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/setting/gloabl_lock.go

@@ -0,0 +1,37 @@
+// Copyright 2024 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package setting
+
+import (
+	"code.gitea.io/gitea/modules/log"
+	"code.gitea.io/gitea/modules/nosql"
+)
+
+// GlobalLock represents configuration of global lock
+var GlobalLock = struct {
+	ServiceType    string
+	ServiceConnStr string
+}{
+	ServiceType: "memory",
+}
+
+func loadGlobalLockFrom(rootCfg ConfigProvider) {
+	sec := rootCfg.Section("global_lock")
+	GlobalLock.ServiceType = sec.Key("SERVICE_TYPE").MustString("memory")
+	switch GlobalLock.ServiceType {
+	case "memory":
+	case "redis":
+		connStr := sec.Key("SERVICE_CONN_STR").String()
+		if connStr == "" {
+			log.Fatal("SERVICE_CONN_STR is empty for redis")
+		}
+		u := nosql.ToRedisURI(connStr)
+		if u == nil {
+			log.Fatal("SERVICE_CONN_STR %s is not a valid redis connection string", connStr)
+		}
+		GlobalLock.ServiceConnStr = connStr
+	default:
+		log.Fatal("Unknown sync lock service type: %s", GlobalLock.ServiceType)
+	}
+}