Open System Services System Calls Reference Manual (G06.29+, H06.08+, J06.03+)

signal(4) OSS System Calls Reference Manual
SIG_IGN Requests that signals be ignored.
SIGSTKSZ Indicates the default size of the alternate signal stack.
SS_DISABLE Indicates that the alternate signal stack is disabled. No signal handling
may be launched at the alternate signal stack.
SS_ONSTACK
Indicates that the alternate signal stack is active. A signal handler is
currently running on the alternate signal stack.
• Declarations of additional symbolic constants used by the sigprocmask() function for
handling process signal masks:
SIG_BLOCK Requests a union of the current mask and a supplied value.
SIG_SETMASK
Creates a mask from the supplied value.
SIG_UNBLOCK
Requests a mask of the current mask less the supplied value.
Note: The MINSIGSTKSZ, SA_ONSTACK, SIGSTKSZ, SS_DISABLE, and SS_ONSTACK
symbolic constants are only supported on systems running J06.10 or later RVUs or H06.21 or
later RVUs.
Signal Generation and Delivery
A signal is said to be generated for (or sent to) a process when the event that causes the signal
first occurs. Examples of such events include detection of hardware faults, timer expiration, and
any operating system trap condition normally detectable by a TNS or accelerated Guardian pro-
cess, in addition to terminal activity, or the invocation of the kill() function.
Note: Signals cannot be sent to a TNS or accelerated Guardian process.
Each process has an action to be taken in response to each signal defined by the system. A signal
is said to be delivered to a process when the appropriate action for the process and signal is
taken.
A process can elect to ignore the delivery of some signals, while allowing the system to perform
default actions upon the delivery of other signals. The system also allows processes to install
process-specific signal-catching functions.
During the time between the generation of a signal and its delivery, the signal is said to be pend-
ing. Usually, this interval cannot be detected by an application.
However, a signal can be blocked from delivery to a process. If the action associated with a
blocked signal is anything other than to ignore the signal, and if that signal is generated for the
process, the signal remains pending until either it is unblocked or the action associated with it is
set to ignore the signal. If the action associated with the blocked signal is to ignore the signal,
and if that signal is generated for the process, it is unspecified whether the signal is discarded
immediately upon generation or remains pending; applications should therefore not depend on
whether the signal is discarded or remains pending.
Each process has a signal mask that defines the set of signals currently blocked from delivery to
it. The signal mask for a process is initialized to that of its parent. The sigaction(), sigproc-
mask(), and sigsuspend( ) functions control the manipulation of the signal mask.
The determination of which action is taken in response to a signal is made at the time the signal
is delivered, allowing for any changes since the time of generation. This determination is
independent of the means by which the signal was originally generated.
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