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  1. #include <stdio.h>
  2. #include <stdlib.h>
  3. #include <string.h>
  4. #include <stdarg.h>
  5. #include <ucontext.h>
  6.  
  7. enum { STATE_ONE, STATE_TWO, STATE_DONE };
  8.  
  9. struct execution_state {
  10.     int state_;
  11.     ucontext_t main_ctx_;
  12.     ucontext_t alt_ctx_;
  13.     char alt_stack_[32*1024];
  14. } es;
  15.  
  16. void deferred_print (const char *fmt, ...) {
  17.     va_list ap;
  18.     while (es.state_ == STATE_ONE) {
  19.         es.state_ = STATE_TWO;
  20.         swapcontext(&es.main_ctx_, &es.alt_ctx_);
  21.     }
  22.     va_start(ap, fmt);
  23.     vprintf(fmt, ap);
  24.     va_end(ap);
  25. }
  26.  
  27. void state_one () {
  28.     puts(__func__);
  29.     deferred_print("this is a deferred print from %s\n", __func__);
  30.     es.state_ = STATE_DONE;
  31. }
  32.  
  33. void state_two () {
  34.     puts(__func__);
  35.     if (rand() > RAND_MAX/4) es.state_ = STATE_ONE;
  36.     setcontext(&es.main_ctx_);
  37. }
  38.  
  39. void state_machine () {
  40.     while (es.state_ != STATE_DONE) {
  41.         (void (*[])()){ state_one, state_two }[es.state_]();
  42.     }
  43. }
  44.  
  45. void es_init () {
  46.     es.state_ = STATE_ONE;
  47.     getcontext(&es.alt_ctx_);
  48.     es.alt_ctx_.uc_stack.ss_sp = es.alt_stack_;
  49.     es.alt_ctx_.uc_stack.ss_size = sizeof(es.alt_stack_);
  50.     es.alt_ctx_.uc_link = &es.main_ctx_;
  51.     makecontext(&es.alt_ctx_, state_machine, 0);
  52.     srand((unsigned)time(0));
  53. }
  54.  
  55. int main () {
  56.     es_init();
  57.     puts("start");
  58.     state_machine();
  59.     puts("finish");
  60.     return 0;
  61. }
  62.  
Success #stdin #stdout 0s 2324KB
comments (?)
stdin
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Standard input is empty
stdout
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start
state_one
state_two
state_two
state_two
this is a deferred print from state_one
finish
https://ideone.com/S6qCdq
language:
C (gcc 8.3)
created:
12 years ago
visibility:
public

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