1 | /* Complete Context Control |
2 | Copyright (C) 1991-2022 Free Software Foundation, Inc. |
3 | |
4 | This program is free software; you can redistribute it and/or |
5 | modify it under the terms of the GNU General Public License |
6 | as published by the Free Software Foundation; either version 2 |
7 | of the License, or (at your option) any later version. |
8 | |
9 | This program is distributed in the hope that it will be useful, |
10 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
11 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
12 | GNU General Public License for more details. |
13 | |
14 | You should have received a copy of the GNU General Public License |
15 | along with this program; if not, see <https://www.gnu.org/licenses/>. |
16 | */ |
17 | |
18 | #include <signal.h> |
19 | #include <stdio.h> |
20 | #include <stdlib.h> |
21 | #include <ucontext.h> |
22 | #include <sys/time.h> |
23 | |
24 | /* Set by the signal handler. */ |
25 | static volatile int expired; |
26 | |
27 | /* The contexts. */ |
28 | static ucontext_t uc[3]; |
29 | |
30 | /* We do only a certain number of switches. */ |
31 | static int switches; |
32 | |
33 | |
34 | /* This is the function doing the work. It is just a |
35 | skeleton, real code has to be filled in. */ |
36 | static void |
37 | f (int n) |
38 | { |
39 | int m = 0; |
40 | while (1) |
41 | { |
42 | /* This is where the work would be done. */ |
43 | if (++m % 100 == 0) |
44 | { |
45 | putchar (c: '.'); |
46 | fflush (stdout); |
47 | } |
48 | |
49 | /* Regularly the @var{expire} variable must be checked. */ |
50 | if (expired) |
51 | { |
52 | /* We do not want the program to run forever. */ |
53 | if (++switches == 20) |
54 | return; |
55 | |
56 | printf (format: "\nswitching from %d to %d\n" , n, 3 - n); |
57 | expired = 0; |
58 | /* Switch to the other context, saving the current one. */ |
59 | swapcontext (oucp: &uc[n], ucp: &uc[3 - n]); |
60 | } |
61 | } |
62 | } |
63 | |
64 | /* This is the signal handler which simply set the variable. */ |
65 | void |
66 | handler (int signal) |
67 | { |
68 | expired = 1; |
69 | } |
70 | |
71 | |
72 | int |
73 | main (void) |
74 | { |
75 | struct sigaction sa; |
76 | struct itimerval it; |
77 | char st1[8192]; |
78 | char st2[8192]; |
79 | |
80 | /* Initialize the data structures for the interval timer. */ |
81 | sa.sa_flags = SA_RESTART; |
82 | sigfillset (&sa.sa_mask); |
83 | sa.sa_handler = handler; |
84 | it.it_interval.tv_sec = 0; |
85 | it.it_interval.tv_usec = 1; |
86 | it.it_value = it.it_interval; |
87 | |
88 | /* Install the timer and get the context we can manipulate. */ |
89 | if (sigaction (SIGPROF, act: &sa, NULL) < 0 |
90 | || setitimer (ITIMER_PROF, new: &it, NULL) < 0 |
91 | || getcontext (ucp: &uc[1]) == -1 |
92 | || getcontext (ucp: &uc[2]) == -1) |
93 | abort (); |
94 | |
95 | /* Create a context with a separate stack which causes the |
96 | function @code{f} to be call with the parameter @code{1}. |
97 | Note that the @code{uc_link} points to the main context |
98 | which will cause the program to terminate once the function |
99 | return. */ |
100 | uc[1].uc_link = &uc[0]; |
101 | uc[1].uc_stack.ss_sp = st1; |
102 | uc[1].uc_stack.ss_size = sizeof st1; |
103 | makecontext (ucp: &uc[1], func: (void (*) (void)) f, argc: 1, 1); |
104 | |
105 | /* Similarly, but @code{2} is passed as the parameter to @code{f}. */ |
106 | uc[2].uc_link = &uc[0]; |
107 | uc[2].uc_stack.ss_sp = st2; |
108 | uc[2].uc_stack.ss_size = sizeof st2; |
109 | makecontext (ucp: &uc[2], func: (void (*) (void)) f, argc: 1, 2); |
110 | |
111 | /* Start running. */ |
112 | swapcontext (oucp: &uc[0], ucp: &uc[1]); |
113 | putchar (c: '\n'); |
114 | |
115 | return 0; |
116 | } |
117 | |