sigprocmask (BPX1SPM, BPX4SPM) — Examine or change a process's signal mask

Function

The sigprocmask callable service examines, changes, or both examines and changes the calling thread's signal mask.

Requirements

Parameters

How

Supplied parameter

Type:

Structure

Length:

Fullword

The name of a fullword that contains a numeric value that identifies the action that is to be taken on the thread's signal mask. The following constants, which are defined in BPXYSIGH, define the actions to be taken: See BPXYSIGH — Signal constants.

Constant	Description
SIG_BLOCK#	Add the signals in New_signal_mask to those to be blocked for this thread.
SIG_UNBLOCK#	Delete the signals in New_signal_mask from those blocked for this thread.
SIG_SETMASK#	Replace the thread's signal mask with New_signal_mask.

New_signal_mask

Supplied parameter

Type:

Address

Length:

Fullword

The name of a fullword that contains either 0 or the address of an 8-byte area that contains the 64-bit signal mask. The leftmost bit represents signal number 1, and the rightmost bit represents signal number 64. The New_signal_mask parameter is applied to the thread's signal mask as specified by the How parameter. Mask bits that are set on represent signals that are blocked. If zero, the signal mask is not changed, and the How parameter is ignored.

Old_signal_mask

Parameter supplied and returned

Type:

Address

Length:

Fullword

The name of a fullword that contains either 0 or the address of an 8-byte signal-mask return area. The service stores in this area the signal mask that was in effect, showing the signals that were blocked. The leftmost bit represents signal number 1, and the rightmost bit represents signal number 64. Mask bits set on represent signals that are blocked. A zero indicates that no signal mask was returned.

Return_value

Returned parameter

Type:

Integer

Length:

Fullword

The name of a fullword in which the sigprocmask service returns 0 if the request is successful, or -1 if it is not successful.

Return_code

Returned parameter

Type:

Integer

Length:

Fullword

The name of a fullword in which the sigprocmask service stores the return code. The sigprocmask service returns Return_code only if Return_value is -1. For a complete list of possible return code values, see z/OS UNIX System Services Messages and Codes. The sigprocmask service can return one of the following values in the Return_code parameter:

Return_code	Explanation
EFAULT	The specified address for New_signal_mask or Old_signal_mask was incorrect.
EINVAL	The value of the How parameter is not one of the allowable values.

Reason_code

Returned parameter

Type:

Integer

Length:

Fullword

The name of a fullword in which the sigprocmask service stores the reason code. The sigprocmask service returns Reason_code only if Return_value is -1. Reason_code further qualifies the Return_code value. For the reason codes, see z/OS UNIX System Services Messages and Codes.

Usage notes

1. The sigprocmask service examines, changes, or both examines and changes the signal mask for the calling thread. This mask is called the thread's signal mask. If there are any pending unblocked signals, either at the process level or at the current thread's level, after changing the signal mask, at least one of the signals is delivered to the thread before the sigprocmask service returns.
2. In a multithreaded process, the sigprocmask service is used to control to which thread in the process a signal that is generated by the kill service is delivered. For example, if two threads in a process have SIGUSR1 signals blocked and one thread does not, the SIGUSR1 signal that is generated by the kill service from another process is delivered to the thread that does not have the signal blocked.
3. You cannot block the SIGKILL, SIGSTOP, SIGTHSTOP, and SIGTHCONT signals. If you call the sigprocmask service with a request that would block those signals, that part of your request is ignored and no error is indicated.
4. A request to block signals that are not supported is accepted, and a return value of zero is returned.
5. All pending unblocked signals are moved from the process level to the current thread.
6. See Optimizing performance using process- and thread-level information.

Related services

• kill (BPX1KIL, BPX4KIL) — Send a signal to a process
• mvssigsetup (BPX1MSS, BPX4MSS) — Set up MVS signals
• sigaction (BPX1SIA, BPX4SIA) — Examine or change a signal action
• sigpending (BPX1SIP, BPX4SIP) — Examine pending signals
• sigsuspend (BPX1SSU, BPX4SSU) — Change the signal mask and suspend the thread until a signal is delivered

Characteristics and restrictions

See The relationship of z/OS UNIX signals to callable services.