3 files changed, 157 insertions, 0 deletions

diff --git a/modules/sync/exclusive_pool.go b/modules/sync/exclusive_pool.go
new file mode 100644
index 0000000..fbfc1f2
--- /dev/null
+++ b/modules/sync/exclusive_pool.go
@@ -0,0 +1,69 @@
+// Copyright 2016 The Gogs Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+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 identity 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]--
+	}
+}
diff --git a/modules/sync/status_pool.go b/modules/sync/status_pool.go
new file mode 100644
index 0000000..6f075d5
--- /dev/null
+++ b/modules/sync/status_pool.go
@@ -0,0 +1,57 @@
+// Copyright 2016 The Gogs Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package sync
+
+import (
+	"sync"
+
+	"code.gitea.io/gitea/modules/container"
+)
+
+// 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 {
+	lock sync.RWMutex
+	pool container.Set[string]
+}
+
+// NewStatusTable initializes and returns a new StatusTable object.
+func NewStatusTable() *StatusTable {
+	return &StatusTable{
+		pool: make(container.Set[string]),
+	}
+}
+
+// StartIfNotRunning sets value of given name to true if not already in pool.
+// Returns whether set value was set to true
+func (p *StatusTable) StartIfNotRunning(name string) bool {
+	p.lock.Lock()
+	added := p.pool.Add(name)
+	p.lock.Unlock()
+	return added
+}
+
+// Start sets value of given name to true in the pool.
+func (p *StatusTable) Start(name string) {
+	p.lock.Lock()
+	p.pool.Add(name)
+	p.lock.Unlock()
+}
+
+// Stop sets value of given name to false in the pool.
+func (p *StatusTable) Stop(name string) {
+	p.lock.Lock()
+	p.pool.Remove(name)
+	p.lock.Unlock()
+}
+
+// IsRunning checks if value of given name is set to true in the pool.
+func (p *StatusTable) IsRunning(name string) bool {
+	p.lock.RLock()
+	exists := p.pool.Contains(name)
+	p.lock.RUnlock()
+	return exists
+}
diff --git a/modules/sync/status_pool_test.go b/modules/sync/status_pool_test.go
new file mode 100644
index 0000000..e2e4886
--- /dev/null
+++ b/modules/sync/status_pool_test.go
@@ -0,0 +1,31 @@
+// Copyright 2017 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package sync
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func Test_StatusTable(t *testing.T) {
+	table := NewStatusTable()
+
+	assert.False(t, table.IsRunning("xyz"))
+
+	table.Start("xyz")
+	assert.True(t, table.IsRunning("xyz"))
+
+	assert.False(t, table.StartIfNotRunning("xyz"))
+	assert.True(t, table.IsRunning("xyz"))
+
+	table.Stop("xyz")
+	assert.False(t, table.IsRunning("xyz"))
+
+	assert.True(t, table.StartIfNotRunning("xyz"))
+	assert.True(t, table.IsRunning("xyz"))
+
+	table.Stop("xyz")
+	assert.False(t, table.IsRunning("xyz"))
+}