = slab.clone();
let thread2 = std::thread::spawn(move || {
// Depending on when this thread begins executing, the item may
// or may not have already been removed...
if let Some(item) = slab2.get(key) {
assert_eq!(item, "hello world");
}
});
// The item will be removed by thread2 when it finishes accessing it.
assert!(slab.remove(key));
thread2.join().unwrap();
assert!(!slab.contains(key));
sourcepub fn take(&self, idx: usize) -> Option<T>
pub fn take(&self, idx: usize) -> Option<T>
Removes the value associated with the given key from the slab, returning it.
If the slab does not contain a value for that key, None
is returned
instead.
If the value associated with the given key is currently being
accessed by another thread, this method will block the current thread
until the item is no longer accessed. If this is not desired, use
remove
instead.
Note: This method blocks the calling thread by spinning until the
currently outstanding references are released. Spinning for long periods
of time can result in high CPU time and power consumption. Therefore,
take
should only be called when other references to the slot are
expected to be dropped soon (e.g., when all accesses are relatively
short).
Examples
let slab = sharded_slab::Slab::new();
let key = slab.insert("hello world").unwrap();
// Remove the item from the slab, returning it.
assert_eq!(slab.take(key), Some("hello world"));
// Now, the slot is empty.
assert!(!slab.contains(key));
use std::sync::Arc;
let slab = Arc::new(sharded_slab::Slab::new());
let key = slab.insert("hello world").unwrap();
let slab2 = slab.clone();
let thread2 = std::thread::spawn(move || {
// Depending on when this thread begins executing, the item may
// or may not have already been removed...
if let Some(item) = slab2.get(key) {
assert_eq!(item, "hello world");
}
});
// The item will only be removed when the other thread finishes
// accessing it.
assert_eq!(slab.take(key), Some("hello world"));
thread2.join().unwrap();
assert!(!slab.contains(key));
sourcepub fn get(&self, key: usize) -> Option<Entry<'_, T, C>>
pub fn get(&self, key: usize) -> Option<Entry<'_, T, C>>
Return a reference to the value associated with the given key.
If the slab does not contain a value for the given key, or if the
maximum number of concurrent references to the slot has been reached,
None
is returned instead.
Examples
let slab = sharded_slab::Slab::new();
let key = slab.insert("hello world").unwrap();
assert_eq!(slab.get(key).unwrap(), "hello world");
assert!(slab.get(12345).is_none());
sourcepub fn get_owned(self: Arc<Self>, key: usize) -> Option<OwnedEntry<T, C>>
pub fn get_owned(self: Arc<Self>, key: usize) -> Option<OwnedEntry<T, C>>
Return an owned reference to the value at the given index.
If the slab does not contain a value for the given key, None
is
returned instead.
Unlike get
, which borrows the slab, this method clones the Arc
around the slab. This means that the returned OwnedEntry
can be held
for an arbitrary lifetime. However, this method requires that the slab
itself be wrapped in an Arc
.
Examples
use std::sync::Arc;
let slab: Arc<Slab<&'static str>> = Arc::new(Slab::new());
let key = slab.insert("hello world").unwrap();
// Look up the created key, returning an `OwnedEntry`.
let value = slab.clone().get_owned(key).unwrap();
// Now, the original `Arc` clone of the slab may be dropped, but the
// returned `OwnedEntry` can still access the value.
assert_eq!(value, "hello world");
Unlike Entry
, an OwnedEntry
may be stored in a struct which must live
for the 'static
lifetime:
use sharded_slab::OwnedEntry;
use std::sync::Arc;
pub struct MyStruct {
entry: OwnedEntry<&'static str>,
// ... other fields ...
}
// Suppose this is some arbitrary function which requires a value that
// lives for the 'static lifetime...
fn function_requiring_static<T: 'static>(t: &T) {
// ... do something extremely important and interesting ...
}
let slab: Arc<Slab<&'static str>> = Arc::new(Slab::new());
let key = slab.insert("hello world").unwrap();
// Look up the created key, returning an `OwnedEntry`.
let entry = slab.clone().get_owned(key).unwrap();
let my_struct = MyStruct {
entry,
// ...
};
// We can use `my_struct` anywhere where it is required to have the
// `'static` lifetime:
function_requiring_static(&my_struct);
OwnedEntry
s may be sent between threads:
use std::{thread, sync::Arc};
let slab: Arc<Slab<&'static str>> = Arc::new(Slab::new());
let key = slab.insert("hello world").unwrap();
// Look up the created key, returning an `OwnedEntry`.
let value = slab.clone().get_owned(key).unwrap();
thread::spawn(move || {
assert_eq!(value, "hello world");
// ...
}).join().unwrap();
sourcepub fn contains(&self, key: usize) -> bool
pub fn contains(&self, key: usize) -> bool
Returns true
if the slab contains a value for the given key.
Examples
let slab = sharded_slab::Slab::new();
let key = slab.insert("hello world").unwrap();
assert!(slab.contains(key));
slab.take(key).unwrap();
assert!(!slab.contains(key));
sourcepub fn unique_iter(&mut self) -> UniqueIter<'_, T, C>
pub fn unique_iter(&mut self) -> UniqueIter<'_, T, C>
Returns an iterator over all the items in the slab.