method createServiceIfAbsent in ServiceManager require sync

[robinZhao]

method createServiceIfAbsent in ServiceManager have possibility of concurrent creation
require a sync here

public void createServiceIfAbsent(String namespaceId, String serviceName, boolean local, Cluster cluster)
throws NacosException {
Service service = getService(namespaceId, serviceName);
if (service == null) {
synchronized (this){
service = getService(namespaceId, serviceName);
if(null!=service){
return;
}
Loggers.SRV_LOG.info("creating empty service {}:{}", namespaceId, serviceName);
service = new Service();
service.setName(serviceName);
service.setNamespaceId(namespaceId);
service.setGroupName(NamingUtils.getGroupName(serviceName));
// now validate the service. if failed, exception will be thrown
service.setLastModifiedMillis(System.currentTimeMillis());
service.recalculateChecksum();
if (cluster != null) {
cluster.setService(service);
service.getClusterMap().put(cluster.getName(), cluster);
}
service.validate();
putServiceAndInit(service);
if (!local) {
addOrReplaceService(service);
}
}
}
}

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Expected behavior
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Acutally behavior
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How to Reproduce
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2. Click on '....'
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4. See error

Desktop (please complete the following information):

• OS: [e.g. Centos]
• Version [e.g. nacos-server 1.3.1, nacos-client 1.3.1]
• Module [e.g. naming/config]
• SDK [e.g. original, spring-cloud-alibaba-nacos, dubbo]

Additional context
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[KomachiSion]

Current logic, if there are many thread create Service, they will enter the putServiceAndInit method and then putService method
In putService method, it contain an putServiceLock and make sure the service map only contain one service.
So I think there is no need to lock in outer method

[KomachiSion]

I read the source code again, and found that there are some problem indeed. We will enhance this problem.

[a7217107]

i will solve it