setjmp man page on SmartOS

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SETJMP(3C)							    SETJMP(3C)

NAME
       setjmp, sigsetjmp, longjmp, siglongjmp - non-local goto

SYNOPSIS
       #include <setjmp.h>

       int setjmp(jmp_buf env);

       int sigsetjmp(sigjmp_buf env, int savemask);

       void longjmp(jmp_buf env, int val);

       void siglongjmp(sigjmp_buf env, int val);

DESCRIPTION
       These  functions	 are  useful  for  dealing with errors	and interrupts
       encountered in a low-level subroutine of a program.

       The setjmp() function saves its stack environment in env for later  use
       by longjmp().

       The  sigsetjmp()	 function  saves  the  calling process's registers and
       stack environment (see sigaltstack(2)) in  env for later	 use  by  sig‐
       longjmp().  If  savemask is non-zero, the calling process's signal mask
       (see sigprocmask(2)) and scheduling parameters  (see  priocntl(2))  are
       also saved.

       The  longjmp() function restores the environment saved by the last call
       of setjmp() with the corresponding env argument. After  longjmp()  com‐
       pletes,	program	 execution  continues  as if the corresponding call to
       setjmp() had just returned the value val. The caller of	setjmp()  must
       not  have returned in the interim.  The longjmp() function cannot cause
       setjmp() to return the value 0.	If longjmp() is invoked with a	second
       argument of 0, setjmp() will return 1. At the time of the second return
       from setjmp(), all external and static variables have values as of  the
       time longjmp() is called (see EXAMPLES).

       The  siglongjmp()  function  restores the environment saved by the last
       call of sigsetjmp() with the corresponding  env	argument.  After  sig‐
       longjmp()  completes, program execution continues as if the correspond‐
       ing call to sigsetjmp() had just returned  the  value  val.   The  sig‐
       longjmp()  function cannot cause sigsetjmp() to return the value 0.  If
       siglongjmp() is invoked with a second argument of 0,  sigsetjmp()  will
       return 1. At the time of the second return from sigsetjmp(), all exter‐
       nal and static variables have values as of the  time  siglongjmp()  was
       called.

       If  a  signal-catching  function	 interrupts  sleep(3C)	and calls sig‐
       longjmp() to restore an environment saved prior to  the	sleep()	 call,
       the  action associated with SIGALRM and time it is scheduled to be gen‐
       erated are unspecified. It is also unspecified whether the SIGALRM sig‐
       nal is blocked, unless the process's signal mask is restored as part of
       the environment.

       The  siglongjmp() function restores the saved signal mask if  and  only
       if the  env argument was initialized by a call to the sigsetjmp() func‐
       tion with a non-zero  savemask argument.

       The values of register and automatic variables are undefined.  Register
       or automatic variables whose value must be relied upon must be declared
       as volatile.

RETURN VALUES
       If the return is from a direct  invocation,  setjmp()  and  sigsetjmp()
       return 0. If the return is from a call to longjmp(), setjmp() returns a
       non-zero	 value.	 If  the  return  is  from  a  call  to	 siglongjmp(),
       sigsetjmp() returns a non-zero value.

       After  longjmp()	 is  completed,	 program execution continues as if the
       corresponding invocation of setjmp() had just returned the value speci‐
       fied  by val. The longjmp() function cannot cause setjmp() to return 0;
       if val is 0, setjmp() returns 1.

       After siglongjmp() is completed, program execution continues as if  the
       corresponding  invocation  of  sigsetjmp()  had just returned the value
       specified by val. The siglongjmp() function cannot cause sigsetjmp() to
       return 0; if val is 0, sigsetjmp() returns 1.

EXAMPLES
       Example 1 Example of setjmp() and longjmp() functions.

       The  following  example	uses both setjmp() and longjmp() to return the
       flow of control to the appropriate instruction block:

	 #include <stdio.h>
	 #include <setjmp.h>
	 #include <signal.h>
	 #include <unistd.h>
	 jmp_buf env; static void signal_handler();

	 main()	 {
		 int returned_from_longjump, processing = 1;
		 unsigned int time_interval = 4;
		 if ((returned_from_longjump = setjmp(env)) != 0)
		     switch (returned_from_longjump)	 {
		       case SIGINT:
			 printf("longjumped from interrupt %d\n",SIGINT);
			 break;
		       case SIGALRM:
			 printf("longjumped from alarm %d\n",SIGALRM);
			 break;
		     }
		 (void) signal(SIGINT, signal_handler);
		 (void) signal(SIGALRM, signal_handler);
		 alarm(time_interval);
		 while (processing)	   {
		   printf(" waiting for you to INTERRUPT (cntrl-C) ...\n");
		   sleep(1);
		 }	 /* end while forever loop */
	 }

	 static void signal_handler(sig)
	 int sig; {
		 switch (sig)	  {
		   case SIGINT:	  ...	 /* process for interrupt */
				  longjmp(env,sig);
					 /* break never reached */
		   case SIGALRM:  ...	 /* process for alarm */
				  longjmp(env,sig);
					/* break never reached */
		   default:	  exit(sig);
		 }
	 }

       When this example is compiled and  executed,  and  the  user  sends  an
       interrupt signal, the output will be:

	 longjumped from interrupt

       Additionally,  every  4	seconds the alarm will expire, signalling this
       process, and the output will be:

	 longjumped from alarm

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

       ┌────────────────────┬─────────────────┐
       │  ATTRIBUTE TYPE    │ ATTRIBUTE VALUE │
       ├────────────────────┼─────────────────┤
       │Interface Stability │ Standard	      │
       ├────────────────────┼─────────────────┤
       │MT-Level	    │ Unsafe	      │
       └────────────────────┴─────────────────┘

SEE ALSO
       getcontext(2),  priocntl(2),  sigaction(2),  sigaltstack(2),   sigproc‐
       mask(2), signal(3C), attributes(5), standards(5)

WARNINGS
       If  longjmp()  or  siglongjmp()	are  called  even though env was never
       primed by a call to setjmp() or sigsetjmp(), or when the last such call
       was in a function that has since returned, the results are undefined.

				 Aug 14, 2002			    SETJMP(3C)
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