🚀 go-pugleaf

Author := "NICs";

| Assume that we have a class TMyObject which will be exported from a
| DLL in Windows or a dynamic object in Linux.
| [A] How to define a DLL and its equivalent in Linux to export a class
| ? (Can somone give us a skeleton code)
| [B] How to create multiple instances of the imported the class from a
| DLL?  (Can somone give us a skeleton code)

Why can't you use a runtime package? After all r/t packages *are*
dll's/so's.

| [C] How to count number of instances of a class imported from a DLL?
| (Note that DLL (and its equivalent in Linux ) can be used by more
| than one application in the same time)

The class must provide this functionality. Define a global variable
InstanceCount in the unit where the class is implemented and then
override the methods AfterConstruction and BeforeDestruction of your
class to InterlockedIncrement and InterlockedDecrement it respectively.
Then add a class method to your class that returns the value of the
global variable.

interface

type
  TMyClass = class
  ...
  public
    procedure AfterConstruction; override;
    procedure BeforeDestruction; override;
    class function GetInstanceCount: Integer;
  end;

implementation

var
  InstanceCount: Integer = 0;

procedure TMyClass.AfterConstruction;
begin
  inherited; 
  InterlockedIncrement(InstanceCount);
end;

procedure TMyClass.BeforeDestruction;
begin
  inherited; 
  InterlockedDecrement(InstanceCount);
end;


class function TMyClass.GetInstanceCount: Integer;
begin
  Result := InstanceCount;
end;

HTH

-- 
Constantine