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    <p>The approach given by <a href="https://stackoverflow.com/users/255257/jachguate">jachgate</a> is great, and probably better, but in case you do want to implement this, you will need a <code>TThreadList</code> on the server that is created when the service is started. Use the <code>TThreadList</code> because it's thread-safe. You can have on <code>TThreadList</code> per table so that you can minimize the performance hit of navigating the lists. To control what's locked, you'll need an object that's created and passed to the list</p> <pre><code> TLockedItem = class(TObject) public iPK: Integer; iClientID: Integer; end; </code></pre> <p>To do the actual locking, you'd need something like this:</p> <pre><code>function LockItem(pPK, pClientID: Integer): Boolean; var oLockedItem: TLockedItem; oInternalList: TList; iCont: Integer; bExists: Boolean; begin bExists := False; if (Assigned(oLockedList)) then begin oInternalList := oLockedList.LockList; try if (oInternalList.Count &gt; 0) then begin iCont := 0; while ((not bExists) and (iCont &lt; oInternalList.Count)) do begin oLockedItem := TLockedItem(oInternalList[iCont]); if (oLockedItem.iPK = pPk) then bExists := True else Inc(iCont); end; end; finally oLockedList.UnlockList; end; if (not bExists) then begin oLockedItem := TLockedItem.Create; oLockedItem.iPK := pPK; oLockedItem.iClientID := pClientID; oInternalList := oLockedList.LockList; try oInternalList.Add(oLockedItem); finally oLockedList.UnlockList; end; end; end; Result := bExists; end; </code></pre> <p>That's just an ideia of what you'd need. You would have to do an unlock method with similar logic. You'd probably need a list for the clients, that would keep a point of each TLockItem held by each client, in case of lost connection. This is not a definitive answer, just a push on the direction, in case you want to implement this approach. <br> Good luck</p>
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    1. POConcurrency control
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    1. COsorry, what are you implementing here? With an OPF and pessimistic locking you might lock the objects using something like this, but your answer is too much code, not enough explanation at this stage.
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    2. CO@Pascal: thanks for the code will be helpful
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    3. CO@pascal Can you explain how this approach will scale in a failover/load-balancing scenario?. I think with this you stuck with 1 app-server limit.
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