sigprocmask: Examine and change blocked signals

This function allows the calling process to examine (query) or change its signal mask. Each process has a signal mask that specifies a set of signals that cannot be raised. These are called blocked signals. A blocked signal can be sent to a process, but it remains pending until it is unblocked and subsequently raised.

Format

#include <signal.h>
int sigprocmask(int change,
                const sigset_t  *set,
                      sigset_t  *oset);
change
If the signal set pointed to by the set parameter is not NULL, the change parameter indicates the way in which the signal mask (the set of signals currently blocked) is changed. This parameter must be specified as one of the following:
SIG_BLOCK
All signals in the signal set pointed to by the set parameter are to be added to the current signal set for the process.
SIG_SETMASK
The signal set pointed to by the set parameter replaces the current signal mask for the process.
SIG_UNBLOCK
All signals in the signal set pointed to by the set parameter are to be removed from the current signal set for the process.

If the signal set pointed to by the set parameter is NULL, the change parameter is ignored.

set
One of the following:
  • A pointer to a signal set that is used to modify the signal mask according to the change parameter. The signal set is of the sigset_t type.
    • If the oset parameter is a pointer to a signal set, the value of the signal mask before the sigprocmask function call is stored in the signal set referenced by the oset parameter, and the signal mask is changed as specified by the change and set parameters.
    • If the oset parameter is NULL, the signal mask is changed as specified by the change and set parameters.
  • A value of NULL.
    • If the oset parameter is a pointer, the value of the signal mask stored in the signal set referenced by the oset parameter and the signal mask is not changed.
    • If the oset parameter is NULL, the signal mask is not examined or changed.
oset
One of the following:
  • A pointer to a signal set where the signal mask for the process is stored when the sigprocmask function is called. The signal set is of the sigset_t type.
  • A value of NULL.
Note: The description of the set parameter describes the results of sigprocmask function processing based on the value specified for the oset parameter.

Normal return

If successful, the sigprocmask function returns a value of zero.

Error return

If unsuccessful, the signal mask for the process is not changed and the sigprocmask function returns a value of -1 and sets errno to the following:

EINVAL
The value of the change parameter is not valid; it must be one of the values listed for the change parameter.

Programming considerations

  • The signal mask is managed by the sigprocmask function and also by the z/TPF system.
  • The sigprocmask function is intended only for use in a single-threaded process.
  • To query the current signal mask without changing it, specify:
    • NULL for the set parameter
    • A pointer to a signal set for the oset parameter.

    The results of the query are in the signal set referenced by the oset parameter.

  • This function operates on a thread level when it runs in a threaded environment.

Examples

The following example shows how to block all signals. 
#include <signal.h>
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{
struct sigaction       act, oact;

sigset_t new_mask;
sigset_t old_mask;

/* initialize the new signal mask */
sigfillset(&new_mask);

/* block all signals */
sigprocmask(SIG_SETMASK, &new_mask, &old_mask);

/* call function */
somefunc();

/* restore signal mask */
sigprocmask(SIG_SETMASK, &old_mask, NULL);
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}

Related information

See z/TPF C functions overview for more information about z/TPF C/C++ language support.