Use global lock instead of NewExclusivePool to allow distributed lock between multiple Gitea instances (#31813)

Replace #26486 
Fix #19620

---------

Co-authored-by: Jason Song <i@wolfogre.com>

modules/sync/exclusive_pool.go

@@ -1,69 +0,0 @@
-// 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]--
-	}
-}