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//! Service cacheing
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use super::*;
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use std::{
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hash::Hash,
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marker::{Send, Sync},
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fmt,
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};
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use std::sync::{
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RwLock,
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atomic::AtomicUsize,
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};
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use std::path::PathBuf;
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use std::num::NonZeroUsize;
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use std::collections::HashMap;
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use chrono::DateTime;
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use ::bytes::Bytes;
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pub type Timezone = chrono::Utc;
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/// A type that can be used for the cache key
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pub trait Key: Sized +
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Send +
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Sync +
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Hash +
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PartialEq +
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Eq +
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fmt::Display +
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Serialize +
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for<'a> Deserialize<'a> +
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'static
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{}
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basic_enum!(pub PurgeOrder; "How should a cache determine what to purge": Oldest => "Purge the oldest entries first", LeastUsed => "Purge the least accessed entries first", OldestUsed => "Purge the oldest accessed entries first");
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default!(PurgeOrder: Self::LeastUsed);
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/// Config for a cache
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#[derive(Debug, Clone, PartialEq, Eq)]
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pub struct Config
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{
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// General
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// Disk cache
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/// The directory to save to data to.
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/// If `None`, se memory cache only.
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pub disk_location: Option<PathBuf>,
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// Memory cache
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/// Max size of an entry to cache in memory
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pub mem_max_ent_size: Option<NonZeroUsize>,
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/// Max entries in memory cache
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pub mem_max_ent: Option<NonZeroUsize>,
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/// Max total bytes to keep in memcache before purging older entries.
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pub mem_max_total_size: Option<NonZeroUsize>,
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/// When purging entries from memcache, how to select ones to purge
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pub mem_purge_order: PurgeOrder,
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}
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/// The memory hold of a cahce.
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#[derive(Debug, Clone, PartialEq, Eq, Hash, Default)]
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struct Memory(Bytes);
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/// An entry in a `ByteCache`.
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#[derive(Debug)]
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pub struct CacheEntry //<K: Key> // `K` is the key in `entries`.
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{
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tm_accessed: RwLock<DateTime<Timezone>>, // Can be mutated when read, so must be mutable by the reader, hence the `RwLock`.
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tm_created: DateTime<Timezone>,
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accesses: AtomicUsize, // Can be mutated when read, hence the atomic.
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memory: Option<Memory>,
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// Pathname is computed from `key`.
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}
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/// A byte-stream cache. Caches both to memory and also writes entries to disk.
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#[derive(Debug)]
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pub struct ByteCache<K: Key>
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{
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// Config is big, box it.
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cfg: Box<Config>,
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/// Frozen entries.
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entries: HashMap<K, CacheEntry>,
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}
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