fork join does not wokr!

[b01010101]

I use the "fork join" in my testbench, but I find that the modelsim execute the first part firstly, when all the N times are finished, the second part is then executed.
I think the fork join doesn't work in my code.

Can anybody tell me why? Thank you.

The following is my code:

....
fork
begin
///////////////// first part////////////////
for(cnt=0; cnt<N; cnt=cnt+1) begin
for(i=0;i<=5;i=i+1) begin h=$random; end
x00=$random;x01=$random;x02=$random;x03=$random;x04=$random;
x10=$random;x11=$random;x12=$random;x13=$random;x14=$random;
x20=$random;x21=$random;x22=$random;x23=$random;x24=$random;
x30=$random;x31=$random;x32=$random;x33=$random;x34=$random;
x40=$random;x41=$random;x42=$random;x43=$random;x44=$random
full_result =x00*h[0]+(x01+x04+x10+x40)*h[1]+
(x02+x20+x03+x30)*h[2]+(x11+x14+x41+x44)*h[3]+
(x12+x13+x21+x31+x24+x34+x42+x43)*h[4]+
(x22+x23+x32+x33)*h[5];
right_result[0]=full_result[36:21]; // high 16bits
for(j=0;j<DELTA;j=j+1) begin
@(posedge clk);
end
end
end

///////////////// second part////////////////
begin
for(i=0;i<LAMDA;i=i+1) begin
@(posedge clk);
end
for(cnt2=0; cnt2<Times; cnt2=cnt2+1) begin
if(right_result[LAMDA-1]!=dout) begin
$display ("Caculate Error!\n");
$stop;
end
end
$display ("Test Successful!\n");
$stop;
end
join
...