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-rw-r--r--modules/sync/single_instance_pool.go67
1 files changed, 67 insertions, 0 deletions
diff --git a/modules/sync/single_instance_pool.go b/modules/sync/single_instance_pool.go
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+// 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"
+)
+
+// SingleInstancePool 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 exist
+// at the same time.
+//
+// This pool is particularly useful for performing tasks on same resource
+// on the file system in different goroutines.
+type SingleInstancePool 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.
+ count map[string]int
+}
+
+// NewSingleInstancePool initializes and returns a new SingleInstancePool object.
+func NewSingleInstancePool() *SingleInstancePool {
+ return &SingleInstancePool{
+ 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 *SingleInstancePool) 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 *SingleInstancePool) 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]--
+ }
+}