MycLib/Src/Myc.Signals.pas

//////////////////////////////////////////////////////////////////////////////
//////////////////////////////////////////////////////////////////////////////
///
///  Mycelium Framework
///  ------------------
///
///  (c)2007-2019 Michael Schimmel
///               Ehrenhainstraße 40
///               42329 Wuppertal / Germany
///               info@mycelium.net
///
///  All rights reserved.
///
//////////////////////////////////////////////////////////////////////////////
//////////////////////////////////////////////////////////////////////////////

unit Myc.Signals;

interface

uses
    System.SysUtils, System.SyncObjs,
    Myc.Atomic;

{.$define DEBUG_SIGNALS}

type
    IMyc2Sink = interface
        function Notify: Boolean;
    end;

    IMyc2Flag = interface( IMyc2Sink )
        function Reset: Boolean;
    end;

    {$message hint 'Replace TSignalTag by IMycDeletable? '}
    TSignalTag = NativeInt;

    IMyc2Signal = interface
        function Advise( const Sink: IMyc2Sink ): TSignalTag;
        procedure Unadvise( Tag: TSignalTag );
    end;

    IMyc2Notifier = interface( IMyc2Sink )
        {$region 'property access'}
        function GetSignal: IMyc2Signal;
        {$endregion}
        property Signal: IMyc2Signal read GetSignal;
    end;

    IMyc2State = interface( IMyc2Signal )
        {$region 'property access'}
        function GetIsSet: Boolean;
        {$endregion}
        property IsSet: Boolean read GetIsSet;
    end;

    IMyc2Condition = interface( IMyc2Sink )
        {$region 'property access'}
        function GetState: IMyc2State;
        {$endregion}
        property State: IMyc2State read GetState;
    end;

    IMyc2Event = interface( IMyc2Condition )
        function Reset: Boolean;
    end;

    TMycSinkList = record
    type
        PItem = ^TItem;

        TItem = record
            Next, Prev: PItem;
            Sink: IMyc2Sink;
        end;

    strict private
        FFirst: NativeUInt;
        FList: PItem;

        {$ifdef DEBUG_SIGNALS}
        FCount: Integer;
        {$endif}
        class var
            [volatile] FItems: TMycAtomicStack<TItem>;
        [volatile]
        FPendingCnt: Int64;
        [volatile]
        FUsedCnt: Int64;

        class constructor CreateClass;
        class destructor DestroyClass;
        class function AllocItem: PItem; static; inline;
        class procedure FreeItem( Item: PItem ); static; inline;

    public
        procedure Create;
        procedure Destroy;
        function Advise( const Sink: IMyc2Sink ): TSignalTag;
        procedure Unadvise( Tag: TSignalTag );
        procedure UnadviseAll;
        procedure Finalize;
        procedure Lock; inline;
        procedure Release; inline;
        function IsLocked: Boolean; inline;
        function IsFinalized: Boolean; inline;
        procedure Notify;
    end;

    TMyc2Signal = class( TInterfacedObject, IMyc2Signal, IMyc2State, IMyc2Sink )
    private
        FList: TMycSinkList;

        class var
            FNull: IMyc2Condition;

    protected
        class constructor CreateClass;
        class destructor DestroyClass;
        function GetIsSet: Boolean; virtual;
        function DoNotify: Boolean; virtual;
    public
        constructor Create;
        destructor Destroy; override;

        function Advise( const Sink: IMyc2Sink ): TSignalTag;
        procedure Unadvise( Tag: TSignalTag );
        function Notify: Boolean;

        class function CreateAdvised( Count: Integer; const Getter: TFunc<Integer, IMyc2Signal> ): IMyc2Signal; overload;
        class function IsStatic( const Signal: IMyc2Signal ): Boolean; overload; inline;
        class function IsStatic( const Sink: IMyc2Sink ): Boolean; overload; inline;

        class function MakeValid( const Signal: IMyc2Signal ): IMyc2Signal; overload; static; inline;
        class function MakeValid( const Signals: array of IMyc2Signal ): TArray<IMyc2Signal>; overload; static;

        class function CreateCounter( Count: Integer ): IMyc2Condition; static; inline;
        class function CreateEvent( Init: Boolean ): IMyc2Event; static; inline;
        class function CreateGroup( Count: Integer; const Getter: TFunc<Integer, IMyc2Signal> ): IMyc2Signal; overload;
        class function CreateNotifier: IMyc2Notifier; static; inline;

        class function CreateUnion( const Sigs: array of IMyc2Signal ): IMyc2Signal; static;
        class function CreateConcat( const States: array of IMyc2State ): IMyc2State; static;

        property IsSet: Boolean read GetIsSet;
        class property Null: IMyc2Condition read FNull;
    end;

    TMyc2Notifier = class( TMyc2Signal, IMyc2Notifier )
    protected
        function GetSignal: IMyc2Signal;
    end;

    TMyc2Condition = class( TMyc2Signal, IMyc2Condition )
    protected
        function GetState: IMyc2State;
    end;

    TMyc2Event = class( TMyc2Condition, IMyc2Event )
    private
        [volatile]
        FValue: Integer;

    protected
        function DoNotify: Boolean; override;
        function GetIsSet: Boolean; override;

    public
        constructor Create( AInit: Boolean );
        function Reset: Boolean; virtual;
        property IsSet: Boolean read GetIsSet;
    end;

    TMyc2CountSignal = class sealed( TMyc2Condition )
    private
        [volatile]
        FCount: Integer;

    protected
        function GetIsSet: Boolean; override;
        function DoNotify: Boolean; override;

    public
        constructor Create( ACount: Integer );
    end;

    TMyc2SinkProc = class sealed( TInterfacedObject, IMyc2Sink )
    private
        FOnce: Boolean;
        FProc: TProc;

        function Notify: Boolean;

    public
        constructor Create( AOnce: Boolean; const AProc: TProc );
        class function CreateSink( Once: Boolean; const Proc: TProc ): IMyc2Sink; static;
    end;

    TMyc2NullState = class sealed( TInterfacedObject, IMyc2Signal, IMyc2State )
    protected
        function Advise( const Sink: IMyc2Sink ): TSignalTag;
        function GetIsSet: Boolean;
        procedure Unadvise( Tag: TSignalTag );
        procedure UnadviseAll;
    end;

    TMyc2NullSink = class sealed( TInterfacedObject, IMyc2Sink, IMyc2Condition )
    private
        FState: IMyc2State;
        function GetState: IMyc2State;

    protected
        function Notify: Boolean;

    public
        constructor Create;
        destructor Destroy; override;
    end;

    TMyc2Flag = class( TInterfacedObject, IMyc2Sink, IMyc2Flag )
    private
        FFlag: Integer;
        function Notify: Boolean;
        function Reset: Boolean;

    public
        constructor Create( AFlag: Boolean );
    end;

    TMycObserver<T: IMyc2Sink> = class
    type
        TNull = class( TInterfacedObject, IMycObserver<T> )
        private
            FSink: T;
            function GetItem: T;

        public
            constructor Create( const ASink: T );
        end;

        TOne = class( TNull )
        private
            FSignal: IMyc2Signal;
            FTag: TSignalTag;

        public
            constructor Create( const ASignal: IMyc2Signal; const ASink: T );
            destructor Destroy; override;
        end;

        TArr = class( TNull )
        private
            FSignals: TArray<IMyc2Signal>;
            FTags: TArray<TSignalTag>;

        public
            constructor Create( const ASignals: TArray<IMyc2Signal>; const ASink: T );
            destructor Destroy; override;
        end;

    public
        class function CreateObserver( const Signals: array of IMyc2Signal; const Item: T ): IMycObserver<T>; static;
    end;

    TMycSignalUnion = class( TInterfacedObject, IMyc2Signal )
    private
        FNotifier: IMyc2Notifier;
        FSignals: TArray<IMyc2Signal>;
        FTags: TArray<TSignalTag>;

        function Advise( const Sink: IMyc2Sink ): TSignalTag;
        procedure Unadvise( Tag: TSignalTag );

    public
        constructor Create( const ASignals: array of IMyc2Signal );
        destructor Destroy; override;
    end;

implementation

{ TMyc2Signal }

constructor TMyc2Signal.Create;
begin
    inherited Create;
    FList.Create;
end;

destructor TMyc2Signal.Destroy;
begin
    FList.Destroy;
    inherited Destroy;
end;

class function TMyc2Signal.CreateAdvised( Count: Integer; const Getter: TFunc<Integer, IMyc2Signal> ): IMyc2Signal;
var
    i, j: Integer;
    Sig: IMyc2Signal;
    Res: IMyc2Condition;
begin
    for i := 0 to Count - 1 do
    begin
        Sig := Getter( i );
        if not IsStatic( Sig ) then
        begin
            Res := TMyc2Condition.Create;

            Sig.Advise( Res );

            for j := i + 1 to Count - 1 do
            begin
                Sig := Getter( j );
                if not IsStatic( Sig ) then
                    Sig.Advise( Res );
            end;

            exit( Res.State );
        end;
    end;

    exit( Null.State );
end;

class constructor TMyc2Signal.CreateClass;
begin
    FNull := TMyc2NullSink.Create;
end;

class destructor TMyc2Signal.DestroyClass;
begin
    FNull := nil;
end;

class function TMyc2Signal.IsStatic( const Signal: IMyc2Signal ): Boolean;
begin
    Result := ( Signal = nil ) or ( Signal = FNull.State );
end;

class function TMyc2Signal.MakeValid( const Signal: IMyc2Signal ): IMyc2Signal;
begin
    Result := Signal;
    if Result = nil then
        Result := Null.State;
end;

function TMyc2Signal.Advise( const Sink: IMyc2Sink ): TSignalTag;
begin
    if IsStatic( Sink ) then
        exit( 0 );

    FList.Lock;
    try
        Result := FList.Advise( Sink );

        if IsSet then
            Sink.Notify;
    finally
        FList.Release;
    end;
end;

class function TMyc2Signal.CreateConcat( const States: array of IMyc2State ): IMyc2State;

    function CreatePair( const A, B: IMyc2State ): IMyc2State;
    var
        Counter: IMyc2Condition;
    begin
        if A=B then
        begin
            Result := A;
        end
        else if IsStatic( A ) then
        begin
            if IsStatic( B ) then
                Result := Signals.Null.State
            else
                Result := B;
        end
        else if IsStatic( B ) then
        begin
            Result := A;
        end
        else
        begin
            Counter := CreateCounter( 2 );
            A.Advise( Counter );
            B.Advise( Counter );
            Result := Counter.State;
        end;
    end;

    function CreateSet( const States: array of IMyc2State ): IMyc2State;
    var
        Counter: IMyc2Condition;
        i, n: Integer;
    begin
        n := 0;
        for i := 0 to High( States ) do
            if not IsStatic( States[i] ) then
                inc( n );

        Counter := CreateCounter( n );
        for i := 0 to High( States ) do
            if not IsStatic( States[i] ) then
                States[i].Advise( Counter );

        Result := Counter.State;
    end;

begin
    {TODO -oMS: Potentielles Speicherloch. Im Gegensatz zur Union werden hier die States nicht explizit un-advised. Andererseits
     kann man eigentlich davon ausgehen, das States im Gegensatz zu einfachen Notifications irgendwann gesetzt und dann aufgeräumt
     werden. Im Auge behalten! }

    case Length( States ) of
    0:
        Result := Signals.Null.State;
    1:
        Result := States[0];
    2:
        Result := CreatePair( States[0], States[1] );
    else
        Result := CreateSet( States );
    end;
end;

class function TMyc2Signal.CreateCounter( Count: Integer ): IMyc2Condition;
begin
    Assert( Count >=0 );

    if Count > 0 then
        Result := TMyc2CountSignal.Create( Count )
    else
        Result := Null;
end;

class function TMyc2Signal.CreateEvent( Init: Boolean ): IMyc2Event;
begin
    Result := TMyc2Event.Create( Init )
end;

class function TMyc2Signal.CreateGroup( Count: Integer; const Getter: TFunc<Integer, IMyc2Signal> ): IMyc2Signal;
var
    i, n: Integer;
    Sigs: TArray<IMyc2Signal>;
    Res: IMyc2Condition;
begin
    if Count = 0 then
        exit( Null.State );

    SetLength( Sigs, Count );
    n := 0;
    for i := 0 to Count - 1 do
    begin
        Sigs[n] := Getter( i );
        if not IsStatic( Sigs[n] ) then
            inc( n );
    end;

    if n = 0 then
        exit( Null.State );

    Res := CreateCounter( n );
    for i := 0 to n - 1 do
        Sigs[i].Advise( Res );

    exit( Res.State );
end;

class function TMyc2Signal.CreateNotifier: IMyc2Notifier;
begin
    Result := TMyc2Notifier.Create;
end;

class function TMyc2Signal.MakeValid( const Signals: array of IMyc2Signal ): TArray<IMyc2Signal>;
var
    i, n: Integer;
begin
    n := 0;
    for i := 0 to High( Signals ) do
        if not IsStatic( Signals[i] ) then
            inc( n );

    SetLength( Result, n );
    n := 0;
    for i := 0 to High( Signals ) do
        if not IsStatic( Signals[i] ) then
        begin
            Result[n] := Signals[i];
            inc( n );
        end;
end;

class function TMyc2Signal.CreateUnion( const Sigs: array of IMyc2Signal ): IMyc2Signal;
begin
    case Length( Sigs ) of
    0:
        Result := Signals.Null.State;
    1:
        Result := Sigs[0];
    else
        Result := TMycSignalUnion.Create( Sigs );
    end;
end;

function TMyc2Signal.DoNotify: Boolean;
begin
    FList.Notify;
    exit( true );
end;

function TMyc2Signal.GetIsSet: Boolean;
begin
    Result := true;
end;

class function TMyc2Signal.IsStatic( const Sink: IMyc2Sink ): Boolean;
begin
    Result := ( Sink = nil ) or ( Sink = FNull );
end;

function TMyc2Signal.Notify: Boolean;
begin
    FList.Lock;
    try
        Result := DoNotify;
        if not Result then
            FList.Finalize;
    finally
        FList.Release;
    end;
end;

procedure TMyc2Signal.Unadvise( Tag: TSignalTag );
begin
    if Tag=0 then
        exit;

    FList.Lock;
    try
        FList.Unadvise( Tag );
    finally
        FList.Release;
    end;
end;

{ TMyc2Event }

constructor TMyc2Event.Create( AInit: Boolean );
begin
    inherited Create;
    if AInit then
        inc( FValue );
end;

function TMyc2Event.GetIsSet: Boolean;
begin
    Result := FValue <> 0;
end;

function TMyc2Event.DoNotify: Boolean;
begin
    if TInterlocked.Exchange( FValue, 1 ) = 0 then
        inherited;
    exit( true );
end;

function TMyc2Event.Reset: Boolean;
begin
    Result := TInterlocked.Exchange( FValue, 0 ) = 1;
end;

{ TMyc2CountownSignal }

constructor TMyc2CountSignal.Create( ACount: Integer );
begin
    inherited Create;
    FCount := ACount;
end;

function TMyc2CountSignal.GetIsSet: Boolean;
begin
    Result := FCount <= 0;
end;

function TMyc2CountSignal.DoNotify: Boolean;
var
    n: Integer;
begin
    n := TInterlocked.Decrement( FCount );
    if n < -MaxInt div 2 then
        TInterlocked.Increment( FCount );

    if n = 0 then
        inherited;

    Result := n > 0;
end;

{ TMyc2SinkProc }

constructor TMyc2SinkProc.Create( AOnce: Boolean; const AProc: TProc );
begin
    inherited Create;
    FProc := AProc;
    FOnce := AOnce;
end;

class function TMyc2SinkProc.CreateSink( Once: Boolean; const Proc: TProc ): IMyc2Sink;
begin
    if Assigned( Proc ) then
        Result := TMyc2SinkProc.Create( Once, Proc )
    else
        Result := TMyc2Signal.Null;
end;

function TMyc2SinkProc.Notify: Boolean;
begin
    if Assigned( FProc ) then
    begin
        FProc( );
        if FOnce then
            FProc := nil;
    end;

    Result := Assigned( FProc );
end;

{ TMyc2NullState }

function TMyc2NullState.Advise( const Sink: IMyc2Sink ): TSignalTag;
begin
    Sink._AddRef;
    try
        Sink.Notify;
    finally
        Sink._Release;
    end;
    exit( 0 );
end;

function TMyc2NullState.GetIsSet: Boolean;
begin
    exit( true );
end;

procedure TMyc2NullState.Unadvise( Tag: TSignalTag );
begin
end;

procedure TMyc2NullState.UnadviseAll;
begin

end;

constructor TMyc2NullSink.Create;
begin
    inherited Create;
    FState := TMyc2NullState.Create;
end;

destructor TMyc2NullSink.Destroy;
begin
    inherited Destroy;
end;

function TMyc2NullSink.GetState: IMyc2State;
begin
    Result := FState;
end;

function TMyc2NullSink.Notify: Boolean;
begin
    Result := false;
end;

{ TMyc2Notifier }

function TMyc2Notifier.GetSignal: IMyc2Signal;
begin
    Result := Self;
end;

{ TMyc2Condition }

function TMyc2Condition.GetState: IMyc2State;
begin
    Result := Self;
end;

{ TMycSinkList }

class constructor TMycSinkList.CreateClass;
begin
    FItems := TMycAtomicStack<TItem>.Create;
    FPendingCnt := 0;
    FUsedCnt := 0;
end;

class destructor TMycSinkList.DestroyClass;
begin
    Assert( FUsedCnt = 0 );
    Assert( FPendingCnt = 0 );

    FItems.Free;
end;

procedure TMycSinkList.Create;
begin
    FFirst := 1;
    FList := nil;
    {$ifdef DEBUG_SIGNALS}
    FCount := 0;
    {$endif}
end;

procedure TMycSinkList.Destroy;
begin
    // Because refcounting is thread-safe, this will always be entered once after all references
    // to Self are dropped. No locking needed!
    Assert( not IsLocked, 'Signal must not be locked!' );
    FFirst := FFirst and not 3;
    UnadviseAll;
end;

function TMycSinkList.Advise( const Sink: IMyc2Sink ): TSignalTag;
var
    Item: PItem;
begin
    Assert( IsLocked, 'Signal has to be locked' );

    if IsFinalized then
        exit( 0 );

    {$ifdef DEBUG_SIGNALS}
    inc( FCount );
    Assert( FCount < 40000 );
    {$endif}
    if FFirst=0 then
    begin
        IMyc2Sink( FFirst ) := Sink;
        exit( TSignalTag( Sink ) );
    end;

    Item := AllocItem;
    Item.Sink := Sink;
    Item.Prev := nil;
    Item.Next := FList;
    if Item.Next<>nil then
        Item.Next.Prev := Item;

    FList := Item;

    exit( TSignalTag( Item ) );
end;

procedure TMycSinkList.Lock;
begin
    repeat
        if FFirst and 1 = 0 then
        begin
            YieldProcessor;
            continue;
        end;
    until TInterlocked.BitTestAndClear( PInteger( @FFirst )^, 0 );

    Assert( IsLocked, 'Locking failed' );
end;

procedure TMycSinkList.Notify;
var
    Item, P: PItem;
begin
    Assert( IsLocked, 'Signal has to be locked' );

    if IsFinalized then
        exit;

    if FFirst<>0 then
        if not IMyc2Sink( FFirst ).Notify then
            IMyc2Sink( FFirst ) := nil;

    Item := FList;
    while Item<>nil do
    begin
        P := Item.Next;
        if not Item.Sink.Notify then
            Unadvise( TSignalTag( Item ) );
        Item := P;
    end;
end;

class function TMycSinkList.AllocItem: PItem;
begin
    GetMem( Result, sizeof( TItem ) );
    Pointer( Result.Sink ) := nil;
end;

procedure TMycSinkList.Finalize;
begin
    Assert( IsLocked, 'Signal has to be locked' );
    UnadviseAll;
    FFirst := FFirst or 2;
end;

class procedure TMycSinkList.FreeItem( Item: PItem );
begin
    FreeMem( Item, sizeof( TItem ) );
end;

function TMycSinkList.IsLocked: Boolean;
begin
    Result := FFirst and 1 = 0;
end;

function TMycSinkList.IsFinalized: Boolean;
begin
    Result := FFirst and 2 <> 0;
end;

procedure TMycSinkList.Release;
begin
    Assert( IsLocked, 'Signal not locked' );
    TInterlocked.Exchange( Pointer( FFirst ), Pointer( FFirst or 1 ) );
end;

procedure TMycSinkList.Unadvise( Tag: TSignalTag );
var
    Item: PItem;
begin
    Assert( IsLocked, 'Signal not locked' );

    if IsFinalized then
        exit;

    {$ifdef DEBUG_SIGNALS}
    dec( FCount );
    {$endif}
    if Tag = FFirst then
    begin
        IMyc2Sink( FFirst ) := nil;
        exit;
    end;

    Item := PItem( Tag );

    if Item = FList then
        FList := Item.Next;

    if Item.Prev<>nil then
        Item.Prev.Next := Item.Next;
    if Item.Next<>nil then
        Item.Next.Prev := Item.Prev;

    Item.Sink := nil;

    FreeItem( Item );
end;

procedure TMycSinkList.UnadviseAll;
begin
    Assert( IsLocked, 'Signal has to be locked' );

    if IsFinalized then
        exit;

    IMyc2Sink( FFirst ) := nil;
    while FList<>nil do
        Unadvise( TSignalTag( FList ) );
end;

{ TMycObserver<T> }

class function TMycObserver<T>.CreateObserver( const Signals: array of IMyc2Signal; const Item: T ): IMycObserver<T>;
var
    Arr: TArray<IMyc2Signal>;
begin
    {$message hint 'Design-Fehler!! Der Null-Observer ist nicht statisch!!'}
    if Length( Signals ) = 0 then
        Result := TNull.Create( Item )
    else if ( Length( Signals )=1 ) and not TMyc2Signal.IsStatic( Signals[0] ) then
        Result := TOne.Create( Signals[0], Item )
    else
    begin
        Arr := TMyc2Signal.MakeValid( Signals );
        if Arr = nil then
            Result := TNull.Create( Item )
        else if Length( Arr )=1 then
            Result := TOne.Create( Arr[0], Item )
        else
            Result := TArr.Create( Arr, Item );
    end;
end;

{ TMycObserver<T>.TNull }

constructor TMycObserver<T>.TNull.Create( const ASink: T );
begin
    inherited Create;
    FSink := ASink;
end;

function TMycObserver<T>.TNull.GetItem: T;
begin
    Result := FSink;
end;

{ TMycObserver<T>.TOne }

constructor TMycObserver<T>.TOne.Create( const ASignal: IMyc2Signal; const ASink: T );
begin
    inherited Create( ASink );
    FSignal := ASignal;
    FTag := FSignal.Advise( FSink );
end;

destructor TMycObserver<T>.TOne.Destroy;
begin
    FSignal.Unadvise( FTag );
    inherited;
end;

{ TMycObserver<T>.TArr }

constructor TMycObserver<T>.TArr.Create( const ASignals: TArray<IMyc2Signal>; const ASink: T );
var
    i: Integer;
begin
    inherited Create( ASink );
    FSignals := ASignals;

    SetLength( FTags, Length( FSignals ) );
    for i := 0 to High( FTags ) do
    begin
        if not Signals.IsStatic( FSignals[i] ) then
            FTags[i] := FSignals[i].Advise( FSink )
        else
            FTags[i] := 0;
    end;
end;

destructor TMycObserver<T>.TArr.Destroy;
var
    i: Integer;
begin
    for i := High( FSignals ) downto 0 do
        if FTags[i]<>0 then
            FSignals[i].Unadvise( FTags[i] );
    inherited;
end;

{ TMycSignalUnion }

constructor TMycSignalUnion.Create( const ASignals: array of IMyc2Signal );
var
    i: Integer;
begin
    inherited Create;

    FNotifier := Signals.CreateNotifier;
    SetLength( FTags, Length( ASignals ) );
    SetLength( FSignals, Length( ASignals ) );
    for i := 0 to High( FSignals ) do
    begin
        FSignals[i] := ASignals[i];
        FTags[i] := FSignals[i].Advise( FNotifier );
    end;
end;

destructor TMycSignalUnion.Destroy;
var
    i: Integer;
begin
    for i := High( FTags ) downto 0 do
        FSignals[i].Unadvise( FTags[i] );

    inherited;
end;

function TMycSignalUnion.Advise( const Sink: IMyc2Sink ): TSignalTag;
begin
    Result := FNotifier.Signal.Advise( Sink );
end;

procedure TMycSignalUnion.Unadvise( Tag: TSignalTag );
begin
    FNotifier.Signal.Unadvise( Tag );
end;

{ TMyc2Flag }

constructor TMyc2Flag.Create( AFlag: Boolean );
begin
    inherited Create;
    FFlag := Integer( AFlag );
end;

function TMyc2Flag.Notify: Boolean;
begin
    Result := TInterlocked.Exchange( FFlag, 1 ) = 0;
end;

function TMyc2Flag.Reset: Boolean;
begin
    Result := TInterlocked.Exchange( FFlag, 0 ) = 1;
end;

end.