system verilog- Mail Box - system-verilog

Question

Below I have posted the complete code for mailbox. It has a class Generator, class Driver and there is a top level code. My question is in the below code, inside Class Generator, how Transation tr and mailbox mbx are used? Also, in function new how mbx is used?
program mailbox_example(bus_if.TB bus...);
class Generator; // Class Generator
Transaction tr;
mailbox mbx;
function new (mailbox mbx);
this.mbx=mbx;
endfunction
task run;
repeat (10) begin
tr=new;
assert(tr.randomize);
mbx.put(tr); //send out transaction
end
endtask
endclass
class Driver; //Class Driver
Transaction tr;
mailbox mbx;
function new(mailbox mbx);
this.mbx=mbx;
endfunction
task run;
repeat(10) begin
mbx.get(tr);
#(posedge busif.cb.ack);
bus.cb.kind<=tr.kind;
...
end
endtask
endclass
mailbox mbx; //Top level
Generator gen;
Driver drv;
initial begin
mbx=new;
gen=new(mbx);
drv=new(mbx);
fork
gen.run();
drv.run();
join
end
endprogram

Answer 1

Mailbox is a medium, used to communicate between two blocks.
Why mailbox is in constructor..??
To communicate between two blocks, like driver and generator, there should be a common mailbox between them (like a common cable is used to carry information from DTH antenna to set-top box).
To share a common mailbox between Driver and Generator, the mailbox is instantiated in top level block (e.g. Env) and its handle is passed to the driver and generator through a constructor.
How transaction and mailbox are used?
A mailbox has default methods to store and get transactions like put(), try_put(), get(), try_get(), peek() and try_peek(). In generator, the transaction is stored into mailbox using put() or try_put() method. In driver, the transaction is retrieved using get(), try_get(), peek() or try_peek() method.
Please refer Section 15.4 Mailboxes in SV LRM for more details. :)