Use of this function is unspecified in a multi-threaded process.
The signal() function chooses one of three ways in which receipt of the
signal number sig is to be subsequently handled. If the value of
func is SIG_DFL, default handling for that signal shall occur. If the
value of func is SIG_IGN, the signal shall be ignored. Otherwise, the
application shall ensure that func points to a function to be called
when that signal occurs. An invocation of such a function because of a signal,
or (recursively) of any further functions called by that invocation (other
than functions in the standard library), is called a "signal
When a signal occurs, and func points to a function, it is
implementation-defined whether the equivalent of a:
is executed or the implementation prevents some implementation-defined set of
signals (at least including sig) from occurring until the current
signal handling has completed. (If the value of sig is SIGILL, the
implementation may alternatively define that no action is taken.) Next the
is executed. If and when the function returns, if the value of sig was
SIGFPE, SIGILL, or SIGSEGV or any other implementation-defined value
corresponding to a computational exception, the behavior is undefined.
Otherwise, the program shall resume execution at the point it was interrupted.
If the signal occurs as the result of calling the abort(),
raise(), kill(), pthread_kill(), or sigqueue()
function, the signal handler shall not call the raise() function.
If the signal occurs other than as the result of calling abort(),
raise(), kill(), pthread_kill(), or sigqueue(),
the behavior is undefined if the signal handler refers to any object
with static storage duration other than by assigning a value to an object
declared as volatile sig_atomic_t, or if the signal handler calls any
function in the standard library other than one of the functions listed in
Signal Concepts . Furthermore, if such a call fails, the value of
errno is unspecified.
At program start-up, the equivalent of:
is executed for some signals, and the equivalent of:
If the request can be honored, signal() shall return the value of
func for the most recent call to signal() for the specified
signal sig. Otherwise, SIG_ERR shall be returned and a positive value
shall be stored in errno.
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html