synchronize access to mutable shared maps (GC-399)
synchronize access to mutable shared maps (GC-399)

We now properly synchronize access to _tx_stacks and _connections, which can be
concurrently mutated by different threads. This way I don't have to worry about
GIL semantics: DRF => SC!

andremiller/beets,moodboom/beets,PierreRust/beets,mathstuf/beets,pkess/beets,pdf/beets,m-urban/beets,jcoady9/beets,randybias/beets,jcoady9/beets,shamangeorge/beets,jmwatte/beets,marcuskrahl/beets,lengtche/beets,m-urban/beets,jayme-github/beets,beetbox/beets,SusannaMaria/beets,beetbox/beets,PierreRust/beets,LordSputnik/beets,kareemallen/beets,artemutin/beets,lightwang1/beets,YetAnotherNerd/beets,mosesfistos1/beetbox,sampsyo/beets,randybias/beets,multikatt/beets,ttsda/beets,untitaker/beets,lightwang1/beets,Andypsamp/CODfinalJUNIT,Andypsamp/CODjunit,parapente/beets,Andypsamp/CODfinalJUNIT,moodboom/beets,kareemallen/beets,bj-yinyan/beets,shanemikel/beets,pdf/beets,andremiller/beets,jayme-github/beets,mried/beets,arabenjamin/beets,Freso/beets,Andypsamp/CODjunit,ibmibmibm/beets,moodboom/beets,randybias/beets,artemutin/beets,ttsda/beets,lengtche/beets,sampsyo/beets,diego-plan9/beets,MyTunesFreeMusic/privacy-policy,jcoady9/beets,swt30/beets,diego-plan9/beets,aspidites/beets,jcoady9/beets,swt30/beets,multikatt/beets,mried/beets,sadatay/beets,gabrielaraujof/beets,pkess/beets,ttsda/beets,swt30/beets,untitaker/beets,Andypsamp/CODjunit,mried/beets,imsparsh/beets,ruippeixotog/beets,diego-plan9/beets,beetbox/beets,Andypsamp/CODfinalJUNIT,Andypsamp/CODfinalJUNIT,arabenjamin/beets,kelvinhammond/beets,Andypsamp/CODjunit,LordSputnik/beets,parapente/beets,kareemallen/beets,dfc/beets,gabrielaraujof/beets,tima/beets,SusannaMaria/beets,kelvinhammond/beets,jackwilsdon/beets,bj-yinyan/beets,mosesfistos1/beetbox,andremiller/beets,drm00/beets,madmouser1/beets,jmwatte/beets,shanemikel/beets,dfc/beets,YetAnotherNerd/beets,jbaiter/beets,jbaiter/beets,lightwang1/beets,madmouser1/beets,krig/beets,Freso/beets,sampsyo/beets,Andypsamp/CODfinalJUNIT,shanemikel/beets,xsteadfastx/beets,moodboom/beets,ruippeixotog/beets,PierreRust/beets,krig/beets,xsteadfastx/beets,lightwang1/beets,ruippeixotog/beets,YetAnotherNerd/beets,m-urban/beets,imsparsh/beets,LordSputnik/beets,madmouser1/beets,kelvinhammond/beets,asteven/beets,marcuskrahl/beets,marcuskrahl/beets,arabenjamin/beets,Dishwishy/beets,m-urban/beets,swt30/beets,mathstuf/beets,mathstuf/beets,Wen777/beets,jmwatte/beets,multikatt/beets,mathstuf/beets,asteven/beets,sadatay/beets,jackwilsdon/beets,pkess/beets,jackwilsdon/beets,mried/beets,shanemikel/beets,MyTunesFreeMusic/privacy-policy,krig/beets,mosesfistos1/beetbox,beetbox/beets,imsparsh/beets,randybias/beets,SusannaMaria/beets,mosesfistos1/beetbox,artemutin/beets,arabenjamin/beets,asteven/beets,YetAnotherNerd/beets,pkess/beets,drm00/beets,jackwilsdon/beets,tima/beets,SusannaMaria/beets,dfc/beets,bj-yinyan/beets,jmwatte/beets,gabrielaraujof/beets,xsteadfastx/beets,kareemallen/beets,shamangeorge/beets,Freso/beets,multikatt/beets,Dishwishy/beets,aspidites/beets,ttsda/beets,Wen777/beets,PierreRust/beets,bj-yinyan/beets,asteven/beets,Dishwishy/beets,LordSputnik/beets,Kraymer/beets,ibmibmibm/beets,parapente/beets,lengtche/beets,dfc/beets,ibmibmibm/beets,tima/beets,sadatay/beets,tima/beets,imsparsh/beets,MyTunesFreeMusic/privacy-policy,sadatay/beets,Freso/beets,parapente/beets,untitaker/beets,drm00/beets,artemutin/beets,marcuskrahl/beets,Kraymer/beets,untitaker/beets,Kraymer/beets,gabrielaraujof/beets,sampsyo/beets,diego-plan9/beets,Andypsamp/CODjunit,Wen777/beets,shamangeorge/beets,Kraymer/beets,drm00/beets,MyTunesFreeMusic/privacy-policy,ibmibmibm/beets,ruippeixotog/beets,xsteadfastx/beets,Dishwishy/beets,kelvinhammond/beets,shamangeorge/beets,madmouser1/beets,lengtche/beets