program ScheduleTest;

{＄APPTYPE CONSOLE}

uses
 SysUtils, Windows, Messages;

type
 TTaskRect = record
   t_esp: integer;//当前任务的esp寄存器的备份
   t_eip: integer;//当前任务的eip寄存器的备份
end;

const TaskNum = 4;
 WaitCount = ＄7FFFFFFF;

var
 task: array[0..3] of TTaskRect;
 current: integer = 3;

function SetJmp(var p: TTaskRect): integer;
asm
 mov dword ptr [p+0],esp
 mov ecx,dword ptr [esp]
 mov dword ptr [p+4],ecx
 mov eax,0
end;

procedure LongJmp(var p: TTaskRect; code: integer);
asm
 mov esp,dword ptr [p+0]
 push ecx
 mov ecx,dword ptr [p+4]
 mov dword ptr [esp+4],ecx
 pop ecx
 mov eax,code
end;

procedure schedule();//调度的核心函数
var
 prev, i: integer;
begin
 prev := current;
 current := current + 1;
if current = TaskNum then
begin
   SetJmp(task[prev]);
   current := 0;
   LongJmp(task[current], 1);
end
else
begin
   i := SetJmp(task[prev]);
if i <> 0 then exit;
if current >= 3 then
     current := 0;
   LongJmp(task[current], 1);
end;
end;

procedure wait();
var
 index: integer;
begin
for index := WaitCount downto 0 do ;
end;

procedure Task0; //任务0
begin
 writeln('Task0 is begin....');
while true do
begin
   schedule();
   writeln('   Task0 is Running...'); 
   wait();
end;
end;

procedure Task1; //任务1
begin
 writeln('Task1 is begin....');
while true do
begin
   schedule();
   writeln('           Task1 is Running...');
   wait();
end;
end;

procedure Task2; //任务2
begin
 writeln('Task2 is begin....');
while true do
begin
   schedule();
   writeln('                   Task2 is Running...');
   wait();
end;
end;

procedure Task_wait;
begin
while true do
begin
   schedule();
   writeln('                   wait_for is Running...');
end;
end;

var
 t_esp: integer;
begin
asm
   mov t_esp,esp //取得当前栈顶地址
end;
 task[0].t_esp := t_esp - 100; //这里使用一个栈的不同部分来模拟多个栈。
 task[1].t_esp := t_esp - 200; //栈边界必须为4的倍数，因为栈的操作都是32位的
 task[2].t_esp := t_esp - 320; 
 task[0].t_eip := integer(@Task0); //初始化各个任务的eip初始值(开始运行的地址)
 task[1].t_eip := integer(@Task1);
 task[2].t_eip := integer(@Task2);
 schedule(); //开始调度
end.