How to dealloc complex object correctly?

[r3d9u11]

Hi. I have a complex object declared in shared memory: 
    
    
    type
      SubObj = object
        idata: int
        fdata: float
        sdata: string
      MyObj = object
        title: string
        data: SubObj
    
    var lock: Lock
    var shrObj {.guard: lock.}: ptr MyObj
    
    shrObj = cast[ptr MyObj](allocShared0(sizeof(MyObj)))
    shrObj.title = "abc"
    shrObj.data.idata = 123
    shrObj.data.fdata = 0.01
    shrObj.data.sdata = "text data..."
    
    #GCunref(shrObj.title)
    #GCunref(shrObj.data.sdata)
    
    dealloc(shrObj)
    

dealloc function will excepted (alloc.nim:399 
    
    
    c.prev.next = c.next

). What I'm doing wrong? Also, is it necessary to call a function GCunref? (I 
saw it in manual)