87 lines
2.0 KiB
Go
87 lines
2.0 KiB
Go
package fusefrontend
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import (
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"sync"
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"sync/atomic"
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)
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func init() {
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wlock.inodeLocks = 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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// opCount counts lock() calls. As every operation that modifies a file should
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// call it, this effectively serves as a write-operation counter.
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// The variable is accessed without holding any locks so atomic operations
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// must be used. It must be the first element of the struct to guarantee
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// 64-bit alignment.
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opCount uint64
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// Protects map access
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sync.Mutex
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inodeLocks map[uint64]*refCntMutex
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}
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// refCntMutex - mutex with reference count
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type refCntMutex struct {
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// Write lock for this inode
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sync.Mutex
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// Reference count
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refCnt int
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}
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// register creates an entry for "ino", or incrementes the reference count
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// if the entry already exists.
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func (w *wlockMap) register(ino uint64) {
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w.Lock()
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defer w.Unlock()
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r := w.inodeLocks[ino]
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if r == nil {
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r = &refCntMutex{}
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w.inodeLocks[ino] = r
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}
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r.refCnt++
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}
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// unregister decrements the reference count for "ino" and deletes the entry if
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// the reference count has reached 0.
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func (w *wlockMap) unregister(ino uint64) {
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w.Lock()
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defer w.Unlock()
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r := w.inodeLocks[ino]
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r.refCnt--
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if r.refCnt == 0 {
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delete(w.inodeLocks, ino)
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}
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}
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// lock retrieves the entry for "ino" and locks it.
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func (w *wlockMap) lock(ino uint64) {
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atomic.AddUint64(&w.opCount, 1)
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w.Lock()
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r := w.inodeLocks[ino]
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w.Unlock()
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// this can take a long time - execute outside the wlockMap lock
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r.Lock()
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}
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// unlock retrieves the entry for "ino" and unlocks it.
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func (w *wlockMap) unlock(ino uint64) {
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w.Lock()
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r := w.inodeLocks[ino]
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w.Unlock()
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r.Unlock()
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}
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