From 77813bdc13118fd08bbff7a68c9d5268080a2a15 Mon Sep 17 00:00:00 2001
From: Jakob Unterwurzacher
Date: Sun, 29 May 2016 22:40:05 +0200
Subject: fusefrontend: simplify wlockMap

mapMutex can be anonymous and using an RWMutex is overkill
because the lock protects very short sections.
---
 internal/fusefrontend/write_lock.go | 62 ++++++++++++++++++++++---------------
 1 file changed, 37 insertions(+), 25 deletions(-)

(limited to 'internal/fusefrontend/write_lock.go')

diff --git a/internal/fusefrontend/write_lock.go b/internal/fusefrontend/write_lock.go
index a8ec6b6..2f8ea4e 100644
--- a/internal/fusefrontend/write_lock.go
+++ b/internal/fusefrontend/write_lock.go
@@ -5,7 +5,7 @@ import (
 )
 
 func init() {
-	wlock.m = make(map[uint64]*refCntMutex)
+	wlock.inodeLocks = make(map[uint64]*refCntMutex)
 }
 
 // wlock - serializes write accesses to each file (identified by inode number)
@@ -20,47 +20,59 @@ var wlock wlockMap
 // 2) lock ... unlock ...
 // 3) unregister
 type wlockMap struct {
-	mapMutex sync.RWMutex
-	m        map[uint64]*refCntMutex
+	// Protects map access
+	sync.Mutex
+	inodeLocks map[uint64]*refCntMutex
+}
+
+// refCntMutex - mutex with reference count
+type refCntMutex struct {
+	// Write lock for this inode
+	sync.Mutex
+	// Reference count
+	refCnt int
 }
 
+// register creates an entry for "ino", or incrementes the reference count
+// if the entry already exists.
 func (w *wlockMap) register(ino uint64) {
-	w.mapMutex.Lock()
-	r := w.m[ino]
+	w.Lock()
+	defer w.Unlock()
+
+	r := w.inodeLocks[ino]
 	if r == nil {
 		r = &refCntMutex{}
-		w.m[ino] = r
+		w.inodeLocks[ino] = r
 	}
-	r.refCnt++ // this must happen inside the mapMutex lock
-	w.mapMutex.Unlock()
+	r.refCnt++
 }
 
+// unregister decrements the reference count for "ino" and deletes the entry if
+// the reference count has reached 0.
 func (w *wlockMap) unregister(ino uint64) {
-	w.mapMutex.Lock()
-	r := w.m[ino]
+	w.Lock()
+	defer w.Unlock()
+
+	r := w.inodeLocks[ino]
 	r.refCnt--
 	if r.refCnt == 0 {
-		delete(w.m, ino)
+		delete(w.inodeLocks, ino)
 	}
-	w.mapMutex.Unlock()
 }
 
+// lock retrieves the entry for "ino" and locks it.
 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
+	w.Lock()
+	r := w.inodeLocks[ino]
+	w.Unlock()
+	// this can take a long time - execute outside the wlockMap lock
+	r.Lock()
 }
 
+// unlock retrieves the entry for "ino" and unlocks it.
 func (w *wlockMap) unlock(ino uint64) {
-	w.mapMutex.RLock()
-	r := w.m[ino]
-	w.mapMutex.RUnlock()
+	w.Lock()
+	r := w.inodeLocks[ino]
+	w.Unlock()
 	r.Unlock()
 }
-
-// refCntMutex - mutex with reference count
-type refCntMutex struct {
-	sync.Mutex
-	refCnt int
-}
-- 
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