avoid synchronization for Jenkinsget/setJDKs, use a volatile field instead
avoid synchronization for Jenkinsget/setJDKs, use a volatile field instead

[FIXES JENKINS-31932]

ErikVerheul/jenkins,DanielWeber/jenkins,SebastienGllmt/jenkins,azweb76/jenkins,NehemiahMi/jenkins,MarkEWaite/jenkins,protazy/jenkins,ydubreuil/jenkins,DanielWeber/jenkins,dariver/jenkins,azweb76/jenkins,bkmeneguello/jenkins,patbos/jenkins,olivergondza/jenkins,v1v/jenkins,varmenise/jenkins,FarmGeek4Life/jenkins,dariver/jenkins,jglick/jenkins,ErikVerheul/jenkins,MichaelPranovich/jenkins_sc,MarkEWaite/jenkins,jenkinsci/jenkins,evernat/jenkins,sathiya-mit/jenkins,pjanouse/jenkins,NehemiahMi/jenkins,SebastienGllmt/jenkins,Ykus/jenkins,varmenise/jenkins,csimons/jenkins,bpzhang/jenkins,ajshastri/jenkins,hplatou/jenkins,samatdav/jenkins,patbos/jenkins,rsandell/jenkins,samatdav/jenkins,ErikVerheul/jenkins,ydubreuil/jenkins,MarkEWaite/jenkins,Jimilian/jenkins,Jochen-A-Fuerbacher/jenkins,ydubreuil/jenkins,ErikVerheul/jenkins,olivergondza/jenkins,csimons/jenkins,fbelzunc/jenkins,ndeloof/jenkins,evernat/jenkins,azweb76/jenkins,FarmGeek4Life/jenkins,wuwen5/jenkins,wuwen5/jenkins,dariver/jenkins,varmenise/jenkins,fbelzunc/jenkins,lilyJi/jenkins,gusreiber/jenkins,batmat/jenkins,godfath3r/jenkins,lilyJi/jenkins,amruthsoft9/Jenkis,Jochen-A-Fuerbacher/jenkins,escoem/jenkins,aldaris/jenkins,recena/jenkins,MichaelPranovich/jenkins_sc,oleg-nenashev/jenkins,daniel-beck/jenkins,pjanouse/jenkins,godfath3r/jenkins,rlugojr/jenkins,rsandell/jenkins,viqueen/jenkins,bkmeneguello/jenkins,evernat/jenkins,kohsuke/hudson,MarkEWaite/jenkins,tfennelly/jenkins,aldaris/jenkins,recena/jenkins,jglick/jenkins,protazy/jenkins,ndeloof/jenkins,protazy/jenkins,viqueen/jenkins,Ykus/jenkins,tfennelly/jenkins,wuwen5/jenkins,Vlatombe/jenkins,dariver/jenkins,damianszczepanik/jenkins,ikedam/jenkins,FarmGeek4Life/jenkins,MarkEWaite/jenkins,gusreiber/jenkins,damianszczepanik/jenkins,andresrc/jenkins,dariver/jenkins,dennisjlee/jenkins,stephenc/jenkins,pjanouse/jenkins,aldaris/jenkins,Ykus/jenkins,ikedam/jenkins,dennisjlee/jenkins,protazy/jenkins,gusreiber/jenkins,jpbriend/jenkins,stephenc/jenkins,olivergondza/jenkins,sathiya-mit/jenkins,andresrc/jenkins,gitaccountforprashant/gittest,alvarolobato/jenkins,rlugojr/jenkins,lilyJi/jenkins,amuniz/jenkins,Vlatombe/jenkins,tangkun75/jenkins,olivergondza/jenkins,alvarolobato/jenkins,alvarolobato/jenkins,batmat/jenkins,bpzhang/jenkins,daniel-beck/jenkins,godfath3r/jenkins,Ykus/jenkins,viqueen/jenkins,FarmGeek4Life/jenkins,patbos/jenkins,v1v/jenkins,ajshastri/jenkins,Vlatombe/jenkins,pjanouse/jenkins,stephenc/jenkins,Ykus/jenkins,csimons/jenkins,stephenc/jenkins,v1v/jenkins,fbelzunc/jenkins,evernat/jenkins,ErikVerheul/jenkins,ndeloof/jenkins,evernat/jenkins,varmenise/jenkins,escoem/jenkins,stephenc/jenkins,rsandell/jenkins,ikedam/jenkins,amruthsoft9/Jenkis,MichaelPranovich/jenkins_sc,amuniz/jenkins,gusreiber/jenkins,wuwen5/jenkins,v1v/jenkins,amuniz/jenkins,ajshastri/jenkins,sathiya-mit/jenkins,andresrc/jenkins,fbelzunc/jenkins,damianszczepanik/jenkins,SebastienGllmt/jenkins,protazy/jenkins,ydubreuil/jenkins,dariver/jenkins,alvarolobato/jenkins,Jochen-A-Fuerbacher/jenkins,sathiya-mit/jenkins,samatdav/jenkins,jglick/jenkins,FarmGeek4Life/jenkins,sathiya-mit/jenkins,oleg-nenashev/jenkins,sathiya-mit/jenkins,gusreiber/jenkins,csimons/jenkins,dennisjlee/jenkins,ajshastri/jenkins,samatdav/jenkins,azweb76/jenkins,recena/jenkins,rlugojr/jenkins,aldaris/jenkins,jpbriend/jenkins,varmenise/jenkins,vjuranek/jenkins,NehemiahMi/jenkins,amruthsoft9/Jenkis,jpbriend/jenkins,bkmeneguello/jenkins,jenkinsci/jenkins,kohsuke/hudson,christ66/jenkins,christ66/jenkins,DanielWeber/jenkins,tangkun75/jenkins,patbos/jenkins,Jimilian/jenkins,recena/jenkins,daniel-beck/jenkins,damianszczepanik/jenkins,ndeloof/jenkins,lilyJi/jenkins,amruthsoft9/Jenkis,Jimilian/jenkins,patbos/jenkins,vjuranek/jenkins,SebastienGllmt/jenkins,oleg-nenashev/jenkins,Vlatombe/jenkins,andresrc/jenkins,gitaccountforprashant/gittest,Jochen-A-Fuerbacher/jenkins,FarmGeek4Life/jenkins,vjuranek/jenkins,lilyJi/jenkins,christ66/jenkins,lilyJi/jenkins,viqueen/jenkins,hplatou/jenkins,SebastienGllmt/jenkins,rlugojr/jenkins,alvarolobato/jenkins,escoem/jenkins,aldaris/jenkins,hplatou/jenkins,pjanouse/jenkins,alvarolobato/jenkins,amuniz/jenkins,godfath3r/jenkins,lilyJi/jenkins,escoem/jenkins,amruthsoft9/Jenkis,hplatou/jenkins,jpbriend/jenkins,Jochen-A-Fuerbacher/jenkins,azweb76/jenkins,bpzhang/jenkins,ikedam/jenkins,fbelzunc/jenkins,ikedam/jenkins,bkmeneguello/jenkins,jpbriend/jenkins,ydubreuil/jenkins,ndeloof/jenkins,tangkun75/jenkins,vjuranek/jenkins,DanielWeber/jenkins,stephenc/jenkins,bpzhang/jenkins,christ66/jenkins,csimons/jenkins,ajshastri/jenkins,oleg-nenashev/jenkins,daniel-beck/jenkins,kohsuke/hudson,bkmeneguello/jenkins,vjuranek/jenkins,jenkinsci/jenkins,hplatou/jenkins,kohsuke/hudson,jenkinsci/jenkins,Vlatombe/jenkins,csimons/jenkins,pjanouse/jenkins,rsandell/jenkins,viqueen/jenkins,viqueen/jenkins,MarkEWaite/jenkins,tfennelly/jenkins,godfath3r/jenkins,protazy/jenkins,oleg-nenashev/jenkins,rlugojr/jenkins,tangkun75/jenkins,gitaccountforprashant/gittest,azweb76/jenkins,gitaccountforprashant/gittest,rlugojr/jenkins,MichaelPranovich/jenkins_sc,ydubreuil/jenkins,varmenise/jenkins,daniel-beck/jenkins,gitaccountforprashant/gittest,ndeloof/jenkins,oleg-nenashev/jenkins,tfennelly/jenkins,aldaris/jenkins,ajshastri/jenkins,varmenise/jenkins,kohsuke/hudson,jenkinsci/jenkins,aldaris/jenkins,samatdav/jenkins,amuniz/jenkins,tfennelly/jenkins,andresrc/jenkins,bkmeneguello/jenkins,Jimilian/jenkins,amuniz/jenkins,FarmGeek4Life/jenkins,ikedam/jenkins,jenkinsci/jenkins,SebastienGllmt/jenkins,daniel-beck/jenkins,amruthsoft9/Jenkis,jenkinsci/jenkins,ikedam/jenkins,rsandell/jenkins,gitaccountforprashant/gittest,ndeloof/jenkins,v1v/jenkins,pjanouse/jenkins,MarkEWaite/jenkins,kohsuke/hudson,jenkinsci/jenkins,recena/jenkins,MichaelPranovich/jenkins_sc,jglick/jenkins,tangkun75/jenkins,jpbriend/jenkins,andresrc/jenkins,godfath3r/jenkins,NehemiahMi/jenkins,jglick/jenkins,DanielWeber/jenkins,rsandell/jenkins,gusreiber/jenkins,vjuranek/jenkins,vjuranek/jenkins,dennisjlee/jenkins,kohsuke/hudson,samatdav/jenkins,wuwen5/jenkins,stephenc/jenkins,Vlatombe/jenkins,rsandell/jenkins,amuniz/jenkins,MarkEWaite/jenkins,olivergondza/jenkins,hplatou/jenkins,christ66/jenkins,dennisjlee/jenkins,dariver/jenkins,tangkun75/jenkins,ajshastri/jenkins,tfennelly/jenkins,damianszczepanik/jenkins,fbelzunc/jenkins,Ykus/jenkins,Jochen-A-Fuerbacher/jenkins,oleg-nenashev/jenkins,godfath3r/jenkins,viqueen/jenkins,MichaelPranovich/jenkins_sc,csimons/jenkins,olivergondza/jenkins,v1v/jenkins,escoem/jenkins,christ66/jenkins,ErikVerheul/jenkins,daniel-beck/jenkins,alvarolobato/jenkins,Ykus/jenkins,v1v/jenkins,ErikVerheul/jenkins,rsandell/jenkins,bpzhang/jenkins,amruthsoft9/Jenkis,azweb76/jenkins,batmat/jenkins,andresrc/jenkins,gusreiber/jenkins,daniel-beck/jenkins,wuwen5/jenkins,ikedam/jenkins,fbelzunc/jenkins,NehemiahMi/jenkins,Jimilian/jenkins,olivergondza/jenkins,jpbriend/jenkins,batmat/jenkins,recena/jenkins,batmat/jenkins,rlugojr/jenkins,recena/jenkins,bpzhang/jenkins,christ66/jenkins,NehemiahMi/jenkins,wuwen5/jenkins,protazy/jenkins,Vlatombe/jenkins,Jimilian/jenkins,tangkun75/jenkins,SebastienGllmt/jenkins,patbos/jenkins,batmat/jenkins,jglick/jenkins,hplatou/jenkins,jglick/jenkins,evernat/jenkins,kohsuke/hudson,escoem/jenkins,bpzhang/jenkins,damianszczepanik/jenkins,DanielWeber/jenkins,batmat/jenkins,gitaccountforprashant/gittest,Jimilian/jenkins,damianszczepanik/jenkins,dennisjlee/jenkins,escoem/jenkins,evernat/jenkins,dennisjlee/jenkins,sathiya-mit/jenkins,samatdav/jenkins,tfennelly/jenkins,ydubreuil/jenkins,MichaelPranovich/jenkins_sc,NehemiahMi/jenkins,damianszczepanik/jenkins,Jochen-A-Fuerbacher/jenkins,bkmeneguello/jenkins,DanielWeber/jenkins,patbos/jenkins