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119 lines
2.5 KiB
Go
119 lines
2.5 KiB
Go
/*
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Copyright 2013 The Go4 Authors
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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// package singlereader provides Open and Close operations, reusing existing
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// file descriptors when possible.
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package singlereader // import "go4.org/readerutil/singlereader"
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import (
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"sync"
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"go4.org/readerutil"
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"go4.org/syncutil/singleflight"
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"go4.org/wkfs"
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)
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var (
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openerGroup singleflight.Group
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openFileMu sync.Mutex // guards openFiles
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openFiles = make(map[string]*openFile)
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)
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type openFile struct {
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wkfs.File
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path string // map key of openFiles
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refCount int
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}
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type openFileHandle struct {
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closed bool
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*openFile
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}
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func (f *openFileHandle) Close() error {
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openFileMu.Lock()
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if f.closed {
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openFileMu.Unlock()
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return nil
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}
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f.closed = true
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f.refCount--
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if f.refCount < 0 {
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panic("unexpected negative refcount")
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}
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zero := f.refCount == 0
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if zero {
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delete(openFiles, f.path)
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}
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openFileMu.Unlock()
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if !zero {
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return nil
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}
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return f.openFile.File.Close()
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}
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// Open opens the given file path for reading, reusing existing file descriptors
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// when possible.
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func Open(path string) (readerutil.ReaderAtCloser, error) {
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openFileMu.Lock()
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of := openFiles[path]
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if of != nil {
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of.refCount++
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openFileMu.Unlock()
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return &openFileHandle{false, of}, nil
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}
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openFileMu.Unlock() // release the lock while we call os.Open
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winner := false // this goroutine made it into Do's func
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// Returns an *openFile
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resi, err := openerGroup.Do(path, func() (interface{}, error) {
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winner = true
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f, err := wkfs.Open(path)
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if err != nil {
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return nil, err
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}
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of := &openFile{
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File: f,
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path: path,
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refCount: 1,
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}
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openFileMu.Lock()
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openFiles[path] = of
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openFileMu.Unlock()
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return of, nil
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})
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if err != nil {
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return nil, err
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}
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of = resi.(*openFile)
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// If our os.Open was dup-suppressed, we have to increment our
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// reference count.
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if !winner {
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openFileMu.Lock()
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if of.refCount == 0 {
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// Winner already closed it. Try again (rare).
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openFileMu.Unlock()
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return Open(path)
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}
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of.refCount++
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openFileMu.Unlock()
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}
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return &openFileHandle{false, of}, nil
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}
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