| 1 | #include <ucontext.h> |
| 2 | #include <sys/types.h> |
| 3 | #include <sys/time.h> |
| 4 | #include <signal.h> |
| 5 | #include <stdio.h> |
| 6 | #include <unistd.h> |
| 7 | #include <stdlib.h> |
| 8 | #include <poll.h> |
| 9 | |
| 10 | /* ucontext sample program |
| 11 | |
| 12 | Downloaded from https://gist.github.com/DanGe42/7148946 |
| 13 | A non-trivial example of how to use user contexts for trivial scheduling. |
| 14 | |
| 15 | by Jon Kaplan and Robert Spier (October 24th, 1999) |
| 16 | Updated for 2000 and poll, Robert Spier |
| 17 | sigprocmask gaff fixed by Ben Slusky |
| 18 | ported to Linux by Eric Cronin |
| 19 | $Id: context_demo.c 37 2006-10-12 22:16:59Z ecronin $ |
| 20 | |
| 21 | Demonstrates swapping between multiple processor contexts (in a |
| 22 | _stable_ way). n-1 contexts do nothing. 1 context accepts input |
| 23 | and outputs it. |
| 24 | */ |
| 25 | |
| 26 | |
| 27 | #define NUMCONTEXTS 10 /* how many contexts to make */ |
| 28 | #define STACKSIZE 4096 /* stack size */ |
| 29 | #define INTERVAL 100 /* timer interval in nanoseconds */ |
| 30 | |
| 31 | sigset_t set; /* process wide signal mask */ |
| 32 | ucontext_t signal_context; /* the interrupt context */ |
| 33 | void *signal_stack; /* global interrupt stack */ |
| 34 | |
| 35 | ucontext_t contexts[NUMCONTEXTS]; /* store our context info */ |
| 36 | int curcontext = 0; /* whats the current context? */ |
| 37 | ucontext_t *cur_context; /* a pointer to the current_context */ |
| 38 | |
| 39 | /* The scheduling algorithm; selects the next context to run, then starts it. */ |
| 40 | void |
| 41 | scheduler() |
| 42 | { |
| 43 | printf("scheduling out thread %d\n", curcontext); |
| 44 | |
| 45 | curcontext = (curcontext + 1) % NUMCONTEXTS; /* round robin */ |
| 46 | cur_context = &contexts[curcontext]; |
| 47 | |
| 48 | printf("scheduling in thread %d\n", curcontext); |
| 49 | |
| 50 | setcontext(cur_context); /* go */ |
| 51 | } |
| 52 | |
| 53 | /* |
| 54 | Timer interrupt handler. |
| 55 | Creates a new context to run the scheduler in, masks signals, then swaps |
| 56 | contexts saving the previously executing thread and jumping to the |
| 57 | scheduler. |
| 58 | */ |
| 59 | void |
| 60 | timer_interrupt(int j, siginfo_t *si, void *old_context) |
| 61 | { |
| 62 | /* Create new scheduler context */ |
| 63 | getcontext(&signal_context); |
| 64 | signal_context.uc_stack.ss_sp = signal_stack; |
| 65 | signal_context.uc_stack.ss_size = STACKSIZE; |
| 66 | signal_context.uc_stack.ss_flags = 0; |
| 67 | sigemptyset(&signal_context.uc_sigmask); |
| 68 | makecontext(&signal_context, scheduler, 1); |
| 69 | |
| 70 | /* save running thread, jump to scheduler */ |
| 71 | swapcontext(cur_context,&signal_context); |
| 72 | } |
| 73 | |
| 74 | /* Set up SIGALRM signal handler */ |
| 75 | void |
| 76 | setup_signals(void) |
| 77 | { |
| 78 | struct sigaction act; |
| 79 | |
| 80 | act.sa_sigaction = timer_interrupt; |
| 81 | sigemptyset(&act.sa_mask); |
| 82 | act.sa_flags = SA_RESTART | SA_SIGINFO; |
| 83 | |
| 84 | sigemptyset(&set); |
| 85 | sigaddset(&set, SIGALRM); |
| 86 | |
| 87 | if(sigaction(SIGALRM, &act, NULL) != 0) { |
| 88 | perror("Signal handler"); |
| 89 | } |
| 90 | } |
| 91 | |
| 92 | |
| 93 | /* Thread bodies */ |
| 94 | void |
| 95 | thread1() |
| 96 | { |
| 97 | while(1) { |
| 98 | poll(NULL,0,100); |
| 99 | }; /* do nothing nicely */ |
| 100 | } |
| 101 | |
| 102 | void |
| 103 | thread2() |
| 104 | { |
| 105 | char buf[1024]; |
| 106 | /* get a string.. print a string.. ad infinitum */ |
| 107 | while(1) { |
| 108 | fgets(buf, 1024, stdin); |
| 109 | printf("[[[[[[%s]]]]]]\n",buf); |
| 110 | } |
| 111 | } |
| 112 | |
| 113 | /* helper function to create a context. |
| 114 | initialize the context from the current context, setup the new |
| 115 | stack, signal mask, and tell it which function to call. |
| 116 | */ |
| 117 | void |
| 118 | mkcontext(ucontext_t *uc, void *function) |
| 119 | { |
| 120 | void * stack; |
| 121 | |
| 122 | getcontext(uc); |
| 123 | |
| 124 | stack = malloc(STACKSIZE); |
| 125 | if (stack == NULL) { |
| 126 | perror("malloc"); |
| 127 | exit(1); |
| 128 | } |
| 129 | /* we need to initialize the ucontext structure, give it a stack, |
| 130 | flags, and a sigmask */ |
| 131 | uc->uc_stack.ss_sp = stack; |
| 132 | uc->uc_stack.ss_size = STACKSIZE; |
| 133 | uc->uc_stack.ss_flags = 0; |
| 134 | if (sigemptyset(&uc->uc_sigmask) < 0){ |
| 135 | perror("sigemptyset"); |
| 136 | exit(1); |
| 137 | } |
| 138 | |
| 139 | /* setup the function we're going to, and n-1 arguments. */ |
| 140 | makecontext(uc, function, 1); |
| 141 | |
| 142 | printf("context is %p\n", uc); |
| 143 | } |
| 144 | |
| 145 | |
| 146 | int |
| 147 | main() |
| 148 | { |
| 149 | int i; |
| 150 | struct itimerval it; |
| 151 | |
| 152 | fprintf(stderr,"Process Id: %d\n", (int)getpid()); |
| 153 | |
| 154 | /* allocate the global signal/interrupt stack */ |
| 155 | signal_stack = malloc(STACKSIZE); |
| 156 | if (signal_stack == NULL) { |
| 157 | perror("malloc"); |
| 158 | exit(1); |
| 159 | } |
| 160 | |
| 161 | /* make all our contexts */ |
| 162 | mkcontext(&contexts[0], thread2); |
| 163 | for(i=1; i < NUMCONTEXTS; i++) |
| 164 | mkcontext(&contexts[i], thread1); |
| 165 | |
| 166 | |
| 167 | /* initialize the signal handlers */ |
| 168 | setup_signals(); |
| 169 | |
| 170 | /* setup our timer */ |
| 171 | it.it_interval.tv_sec = 0; |
| 172 | it.it_interval.tv_usec = INTERVAL * 1000; |
| 173 | it.it_value = it.it_interval; |
| 174 | if (setitimer(ITIMER_REAL, &it, NULL) ) perror("setitiimer"); |
| 175 | |
| 176 | /* force a swap to the first context */ |
| 177 | cur_context = &contexts[0]; |
| 178 | setcontext(&contexts[0]); |
| 179 | |
| 180 | return 0; /* make gcc happy */ |
| 181 | } |