Question

I would like to create/use a system-wide independent universal ‘counter object’ that can be called via COM in a thread-safe manner.

The counter object will be passed an ID to identify which counter to return, handle the counting, ‘persist’ the count (occasionally), have reasonable performance (as fast as possible) perhaps capable of 1000 counts per second or better (1mS) and be accessible cross-process/out-of-process. The current count status must be persisted between object restarts/shutdowns.

The counter object is liklely to be a ‘singleton’ type object implemented in some form of free-threaded dictionary, containing maybe 10 counters (perhaps 50 max). The count needs to be monotonic and consistent, (ie: guaranteed unique sequential values).

Each counter should have a few methods, like reset, inc, dec, set, clear, remove. As a luxury, I would like to have a variable-increment (ie: ‘step by’ value). To support thread-safefty, perhaps some sorm of critical-section or mutex call. It just needs to return a long/4byte signed integer.

I really want something that can be called from anywhere, including VBScript, so I figure COM is my preferred solution.

The primary use of this is for database keys. I am unable to use autoinc or guid type keys and have ruled out database-generated counting systems at this point.

I’ve spent days researching this and I have really struggled to find a solution. The best I can find is a free-threaded dictionary object that can be instantiated using COM+ from Motobit – it seems to offer all the ‘basics’ and I guess I could create some form of wrapper for this.

So, here are my questions:

• Does such a ‘general purpose
  counter-object already exist? Can you direct me to it? (MS did
  do an IIS/ASP object called
  ‘MSWC.Counter’ but this isn’t
  ‘cross-process’/ out-of-process
  component and isn’t thread-safe. (but if it was, it would do!)

• What is the best way of creating such
  a Component? (I’d prefer VB6
  right-now, [don’t ask!] but can do in VB.NET2005
  if I had to). I don’t have the
  skills/knowledge/tools to use
  anything else.

I am desparate for a workable solution. I need specific guidance! If anybody can code something up for me I am prepared to pay for it.

Update:

1. Whats wrong with GUIDs? a) 16bytes if I’m lucky (Binary storage), 32+bytes if I’m not (ANSI without formatting) or even worse(64bytes Unicode). b) I have an high-volume replicated app where the GUID is just too big (compared to the actual row data) and c) the overhead of indexing and inserts d) I want a readable number! – I only need 4 byte integer, so why not try and get that? I know you will say that disc-space is cheap, but for my application the cost is in slow inserts, and guids don’t help (and I have tried/tested) but would prefer not to use if I have a choice.

2. Autonumber/autoincs are evil: a) don’t get the value until after the insert, b) session specific, c) easy to lose/screw up on a table alter, d) no good for mutli-table inserts, (its not MS-SQL Svr) plus I have a need for counters outside my DB…

Answer 1

By the sound of it, what you’re looking to create is an ActiveX EXE. They run in their own process but can be accessed from any other process by instantiating an object from it as though it is just another COM object. It handles all the marshaling necessary to sync its internal thread with the threads of any process calling it. Since all you planning on using is integers, there’s no need to worry about the thread safety of objects passed between the threads.

More than likely you can use the MSWC.Counter object within that ActiveX EXE and let it do the counter work.