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rayon: Use parallel iterators within shards #360

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3 changes: 3 additions & 0 deletions Cargo.lock
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1 change: 1 addition & 0 deletions Cargo.toml
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Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,7 @@ categories = ["concurrency", "algorithms", "data-structures"]
all = ["raw-api", "typesize", "serde", "rayon", "arbitrary"]
raw-api = []
typesize = ["dep:typesize"]
rayon = ["dep:rayon", "hashbrown/rayon"]
inline-more = ["hashbrown/inline-more"]

[dependencies]
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21 changes: 9 additions & 12 deletions src/rayon/map.rs
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Expand Up @@ -4,7 +4,10 @@ use crate::{DashMap, HashMap};
use core::hash::{BuildHasher, Hash};
use crossbeam_utils::CachePadded;
use rayon::iter::plumbing::UnindexedConsumer;
use rayon::iter::{FromParallelIterator, IntoParallelIterator, ParallelExtend, ParallelIterator};
use rayon::iter::{
FromParallelIterator, IntoParallelIterator, IntoParallelRefIterator,
IntoParallelRefMutIterator, ParallelExtend, ParallelIterator,
};
use std::sync::Arc;

impl<K, V, S> ParallelExtend<(K, V)> for DashMap<K, V, S>
Expand Down Expand Up @@ -56,12 +59,6 @@ where
}
}

// Implementation note: while the shards will iterate in parallel, we flatten
// sequentially within each shard (`flat_map_iter`), because the standard
// `HashMap` only implements `ParallelIterator` by collecting to a `Vec` first.
// There is real parallel support in the `hashbrown/rayon` feature, but we don't
// always use that map.

impl<K, V, S> IntoParallelIterator for DashMap<K, V, S>
where
K: Send + Eq + Hash,
Expand Down Expand Up @@ -95,7 +92,7 @@ where
{
Vec::from(self.shards)
.into_par_iter()
.flat_map_iter(|shard| shard.into_inner().into_inner().into_iter())
.flat_map(|shard| shard.into_inner().into_inner())
.drive_unindexed(consumer)
}
}
Expand Down Expand Up @@ -134,13 +131,13 @@ where
{
self.shards
.into_par_iter()
.flat_map_iter(|shard| {
.flat_map(|shard| {
// SAFETY: we keep the guard alive with the shard iterator,
// and with any refs produced by the iterator
let (guard, shard) = unsafe { RwLockReadGuardDetached::detach_from(shard.read()) };

let guard = Arc::new(guard);
shard.iter().map(move |(k, v)| {
shard.par_iter().map(move |(k, v)| {
let guard = Arc::clone(&guard);
RefMulti::new(guard, k, v)
})
Expand Down Expand Up @@ -195,14 +192,14 @@ where
{
self.shards
.into_par_iter()
.flat_map_iter(|shard| {
.flat_map(|shard| {
// SAFETY: we keep the guard alive with the shard iterator,
// and with any refs produced by the iterator
let (guard, shard) =
unsafe { RwLockWriteGuardDetached::detach_from(shard.write()) };

let guard = Arc::new(guard);
shard.iter_mut().map(move |(k, v)| {
shard.par_iter_mut().map(move |(k, v)| {
let guard = Arc::clone(&guard);
RefMutMulti::new(guard, k, v)
})
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