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How can I use more than 60 tasks in a Taskgroup? I can loop from 0 to N and create tasks but that will not give me any message handling. I use OTL EventMontior for sending messages from tasks..

The reason I ask is because using Indy I am limited to 60 requests. However if I use a normal TThread I won't have these problems but I will have other problems etc.

.NET Thread Pool MAX:

  • 1023 in Framework 4.0 (32-bit environment)
  • 32768 in Framework 4.0 (64-bit environment)
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Santos Oliveira
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2 Answers2

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According to OtlTaskControl.pas (based on v3.02 source), you can't exceed 64. (Don't know where your 60 came from, but I admit not having tried to exceed it.)

TOmniTaskGroup.WaitForAll (approximately line #3300) uses the WinAPI function WaitForMultipleObjects, and according to the MSDN documentation:

The maximum number of object handles is MAXIMUM_WAIT_OBJECTS.

MAXIMUM_WAIT_OBJECTS is defined in Windows.pas (for XE3, at approximately line # 1017:

MAXIMUM_WAIT_OBJECTS = 64;
{$EXTERNALSYM MAXIMUM_WAIT_OBJECTS}

The declaration itself comes from WinNT.h from the SDK, which contains:

#define MAXIMUM_WAIT_OBJECTS 64     // Maximum number of wait objects

WaitForMultipleObjects returns an error code if you pass it a value higher than MAXIMUM_WAIT_OBJECTS as the nCount parameter. (The error code is returned if any value higher than 64 is send as the nCount parameter, which means this value is built into the implementation of the function itself.)

A quick review of the other API Multiple-object Wait Functions doesn't turn up anything else that will accept more than MAXIMUM_WAIT_OBJECTS items, either.

So the specific answer to your question is: The only way this can be done is to write your own replacement for the WinAPI's WaitForMultipleObjects, and then replace the WaitForMultipleObjects call in TOmniTaskGroup.WaitForAll with a call to your function instead. (That's a very massive undertaking, which is probably why it hasn't been done in OTL, and expecting someone to do it in an answer here would be pretty unrealistic.)

Ken White
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According to an answer to a related question (regarding the rationale for the limit), you can bypass the limit by changing the definitions of FD_SETSIZE in Winsock.pas and CMaxConcurrentWorkers in OtlThreadPool.pas. Set them to whatever limit you prefer. I cannot personally vouch for the advice, though.

Note that by modifying Winsock.pas, you remove the ability to use Delphi-provided run-time packages in your application. (You can still use packages you've compiled yourself; they just can't have the same names a the built-in packages.)

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Rob Kennedy
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  • Rob, the question is not about OtlThreadPool but OtlTaskGroup. – jachguate Dec 19 '12 at 05:22
  • As I said, I cannot vouch for the advice. I'm only repeating what I read, and according to Jachguate, I misunderstood what I read. You're in a better position to test this than I am. – Rob Kennedy Dec 19 '12 at 12:37
  • @RobKennedy Why dont you allow my edit? The question is closed Let the people know how to do it! – Santos Oliveira Dec 19 '12 at 14:44
  • I have no idea what you're talking about. I'm not preventing you from editing anything. What do you want to know how to do, that I haven't already told you? – Rob Kennedy Dec 19 '12 at 15:19
  • I see. You [attempted to edit my answer](http://stackoverflow.com/review/suggested-edits/1207989), but the edit was rejected, although not by me. I'd have rejected it, too, and for the same reason. You need one more vote to open the question. I might yet incorporate some of your attempted edit into my answer. – Rob Kennedy Dec 19 '12 at 15:23