DOCUMENT:Q189888  16-JUL-2001  [iis]
TITLE   :PRB: Stack Size Now 256 K in Internet Information Server 4.0
PRODUCT :Internet Information Server
PROD/VER:winnt:4.0,5.0
OPER/SYS:
KEYWORDS:kbnokeyword kbASP kbISAPI kbDSupport kbiis400 kbiis500

======================================================================
-------------------------------------------------------------------------------
The information in this article applies to:

 - Microsoft Internet Information Server versions 4.0, 5.0 
 - Microsoft Internet Server Application Programming Interface (API) 
 - Microsoft Active Server Pages 
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SYMPTOMS
========

A "Stack overflow" or access violation error, or hanging of the server may occur
due to an ISAPI DLL or custom Active Server Pages (ASP) component in Internet
Information Server (IIS) 4.0. This problem does not occur when the same code and
data are used in Internet Information Server 3.0.

CAUSE
=====

The maximum stack size of a thread has been reduced from 1 MB in IIS 3.0 to 256
KB in IIS 4.0. The stack size is still 256 KB for IIS 5.0 on Windows 2000.

RESOLUTION
==========

Reduce the ISAPI DLL's or ASP component's use of the stack to fit within the
reduced size of the IIS 4.0 stack. See the MORE INFORMATION section below for
hints.

STATUS
======

The change in stack size is by design.

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

The maximum size of a thread's stack is determined by the executable file of the
process, not by the individual ISAPI DLL or ASP component that is running inside
the process. Both the IIS 4.0 version of Inetinfo.exe (for in-process Web
applications) and Mtx.exe (which hosts out-of-process Web applications) are set
to a 256 KB maximum stack size. This follows the changed standard for all
Windows NT system executables.

A function's arguments and local variables are stored on the stack of the thread
they are executing on. Declaring extremely large local variables will rapidly
use up the stack. For example, the following function would require 400,000
bytes of stack space (100,000 integers X 4 bytes per int) to store the array.:

      void func(void)
      {
        int i[100000];
        // more code
        return;
      }

This function could not be successfully called in IIS 4.0, but probably would
have worked in IIS 3.0. To avoid using the stack, allocate the memory
dynamically:

      void func(void)
      {
        int *i

        i = new int[100000];
        // more code
        return;
      }

Dynamically allocated memory is not stored on the stack, so the function no
longer needs 400,000 bytes of stack space, and should work on IIS 4.0

Another way that stack space can be quickly exhausted is with recursive function
calls. If a function requires 40 bytes for local variables and arguments, and
calls itself recursively 10,000 times, then 400,000 bytes of stack space would
be needed. Again, this would likely work on IIS 3.0, but not on IIS 4.0.

A CGI program would not be affected by the change in stack size. A new process is
created when the CGI program is launched, and the stack size is determined from
the CGI executable, not from Inetinfo.exe.

Additional query words:

======================================================================
Keywords          : kbnokeyword kbASP kbISAPI kbDSupport kbiis400 kbiis500 
Technology        : kbiisSearch kbAudDeveloper kbASPsearch kbiis500 kbiis400 kbISAPI kbISAPISearch
Version           : winnt:4.0,5.0
Issue type        : kbprb

=============================================================================

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