sourceafConcurrent::AtomicList.fan

using concurrent::AtomicRef

** A List that provides fast reads and lightweight writes between threads.
** Use when *reads* far out number the *writes*.
**
** The list is stored in an [AtomicRef]`concurrent::AtomicRef` through which all reads are made. 
** Writing makes a 'rw' copy of the list and is thus a more expensive operation.
** 
** > **CAUTION:** 
** Write operations ( 'add', 'remove' & 'clear' ) are not synchronised. 
** This makes them lightweight but also susceptible to **data-loss** during race conditions.
** This may be acceptable for *caching* situations where values is easily re-calculated.
** 
** Note that all values held in the list must be immutable.
const class AtomicList {
    private const AtomicRef atomicList := AtomicRef()
    
    ** Gets or sets a read-only copy of the backing map.
    Obj?[] list {
        get {
            if (atomicList.val == null)
                atomicList.val = [,].toImmutable
            return atomicList.val 
        }
        set { atomicList.val = it.toImmutable }
    }
    
    ** Add the specified item to the end of the list.
    ** Return this. 
    @Operator
    This add(Obj? val) {
        rwList := list.rw
        rwList.add(val)
        list = rwList
        return this
    }

    ** Removes the specified item from the list, returning the removed item.
    ** If the item was not mapped then return 'null'.
    Obj? remove(Obj item) {
        rwList := list.rw
        oVal  := rwList.remove(item)
        list = rwList
        return oVal 
    }

    ** Remove all key/value pairs from the map. Return this.
    This clear() {
        list = list.rw.clear
        return this
    }

    // ---- Common List Methods --------------------------------------------------------------------

    ** Returns 'true' if this list contains the specified item.
    Bool contains(Obj? item) {
        list.contains(item)
    }
    
    ** Call the specified function for every item in the list.
    Void each(|Obj? item, Int index| c) {
        list.each(c)
    }
    
    ** Returns the item at the specified index.
    ** A negative index may be used to access an index from the end of the list.
    @Operator
    Obj? get(Int index) {
        list[index]
    }
    
    ** Return 'true' if size() == 0
    Bool isEmpty() {
        list.isEmpty
    }

    ** Get a read-write, mutable List instance with the same contents.
    Obj?[] rw() {
        list.rw
    }
    
    ** Get the number of values in the map.
    Int size() {
        list.size
    }
}