Per-thread exception management is available to 32-bit EXEs, DLLs, and presentation drivers. The per-thread exception management model is a superset of DosExitList processing found in 16-bit OS/2 programming.

Under 16-bit OS/2 architecture, a process cannot handle access violations. In the event of an access violation, the system terminates the process. Given that the trapping process had registered an exit-list function, it had one final chance to do clean up just prior to termination. Sixteen-bit drivers and DLLs usually add an exitlist. At process termination, 16-bit drivers perform per-process clean up in exit-list functions.

Programmers of 32-bit drivers have a choice concerning per-process clean up. They may use the 32-bit version of DosExitList(), or they may add code for the DLL termination case in the driver function _DLL_InitTerm(). The _DLL_InitTerm() function, if present and exported from the driver, will be called by OS/2 with parameter 0 on DLL instantiation and parameter 1 on DLL termination or unload. The _DLL_InitTerm() function provides process-granular clean up.

Furthermore, 32-bit OS/2 has exception handlers that are thread-granular. OS/2 lets each thread in a process handle exceptions that arise on that thread. Some of these exceptions are:

• Accessing invalid or uncommitted memory
  
• Stack overruns
  
• Thread terminations
  
• Floating point errors
  
• Asynchronous (external) signals
  
• User-raised exceptions (synchronous signals)
  
• Invalid opcodes
  
• Bounds
  
• Divide by zero errors
  
• Overflow errors

The goals of a 32-bit driver that uses exception management are:

• When passed bad parameters that cause exceptions, drivers can call WinSetErrorInfo and return suitable result codes for the application to inspect.

• When threads are terminated while executing driver code, the driver can clean up before the thread exits.