Remove the thread pool from future::Cache

Clean up dependencies and feature flags.

Cargo.toml

@@ -20,10 +20,10 @@ default = ["sync", "atomic64", "quanta"]
 
 # This feature is enabled by default. Disable it when you do not need
 # `moka::sync::{Cache, SegmentedCache}`
-sync = ["_core"]
+sync = ["scheduled-thread-pool"]
 
 # Enable this feature to use `moka::future::Cache`.
-future = ["_core", "async-lock", "async-trait", "futures-util"]
+future = ["async-lock", "async-trait", "futures-util"]
 
 # Enable this feature to activate optional logging from caches.
 # Currently cache will emit log only when it encounters a panic in user provided
@@ -46,41 +46,26 @@ js = ["uuid/js"]
 # performance impacts and is intended for debugging purpose.
 unstable-debug-counters = ["future"]
 
-# A feature used internally.
-_core = [
-    "crossbeam-channel",
-    "crossbeam-epoch",
-    "crossbeam-utils",
-    "once_cell",
-    "parking_lot",
-    "scheduled-thread-pool",
-    "smallvec",
-    "tagptr",
-    "thiserror",
-    "triomphe",
-    "uuid",
-]
-
 [dependencies]
-
-# The "_core" dependencies used by "sync" and "future" features.
-crossbeam-channel = { version = "0.5.5", optional = true }
-crossbeam-utils = { version = "0.8", optional = true }
-once_cell = { version = "1.7", optional = true }
-parking_lot = { version = "0.12", optional = true }
-scheduled-thread-pool = { version = "0.2.7", optional = true }
-smallvec = { version = "1.8", optional = true }
-tagptr = { version = "0.2", optional = true }
+crossbeam-channel = { version = "0.5.5" }
+crossbeam-epoch = { version = "0.9.9" }
+crossbeam-utils = { version = "0.8" }
+once_cell = { version = "1.7" }
+parking_lot = { version = "0.12" }
+smallvec = { version = "1.8" }
+tagptr = { version = "0.2" }
+thiserror = { version = "1.0" }
+uuid = { version = "1.1", features = ["v4"] }
 
 # Opt-out serde and stable_deref_trait features
 # https://github.com/Manishearth/triomphe/pull/5
-triomphe = { version = "0.1.3", default-features = false, optional = true }
+triomphe = { version = "0.1.3", default-features = false }
 
 # Optional dependencies (enabled by default)
-crossbeam-epoch = { version = "0.9.9", optional = true }
 quanta = { version = "0.11.0", optional = true }
-thiserror = { version = "1.0", optional = true }
-uuid = { version = "1.1", features = ["v4"], optional = true }
+
+# Optional dependencies (sync)
+scheduled-thread-pool = { version = "0.2.7", optional = true }
 
 # Optional dependencies (future)
 async-io = { version = "1.4", optional = true }

src/common.rs

@@ -35,6 +35,7 @@ impl From<usize> for CacheRegion {
     }
 }
 
+#[cfg(feature = "future")]
 impl CacheRegion {
     pub(crate) fn name(&self) -> &'static str {
         match self {
@@ -63,6 +64,7 @@ pub(crate) fn sketch_capacity(max_capacity: u64) -> u32 {
     max_capacity.try_into().unwrap_or(u32::MAX).max(128)
 }
 
+#[cfg(feature = "sync")]
 pub(crate) fn available_parallelism() -> usize {
     use std::{num::NonZeroUsize, thread::available_parallelism};
     available_parallelism().map(NonZeroUsize::get).unwrap_or(1)

src/common/builder_utils.rs

@@ -1,5 +1,6 @@
 use std::time::Duration;
 
+#[cfg(feature = "sync")]
 use super::concurrent::housekeeper;
 
 const YEAR_SECONDS: u64 = 365 * 24 * 3600;
@@ -17,6 +18,7 @@ pub(crate) fn ensure_expirations_or_panic(
     }
 }
 
+#[cfg(feature = "sync")]
 pub(crate) fn housekeeper_conf(thread_pool_enabled: bool) -> housekeeper::Configuration {
     if thread_pool_enabled {
         housekeeper::Configuration::new_thread_pool(true)

src/common/concurrent.rs

@@ -8,8 +8,14 @@ use triomphe::Arc as TrioArc;
 pub(crate) mod constants;
 pub(crate) mod deques;
 pub(crate) mod entry_info;
+
+#[cfg(feature = "sync")]
 pub(crate) mod housekeeper;
+
+#[cfg(feature = "sync")]
 pub(crate) mod thread_pool;
+
+#[cfg(feature = "sync")]
 pub(crate) mod unsafe_weak_pointer;
 
 // target_has_atomic is more convenient but yet unstable (Rust 1.55)

src/common/concurrent/constants.rs

@@ -1,14 +1,20 @@
 pub(crate) const MAX_SYNC_REPEATS: usize = 4;
 pub(crate) const PERIODICAL_SYNC_INITIAL_DELAY_MILLIS: u64 = 500;
-pub(crate) const PERIODICAL_SYNC_NORMAL_PACE_MILLIS: u64 = 300;
-pub(crate) const PERIODICAL_SYNC_FAST_PACE_NANOS: u64 = 500;
 
 pub(crate) const READ_LOG_FLUSH_POINT: usize = 512;
 pub(crate) const READ_LOG_SIZE: usize = READ_LOG_FLUSH_POINT * (MAX_SYNC_REPEATS + 2);
 
 pub(crate) const WRITE_LOG_FLUSH_POINT: usize = 512;
-pub(crate) const WRITE_LOG_LOW_WATER_MARK: usize = WRITE_LOG_FLUSH_POINT / 2;
-// pub(crate) const WRITE_LOG_HIGH_WATER_MARK: usize = WRITE_LOG_FLUSH_POINT * (MAX_SYNC_REPEATS - 1);
 pub(crate) const WRITE_LOG_SIZE: usize = WRITE_LOG_FLUSH_POINT * (MAX_SYNC_REPEATS + 2);
 
+#[cfg(feature = "sync")]
+pub(crate) const WRITE_LOG_LOW_WATER_MARK: usize = WRITE_LOG_FLUSH_POINT / 2;
+
+#[cfg(feature = "sync")]
 pub(crate) const WRITE_RETRY_INTERVAL_MICROS: u64 = 50;
+
+#[cfg(feature = "sync")]
+pub(crate) const PERIODICAL_SYNC_NORMAL_PACE_MILLIS: u64 = 300;
+
+#[cfg(feature = "sync")]
+pub(crate) const PERIODICAL_SYNC_FAST_PACE_NANOS: u64 = 500;

src/common/concurrent/deques.rs

@@ -34,6 +34,7 @@ impl<K> Default for Deques<K> {
 }
 
 impl<K> Deques<K> {
+    #[cfg(feature = "future")]
     pub(crate) fn select_mut(
         &mut self,
         selector: CacheRegion,

src/notification.rs

@@ -1,14 +1,17 @@
 //! Common data types for notifications.
 
+#[cfg(feature = "sync")]
 pub(crate) mod notifier;
 
 use std::{future::Future, pin::Pin, sync::Arc};
 
 pub type ListenerFuture = Pin<Box<dyn Future<Output = ()> + Send>>;
 
+#[cfg(feature = "sync")]
 pub(crate) type EvictionListener<K, V> =
     Arc<dyn Fn(Arc<K>, V, RemovalCause) + Send + Sync + 'static>;
 
+#[cfg(feature = "sync")]
 pub(crate) type EvictionListenerRef<'a, K, V> =
     &'a Arc<dyn Fn(Arc<K>, V, RemovalCause) + Send + Sync + 'static>;
 
@@ -26,11 +29,13 @@ pub(crate) type AsyncEvictionListener<K, V> =
 /// Currently only setting the [`DeliveryMode`][delivery-mode] is supported.
 ///
 /// [delivery-mode]: ./enum.DeliveryMode.html
+#[cfg(feature = "sync")]
 #[derive(Clone, Debug, Default)]
 pub struct Configuration {
     mode: DeliveryMode,
 }
 
+#[cfg(feature = "sync")]
 impl Configuration {
     pub fn builder() -> ConfigurationBuilder {
         ConfigurationBuilder::default()
@@ -47,11 +52,13 @@ impl Configuration {
 ///
 /// [conf]: ./struct.Configuration.html
 /// [delivery-mode]: ./enum.DeliveryMode.html
+#[cfg(feature = "sync")]
 #[derive(Default)]
 pub struct ConfigurationBuilder {
     mode: DeliveryMode,
 }
 
+#[cfg(feature = "sync")]
 impl ConfigurationBuilder {
     pub fn build(self) -> Configuration {
         Configuration { mode: self.mode }
@@ -68,6 +75,7 @@ impl ConfigurationBuilder {
 /// For more details, see [the document][delivery-mode-doc] of `sync::Cache`.
 ///
 /// [delivery-mode-doc]: ../sync/struct.Cache.html#delivery-modes-for-eviction-listener
+#[cfg(feature = "sync")]
 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
 pub enum DeliveryMode {
     /// With this mode, a notification should be delivered to the listener
@@ -93,6 +101,7 @@ pub enum DeliveryMode {
     Queued,
 }
 
+#[cfg(feature = "sync")]
 impl Default for DeliveryMode {
     fn default() -> Self {
         Self::Immediate

src/sync_base.rs

@@ -1,6 +1,12 @@
+pub(crate) mod iter;
+
+#[cfg(feature = "sync")]
 pub(crate) mod base_cache;
+
+#[cfg(feature = "sync")]
 mod invalidator;
-pub(crate) mod iter;
+
+#[cfg(feature = "sync")]
 mod key_lock;
 
 /// The type of the unique ID to identify a predicate used by
@@ -9,6 +15,8 @@ mod key_lock;
 /// A `PredicateId` is a `String` of UUID (version 4).
 ///
 /// [invalidate-if]: ./struct.Cache.html#method.invalidate_entries_if
+#[cfg(feature = "sync")]
 pub type PredicateId = String;
 
+#[cfg(feature = "sync")]
 pub(crate) type PredicateIdStr<'a> = &'a str;