memory leak - IUS61 system verilog

Hello,

I have a small piece of code that uses the class and mailbox feature of system verilog.  There is a sender task which generates a transactions and puts the transaction handle in a mailbox.  The receiver task waits on a message from the mailbox and when one arrives it reads the message and print a message.  The mailbox is bounded.

The sender and receiver tasks are forked in an initial block.

I seem to be experiencing a memory leak since the heap continues to grow.  My understanding is system verilog handles garbage collection automatically.

What am I doing wrong in my code.  Attached is code:


module mem_leak ();

/////////////////////////////////////////////////////////////////////
// Generate clock and reset
/////////////////////////////////////////////////////////////////////

reg clk;

initial
begin
    clk = 0;
    forever #(10/2) clk = ~clk;
end

/////////////////////////////////////////////////////////////////////
// Class declarations
/////////////////////////////////////////////////////////////////////

class CpuCmd;
    time startT;
    time stopT;
    reg [1:0] cpu_id;

    reg btype;
    rand reg wr_rdn;

    rand reg [26:0] addr;
    rand reg [ 5:0] size;
    reg [39:0] packed_cmd[1:0];
    reg [10:0] total_wd;

    extern task gen_cpu_addr;
    constraint cpucmd_constraint;
endclass

constraint CpuCmd::cpucmd_constraint
{
    addr inside {[0 : 2000]};
    size inside {1, 4};
}

task CpuCmd::gen_cpu_addr;

    startT    = $time;
    stopT     = startT;
    cpu_id    = 0;

    btype  = 0;

    packed_cmd[0] = {btype,wr_rdn,3'h0,addr,2'h0,size};
    packed_cmd[1] = 40'h0;

    total_wd = size;

endtask

/////////////////////////////////////////////////////////////////////
// Declarations
/////////////////////////////////////////////////////////////////////

// Command queue to hold transactions
mailbox cmdQ;

/////////////////////////////////////////////////////////////////////
// Main client loop
/////////////////////////////////////////////////////////////////////

initial
begin
    repeat (20) @(posedge clk);

    cmdQ  = new(4); // bounded mailbox

    repeat (20) @(posedge clk);

    fork
        begin
            $display("INFO: Fork Sender");
            sender;
        end

        begin
            $display("INFO: Fork receiver");
            receiver;
        end
    join
end

///////////////////////////////////////////
// Sender
///////////////////////////////////////////
task sender;

   int val;
   CpuCmd Scmd;

   while (1)
   begin
    repeat (1000) @(posedge clk);

    Scmd = new;

    val = Scmd.randomize();
    if (val == 0)
    begin
        $display("Scmd randomization failed at %0t", $time);
        @(posedge clk);
        $finish;
    end

    Scmd.gen_cpu_addr(); // generate a command

    cmdQ.put(Scmd); // put command into mailbox
    $display("Sent message at %0t", $time);
   end
endtask

///////////////////////////////////////////
// Receiver
///////////////////////////////////////////

task receiver;

   CpuCmd Rcmd;

   while (1)
   begin
           @(posedge clk);
        cmdQ.get(Rcmd); // Get a message from the mailbox
        $display("Received message at %0t", $time);
   end

endtask

endmodule