PRB: Stack Size Now 256 K in Internet Information Server 4.0 (189888)

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.