Added isEmpty method, changed synchronization to the timer instance to allow for external synchronization.
Added isEmpty method, changed synchronization to the timer instance to allow for external synchronization.

closes #3624

MovingBlocks/libgdx,gouessej/libgdx,FredGithub/libgdx,fwolff/libgdx,yangweigbh/libgdx,cypherdare/libgdx,SidneyXu/libgdx,PedroRomanoBarbosa/libgdx,toa5/libgdx,anserran/libgdx,toa5/libgdx,alex-dorokhov/libgdx,junkdog/libgdx,czyzby/libgdx,BlueRiverInteractive/libgdx,sarkanyi/libgdx,Xhanim/libgdx,kotcrab/libgdx,libgdx/libgdx,stinsonga/libgdx,FredGithub/libgdx,jsjolund/libgdx,tommyettinger/libgdx,bgroenks96/libgdx,js78/libgdx,kotcrab/libgdx,junkdog/libgdx,kotcrab/libgdx,samskivert/libgdx,samskivert/libgdx,NathanSweet/libgdx,MovingBlocks/libgdx,JFixby/libgdx,js78/libgdx,MikkelTAndersen/libgdx,stinsonga/libgdx,codepoke/libgdx,alex-dorokhov/libgdx,gouessej/libgdx,tommyettinger/libgdx,czyzby/libgdx,codepoke/libgdx,ttencate/libgdx,firefly2442/libgdx,UnluckyNinja/libgdx,UnluckyNinja/libgdx,Thotep/libgdx,kotcrab/libgdx,stinsonga/libgdx,tommyettinger/libgdx,js78/libgdx,firefly2442/libgdx,czyzby/libgdx,SidneyXu/libgdx,bsmr-java/libgdx,sarkanyi/libgdx,Xhanim/libgdx,samskivert/libgdx,js78/libgdx,Thotep/libgdx,bgroenks96/libgdx,czyzby/libgdx,Zomby2D/libgdx,nrallakis/libgdx,bsmr-java/libgdx,Xhanim/libgdx,PedroRomanoBarbosa/libgdx,samskivert/libgdx,anserran/libgdx,Dzamir/libgdx,BlueRiverInteractive/libgdx,realitix/libgdx,junkdog/libgdx,Thotep/libgdx,josephknight/libgdx,xoppa/libgdx,gouessej/libgdx,toa5/libgdx,realitix/libgdx,MikkelTAndersen/libgdx,toa5/libgdx,MadcowD/libgdx,Thotep/libgdx,bladecoder/libgdx,hyvas/libgdx,bgroenks96/libgdx,firefly2442/libgdx,ttencate/libgdx,js78/libgdx,bsmr-java/libgdx,MikkelTAndersen/libgdx,BlueRiverInteractive/libgdx,realitix/libgdx,bgroenks96/libgdx,cypherdare/libgdx,Xhanim/libgdx,junkdog/libgdx,UnluckyNinja/libgdx,jsjolund/libgdx,ttencate/libgdx,MovingBlocks/libgdx,anserran/libgdx,anserran/libgdx,BlueRiverInteractive/libgdx,yangweigbh/libgdx,jsjolund/libgdx,czyzby/libgdx,yangweigbh/libgdx,Dzamir/libgdx,alex-dorokhov/libgdx,PedroRomanoBarbosa/libgdx,czyzby/libgdx,josephknight/libgdx,JFixby/libgdx,SidneyXu/libgdx,MadcowD/libgdx,tommyettinger/libgdx,SidneyXu/libgdx,SidneyXu/libgdx,BlueRiverInteractive/libgdx,yangweigbh/libgdx,alex-dorokhov/libgdx,JFixby/libgdx,nrallakis/libgdx,MikkelTAndersen/libgdx,Xhanim/libgdx,codepoke/libgdx,Xhanim/libgdx,toa5/libgdx,Xhanim/libgdx,NathanSweet/libgdx,bsmr-java/libgdx,MikkelTAndersen/libgdx,toa5/libgdx,FredGithub/libgdx,MikkelTAndersen/libgdx,yangweigbh/libgdx,czyzby/libgdx,MovingBlocks/libgdx,jsjolund/libgdx,nrallakis/libgdx,bladecoder/libgdx,xoppa/libgdx,jberberick/libgdx,codepoke/libgdx,realitix/libgdx,SidneyXu/libgdx,fwolff/libgdx,libgdx/libgdx,fwolff/libgdx,JFixby/libgdx,fwolff/libgdx,yangweigbh/libgdx,FredGithub/libgdx,Zomby2D/libgdx,realitix/libgdx,nrallakis/libgdx,js78/libgdx,anserran/libgdx,Dzamir/libgdx,Xhanim/libgdx,hyvas/libgdx,yangweigbh/libgdx,SidneyXu/libgdx,Dzamir/libgdx,JFixby/libgdx,kotcrab/libgdx,ttencate/libgdx,nrallakis/libgdx,realitix/libgdx,js78/libgdx,bladecoder/libgdx,jberberick/libgdx,hyvas/libgdx,BlueRiverInteractive/libgdx,fwolff/libgdx,UnluckyNinja/libgdx,bgroenks96/libgdx,Thotep/libgdx,libgdx/libgdx,nrallakis/libgdx,FredGithub/libgdx,stinsonga/libgdx,BlueRiverInteractive/libgdx,libgdx/libgdx,firefly2442/libgdx,bgroenks96/libgdx,MovingBlocks/libgdx,jberberick/libgdx,samskivert/libgdx,codepoke/libgdx,jsjolund/libgdx,FredGithub/libgdx,NathanSweet/libgdx,sarkanyi/libgdx,junkdog/libgdx,UnluckyNinja/libgdx,MadcowD/libgdx,firefly2442/libgdx,junkdog/libgdx,yangweigbh/libgdx,PedroRomanoBarbosa/libgdx,bladecoder/libgdx,sarkanyi/libgdx,PedroRomanoBarbosa/libgdx,bsmr-java/libgdx,jberberick/libgdx,alex-dorokhov/libgdx,Thotep/libgdx,fwolff/libgdx,NathanSweet/libgdx,jberberick/libgdx,fwolff/libgdx,Zomby2D/libgdx,MadcowD/libgdx,hyvas/libgdx,kotcrab/libgdx,xoppa/libgdx,SidneyXu/libgdx,MovingBlocks/libgdx,bladecoder/libgdx,firefly2442/libgdx,kotcrab/libgdx,bgroenks96/libgdx,xoppa/libgdx,gouessej/libgdx,sarkanyi/libgdx,NathanSweet/libgdx,MadcowD/libgdx,fwolff/libgdx,alex-dorokhov/libgdx,firefly2442/libgdx,FredGithub/libgdx,stinsonga/libgdx,MikkelTAndersen/libgdx,alex-dorokhov/libgdx,nrallakis/libgdx,hyvas/libgdx,tommyettinger/libgdx,BlueRiverInteractive/libgdx,ttencate/libgdx,czyzby/libgdx,ttencate/libgdx,anserran/libgdx,gouessej/libgdx,gouessej/libgdx,Dzamir/libgdx,bgroenks96/libgdx,kotcrab/libgdx,Dzamir/libgdx,jberberick/libgdx,samskivert/libgdx,hyvas/libgdx,junkdog/libgdx,JFixby/libgdx,josephknight/libgdx,UnluckyNinja/libgdx,jsjolund/libgdx,bsmr-java/libgdx,MikkelTAndersen/libgdx,jberberick/libgdx,sarkanyi/libgdx,josephknight/libgdx,PedroRomanoBarbosa/libgdx,hyvas/libgdx,josephknight/libgdx,MovingBlocks/libgdx,josephknight/libgdx,xoppa/libgdx,JFixby/libgdx,Dzamir/libgdx,hyvas/libgdx,gouessej/libgdx,realitix/libgdx,sarkanyi/libgdx,cypherdare/libgdx,PedroRomanoBarbosa/libgdx,ttencate/libgdx,Thotep/libgdx,codepoke/libgdx,junkdog/libgdx,toa5/libgdx,libgdx/libgdx,xoppa/libgdx,alex-dorokhov/libgdx,josephknight/libgdx,jsjolund/libgdx,codepoke/libgdx,bsmr-java/libgdx,codepoke/libgdx,Thotep/libgdx,gouessej/libgdx,PedroRomanoBarbosa/libgdx,cypherdare/libgd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