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/* Complete Context Control
Copyright (C) 1991-2024 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, see <https://www.gnu.org/licenses/>.
*/
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <ucontext.h>
#include <sys/time.h>
/* Set by the signal handler. */
static volatile int expired;
/* The contexts. */
static ucontext_t uc[3];
/* We do only a certain number of switches. */
static int switches;
/* This is the function doing the work. It is just a
skeleton, real code has to be filled in. */
static void
f (int n)
{
int m = 0;
while (1)
{
/* This is where the work would be done. */
if (++m % 100 == 0)
{
putchar ('.');
fflush (stdout);
}
/* Regularly the @var{expire} variable must be checked. */
if (expired)
{
/* We do not want the program to run forever. */
if (++switches == 20)
return;
printf ("\nswitching from %d to %d\n", n, 3 - n);
expired = 0;
/* Switch to the other context, saving the current one. */
swapcontext (&uc[n], &uc[3 - n]);
}
}
}
/* This is the signal handler which simply set the variable. */
void
handler (int signal)
{
expired = 1;
}
int
main (void)
{
struct sigaction sa;
struct itimerval it;
char st1[8192];
char st2[8192];
/* Initialize the data structures for the interval timer. */
sa.sa_flags = SA_RESTART;
sigfillset (&sa.sa_mask);
sa.sa_handler = handler;
it.it_interval.tv_sec = 0;
it.it_interval.tv_usec = 1;
it.it_value = it.it_interval;
/* Install the timer and get the context we can manipulate. */
if (sigaction (SIGPROF, &sa, NULL) < 0
|| setitimer (ITIMER_PROF, &it, NULL) < 0
|| getcontext (&uc[1]) == -1
|| getcontext (&uc[2]) == -1)
abort ();
/* Create a context with a separate stack which causes the
function @code{f} to be call with the parameter @code{1}.
Note that the @code{uc_link} points to the main context
which will cause the program to terminate once the function
return. */
uc[1].uc_link = &uc[0];
uc[1].uc_stack.ss_sp = st1;
uc[1].uc_stack.ss_size = sizeof st1;
makecontext (&uc[1], (void (*) (void)) f, 1, 1);
/* Similarly, but @code{2} is passed as the parameter to @code{f}. */
uc[2].uc_link = &uc[0];
uc[2].uc_stack.ss_sp = st2;
uc[2].uc_stack.ss_size = sizeof st2;
makecontext (&uc[2], (void (*) (void)) f, 1, 2);
/* Start running. */
swapcontext (&uc[0], &uc[1]);
putchar ('\n');
return 0;
}
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