SAS/C Library Reference, Vol. 1

ecbpause -- Wait for Signal

SYNOPSIS

 #include <lcsignal.h>

 int ecbpause(int mask, size_t listsize, struct _ecblist *ecblist);

DESCRIPTION

ecbpause delays program execution until it receives a C signal or an Event Control Block (ECB) is posted. mask specifies the mask of signals managed by SAS/C to be blocked while execution is delayed. listsize specifies the number of _ecblist structures addressed by the ecblist argument.

ecblist is the address of an array of structures, each of which represents one or more contiguous ECBs. Each structure contains two members: a count of the number of ECBs and the address of an array of ECBs. The count may be zero, in which case the ECB array address is ignored.

The declaration for the _ecblist structure is:

 struct _ecblist {
    size_t count;
    unsigned *ecbarr;
 }

The ECB list for ecbpause is passed by the _ecblist structure for several reasons. It enables a static ECB list to be used in many cases since individual ECBs can easily be removed by setting their count member to 0. For applications that have a large number of ECBs, the _ecblist structure facilitates organizing them into arrays; this method may slightly improve the performance of ecbpause because fewer memory accesses are required to determine the addresses of all the ECBs.

ecbpause returns to its caller when one of the following events occurs:

an unblocked signal occurs. A handler for the signal is called after the signal mask is restored but before control returns to the caller from ecbpause.
an ECB is POSTed.

Several conditions for completion of the ecbpause function may occur simultaneously or nearly simultaneously. In such cases, a signal handler may be called even though an ECB was POSTed before or during arrival of the signal. On return from ecbpause, any number of ECBs may be POSTed, and more than one signal handler may have been called if the signal mask permits it.

RETURN VALUE

ecbpause returns the errno value EINTR if an unblocked signal was pending at the completion of its wait. Otherwise, it returns zero.

CAUTIONS

ecbpause does not clear any ECBs addressed with the ecblist argument. It is the caller's responsibility to clear the ECBs after a POST and to initialize them to zero or to some other suitable value.

The value returned by ecbpause may not be completely reliable. An ECB may have been POSTed even though a signal was detected, and a signal may have been received after ecbpause was awakened by a POST but before return to the user program was completely effected.

ecbpause does not permit the caller to change the signal mask for any signals managed by OpenEdition. Programs that handle OpenEdition signals should use the ecbsuspend function instead.

IMPLEMENTATION

ecbpause builds a standard OS ECB list for the ECBs indicated by its arguments, in addition to an ECB used internally by signal handling, and issues the OS WAIT macro to wait for a single ECB to be POSTed.

EXAMPLE

Wait for an alarm signal or for a POST representing a reply from the MVS operator. This example assumes that SIGALRM is not managed by OpenEdition. See the sigsuspend example for a version that works regardless of whether SIGALRM is managed by OpenEdition.

  #include <lcsignal.h>
  #include <ctype.h>

   /* flag for SIGALRM handler   *
  static int toolate = 0;
  static void timesup(int signum);

  int confirm()
  {
     unsigned ECB = 0;
     struct _ecblist myECBs = {1, 0 } ;
     char reply;

     /* Set up ECB list for single ECB. */
     myECBs.ecbarr = &ECB;

     /* Issue WTOR macro via assembler. */
          /* subroutine (not shown)     */
     wtor("Reply U to confirm request.", &reply, &ECB);

     /* Catch SIGALRM signal.      */
     signal(SIGALRM, &timesup);
     toolate = 0;
     /* Wait 2 minutes for reply.  */
     alarm(120);
     ecbpause(0, 1, &myECBs);
     /* Cancel alarm.              */
     alarm(0);
     /* Restore default alarm handling. */
     signal(SIGALRM, SIG_DFL);
        /* If the ECB was posted,     */
        /*  return whether OK given.  */
        if (ECB & 0x40000000)
           return toupper(reply) == 'U';
        /* If we ran out of time,     */
        /* call asm to delete reply.  */
        else if(toolate){
           dom();
          /* Tell caller not to do it.  */
          puts("No reply received, treated as permission denied. ");
          return 0;
        }
  }

  static void timesup(int signum) {
     toolate = 1;
     return;
  }

RELATED FUNCTIONS

ecbsuspend, sigpause, sigsuspend