Prepare for radical source tree reorganization. zack/build-layout-experiment

All top-level files and directories are moved into a temporary storage
directory, REORG.TODO, except for files that will certainly still
exist in their current form at top level when we're done (COPYING,
COPYING.LIB, LICENSES, NEWS, README), all old ChangeLog files (which
are moved to the new directory OldChangeLogs, instead), and the
generated file INSTALL (which is just deleted; in the new order, there
will be no generated files checked into version control).

1 files changed, 116 insertions, 0 deletions

diff --git a/REORG.TODO/manual/examples/swapcontext.c b/REORG.TODO/manual/examples/swapcontext.c
new file mode 100644
index 0000000000..3747230c31
--- /dev/null
+++ b/REORG.TODO/manual/examples/swapcontext.c
@@ -0,0 +1,116 @@
+/* Complete Context Control
+   Copyright (C) 1991-2017 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, if not, see <http://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;
+}