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You are running a Visual Basic 6.0 component in a high throughput, multi-threaded application; such as COM+/MTS, Active Server Pages (ASP), or a Visual Basic 6.0 ActiveX EXE.
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Performance degrades and/or the application encounters high CPU as the component services a large number of client requests.
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The Visual Basic component may be performing an operation that results in a critical section convoy. Internally Visual Basic 6.0 uses critical sections to protect key data structures, which the Visual Basic run-time uses to maintain a wide range of per-thread project information. If the component is executing code that requires access to the critical section, multiple threads may be waiting to take ownership of the critical section. This causes a delay in each thread servicing its request. Performance may decline over time as more and more threads are created, with each one waiting to access the critical section.
Common scenarios for this to occur would be:
1. Calling procedures or variables stored in standard modules (.bas).
2. Making late bound calls on COM components.
3. Using Visual Basic intrinsic file I/O statements, such as Open, Close, Get, Put, Print, or Write.
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Consider making the following changes to the Visual Basic component to help avoid critical section convoys in the Visual Basic run-time.
1. Where possible, move procedures and variables stored in standard standard (.bas) modules into class modules.
2. Modify the component to use early bound calls to COM components, rather than late bound calls.
3. If the component is using the Visual Basic intrinsic file I/O statements, use one of the following alternatives instead.
   a. Use the FileSystemObject from the Scripting run-time.
   b. Use the Win32 API ReadFile and WriteFile functions.
   165942 How To Write Data to a File Using WriteFile API
  Â
http://kbalertz.com/165942 (http://support.microsoft.com/default.aspx?scid=kb;en-us;165942)  c. Reduce the number of times calling the file I/O get and put to read or write data. For example, read and/or write larger chunks of data at a time.
Related Knowledgebase Articles
========================
815053Â INFO: Avoid Global Variables in Visual Basic COM+ Components
http://kbalertz.com/815053 (http://support.microsoft.com/default.aspx?scid=kb;en-us;815053)241896Â Threading issues with Visual Basic 6.0 ActiveX components
http://kbalertz.com/241896 (http://support.microsoft.com/default.aspx?scid=kb;en-us;241896)Back to the top
Visual Basic uses the critical section MSVBVM60!gCSHinst to protect key data structures in per-thread project information. Here are sample call stacks showing threads waiting on this critical section in various situations.
Late bound COM component
=====================
0:000> ~7kbL 123
ChildEBP RetAddr Args to Child
00eef3e4 77f8822a 0000073c 00000000 00000000 NTDLL!NtWaitForSingleObject+0xb
00eef458 77f8819b 6aae0700 6a9e526a 6aae0770 NTDLL!RtlpWaitForCriticalSection+0x9e
00eef460 6a9e526a 6aae0770 00eef788 6a9e4979 NTDLL!RtlEnterCriticalSection+0x46
00eef46c 6a9e4979 110020d6 00eef4a4 69b38658 MSVBVM60!RTIsNativeHandler+0x16
00eef488 6a9e491f 00000000 00eef4a4 02142e40 MSVBVM60!SehTopmostBasicHandler+0x40
00eef49c 6a9f67a4 00000000 6aad1262 00eef4c4 MSVBVM60!GetCurrentEpiProject+0x18
00eef4a4 6aad1262 00eef4c4 02142e40 6aadb361 MSVBVM60!GetProjLcid+0x12
00eef4b8 6aada936 11006394 02142e40 6aabc2a4 MSVBVM60!ExDispidOfHlnam+0x1e
00eef4e4 6aadb37e 11006394 00000000 00eef51c MSVBVM60!ExVarLateMem+0x49Â Â
00eef504 110120d5 00eef698 00eef6a8 11006394 MSVBVM60!__vbaVarLateMemCallLdRf+0x1d <-- Shows a late bound COM call from the component
WARNING: Stack unwind information not available. Following frames may be wrong.
00eef79c 1100ef77 00eef884 00000000 00eef8a8 WICData!DllCanUnloadNow+0x8d7f
Intrinsic File I/O With Get/Put
========================
0:074> kL
ChildEBP RetAddr
0b5df5ac 77f8f295 NTDLL!NtWaitForSingleObject+0xb
0b5df620 77f87f26 NTDLL!RtlpWaitForCriticalSection+0x9e
0b5df628 6a9e5d83 NTDLL!RtlEnterCriticalSection+0x46
0b5df638 6a9e5d5d MSVBVM60!FindPECFromRTContext+0x23
0b5df644 6aaaeed8 MSVBVM60!FindProjExecContext+0x18
0b5df64c 6aa1619e MSVBVM60!epiProject::PeprojinfoMT+0xb
0b5df650 6aab9f86 MSVBVM60!GetProjectHandle+0x2b
0b5df66c 6aaba116 MSVBVM60!PrepGetPut+0x10
0b5df68c 6aab9e5a MSVBVM60!FileGetPut+0x19
0b5df6ac 0043e80f MSVBVM60!__vbaPut3+0x18 <-- Notice that the intrinsic file put is being called.
WARNING: Stack unwind information not available. Following frames may be wrong.
0b5df840 77d79290 DMSWrapper+0x3e80f
0b5df874 77d96aee rpcrt4!Invoke+0x30
0b5dfaf8 77d90719 rpcrt4!NdrStubCall2+0x664
0b5dfb5c 779e92e4 rpcrt4!CStdStubBuffer_Invoke+0x6b
0b5dfb80 7cef55fd OLEAUT32!CUnivStubWrapper::Invoke+0xe4
0b5dfbc4 7cef58d8 OLE32!SyncStubInvoke+0x61
0b5dfc0c 7ce8833d OLE32!StubInvoke+0xa8
0b5dfc70 7ce7a711 OLE32!CCtxComChnl::ContextInvoke+0xbb
0b5dfc8c 7ce7a57b OLE32!MTAInvoke+0x18
0b5dfcbc 7cef54b5 OLE32!STAInvoke+0x56
Critical section details:
0:000> !critlist
CritSec at 6aae0770. Owned by thread 0. Transitioning.
Waiting Threads: 6 7 8 9 10 12 13 14 15 16 20 21 24 25 30 35 38 46 49 52 59 68 72 74
0:000> !locks 6aae0770
CritSec MSVBVM60!gCSHinst+0 at 6AAE0770
LockCount 23
RecursionCount 0
OwningThread 0
EntryCount 6657633
ContentionCount 664323b
*** Locked
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