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