1 files changed, 99 insertions, 0 deletions
diff --git a/manual/examples/swapcontext.c b/manual/examples/swapcontext.c
new file mode 100644
index 0000000000..f733510f88
--- /dev/null
+++ b/manual/examples/swapcontext.c
@@ -0,0 +1,99 @@
+#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;
+}