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//! A lock-free concurrent slab.
mod addr;
pub(crate) use addr::Address;
mod entry;
pub(crate) use entry::Entry;
mod generation;
pub(crate) use generation::Generation;
mod page;
mod shard;
use shard::Shard;
mod slot;
use slot::Slot;
mod stack;
use stack::TransferStack;
#[cfg(all(loom, test))]
mod tests;
use crate::loom::sync::Mutex;
use crate::util::bit;
use std::fmt;
#[cfg(target_pointer_width = "64")]
const MAX_THREADS: usize = 4096;
#[cfg(target_pointer_width = "32")]
const MAX_THREADS: usize = 2048;
/// Max number of pages per slab
const MAX_PAGES: usize = bit::pointer_width() as usize / 4;
cfg_not_loom! {
/// Size of first page
const INITIAL_PAGE_SIZE: usize = 32;
}
cfg_loom! {
const INITIAL_PAGE_SIZE: usize = 2;
}
/// A sharded slab.
pub(crate) struct Slab<T> {
// Signal shard for now. Eventually there will be more.
shard: Shard<T>,
local: Mutex<()>,
}
unsafe impl<T: Send> Send for Slab<T> {}
unsafe impl<T: Sync> Sync for Slab<T> {}
impl<T: Entry> Slab<T> {
/// Returns a new slab with the default configuration parameters.
pub(crate) fn new() -> Slab<T> {
Slab {
shard: Shard::new(),
local: Mutex::new(()),
}
}
/// allocs a value into the slab, returning a key that can be used to
/// access it.
///
/// 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.
pub(crate) fn alloc(&self) -> Option<Address> {
// we must lock the slab to alloc an item.
let _local = self.local.lock().unwrap();
self.shard.alloc()
}
/// Removes the value associated with the given key from the slab.
pub(crate) fn remove(&self, idx: Address) {
// try to lock the slab so that we can use `remove_local`.
let lock = self.local.try_lock();
// if we were able to lock the slab, we are "local" and can use the fast
// path; otherwise, we will use `remove_remote`.
if lock.is_ok() {
self.shard.remove_local(idx)
} else {
self.shard.remove_remote(idx)
}
}
/// Return a reference to the value associated with the given key.
///
/// If the slab does not contain a value for the given key, `None` is
/// returned instead.
pub(crate) fn get(&self, token: Address) -> Option<&T> {
self.shard.get(token)
}
}
impl<T> fmt::Debug for Slab<T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("Slab").field("shard", &self.shard).finish()
}
}
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