SystemVerilog provides constructs that allow one process to terminate or wait for the completion of other processes. The wait fork construct waits for the completion of processes. The disable fork construct stops the execution of processes.

• wait fork
• disable fork

The wait fork statement is used to ensure that all child processes (processes created by the calling process) have completed their execution.

Verilog terminates a simulation run when there is no further activity of any kind. SystemVerilog adds the ability to automatically terminate the simulation when all its program blocks finish executing (i.e, they reach the end of their execute block), regardless of the status of any child processes

  1 module fork_join_wait_process();
  2 
  3 task automatic print_value;
  4   input [7:0] value;
  5   input [7:0] delay;
  6   begin
  7     #(delay) $display("@%g Passed Value %d Delay %d",
  8         $time, value, delay);
  9   end
 10 endtask
 11 
 12 initial begin
 13   fork 
 14      #1  print_value (10,7);
 15      #1  print_value (8,5);
 16      #1  print_value (4,2);
 17   join_none
 18    #5 ;
 19   fork 
 20      #1  print_value (1,1);
 21      #1  print_value (2,2);
 22      #1  print_value (3,3);
 23   join_any
 24   $display("@%g Came out of fork-join", $time);
 25   // Wait till all the forks (threads are completed their execution)
 26   wait fork;
 27   $display("@%g All threads completed execution", $time);
 28    #20  $finish;
 29 end
 30 
 31 endmodule

Simulator Output

 @3 Passed Value   4 Delay   2
 @6 Passed Value   8 Delay   5
 @7 Passed Value   1 Delay   1
 @7 Came out of fork-join
 @8 Passed Value  10 Delay   7
 @8 Passed Value   2 Delay   2
 @9 Passed Value   3 Delay   3
 @9 All threads completed execution

The disable fork statement terminates all descendants of the calling process as well as the descendants of the process descendants. In other words, if any of the child processes have descendants of their own, the disable fork statement shall terminate them as well.

  1 module fork_join_disable_process();
  2 
  3 task automatic print_value;
  4   input [7:0] value;
  5   input [7:0] delay;
  6   begin
  7     #(delay) $display("@%g Passed Value %d Delay %d",
  8       $time, value, delay);
  9   end
 10 endtask
 11 
 12 initial begin
 13   fork 
 14      #1  print_value (10,7);
 15      #1  print_value (8,5);
 16      #1  print_value (4,2);
 17   join_none
 18   $display("@%g Came out of fork-join", $time);
 19   // terminate all the theads
 20    #5  disable fork;
 21   $display("@%g All threads are disabled", $time);
 22    #20  $finish;
 23 end
 24 
 25 endmodule

Simulator Output

 @0 Came out of fork-join
 @3 Passed Value   4 Delay   2
 @5 All threads are disabled

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