Signal-Handling Functions

Terminology Used in Signal Handling

This section introduces some of the terminology used to discuss the signal-handling features of the SAS/C library.

interrupt is a hardware or software event that causes current processing to be suspended while the condition causing the interruption is processed. An interrupt can be processed either by the operating system or an application program or both.

signal is an interrupt processed by the library, usually after processing by the operating system.

synchronous signal is a signal directly resulting from program execution. For example, floating-point division by 0 generates a synchronous signal.

asynchronous signal is a signal resulting from an interrupt external to the program. The timing of an asynchronous interrupt, in terms of program execution, is not predictable. For example, if you press the ATTN key while running a program under TSO, an asynchronous signal is generated. Because any program can send an USS signal to any other program, any signal defined by USS can be asynchronous.

discovery of a signal is the time at which the library suspends normal program execution to respond to a signal. Synchronous signals are always discovered immediately, but asynchronous signals can only be discovered at certain points in execution, as described in Types of Signal Support. Discovery of an asynchronous signal does not have to take place immediately after the occurrence of the original interrupt.

pending is the state of a signal between the time of its occurrence and the time it is discovered.

signal blocking is a processing technique for postponing discovery of an asynchronous signal. The program may specify one or more asynchronous signals that are to be blocked, and the set of blocked signals may be changed at any time. When a blocked signal occurs, program execution is unaffected until the program unblocks the signal. After it is unblocked, the signal will be discovered.

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interrupt	is a hardware or software event that causes current processing to be suspended while the condition causing the interruption is processed. An interrupt can be processed either by the operating system or an application program or both.
signal	is an interrupt processed by the library, usually after processing by the operating system.
synchronous signal	is a signal directly resulting from program execution. For example, floating-point division by 0 generates a synchronous signal.
asynchronous signal	is a signal resulting from an interrupt external to the program. The timing of an asynchronous interrupt, in terms of program execution, is not predictable. For example, if you press the ATTN key while running a program under TSO, an asynchronous signal is generated. Because any program can send an USS signal to any other program, any signal defined by USS can be asynchronous.
discovery of a signal	is the time at which the library suspends normal program execution to respond to a signal. Synchronous signals are always discovered immediately, but asynchronous signals can only be discovered at certain points in execution, as described in Types of Signal Support. Discovery of an asynchronous signal does not have to take place immediately after the occurrence of the original interrupt.
pending	is the state of a signal between the time of its occurrence and the time it is discovered.
signal blocking	is a processing technique for postponing discovery of an asynchronous signal. The program may specify one or more asynchronous signals that are to be blocked, and the set of blocked signals may be changed at any time. When a blocked signal occurs, program execution is unaffected until the program unblocks the signal. After it is unblocked, the signal will be discovered.