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Q107172: Determining the Stack Size of an Application

Article: Q107172
Product(s): Microsoft Windows Software Development Kit
Version(s): WINDOWS:3.1
Operating System(s): 
Keyword(s): kb16bitonly
Last Modified: 06-NOV-1999

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The information in this article applies to:

- Microsoft Windows Software Development Kit (SDK) 3.1 
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SUMMARY
=======

The tool helper library (TOOLHELP.DLL) contains application programming
interface (API) functions that provide information about the task header of a
Windows-based application's default data segment (DGROUP). A Windows- based
application can use this information to determine the maximum stack size, the
optimum stack size for the application, and whether the stack is going to
overflow.

Because the tool helper library is redistributable, this information applies to
Windows 3.0 also.

MORE INFORMATION
================

A Windows-based application's DGROUP consists of several parts: the task header,
initialized and uninitialized static data area, stack, local heap, and an atom
table. The following picture extracted from Chapter 18 of the "Windows 3.1 Power
Programming Techniques" by Peter Norton and Paul Yao, shows the organization of
the DGROUP:

                 ---------------
                 |               |
                 |               |
                 |  Local Heap   |
                 |               |
                  --------------- <-
                 |               |  |
                 |               |  |
                 |    Stack      |<-|-
                 |               |  | |
                  --------------- <-|-|-
                 |               |  | | |
                 |               |  | | |
                 |  Static Data  |  | | |
                 |               |  | | |
              --> ---------------   | | |
             |   | pStackBottom  |--  | |
             |    ---------------     | |
             |   | pStackMin     |----  |
             |    ---------------       |
  Task   ----|   | pStackTop     |------
  Header     |    ---------------
             |   |     .         |
             |   |     .         |
             |   |     .         |
              --> ---------------

The task header is a data structure stored in the first 16 bytes of the DGROUP
and contains information about the stack, the local heap, and the atom table.
Windows stores three variables (pStackTop, pStackBottom, and pStackMin) that
point to various places in the stack as shown in the picture above. pStackTop
and pStackBottom point to the top and bottom of the stack, and these two values
stay constant once initialized. pStackMin changes during run time to indicate
how much of the stack is actually used. Given this information, the following
can be determined:

  Maximum Stack size = pStackBottom - pStackTop
  Dynamic Stack Size = pStackBottom - pStackMin

The maximum stack size is either the size specified in the DEF file with the
STACKSIZE statement or 5K (Windows provides a minimum of 5K stack). Because
Windows updates the pStackMin at run time, monitoring the dynamic size gives an
indication as to how much stack space an application really needs. This value
may also be used to check for stack overflows during run time, although using
stack probes is definitely a better method for checking stack overflows. Some
advanced debuggers such as WDEB386 (included in the Microsoft Windows SDK) and
SoftIce/W (from NuMega Technologies, Inc.) allow breakpoints to be set on
particular memory locations; for example, if a breakpoint is set at the bottom
of the stack, the debugger will break just before a stack overflow.

Windows-based applications can obtain the values of pStackTop, pStackBottom, and
pStackMin by calling the tool help library API functions, which return a
TASKENTRY structure. An application should call GetCurrentTask() to get its task
handle and then call TaskFindHandle(), TaskFirst() or TaskNext() with the task
handle as a parameter. The TASKENTRY structure contains three members wStackTop,
wStackBottom, and wStackMinimum, which correspond to the three pointers
pStackTop, pStackBottom, and pStackMin, respectively.

CodeView for Windows (CVW) debugger can also be used to look at the task header
of an application's DGROUP. For example, using CVW one can periodically check
the first 16 bytes in the DGROUP using the command:

  D DS:0

CVW will then display the following information:

  DS:0006 PLOCALHEAP
  DS:0008 pAtomTable
  DS:000A pStackTop
  DS:000C pStackMin
  DS:000E pStackBot

The three values pStackTop, pStackMin, and pStackBot at locations DS:000A,
DS:000C, and DS:000E, respectively, can be used to determine information about
the application's stack as illustrated above.

Additional query words: no32bit 3.10

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Keywords          : kb16bitonly 
Technology        : kbAudDeveloper kbWin3xSearch kbSDKSearch kbWinSDKSearch kbWinSDK310
Version           : WINDOWS:3.1

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