c# - Thread Synchronisation : Threads having their own copy of string type lock -

recently came across code following:

void callthisindifferentthreads(return return) {  var lock =  "lock";  lock(lock)     {         //do here.     } } 

my first reaction lock in code won't work because creating lock , using in same method. every thread calling method has it's own copy of lock there no synchronisation.

but later realized should work because string goes string pool , there 1 instance of particular string. i'm not sure if i'm correct.

locking on strings super bad. don't it. have no guarantee other clever soul not lock on strings, , because "super" global because of string interning, moment becomes accepted practice, wheels fall off.

lock private object has 1 purpose... locking. strings don't fit description.

locking string. safe/sane?

is ok use string lock object?