Thread: Semaphores

I am currently learning about semaphores as a means of preparing for next semester (Im going back to uni) and while answer questions in an Operating Systems book, I got stuck on a question. Briefly:

A processor concurrently runs process A & B that arrive after each other (execution time and speed not given).

Code:

 
procedure A                   procedure B
begin                             begin
   A;                                   F;
   B;                                   G;
   C;                                   H;
   D;                                   I;
   E;                                   J;
end                                 end

I need to make sure that statement G does not commence until D has completed.

It says I have to do this by determining the number of semaphores, their type, the initial state for each and the placement in the code of the semaphore operations wait and signal

I have done the following but do not know if it is right. Semaphore S1=1 and S2=0 at start

Code:

 
procedure A                   procedure B
begin                             begin
   A;                                   F;
   wait(S1);                        wait(S1);
   B;                                   G;
   C;                                   H;
   signal(S1);                     signal(S1);
   D;                                   I;
   signal(S2);                     wait(S2);
   E;                                   J;
end                                 end

All comments welcome because I want to make sure I understand this properly.

Thanx
Jules

Thanx....what about s2?? and would I be wrong by thinking that both s1 and s2 are mutex's.

So sorry ...It says that each process executes the code in which process A - Procedure A, and process B - Procedure B. That is why I asked about s2....Also, would I be wrong by assuming that they are mutex semaphores.