Refactoring: rename modules -> pkg

Reasons to change:

1. Shorter than 'modules'
2. More generally used by other Go projects
3. Corresponds to the naming of '$GOPATH/pkg' directory

pkg/sync/exclusive_pool.go

@@ -0,0 +1,70 @@
+// Copyright 2016 The Gogs Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package sync
+
+import (
+	"sync"
+)
+
+// ExclusivePool is a pool of non-identical instances
+// that only one instance with same identity is in the pool at a time.
+// In other words, only instances with different identities can be in
+// the pool the same time. If another instance with same identity tries
+// to get into the pool, it hangs until previous instance left the pool.
+//
+// This pool is particularly useful for performing tasks on same resource
+// on the file system in different goroutines.
+type ExclusivePool struct {
+	lock sync.Mutex
+
+	// pool maintains locks for each instance in the pool.
+	pool map[string]*sync.Mutex
+
+	// count maintains the number of times an instance with same identity checks in
+	// to the pool, and should be reduced to 0 (removed from map) by checking out
+	// with same number of times.
+	// The purpose of count is to delete lock when count down to 0 and recycle memory
+	// from map object.
+	count map[string]int
+}
+
+// NewExclusivePool initializes and returns a new ExclusivePool object.
+func NewExclusivePool() *ExclusivePool {
+	return &ExclusivePool{
+		pool:  make(map[string]*sync.Mutex),
+		count: make(map[string]int),
+	}
+}
+
+// CheckIn checks in an instance to the pool and hangs while instance
+// with same indentity is using the lock.
+func (p *ExclusivePool) CheckIn(identity string) {
+	p.lock.Lock()
+
+	lock, has := p.pool[identity]
+	if !has {
+		lock = &sync.Mutex{}
+		p.pool[identity] = lock
+	}
+	p.count[identity]++
+
+	p.lock.Unlock()
+	lock.Lock()
+}
+
+// CheckOut checks out an instance from the pool and releases the lock
+// to let other instances with same identity to grab the lock.
+func (p *ExclusivePool) CheckOut(identity string) {
+	p.lock.Lock()
+	defer p.lock.Unlock()
+
+	p.pool[identity].Unlock()
+	if p.count[identity] == 1 {
+		delete(p.pool, identity)
+		delete(p.count, identity)
+	} else {
+		p.count[identity]--
+	}
+}

pkg/sync/status_pool.go

@@ -0,0 +1,49 @@
+// Copyright 2016 The Gogs Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package sync
+
+import (
+	"sync"
+)
+
+// StatusTable is a table maintains true/false values.
+//
+// This table is particularly useful for un/marking and checking values
+// in different goroutines.
+type StatusTable struct {
+	sync.RWMutex
+	pool map[string]bool
+}
+
+// NewStatusTable initializes and returns a new StatusTable object.
+func NewStatusTable() *StatusTable {
+	return &StatusTable{
+		pool: make(map[string]bool),
+	}
+}
+
+// Start sets value of given name to true in the pool.
+func (p *StatusTable) Start(name string) {
+	p.Lock()
+	defer p.Unlock()
+
+	p.pool[name] = true
+}
+
+// Stop sets value of given name to false in the pool.
+func (p *StatusTable) Stop(name string) {
+	p.Lock()
+	defer p.Unlock()
+
+	p.pool[name] = false
+}
+
+// IsRunning checks if value of given name is set to true in the pool.
+func (p *StatusTable) IsRunning(name string) bool {
+	p.RLock()
+	defer p.RUnlock()
+
+	return p.pool[name]
+}

pkg/sync/unique_queue.go

@@ -0,0 +1,70 @@
+// Copyright 2016 The Gogs Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package sync
+
+import (
+	"github.com/Unknwon/com"
+)
+
+// UniqueQueue is a queue which guarantees only one instance of same
+// identity is in the line. Instances with same identity will be
+// discarded if there is already one in the line.
+//
+// This queue is particularly useful for preventing duplicated task
+// of same purpose.
+type UniqueQueue struct {
+	table *StatusTable
+	queue chan string
+}
+
+// NewUniqueQueue initializes and returns a new UniqueQueue object.
+func NewUniqueQueue(queueLength int) *UniqueQueue {
+	if queueLength <= 0 {
+		queueLength = 100
+	}
+
+	return &UniqueQueue{
+		table: NewStatusTable(),
+		queue: make(chan string, queueLength),
+	}
+}
+
+// Queue returns channel of queue for retrieving instances.
+func (q *UniqueQueue) Queue() <-chan string {
+	return q.queue
+}
+
+// Exist returns true if there is an instance with given indentity
+// exists in the queue.
+func (q *UniqueQueue) Exist(id interface{}) bool {
+	return q.table.IsRunning(com.ToStr(id))
+}
+
+// AddFunc adds new instance to the queue with a custom runnable function,
+// the queue is blocked until the function exits.
+func (q *UniqueQueue) AddFunc(id interface{}, fn func()) {
+	if q.Exist(id) {
+		return
+	}
+
+	idStr := com.ToStr(id)
+	q.table.Lock()
+	q.table.pool[idStr] = true
+	if fn != nil {
+		fn()
+	}
+	q.table.Unlock()
+	q.queue <- idStr
+}
+
+// Add adds new instance to the queue.
+func (q *UniqueQueue) Add(id interface{}) {
+	q.AddFunc(id, nil)
+}
+
+// Remove removes instance from the queue.
+func (q *UniqueQueue) Remove(id interface{}) {
+	q.table.Stop(com.ToStr(id))
+}