sourceafConcurrent::AtomicMap.fan

using concurrent::AtomicRef

** A Map that provides fast reads and lightweight writes between threads.
** Use when *reads* far out number the *writes*.
**
** The map is stored in an [AtomicRef]`concurrent::AtomicRef` through which all reads are made. 
** Writing makes a 'rw' copy of the map and is thus a more expensive operation.
** 
** > **CAUTION:** 
** Write operations ( 'getOrAdd', 'set', '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 objects held in the map must be immutable.
** 
** See [The Good, The Bad and The Ugly of Const Services]`http://www.fantomfactory.org/articles/good-bad-and-ugly-of-const-services#theUgly` for more details.
const class AtomicMap {
    private const AtomicRef atomicMap := AtomicRef()

    ** The default value to use for `get` when a key isn't mapped.
    const Obj? def              := null
    
    ** Configures case sensitivity for maps with 'Str' keys.
    const Bool caseInsensitive  := false

    ** If 'true' the map will maintain the order in which key/value pairs are added.
    const Bool ordered          := false
    
    ** Used to parameterize the backing map.
    ** Must be non-nullable.
    const Type keyType          := Obj#
    
    ** Used to parameterize the backing map. 
    const Type valType          := Obj?#
    
    @NoDoc  // pointless ctor!
    new make(|This|? f := null) { 
        f?.call(this) 
        if (caseInsensitive && keyType == Obj#)
            keyType = Str#
    }
    
    ** Gets or sets a read-only copy of the backing map.
    [Obj:Obj?] map {
        get { 
            if (atomicMap.val == null)
                atomicMap.val = Map.make(Map#.parameterize(["K":keyType, "V":valType])) {
                    if (this.def != null)
                        it.def = this.def 
                    if (this.caseInsensitive) 
                        it.caseInsensitive = this.caseInsensitive 
                    it.ordered = this.ordered 
                }.toImmutable
            return atomicMap.val 
        }
        set { atomicMap.val = it.toImmutable }
    }
    
    ** Returns the value associated with the given key. If it doesn't exist then it is added from 
    ** the value function. 
    ** 
    ** This method is **NOT** thread safe. If two Actors call this method at the same time, the 
    ** value function will be called twice for the same key.
    Obj? getOrAdd(Obj key, |Obj key->Obj?| valFunc) {
        iKey  := key.toImmutable
        if (!containsKey(iKey)) {
            val  := valFunc.call(iKey)
            iVal := val.toImmutable
            set(iKey, iVal)
        }
        return get(iKey)
    }

    ** Sets the key / value pair.
    @Operator
    Void set(Obj key, Obj? val) {
        iKey  := key.toImmutable
        iVal  := val.toImmutable
        rwMap := map.rw
        rwMap[iKey] = iVal
        map = rwMap
    }

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

    ** Remove the key/value pair identified by the specified key
    ** from the map and return the value. 
    ** If the key was not mapped then return 'null'.
    Obj? remove(Obj key) {
        rwMap := map.rw
        oVal  := rwMap.remove(key)
        map = rwMap
        return oVal 
    }

    // ---- Common Map Methods --------------------------------------------------------------------

    ** Returns 'true' if the map contains the given key
    Bool containsKey(Obj key) {
        map.containsKey(key)
    }
    
    ** Returns the value associated with the given key. 
    ** If key is not mapped, then return the value of the 'def' parameter.  
    ** If 'def' is omitted it defaults to 'null'.
    @Operator
    Obj? get(Obj key, Obj? def := this.def) {
        map.get(key, def)
    }
    
    ** Return 'true' if size() == 0
    Bool isEmpty() {
        map.isEmpty
    }

    ** Returns a list of all the mapped keys.
    Obj[] keys() {
        map.keys
    }

    ** Get a read-write, mutable Map instance with the same contents.
    [Obj:Obj?] rw() {
        map.rw
    }

    ** Get the number of key/value pairs in the map.
    Int size() {
        map.size
    }

    ** Returns a list of all the mapped values.
    Obj?[] vals() {
        map.vals
    }   
}