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d9a17c07 | 1 | /* Complete Context Control |
04277e02 | 2 | Copyright (C) 1991-2019 Free Software Foundation, Inc. |
d9a17c07 RM |
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 | |
5a82c748 | 15 | along with this program; if not, see <https://www.gnu.org/licenses/>. |
d9a17c07 RM |
16 | */ |
17 | ||
eacde9d0 UD |
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 ('.'); | |
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 ("\nswitching from %d to %d\n", n, 3 - n); | |
57 | expired = 0; | |
58 | /* Switch to the other context, saving the current one. */ | |
59 | swapcontext (&uc[n], &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, &sa, NULL) < 0 | |
90 | || setitimer (ITIMER_PROF, &it, NULL) < 0 | |
91 | || getcontext (&uc[1]) == -1 | |
92 | || getcontext (&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 (&uc[1], (void (*) (void)) f, 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 (&uc[2], (void (*) (void)) f, 1, 2); | |
110 | ||
111 | /* Start running. */ | |
112 | swapcontext (&uc[0], &uc[1]); | |
113 | putchar ('\n'); | |
114 | ||
115 | return 0; | |
116 | } |