[3.0] fix urlInvokerMap concurrent access issue

[zrlw]

What is the purpose of the change

fix #8675
it might cause chaos that main thread does isAvailable() while main-EventThread does refreshInvoker() if both of them operate urlInvokerMap directly, especially while main-EventThread gets empty url lists to refresh.

github integration test log snippet:

<=== urlInvokerMap will be removed at refreshInvoker() in ServiceDiscoveryRegistryDirectory
[20/09/21 10:06:14:014 UTC] main-EventThread  INFO client.ServiceDiscoveryRegistryDirectory:  [DUBBO] Refreshed invoker size 1, dubbo version: 3.0.3-SNAPSHOT, current host: 172.26.0.3 
...
<=== IllegalStateException will be trigged if urlInvokerMap is empty at checkInvokerAvailable() in ReferenceConfig
[20/09/21 10:06:14:014 UTC] main ERROR deploy.DefaultModuleDeployer:  [DUBBO] Dubbo Module[1.1.1] refer catch error, dubbo version: 3.0.3-SNAPSHOT, current host: 172.26.0.3
java.lang.IllegalStateException: Failed to check the status of the service org.apache.dubbo.samples.async.api.GreetingService. No provider available for the service org.apache.dubbo.samples.async.api.GreetingService from the url dubbo://172.26.0.3/org.apache.dubbo.samples.async.api.GreetingService?application=async-consumer&dubbo=2.0.2&interface=org.apache.dubbo.samples.async.api.GreetingService&metadata-type=remote&methods=greeting,replyGreeting&pid=17&register.ip=172.26.0.3&release=3.0.3-SNAPSHOT&side=consumer&sticky=false&timeout=10000&timestamp=1632132372838 to the consumer 172.26.0.3 use dubbo version 3.0.3-SNAPSHOT
	at org.apache.dubbo.config.ReferenceConfig.checkInvokerAvailable(ReferenceConfig.java:520)

[codecov-commenter]

Codecov Report

Merging #8701 (8bd0479) into 3.0 (d3f7ab4) will increase coverage by 0.05%.
The diff coverage is 86.66%.

@@             Coverage Diff              @@
##                3.0    #8701      +/-   ##
============================================
+ Coverage     63.77%   63.82%   +0.05%     
+ Complexity      315      314       -1     
============================================
  Files          1169     1169              
  Lines         49216    49222       +6     
  Branches       7361     7359       -2     
============================================
+ Hits          31389    31418      +29     
+ Misses        14406    14381      -25     
- Partials       3421     3423       +2     

Impacted Files	Coverage Δ
.../dubbo/registry/integration/RegistryDirectory.java	50.32% <85.71%> (+0.32%)	⬆️
...stry/client/ServiceDiscoveryRegistryDirectory.java	46.25% <87.50%> (-0.18%)	⬇️
...n/java/org/apache/dubbo/rpc/model/ModuleModel.java	83.05% <0.00%> (-9.41%)	⬇️
.../apache/dubbo/remoting/transport/AbstractPeer.java	60.86% <0.00%> (-8.70%)	⬇️
...he/dubbo/remoting/transport/netty/NettyServer.java	70.17% <0.00%> (-3.51%)	⬇️
.../client/metadata/ServiceInstanceMetadataUtils.java	84.90% <0.00%> (-2.84%)	⬇️
.../dubbo/remoting/transport/netty4/NettyChannel.java	64.35% <0.00%> (-1.99%)	⬇️
...a/org/apache/dubbo/monitor/dubbo/DubboMonitor.java	86.66% <0.00%> (-1.91%)	⬇️
.../dubbo/rpc/protocol/dubbo/DecodeableRpcResult.java	51.28% <0.00%> (-1.29%)	⬇️
.../src/main/java/org/apache/dubbo/rpc/RpcStatus.java	70.23% <0.00%> (-1.20%)	⬇️
... and 28 more

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[pinxiong]

Could you provide more detailed info? And why did you use the variable forbidden?

[zrlw]

Could you provide more detailed info? And why did you use the variable forbidden?
it might cause chaos that main thread does isAvailable() while main-EventThread does refreshInvoker() at the same time, especially while main-EventThread gets empty url lists to refresh.
pls see more details in #8675
there are same problem in RegistryDirectory.java. you'd better compare these code with current branch master.