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use cache::Cache;
use priority_function::default_priority_function;
use std::usize;
use concurrent_hashmap::{ConcHashMap, Options};
use std::collections::hash_map::RandomState;
/// Error types that can be encountered when a cache is built.
#[derive(Debug, PartialEq)]
pub enum CacheBuildError {
MinFileSizeIsLargerThanMaxFileSize,
}
/// A builder for Caches.
#[derive(Debug)]
pub struct CacheBuilder {
size_limit: usize,
concurrency: Option<u16>,
priority_function: Option<fn(usize, usize) -> usize>,
min_file_size: Option<usize>,
max_file_size: Option<usize>,
}
impl CacheBuilder {
/// Create a new CacheBuilder.
pub fn new(size_limit: usize) -> CacheBuilder {
CacheBuilder {
size_limit,
concurrency: None,
priority_function: None,
min_file_size: None,
max_file_size: None,
}
}
/// Sets the concurrency setting of the concurrent hashmap backing the cache.
/// A higher concurrency setting allows more threads to access the hashmap at the expense of more memory use.
/// The default is 16.
pub fn concurrency<'a>(&'a mut self, concurrency: u16) -> &mut Self {
self.concurrency = Some(concurrency);
self
}
/// Override the default priority function used for determining if the cache should hold a file.
/// By default a score is calculated using the square root of the size of a file, times the number
/// of times it was accessed.
/// Files with higher priority scores will be kept in the cache when files with lower scores are
/// added.
/// If there isn't room in the cache for two files, the one with the lower score will be removed /
/// won't be added.
///
/// The priority function should be kept simple, as it is calculated on every file in the cache
/// every time a new file is attempted to be added.
///
///
/// ```
/// use rocket_file_cache::Cache;
/// use rocket_file_cache::CacheBuilder;
/// let cache: Cache = CacheBuilder::new(1024 * 1024 * 50) // 50 MB cache
/// .priority_function(|access_count, size| {
/// access_count * access_count * size
/// })
/// .build()
/// .unwrap();
/// ```
pub fn priority_function<'a>(&'a mut self, priority_function: fn(usize, usize) -> usize) -> &mut Self {
self.priority_function = Some(priority_function);
self
}
/// Set the minimum size in bytes for files that can be stored in the cache
pub fn min_file_size<'a>(&'a mut self, min_size: usize) -> &mut Self {
self.min_file_size = Some(min_size);
self
}
/// Set the maximum size in bytes for files that can be stored in the cache
pub fn max_file_size<'a>(&'a mut self, max_size: usize) -> &mut Self {
self.max_file_size = Some(max_size);
self
}
/// Finalize the cache.
///
/// # Example
///
/// ```
/// use rocket_file_cache::Cache;
/// use rocket_file_cache::CacheBuilder;
///
/// let cache: Cache = CacheBuilder::new(1024 * 1024 * 50) // 50 MB cache
/// .min_file_size(1024 * 4) // Don't store files smaller than 4 KB
/// .max_file_size(1024 * 1024 * 6) // Don't store files larger than 6 MB
/// .build()
/// .unwrap();
/// ```
pub fn build(&self) -> Result<Cache, CacheBuildError> {
let priority_function = match self.priority_function {
Some(p) => p,
None => default_priority_function,
};
if let Some(min_file_size) = self.min_file_size {
if let Some(max_file_size) = self.max_file_size {
if min_file_size > max_file_size {
return Err(CacheBuildError::MinFileSizeIsLargerThanMaxFileSize);
}
}
}
let min_file_size: usize = match self.min_file_size {
Some(min) => min,
None => 0,
};
let max_file_size: usize = match self.max_file_size {
Some(max) => max,
None => usize::MAX,
};
let mut options_files_map: Options<RandomState> = Options::default();
let mut options_access_map: Options<RandomState> = Options::default();
if let Some(conc) = self.concurrency {
options_files_map.concurrency = conc;
options_access_map.concurrency = conc;
}
Ok(Cache {
size_limit: self.size_limit,
min_file_size,
max_file_size,
priority_function,
file_map: ConcHashMap::with_options(options_files_map),
access_count_map: ConcHashMap::with_options(options_access_map),
})
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn min_greater_than_max() {
let e: CacheBuildError = CacheBuilder::new(1024 * 1024 * 10)
.min_file_size(1024 * 1024 * 5)
.max_file_size(1024 * 1024 * 4)
.build()
.unwrap_err();
assert_eq!(CacheBuildError::MinFileSizeIsLargerThanMaxFileSize, e);
}
#[test]
fn all_options_used_in_build() {
let _: Cache = CacheBuilder::new(1024 * 1024 * 20)
.priority_function(|access_count: usize, size: usize| access_count * size)
.max_file_size(1024 * 1024 * 10)
.min_file_size(1024 * 10)
.concurrency(20)
.build()
.unwrap();
}
}