DosGetPPID

#define INCL_DOSPROCESS

USHORT  rc = DosGetPPID(PID, PPID);

USHORT           PID;           /* Process whose parent is wanted */
PUSHORT          PPID;          /* Address to put parent's PID */

USHORT           rc;            /* return code */

Example 

The following example demonstrates how to create a process, obtain process 
ID information, and kill a process.  Process1 invokes process2 to run 
asynchronously.  It obtains and prints some PID information, and then 
kills process2. 

/* ---- process1.c ---- */

#define INCL_DOSPROCESS

#include <os2.h>

#define START_PROGRAM "process2.exe"   /* Program pointer */

main()
{
  CHAR          ObjFail [50];       /* Object name buffer */
  RESULTCODES   ReturnCodes;        /*
  PIDINFO       PidInfo;
  PID           ParentID;           /*
  USHORT        rc;

  printf("Process1 now running. \n");

  /** Start a child process. **/
  if(!(DosExecPgm(ObjFail,            /* Object name buffer */
                  sizeof(ObjFail),    /* Length of obj. name buffer */
                  EXEC_ASYNC,         /* Execution flag - asynchronous */
                  NULL,               /* No args. to pass to process2*/
                  NULL,               /* Process2 inherits process1's
                                          environment */
                  &ReturnCodes,       /* Ptr. to resultcodes struct. */
                  START_PROGRAM)))    /* Name of program file */
    printf("Process2 started. \n");

  /** Obtain Process ID information and print it **/
  if(!(rc=DosGetPID(&PidInfo)))       /* Process ID's (returned) */
    printf("DosGetPID: current process ID is %d; thread ID is %d; parent process ID is %d.\n",
            PidInfo.pid, PidInfo.tid, PidInfo.pidParent);
  if(!(rc=DosGetPPID(
           ReturnCodes.codeTerminate, /* Process whose parent is wanted */
           &ParentID)))               /* Address to put parent's PID */
    printf("Child process ID is %d; Parent process ID is %d.\n",
            ReturnCodes.codeTerminate, ParentID);

  /** Terminate process2 **/
  if(!(rc=DosKillProcess(DKP_PROCESSTREE,     /* Action code - kill process
                                                      and descendants */
                ReturnCodes.codeTerminate)))  /* PID of root of process tree */
    printf("Process2 terminated by process1.\n");
}

/* ---- process2.c ---- */

#define INCL_DOSPROCESS

#include <os2.h>

#define SLEEPTIME   500L
#define RETURN_CODE 0

main()
{
  printf("Process2 now running.\n");

  /* Sleep to allow process1 to kill it */
  DosSleep(SLEEPTIME);                /* Sleep interval */
  DosExit(EXIT_PROCESS,               /* Action Code */
          RETURN_CODE);               /* Result Code */
}