67 lines
1.3 KiB
Go
67 lines
1.3 KiB
Go
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package pathfs_frontend
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import (
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"sync"
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)
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func init() {
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wlock.m = make(map[uint64]*refCntMutex)
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}
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// wlock - serializes write accesses to each file (identified by inode number)
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// Writing partial blocks means we have to do read-modify-write cycles. We
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// really don't want concurrent writes there.
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// Concurrent full-block writes could actually be allowed, but are not to
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// keep the locking simple.
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var wlock wlockMap
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// wlockMap - usage:
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// 1) register
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// 2) lock ... unlock ...
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// 3) unregister
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type wlockMap struct {
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mapMutex sync.RWMutex
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m map[uint64]*refCntMutex
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}
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func (w *wlockMap) register(ino uint64) {
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w.mapMutex.Lock()
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r := w.m[ino]
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if r == nil {
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r = &refCntMutex{}
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w.m[ino] = r
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}
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r.refCnt++ // this must happen inside the mapMutex lock
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w.mapMutex.Unlock()
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}
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func (w *wlockMap) unregister(ino uint64) {
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w.mapMutex.Lock()
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r := w.m[ino]
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r.refCnt--
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if r.refCnt == 0 {
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delete(w.m, ino)
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}
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w.mapMutex.Unlock()
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}
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func (w *wlockMap) lock(ino uint64) {
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w.mapMutex.RLock()
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r := w.m[ino]
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w.mapMutex.RUnlock()
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r.Lock() // this can take a long time - execute outside the mapMutex lock
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}
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func (w *wlockMap) unlock(ino uint64) {
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w.mapMutex.RLock()
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r := w.m[ino]
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w.mapMutex.RUnlock()
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r.Unlock()
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}
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// refCntMutex - mutex with reference count
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type refCntMutex struct {
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sync.Mutex
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refCnt int
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}
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