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 sigspace(2)							 sigspace(2)




 NAME
      sigspace - assure sufficient signal stack space

 SYNOPSIS
      #include <&lt&lt&lt;signal.h>&gt&gt&gt;

      ssize_t sigspace(ssize_t stacksize);

 DESCRIPTION
      sigspace() requests additional stack space that is guaranteed to be
      available for processing signals received by the calling process.

      If the value of stacksize is positive, it specifies the size of a
      space, in bytes, which the system guarantees to be available when
      processing a signal.  If the value of stacksize is zero, any guarantee
      of space is removed.  If the value is negative, the guarantee is left
      unchanged; this can be used to interrogate the current guaranteed
      value.

      When a signal's action indicates that its handler should use the
      guaranteed space (specified with a sigaction(), sigvector(), or
      sigvec() call (see bsdproc(3C)), the system checks to see if the
      process is currently using that space.  If the process is not
      currently using that space, the system arranges for that space to be
      available for the duration of the signal handler's execution.  If that
      space has already been made available (due to a previous signal), no
      change is made.  Normal stack discipline is resumed when the signal
      handler first using the guaranteed space is exited.

      The guaranteed space is inherited by child processes resulting from a
      successful fork() system call, but the guarantee of space is removed
      after any exec() system call (see fork(2) and exec(2)).

      The guaranteed space cannot be increased in size automatically, as is
      done for the normal stack.  If the stack overflows the guaranteed
      space, the resulting behavior of the process is undefined.

      Guaranteeing space for a stack can interfere with other memory
      allocation routines in an implementation-dependent manner.

      During normal execution of the program, the system checks for possible
      overflow of the stack.  Guaranteeing space might cause the space
      available for normal execution to be reduced.

      Leaving the context of a service routine abnormally, such as by
      longjmp() (see setjmp(3C)), removes the guarantee that the ordinary
      execution of the program will not extend into the guaranteed space.
      It might also cause the program to lose forever its ability to
      automatically increase the stack size, causing the program to be
      limited to the guaranteed space.




 Hewlett-Packard Company	    - 1 -   HP-UX Release 11i: November 2000






 sigspace(2)							 sigspace(2)




 RETURN VALUE
      Upon successful completion, sigspace() returns the size of the former
      guaranteed space.	 Otherwise, it returns -1 and sets errno to indicate
      the error.

 ERRORS
      sigspace() fails and the guaranteed amount of space remains unchanged
      if the following occurs:

	   [ENOMEM]	       The requested space cannot be guaranteed,
			       either because of hardware limitations or
			       because some software-imposed limit would be
			       exceeded.

 WARNINGS
      The guaranteed space is allocated using malloc(3C).  This use might
      interfere with other heap management mechanisms.

      Methods for calculating the required size are not well developed.

      Do not use sigspace() in conjunction with the facilities described
      under sigset(3C).

      Do not use sigspace() in conjunction with sigstack(2).

      In HP-UX release 11.11, use of sigspace() in threads created with
      process contention scope could result in undefined behavior.  This
      function will continue to be reliable in threads created with system
      contention scope.

 APPLICATION USAGE
    Threads Considerations
      Each thread may define an alternate signal handling stack.

    LWP (Lightweight Processes) Considerations
      Each LWP may define an alternate signal handling stack.

 AUTHOR
      sigspace() was developed by HP.

 SEE ALSO
      sigaction(2), sigstack(2), sigvector(2), malloc(3C), setjmp(3C).












 Hewlett-Packard Company	    - 2 -   HP-UX Release 11i: November 2000