Manual Pages for UNIX Operating System command usage for man signal

Standard C Library Functions                           signal(3C)



NAME
     signal, sigset, sighold,  sigrelse,  sigignore,  sigpause  -
     simplified signal management for application processes

SYNOPSIS
     #include 

     void (*signal(int sig, void (*disp)(int)))(int);


     void (*sigset(int sig, void (*disp)(int)))(int);


     int sighold(int sig);


     int sigrelse(int sig);


     int sigignore(int sig);


     int sigpause(int sig);


DESCRIPTION
     These functions provide  simplified  signal  management  for
     application  processes.  See signal.h(3HEAD) for an explana-
     tion of general signal concepts.


     The signal() and sigset() functions modify  signal  disposi-
     tions.  The  sig argument specifies the signal, which may be
     any signal except SIGKILL and  SIGSTOP.  The  disp  argument
     specifies  the  signal's  disposition, which may be SIG_DFL,
     SIG_IGN, or the address of a signal handler. If signal()  is
     used,  disp  is  the address of a signal handler, and sig is
     not  SIGILL, SIGTRAP, or  SIGPWR, the system first sets  the
     signal's disposition to  SIG_DFL before executing the signal
     handler. If sigset() is used and disp is the  address  of  a
     signal handler, the system adds sig to the calling process's
     signal  mask before executing the signal handler;  when  the
     signal  handler  returns,  the  system  restores the calling
     process's signal mask to its state prior to the delivery  of
     the  signal.  In  addition,  if sigset() is used and disp is
     equal to  SIG_HOLD, sig is added to  the  calling  process's
     signal mask and the signal's disposition remains unchanged.


     The sighold() function adds sig  to  the  calling  process's
     signal mask.




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Standard C Library Functions                           signal(3C)



     The  sigrelse()  function  removes  sig  from  the   calling
     process's signal mask.


     The sigignore() function sets  the  disposition  of  sig  to
     SIG_IGN.


     The  sigpause()  function  removes  sig  from  the   calling
     process's  signal  mask   and  suspends  the calling process
     until a signal is received.

RETURN VALUES
     Upon successful completion, signal()  returns  the  signal's
     previous  disposition.  Otherwise,  it  returns  SIG_ERR and
     sets errno to indicate the error.


     Upon successful completion, sigset() returns SIG_HOLD if the
     signal had been blocked or the signal's previous disposition
     if it had not been blocked. Otherwise, it  returns   SIG_ERR
     and sets errno to indicate the error.


     Upon successful completion,  sighold(),  sigrelse(),  sigig-
     nore(),  and  sigpause(),  return  0. Otherwise, they return
     -1 and set  errno to indicate the error.

ERRORS
     These functions fail if:

     EINTR     A signal was  caught  during  the  execution  sig-
               pause().


     EINVAL    The value of the sig argument is not a valid  sig-
               nal or is equal to  SIGKILL or  SIGSTOP.


USAGE
     The sighold() function used in conjunction  with  sigrelse()
     or  sigpause()  may be used to establish critical regions of
     code that require the delivery of a signal to be temporarily
     deferred.


     If signal() or sigset() is used to set   SIGCHLD's  disposi-
     tion  to a signal handler, SIGCHLD will not be sent when the
     calling process's children are stopped or continued.






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Standard C Library Functions                           signal(3C)



     If any of the above functions  are  used  to  set  SIGCHLD's
     disposition   to   SIG_IGN,   the  calling  process's  child
     processes will not create zombie processes  when  they  ter-
     minate  (see  exit(2)).  If the calling process subsequently
     waits for its children, it blocks until all of its  children
     terminate;  it then returns -1 with errno set to ECHILD (see
     wait(3C) and waitid(2)).


     The system guarantees that if more than one instance of  the
     same  signal  is generated to a process, at least one signal
     will be received.  It does not guarantee  the  reception  of
     every generated signal.

ATTRIBUTES
     See attributes(5) for descriptions of the  following  attri-
     butes:



     ____________________________________________________________
    |       ATTRIBUTE TYPE        |       ATTRIBUTE VALUE       |
    |_____________________________|_____________________________|
    | Interface Stability         | Committed                   |
    |_____________________________|_____________________________|
    | MT-Level                    | MT-Safe                     |
    |_____________________________|_____________________________|
    | Standard                    | See standards(5).           |
    |_____________________________|_____________________________|


SEE ALSO
     exit(2),  kill(2),   pause(2),   sigaction(2),   sigsend(2),
     waitid(2),  signal.h(3HEAD),  wait(3C), attributes(5), stan-
     dards(5)




















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