Vera supports features to help model parallel, independent activities. We will be covering following features of Vera language.

• fork - join
• wait_var()
• event methods
• semaphores
• region
• mailboxes
• timeouts

fork join is basic construct in Vera for executing code in parallel. THis is same as fork and join in Verilog with more advance control.

Syntax : fork-join

fork
{
  statement1;
}
{
  statement2;
}
  ...
{
  statementN;
}
join [all | any | none]

Below Table shows the details of all join

  1 program fork_join {
  2   integer thread1 = 1;
  3   integer thread2 = 2;
  4   integer thread3 = 3;
  5   printf("----------JOIN ALL---------\n");
  6   fork
  7     {
  8       delay(400) ;
  9       printf("[%0d] thread=%0d\n", get_time(LO),thread1);
 10     }
 11     {
 12       delay(200) ;
 13       printf("[%0d] thread=%0d\n", get_time(LO), thread2);
 14     }
 15     {
 16       delay(100) ;
 17       printf("[%0d] thread=%0d\n", get_time(LO), thread3);
 18     }
 19   join all
 20   printf("[%0d] After join all\n", get_time(LO) );
 21   printf("----------JOIN ANY---------\n");
 22   fork
 23     {
 24       delay(400) ;
 25       printf("[%0d] thread=%0d\n", get_time(LO),thread1);
 26     }
 27     {
 28       delay(200) ;
 29       printf("[%0d] thread=%0d\n", get_time(LO), thread2);
 30     }
 31     {
 32       delay(100) ;
 33       printf("[%0d] thread=%0d\n", get_time(LO), thread3);
 34     }
 35   join any
 36   printf("[%0d] After join any\n", get_time(LO) );
 37   delay (400);
 38   printf("----------JOIN NONE---------\n");
 39   fork
 40     {
 41       delay(400) ;
 42       printf("[%0d] thread=%0d\n", get_time(LO),thread1);
 43     }
 44     {
 45       delay(200) ;
 46       printf("[%0d] thread=%0d\n", get_time(LO), thread2);
 47     }
 48     {
 49       delay(100) ;
 50       printf("[%0d] thread=%0d\n", get_time(LO), thread3);
 51     }
 52   join none
 53   printf("[%0d] After join none\n", get_time(LO) );
 54   delay (400);
 55   printf("[%0d] End of program\n", get_time(LO) ) ;
 56 }

 ----------JOIN ALL---------
 [100] thread=3
 [200] thread=2
 [400] thread=1
 [400] After join all
 ----------JOIN ANY---------
 [500] thread=3
 [500] After join any
 [600] thread=2
 [800] thread=1
 ----------JOIN NONE---------
 [900] After join none
 [1000] thread=3
 [1100] thread=2
 [1300] End of program

By default, all child processes have access to the parent´s variables. However, if multiple processes independently use the same variable, races can occur. To avoid races within fork/join blocks, shadow variables should be used.

• A variable cannot be declared as a shadow variable in a task or function's formal argument list.
• Shadow variables cannot be declared in a global context.

  1 program shadow_variable {
  2   spawn_process() ;
  3   delay(100) ;
  4   spawn_process_with_shawdow();
  5   delay(100) ;
  6 }
  7 
  8 task print(integer i) {
  9   printf("   n = %0d\n", i);
 10 }
 11 
 12 task spawn_process () {
 13   integer n;
 14   printf("In spawn_process\n");
 15   for(n=0; n<3 ; n++) {
 16     fork
 17       print(n) ;
 18     join none
 19   }
 20 }
 21 
 22 task spawn_process_with_shawdow () {
 23   shadow integer n;
 24   printf("In spawn_process_with_shadow_variable\n");
 25   for(n=0; n<3 ; n++) {
 26     fork
 27       print(n) ;
 28     join none
 29   }
 30 }

 In spawn_process
    n = 3
    n = 3
    n = 3
 In spawn_process_with_shadow_variable
    n = 0
    n = 1
    n = 2

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Deepak Kumar Tala - All rights reserved

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