DosSetSigHandler

#define INCL_DOSSIGNALS

USHORT  rc = DosSetSigHandler(Routine, PrevAddress, PrevAction, Action,
                             SigNumber);

PFNSIGHANDLER       Routine;     /* Signal handler */
PFNSIGHANDLER FAR * PrevAddress; /* Previous handler (returned) */
PUSHORT             PrevAction;  /* Previous action (returned) */
USHORT              Action;      /* Indicate request type */
USHORT              SigNumber;   /* Signal number of interest */

USHORT              rc;          /* return code */

Example 

The following example illustrates the use of a user-defined flag to signal 
time-critical events.  The main thread installs a routine, named 
FlagA_Handler(), as the signal handler for user-defined Flag A.  It then 
creates a thread and blocks on a reserved RAM semaphore; this thread 
obtains its process ID and signals the main thread via Flag A.  The main 
thread responds by executing the signal handler. 

#define INCL_DOSPROCESS
#define INCL_DOSSIGNALS
#define INCL_DOSERRORS

#include <os2.h>

#define TIMEOUT           5000L

TID         ThreadID;
BYTE        ThreadStack[4000];

VOID APIENTRY FlagA_Handler(arg1, arg2)       /* Define signal handler */
  USHORT      arg1;
  USHORT      arg2;
{
  printf("Handler for Flag A now running.\n");
  return;
}

VOID APIENTRY Thread_A()
{
  PIDINFO     PidInfo;
  USHORT      FlagArg;
  USHORT      rc;

  DosGetPID(&PidInfo);
  printf("Process ID is %d\n", PidInfo.pid);
  if(!(rc = DosFlagProcess(PidInfo.pid,
                           FLGP_PID,
                           PFLG_A,
                           FlagArg)))
    printf("FlagA signal sent from ThreadA to main thread.\n");
  else
    printf("FlagProcess rc is %d\n", rc)/* Error processing on rc */;
  DosExit(EXIT_THREAD,                 /* Action Code */
          RETURN_CODE);                /* Result Code */

}

main()
{
  ULONG            RamSem = 0L;
  ULONG far        *RamSemHandle = &RamSem;
  USHORT           rc;

  if(!(rc=DosSetSigHandler((PFNSIGHANDLER) FlagA_Handler,
                           NULL,
                           NULL,
                           SIGA_ACCEPT,
                           SIG_PFLG_A)))
    printf("Main thread has set FlagA handler.\n");
  else
    /* Error processing on rc */;
  if(!(rc=DosSemRequest(RamSemHandle,
                        TIMEOUT)))
    printf("Semaphore obtained.\n");
  if(!(DosCreateThread((PFNTHREAD) Thread_A,
                        &ThreadID,
                        &ThreadStack[3999])))
    printf("ThreadA created.\n");
  printf("Main thread will now wait on a Ramsem for a while.\n");
  if((rc=DosSemRequest(RamSemHandle,
                       TIMEOUT))
       == ERROR_INTERRUPT)
  printf("Main thread interrupted while waiting, rc is %d.\n", rc);
}