text: #include "fiber.h"
  
  #include <malloc.h>
  #include <ucontext.h>
  
  typedef struct fiber {
  	ucontext_t ctx;
  	int active;
  } fiber_t;
  
  static fiber_t g_fiber_arr[MAX_FIBERS];
  static int g_curr_fiber = -1;
  static int g_in_fiber = 0;
  static int g_num_fibers = 0;
  
  static ucontext_t g_ctx_main;
  
  void fiber_init(void)
  {
  	int i;
  	for (i = 0; i < MAX_FIBERS; i++ )
  		g_fiber_arr[i].active = 0;
  }
  
  void fiber_yield(void)
  {
  	if (g_in_fiber) {
  		swapcontext(&g_fiber_arr[g_curr_fiber].ctx, &g_ctx_main);
  	} else {
  		if (g_num_fibers == 0)
  			return;
  		g_curr_fiber = (g_curr_fiber + 1) % g_num_fibers;
  		g_in_fiber = 1;
  		swapcontext(&g_ctx_main, &g_fiber_arr[g_curr_fiber].ctx);
  		g_in_fiber = 0;
  		
  		if (g_fiber_arr[g_curr_fiber].active == 0) {
  			free(g_fiber_arr[g_curr_fiber].ctx.uc_stack.ss_sp);
  			-- g_num_fibers;
  			if (g_curr_fiber != g_num_fibers) {
  				g_fiber_arr[g_curr_fiber] = g_fiber_arr[g_num_fibers];
  			}
  			g_fiber_arr[g_num_fibers].active = 0;		
  		}
  	}
  }
  
  static void _start( void (*func)(void) )
  {
  	g_fiber_arr[g_curr_fiber].active = 1;
  	func();
  	g_fiber_arr[g_curr_fiber].active = 0;
  	fiber_yield();
  }
  
  int fiber_spawn(void (*func)(void) )
  {
  	if (g_num_fibers == MAX_FIBERS) return -1;
  	
  	getcontext(&g_fiber_arr[g_num_fibers].ctx);
  
  	g_fiber_arr[g_num_fibers].ctx.uc_link = 0;
  	g_fiber_arr[g_num_fibers].ctx.uc_stack.ss_sp = malloc(STACK_SIZE);
  	g_fiber_arr[g_num_fibers].ctx.uc_stack.ss_size = STACK_SIZE;
  	g_fiber_arr[g_num_fibers].ctx.uc_stack.ss_flags = 0;	
  	
  	if (g_fiber_arr[g_num_fibers].ctx.uc_stack.ss_sp == 0) {
  		printf("Allocate stack failed.\n");
  		return -1;
  	}
  	
  	makecontext(&g_fiber_arr[g_num_fibers].ctx, (void (*)(void)) &_start, 1, func);
  	++ g_num_fibers;
  	
  	return 0;
  }
  
  int fiber_wait(void)
  {
  	int fibers = 0;
  	
  	if (g_in_fiber) fibers = 1;
  	
  	while (g_num_fibers > fibers)
  		fiber_yield();
  	
  	return 0;		
  }
  