sequence processing

[DS1701]

I have a simple code as bellow:

class Tmodel{
private:
   sc_event notify_method_2;
   sc_event notify_method_4;
public:
  sc_event notify_method_3;
  sc_in<bool> input_port;
  ...
   SC_METHOD(method_1);
   dont_initialize();
   sensitive << input_port;

  SC_METHOD(method_2);
   dont_initialize();
   sensitive << notify_method_2;
  
  SC_METHOD(method_3);
   dont_initialize();
   sensitive << notify_method_3;
  
  SC_METHOD(method_4);
   dont_initialize();
   sensitive << notify_method_4;
  ...
  void method_1(void){
       ...
       notify_method_2.notify(SC_ZERO_TIME);
  }
  void method_2(void){
       ...
       printf("method_2\n");
  }
  void method_3(void){
       notify_method_4.notify(SC_ZERO_TIME);
  }
  void method_4(void){
       printf("method_4\n");
  }
  
};

int sc_main(int , char *){
  ...
   objectDUT->input_port.write(true);
  objectDUT->notify_method_3.notify(SC_ZERO_TIME);
  sc_start(200,SC_PS);
  ...
}

when debug, steps as bellow:

1. method_1 , call notify_method_2

2. method_3, call notify_method_4

3. method_4

4. method_2

I dont understand why at step 3 is method_4 ( I think it is method_2 ). 

if in sc_main, I insert sc_start(0,SC_PS);

int sc_main(int , char *){
  ...
   objectDUT->input_port.write(true);
sc_start(0,SC_PS);
  objectDUT->notify_method_3.notify(SC_ZERO_TIME);
  sc_start(200,SC_PS);
  ...
}

steps is correct:

1. method_1 , call notify_method_2

2. method_3, call notify_method_4

3. method_2

4. method_4

[Roman Popov]

SystemC standard does not guarantee any order of process evaluation within a single delta cycle. So in first example  both 2,4 and 4,2 will be correct.