117 lines
3.1 KiB
C
117 lines
3.1 KiB
C
/* Complete Context Control
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Copyright (C) 1991-2022 Free Software Foundation, Inc.
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This program is free software; you can redistribute it and/or
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modify it under the terms of the GNU General Public License
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as published by the Free Software Foundation; either version 2
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of the License, or (at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, see <https://www.gnu.org/licenses/>.
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*/
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#include <signal.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <ucontext.h>
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#include <sys/time.h>
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/* Set by the signal handler. */
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static volatile int expired;
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/* The contexts. */
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static ucontext_t uc[3];
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/* We do only a certain number of switches. */
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static int switches;
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/* This is the function doing the work. It is just a
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skeleton, real code has to be filled in. */
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static void
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f (int n)
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{
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int m = 0;
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while (1)
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{
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/* This is where the work would be done. */
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if (++m % 100 == 0)
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{
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putchar ('.');
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fflush (stdout);
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}
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/* Regularly the @var{expire} variable must be checked. */
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if (expired)
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{
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/* We do not want the program to run forever. */
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if (++switches == 20)
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return;
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printf ("\nswitching from %d to %d\n", n, 3 - n);
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expired = 0;
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/* Switch to the other context, saving the current one. */
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swapcontext (&uc[n], &uc[3 - n]);
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}
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}
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}
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/* This is the signal handler which simply set the variable. */
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void
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handler (int signal)
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{
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expired = 1;
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}
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int
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main (void)
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{
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struct sigaction sa;
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struct itimerval it;
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char st1[8192];
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char st2[8192];
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/* Initialize the data structures for the interval timer. */
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sa.sa_flags = SA_RESTART;
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sigfillset (&sa.sa_mask);
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sa.sa_handler = handler;
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it.it_interval.tv_sec = 0;
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it.it_interval.tv_usec = 1;
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it.it_value = it.it_interval;
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/* Install the timer and get the context we can manipulate. */
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if (sigaction (SIGPROF, &sa, NULL) < 0
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|| setitimer (ITIMER_PROF, &it, NULL) < 0
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|| getcontext (&uc[1]) == -1
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|| getcontext (&uc[2]) == -1)
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abort ();
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/* Create a context with a separate stack which causes the
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function @code{f} to be call with the parameter @code{1}.
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Note that the @code{uc_link} points to the main context
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which will cause the program to terminate once the function
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return. */
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uc[1].uc_link = &uc[0];
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uc[1].uc_stack.ss_sp = st1;
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uc[1].uc_stack.ss_size = sizeof st1;
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makecontext (&uc[1], (void (*) (void)) f, 1, 1);
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/* Similarly, but @code{2} is passed as the parameter to @code{f}. */
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uc[2].uc_link = &uc[0];
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uc[2].uc_stack.ss_sp = st2;
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uc[2].uc_stack.ss_size = sizeof st2;
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makecontext (&uc[2], (void (*) (void)) f, 1, 2);
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/* Start running. */
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swapcontext (&uc[0], &uc[1]);
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putchar ('\n');
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return 0;
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}
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