DosExitList is issued to define a routine that is to be given control when a process completes its execution. Multiple routines may be defined to receive control when a process is ending. For each process, the operating system maintains a list of addresses of defined exit list routines.

When the process is ending, the operating system transfers control to each address in this list. If there are multiple addresses in the list, they will each get control in numerical order by function invocation order, that is, low (0) will be first, and high (0xFF) will be last. In case of duplicate entries for the same value, the routines will be run in LIFO (last in, first out) order.

Library modules can issue DosExitList to free resources or to clear flags and semaphores in case the client process ends without notifying them.

Before transferring control to the routines in the termination list, the operating system resets the stack to its initial value. The routine must be in the address space of the ending process. The termination routine should perform its processing and then issue DosExitList with a value of 3 (EXLST_EXIT) for ordercode. The termination routine should be as short as possible.

Most system functions are allowed in an exit list routine. However, DosCreateThread and DosExecPgm are not.

An exit list routine must not call functions that have a better function order priority (that is, a lower value for ordercode) than itself. For example, an exit list routine with a function order value of 0x9A can use Presentation Services functions but not Communications Manager functions.

When the exit list routine receives control, the first parameter on the stack (located at ESP+4) contains a termination code that describes why the process ended. The values of the termination codes are as follows:

• TC_EXIT
  Normal exit

• TC_HARDERROR
  Hard-error halt

• TC_TRAP
  Trap operation for a 16-bit child process

• TC_KILLPROCESS
  Unintercepted DosKillProcess

• TC_EXCEPTION
  Exception operation for a 32-bit child process
  

  When the exit list routine receives control, all system semaphores owned by the process have their ownership transferred to the thread that performs exit list processing. This allows the thread to request serialization semaphores without danger of blocking in case the semaphore was held by another thread in the process that has already ended.

  Note: All exit list routines must be declared as VOID APIENTRY. This ensures the integrity of the stack.

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