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 sigvector(2)							sigvector(2)

      sigvector - software signal facilities

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

      int sigvector(
	   int sig,
	   const struct sigvec *vec,
	   struct sigvec *ovec

      The system defines a set of signals that can be delivered to a
      process.	The set of signals is defined in signal(5), along with the
      meaning and side effects of each signal.	This manual entry, along
      with those for sigblock(2), sigsetmask(2), sigpause(3C), and
      sigspace(2), defines an alternate mechanism for handling these signals
      that ensures the delivery of signals and the integrity of signal
      handling procedures.  The facilities described here should not be used
      in the same program as signal(2).

      With the sigvector() interface, signal delivery resembles the
      occurrence of a hardware interrupt: the signal is blocked from further
      occurrence, the current process context is saved, and a new one is
      built.  A process can specify a handler function to be invoked when a
      signal is delivered, or specify that a signal should be blocked or
      ignored.	A process can also specify that a default action should be
      taken by the system when a signal occurs.	 It is possible to ensure a
      minimum amount of stack space for processing signals using sigspace()
      (see sigspace(2)).

      All signals have the same priority.  Signal routines execute with the
      signal that causes their invocation to be blocked, although other
      signals can yet occur.  A global signal mask defines the set of
      signals currently blocked from delivery to a process.  The signal mask
      for a process is initialized from that of its parent (normally 0).  It
      can be changed with a sigblock(), sigsetmask(), or sigpause() call, or
      when a signal is delivered to the process.

      A signal mask is represented as a long, with one bit representing each
      signal being blocked.  The following macro defined in <signal.h> is
      used to convert a signal number to its corresponding bit in the mask:

	   #define sigmask(signo)     (1L <&lt&lt&lt;<&lt&lt&lt; (signo-1))

      When a signal condition arises for a process, the signal is added to a
      set of signals pending for the process.  If the signal is not
      currently blocked by the process, it is delivered to the process.
      When a signal is delivered, the current state of the process is saved,
      a new signal mask is calculated (as described below), and the signal

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

 sigvector(2)							sigvector(2)

      handler is invoked.  The call to the handler is arranged so that if
      the signal handling routine returns normally, the process resumes
      execution in the same context as before the signal's delivery.  If the
      process wishes to resume in a different context, it must arrange to
      restore the previous context itself.

      When a signal is delivered to a process, a new signal mask is
      installed for the duration of the process' signal handler (or until a
      sigblock() or sigsetmask() call is made).	 This mask is formed by
      taking the current signal mask, computing the bit-wise inclusive OR
      with the value of vec.sv_mask (see below) from the most recent call to
      sigvector() for the signal to be delivered, and, unless the
      SV_RESETHAND flag is set (see below), setting the bit corresponding to
      the signal being delivered.  When the user's signal handler returns
      normally, the original mask is restored.

      sigvector() assigns a handler for the signal specified by sig.  vec
      and ovec are pointers to sigvec structures that include the following

	   void	   (*sv_handler)();
	   long	   sv_mask;
	   long	   sv_flags;

      If vec is non-zero, it specifies a handler routine (sv_handler), a
      mask (sv_mask) that the system should use when delivering the
      specified signal, and a set of flags (sv_flags) that modify the
      delivery of the signal.  If ovec is non-zero, the previous handling
      information for the signal is returned to the user.  If vec is zero,
      signal handling is unchanged.  Thus, the call can be used to enquire
      about the current handling of a given signal.  If vec and ovec point
      to the same structure, the value of vec is read prior to being

      The sv_flags field can be used to modify the receipt of signals.	The
      following flag bits are defined:

	   SV_ONSTACK		    Use the sigspace() allocated space.
	   SV_BSDSIG		    Use the Berkeley signal semantics.
	   SV_RESETHAND		    Use the semantics of signal(2).

      If SV_ONSTACK is set, the system uses or permits the use of the space
      reserved for signal processing in the sigspace() system call.

      If SV_BSDSIG is set, the signal is given the Berkeley semantics.	The
      following signal is affected by this flag:

	   SIGCLD	  In addition to being sent when a child process
			  dies, the signal is also sent when any child's
			  status changes from running to stopped.  This
			  would normally be used by a program such as csh

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 sigvector(2)							sigvector(2)

			  (see csh(1)) when maintaining process groups under
			  Berkeley job control.

      If SV_RESETHAND is set, the signal handler is installed with the same
      semantics as a handler installed with signal(2).	This affects signal
      mask set-up during the signal handler (see above) and whether the
      handler is reset after a signal is caught (see below).

      If SV_RESETHAND is not set, once a signal handler is installed, it
      remains installed until another sigvector() call is made or an exec()
      system call is performed (see exec(2)).  If SV_RESETHAND is set and
      the signal is not one of those marked "not reset when caught" under
      signal(5), the default action is reinstated when the signal is caught,
      prior to entering the signal-catching function.  The "not reset when
      caught" distinction is not significant when sigvector() is called and
      SV_RESETHAND is not set.

      The default action for a signal can be reinstated by setting
      sv_handler to SIG_DFL; this default usually results in termination of
      the process.  If sv_handler is SIG_IGN the signal is usually
      subsequently ignored, and pending instances of the signal are
      discarded.  The exact meaning of SIG_DFL and SIG_IGN for each signal
      is discussed in signal(5).

      Certain system calls can be interrupted by a signal; all other system
      calls complete before the signal is serviced.  The scp pointer
      described in signal(5) is never null if sigvector() is supported.	 scp
      points to a machine-dependent sigcontext structure.  All
      implementations of this structure include the fields:

	   int	     sc_syscall;
	   char	     sc_syscall_action;

      The value SYS_NOTSYSCALL for the sc_syscall field indicates that the
      signal is not interrupting a system call; any other value indicates
      which system call it is interrupting.

      If a signal that is being caught occurs during a system call that can
      be interrupted, the signal handler is immediately invoked.  If the
      signal handler exits normally, the value of the sc_syscall_action
      field is inspected; if the value is SIG_RETURN, the system call is
      aborted and the interrupted program continues past the call.  The
      result of the interrupted call is -1 and errno is set to EINTR.  If
      the value of the sc_syscall_action field is SIG_RESTART, the call is
      restarted.  A call is restarted if, in the case of a read() or write()
      system call (see read(2) or write(2)), it had transferred no data.  If
      some data had been transferred, the operation is considered to have
      completed with a partial transfer, and the sc_syscall value is
      SYS_NOTSYSCALL.  Other values are undefined and reserved for future

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 sigvector(2)							sigvector(2)

      Exiting the handler abnormally (such as with longjmp() - see
      setjmp(3C)) aborts the call, leaving the user responsible for the
      context of further execution.  The value of scp->sc_syscall_action is
      ignored when the value of scp->sc_syscall is SYS_NOTSYSCALL.
      scp->sc_syscall_action is always initialized to SIG_RETURN before
      invocation of a signal handler.  When an system call that can be
      interrupted is interrupted by multiple signals, if any signal handler
      returns a value of SIG_RETURN in scp->sc_syscall_action, all
      subsequent signal handlers are passed a value of SYS_NOTSYSCALL in

      Note that calls to read(), write(), or ioctl() on fast devices (such
      as disks) cannot be interrupted, but I/O to a slow device (such as a
      printer) can be interrupted.  Other system calls, such as those used
      for networking, also can be interrupted on some implementations.	In
      these cases additional values can be specified for scp->sc_syscall.
      Programs that look at the values of scp->sc_syscall always should
      compare them to these symbolic constants; the numerical values
      represented by these constants might vary among implementations.
      System calls that can be interrupted and their corresponding values
      for scp->sc_syscall are listed below:

		     Call		   | sc_syscall value
		     read (slow devices)   | SYS_READ
		     readv (slow devices)  | SYS_READV
		     write (slow devices)  | SYS_WRITE
		     writev (slow devices) | SYS_WRITEV
		     open (slow devices)   | SYS_OPEN
		     ioctl (slow requests) | SYS_IOCTL
		     close (slow requests) | SYS_CLOSE
		     wait		   | SYS_WAIT
		     select		   | SYS_SELECT
		     pause		   | SYS_PAUSE
		     sigpause		   | SYS_SIGPAUSE
		     semop		   | SYS_SEMOP
		     msgsnd		   | SYS_MSGSND
		     msgrcv		   | SYS_MSGRCV

      These system calls are not defined if the preprocessor macro _XPG2 is
      defined when <signal.h> is included.  This is because the X/Open
      Portability Guide, Issue 2 specifies a different meaning for the
      symbol SYS_OPEN (see limits(5)).

      After a fork() or vfork() system call, the child inherits all signals,
      the signal mask, and the reserved signal stack space.

      exec(2) resets all caught signals to the default action; ignored
      signals remain ignored, the signal mask remains unchanged, and the
      reserved signal stack space is released.

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 sigvector(2)							sigvector(2)

      The mask specified in vec is not allowed to block signals that cannot
      be ignored, as defined in signal(5).  This is enforced silently by the

      If sigvector() is called to catch SIGCLD in a process that currently
      has terminated (zombie) children, a SIGCLD signal is delivered to the
      calling process immediately, or as soon as SIGCLD is unblocked if it
      is currently blocked.  Thus, in a process that spawns multiple
      children and catches SIGCLD, it is sometimes advisable to reinstall
      the handler for SIGCLD after each invocation in case there are
      multiple zombies present.	 This is true even though the handling of
      the signal is not reset by the system, as with signal(2), because
      deaths of multiple processes while SIGCLD is blocked in the handler
      result in delivery of only a single signal.  Note that the function
      must reinstall itself after it has called wait() or wait3().
      Otherwise the presence of the child that caused the original signal
      always causes another signal to be delivered.

      Upon successful completion, sigvector() returns 0; otherwise, it
      returns -1 and sets errno to indicate the reason.

      sigvector() fails and no new signal handler is installed if any of the
      following conditions are encountered:

	   [EFAULT]	       Either vec or ovec points to memory that is
			       not a valid part of the process address
			       space.  Reliable detection of this error is
			       implementation dependent.

	   [EINVAL]	       sig is not a valid signal number.

	   [EINVAL]	       An attempt was made to ignore or supply a
			       handler for a signal that cannot be caught or
			       ignored; see signal(5).

      Restarting a select(2) call can sometimes cause unexpected results.
      If the select() call has a timeout specified, the timeout is restarted
      with the call, ignoring any portion that had elapsed prior to
      interruption by the signal.  Normally this simply extends the timeout
      and is not a problem.  However, if a handler repeatedly catches
      signals, and the timeout specified to select() is longer than the time
      between those signals, restarting the select() call effectively
      renders the timeout infinite.

      sigvector() should not be used in conjunction with the facilities
      described under sigset(3C).

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 sigvector(2)							sigvector(2)

    Obsolescent Interfaces
      sigvector() is to be obsoleted at a future date.

    Threads Considerations
      The signal disposition (such as catch/ignore/default) established by
      sigvector() is shared by all threads in the process.  Each thread
      maintains its own blocked signal mask.  For more information regarding
      signals and threads, refer to signal(5).

      sigvector() was developed by HP and the University of California,

      kill(1), kill(2), ptrace(2), sigblock(2), signal(2), sigpause(3C),
      sigsetmask(2), sigspace(2), setjmp(3C), signal(5), termio(7).

 Hewlett-Packard Company	    - 6 -   HP-UX Release 11i: November 2000