71 lines
2.2 KiB
TeX
71 lines
2.2 KiB
TeX
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@node Signals
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@chapter Signal Handling (@file{signal.h})
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A @dfn{signal} is an event that interrupts the normal flow of control
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in your program. Your operating environment normally defines the full
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set of signals available (see @file{sys/signal.h}), as well as the
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default means of dealing with them---typically, either printing an
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error message and aborting your program, or ignoring the signal.
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All systems support at least the following signals:
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@table @code
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@item SIGABRT
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Abnormal termination of a program; raised by the <<abort>> function.
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@item SIGFPE
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A domain error in arithmetic, such as overflow, or division by zero.
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@item SIGILL
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Attempt to execute as a function data that is not executable.
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@item SIGINT
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Interrupt; an interactive attention signal.
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@item SIGSEGV
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An attempt to access a memory location that is not available.
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@item SIGTERM
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A request that your program end execution.
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@end table
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Two functions are available for dealing with asynchronous
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signals---one to allow your program to send signals to itself (this is
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called @dfn{raising} a signal), and one to specify subroutines (called
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@dfn{handlers} to handle particular signals that you anticipate may
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occur---whether raised by your own program or the operating environment.
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To support these functions, @file{signal.h} defines three macros:
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@table @code
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@item SIG_DFL
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Used with the @code{signal} function in place of a pointer to a
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handler subroutine, to select the operating environment's default
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handling of a signal.
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@item SIG_IGN
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Used with the @code{signal} function in place of a pointer to a
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handler, to ignore a particular signal.
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@item SIG_ERR
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Returned by the @code{signal} function in place of a pointer to a
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handler, to indicate that your request to set up a handler could not
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be honored for some reason.
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@end table
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@file{signal.h} also defines an integral type, @code{sig_atomic_t}.
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This type is not used in any function declarations; it exists only to
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allow your signal handlers to declare a static storage location where
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they may store a signal value. (Static storage is not otherwise
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reliable from signal handlers.)
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@menu
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* raise:: Send a signal
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* signal:: Specify handler subroutine for a signal
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@end menu
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@page
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@include signal/raise.def
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@page
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@include signal/signal.def
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