63 lines
1.4 KiB
Go
63 lines
1.4 KiB
Go
package storage
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import (
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"math/rand"
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"os"
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)
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// A `FileCache` stores open file descriptors for all files that have been
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// requested, and returns them when requested
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type FileCache struct {
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cacheSize int
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fileNames map[string]int
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indexesOfFiles map[int]string
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files []*os.File
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}
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func NewFileCache(cacheSize int) FileCache {
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var c FileCache
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c.cacheSize = cacheSize
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c.fileNames = make(map[string]int)
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c.indexesOfFiles = make(map[int]string)
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c.files = make([]*os.File, cacheSize)
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return c
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}
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// `FetchFile` takes in a file's name and returns its file descriptor
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//
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// If the file is not found in the cache, the file is added to the cache
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func (fc *FileCache) FetchFile(fileName string) (*os.File, error) {
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// The file is already in the cache
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if index, contains := fc.fileNames[fileName]; contains {
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return fc.files[index], nil
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}
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// The file was not in the cache, try and insert it
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// Random cache eviction
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indexToRemove := rand.Intn(fc.cacheSize)
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// Remove the old value
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oldName, present := fc.indexesOfFiles[indexToRemove]
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// If there is already a value, delete its mapping
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if present {
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delete(fc.fileNames, oldName)
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delete(fc.indexesOfFiles, indexToRemove)
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}
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f, err := os.Open(fileName)
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if err != nil {
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return nil, err
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}
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// Insert the new value
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fc.files[indexToRemove] = f
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fc.fileNames[fileName] = indexToRemove
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fc.indexesOfFiles[indexToRemove] = fileName
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return f, nil
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}
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