ucontext.c

/*
  libco.ucontext (2008-01-28)
  author: Nach
  license: public domain
*/

/*
 * WARNING: the overhead of POSIX ucontext is very high,
 * assembly versions of libco or libco_sjlj should be much faster
 *
 * This library only exists for two reasons:
 * 1 - as an initial test for the viability of a ucontext implementation
 * 2 - to demonstrate the power and speed of libco over existing implementations,
 *     such as pth (which defaults to wrapping ucontext on unix targets)
 *
 * Use this library only as a *last resort*
 */

#define LIBCO_C
#include "libco.h"
#include <stdlib.h>
#include <ucontext.h>

#ifdef __cplusplus
extern "C" {
#endif

static thread_local ucontext_t co_primary;
static thread_local ucontext_t *co_running = 0;

cothread_t co_active() {
  if(!co_running) co_running = &co_primary;
  return (cothread_t)co_running;
}

cothread_t co_create(unsigned int heapsize, void (*coentry)(void)) {
  if(!co_running) co_running = &co_primary;
  ucontext_t *thread = (ucontext_t*)malloc(sizeof(ucontext_t));
  if(thread) {
    if((!getcontext(thread) && !(thread->uc_stack.ss_sp = 0)) && (thread->uc_stack.ss_sp = malloc(heapsize))) {
      thread->uc_link = co_running;
      thread->uc_stack.ss_size = heapsize;
      makecontext(thread, coentry, 0);
    } else {
      co_delete((cothread_t)thread);
      thread = 0;
    }
  }
  return (cothread_t)thread;
}

void co_delete(cothread_t cothread) {
  if(cothread) {
    if(((ucontext_t*)cothread)->uc_stack.ss_sp) { free(((ucontext_t*)cothread)->uc_stack.ss_sp); }
    free(cothread);
  }
}

void co_switch(cothread_t cothread) {
  ucontext_t *old_thread = co_running;
  co_running = (ucontext_t*)cothread;
  swapcontext(old_thread, co_running);
}

#ifdef __cplusplus
}
#endif