add read lock for eventsHandler when only it is necessary.
add read lock for eventsHandler when only it is necessary.

Signed-off-by: Sun Hongliang <36603fc76d0c5a59db517817381acc1be27b9499@daocloud.io>

swarm-hooks/swarm,joeuo/docker.github.io,denverdino/denverdino.github.io,auzias/swarm,aduermael/docker.github.io,troy0820/docker.github.io,denverdino/docker.github.io,denverdino/denverdino.github.io,joeuo/docker.github.io,doronp/swarm,moxiegirl/swarm,resouer/swarm,gdevillele/docker.github.io,londoncalling/docker.github.io,allencloud/swarm,bdwill/docker.github.io,troy0820/docker.github.io,thaJeztah/docker.github.io,gdevillele/docker.github.io,phiroict/docker,sanscontext/docker.github.io,alexisbellido/docker.github.io,londoncalling/docker.github.io,LukasBacigal/swarm,menglingwei/denverdino.github.io,aduermael/docker.github.io,denverdino/docker.github.io,docker-zh/docker.github.io,ezrasilvera/swarm,liubin/swarm,rillig/docker.github.io,resouer/swarm,rillig/docker.github.io,anweiss/docker.github.io,swarm-hooks/swarm,shin-/docker.github.io,barais/swarm,menglingwei/denverdino.github.io,LuisBosquez/docker.github.io,JimGalasyn/docker.github.io,auzias/swarm,londoncalling/docker.github.io,bdwill/docker.github.io,LuisBosquez/docker.github.io,fugr/swarm,atlassian/swarm,BSWANG/denverdino.github.io,alexisbellido/docker.github.io,phiroict/docker,CodeNow/swarm,BSWANG/denverdino.github.io,thaJeztah/docker.github.io,jzwlqx/denverdino.github.io,docker-zh/docker.github.io,troy0820/docker.github.io,kyhavlov/swarm,danix800/docker.github.io,sfsmithcha/swarm,moxiegirl/swarm,denverdino/docker.github.io,docker/docker.github.io,shin-/docker.github.io,anweiss/docker.github.io,thaJeztah/docker.github.io,gradywang/swarm,danix800/docker.github.io,jzwlqx/denverdino.github.io,denverdino/denverdino.github.io,echupriyanov/swarm,joeuo/docker.github.io,JimGalasyn/docker.github.io,sfsmithcha/swarm,echupriyanov/swarm,xFragger/swarm,liubin/swarm,shubheksha/docker.github.io,docker-zh/docker.github.io,sanscontext/docker.github.io,jimmycmh/swarm,menglingwei/denverdino.github.io,BSWANG/denverdino.github.io,jimmycmh/swarm,shubheksha/docker.github.io,linecheng/swarm,shubheksha/docker.github.io,LukasBacigal/swarm,LuisBosquez/docker.github.io,johnstep/docker.github.io,joeuo/docker.github.io,rchicoli/swarm,alexisbellido/docker.github.io,rchicoli/swarm,denverdino/denverdino.github.io,anweiss/docker.github.io,shin-/docker.github.io,LuisBosquez/docker.github.io,johnstep/docker.github.io,anweiss/docker.github.io,joeuo/docker.github.io,joaofnfernandes/docker.github.io,docker/docker.github.io,docker/docker.github.io,xFragger/swarm,LuisBosquez/docker.github.io,gdevillele/docker.github.io,phiroict/docker,barais/swarm,jzwlqx/denverdino.github.io,menglingwei/denverdino.github.io,BSWANG/denverdino.github.io,shin-/docker.github.io,troy0820/docker.github.io,docker/docker.github.io,shubheksha/docker.github.io,anweiss/docker.github.io,gdevillele/docker.github.io,shubheksha/docker.github.io,thaJeztah/docker.github.io,gdevillele/docker.github.io,denverdino/denverdino.github.io,danix800/docker.github.io,phiroict/docker,fugr/swarm,alexisbellido/docker.github.io,JimGalasyn/docker.github.io,joaofnfernandes/docker.github.io,menglingwei/denverdino.github.io,sanscontext/docker.github.io,shin-/docker.github.io,jzwlqx/denverdino.github.io,doronp/swarm,bdwill/docker.github.io,kyhavlov/swarm,docker/docker.github.io,rillig/docker.github.io,bdwill/docker.github.io,Spritekin/swarm,johnstep/docker.github.io,bdwill/docker.github.io,ezrasilvera/swarm,londoncalling/docker.github.io,denverdino/docker.github.io,aduermael/docker.github.io,JimGalasyn/docker.github.io,BSWANG/denverdino.github.io,linecheng/swarm,danix800/docker.github.io,londoncalling/docker.github.io,joaofnfernandes/docker.github.io,johnstep/docker.github.io,atlassian/swarm,joaofnfernandes/docker.github.io,denverdino/docker.github.io,allencloud/swarm,gradywang/swarm,jzwlqx/denverdino.github.io,docker-zh/docker.github.io,JimGalasyn/docker.github.io,sanscontext/docker.github.io,docker-zh/docker.github.io,rillig/docker.github.io,sanscontext/docker.github.io,alexisbellido/docker.github.io,CodeNow/swarm,johnstep/docker.github.io,joaofnfernandes/docker.github.io,thaJeztah/docker.github.io,phiroict/docker,aduermael/docker.github.io,Spritekin/swarm