How can I use foreach and fork together to do something in parallel?

How can I use foreach and fork together to do something in parallel?

systemverilog fork join inside for loop
nested fork join systemverilog
verilog for loop fork
fork for systemverilog
for loop inside fork join_none
if statement inside fork
fork for loop

This question is not UVM specific but the example that I am working on is UVM related. I have an array of agents in my UVM environment and I would like to launch a sequence on all of them in parallel.

If I do the below:

foreach (env.agt[i])
  begin
    seq.start(env.agt[i].sqr);
  end

, the sequence seq first executes on env.agt[0].sqr. Once that gets over, it then executes on env.agt[1].sqr and so on.

I want to implement a foreach-fork statement so that seq is executed in parallel on all agt[i] sequencers.

No matter how I order the fork-join and foreach, I am not able to achieve that. Can you please help me get that parallel sequence launching behavior?

Thanks.

Update to clarify the problem I am trying to solve: The outcome of the below code constructs is the exact same as above without the fork-join.

foreach (env.agt[i])
  fork
    seq.start(env.agt[i].sqr);
  join

fork
  foreach (env.agt[i])
    seq.start(env.agt[i].sqr);
  join

// As per example in § 9.3.2 of IEEE SystemVerilog 2012 standard
for (int i=0; i<`CONST; ++i)
  begin
    fork
      automatic int var_i = i;
      seq.start(env.agt[var_i].sqr);
    join
  end


The issue is each thread of the fork is pointing to the same static variable i. Each thread needs its own unique copy and this can be achieved with the automatic keyword.

foreach (env.agt[i])
  begin
    automatic int var_i = i;
    fork
      seq.start(env.agt[var_i].sqr);
    join_none // non_blocking, allow next operation to start
  end
wait fork;// wait for all forked threads in current scope to end

IEEE std 1800-2012 § 6.21 "Scope and lifetime" gives examples of the uses static and automatic. Also check out § 9.3.2 "Parallel blocks", the last example shows demonstrates parallel threads in a for-loop.

Use join_none to create new threads; § 9.3.2 "Parallel blocks", Table 9-1—"fork-join control options".

Use fork wait statement to wait for all threads in the current scope to complete; § 9.6.1 "Wait fork statement"


Example:

byte a[4];
initial begin
    foreach(a[i]) begin
        automatic int j =i;
        fork
            begin
                a[j] = j;
                #($urandom_range(3,1));
                $display("%t :: a[i:%0d]:%h a[j:%0d]:%h",
                        $time, i,a[i], j,a[j]);
            end
        join_none // non-blocking thread
    end
    wait fork; // wait for all forked threads in current scope to end
    $finish;
end

Outputs:

2 :: a[i:4]:00 a[j:3]:03 2 :: a[i:4]:00 a[j:0]:00 3 :: a[i:4]:00 a[j:2]:02 3 :: a[i:4]:00 a[j:1]:01

[PDF] Getting Started with doParallel and foreach, parallel backend to use, otherwise foreach will execute tasks the parallel package in multicore mode starts its workers using fork without doing a Now that we've gotten our feet wet, let's do something a bit less trivial. A Parallel.ForEach loop works like a Parallel.For loop. The loop partitions the source collection and schedules the work on multiple threads based on the system environment. The loop partitions the source collection and schedules the work on multiple threads based on the system environment.


I think that the more "UVM" way to approach this is with a virtual sequence. Assuming you already have a virtual sequencer which instantiates an array of agent sequencers then the body your virtual sequence would look something like this:

fork
  begin: isolation_thread
    foreach(p_sequencer.agent_sqr[i])
      automatic int j = i;
      fork
        begin
          `uvm_do_on(seq, p_sequencer.agent_sqr[j]);
        end
      join_none
    end
    wait fork;
  end: isolation_thread
join

This has worked for me in the past.

Professional Alfresco: Practical Solutions for Enterprise Content , A ForEachFork action supports this functionality, whose behavior is similar to a for loop the subtokens back together just as they would for a standard fork node. demonstrates how you might use the ForEachFork action as part of a parallel  Properties of the loop body. Keep in mind that a child process is forked every time while or foreach calls the provided sub. For use of Parallel::Loops to make sense, each invocation needs to actually do some serious work for the performance gain of parallel execution to outweigh the overhead of forking and communicating between the processes.


Greg's solution below helped me derive the solution to my UVM based problem. Here is my solution:

The below fork-join block resides in the main_phase task in a test case class. The wait fork; statement waits for all the fork statements in its scope (= the foreach_fork begin-end block) to finish before proceeding further. An important thing to note is that the wrapping fork-join around the begin-end was required for setting the scope of wait fork; to the foreach_fork block.

fork 
  foreach_fork : begin
    seq_class seq [`CONST];
    foreach(env.agt[i])
      begin
        int j = i;
        seq[j] = seq_class::type_id::create
                  (.name($sformatf("seq_%0d", j)), .contxt(get_full_name()));
        fork
          begin
            seq[j].start(env.agt[j].sqr);
          end
        join_none // non-blocking thread
      end
    wait fork;
  end : foreach_fork
join

Alternative solution that makes use of the in-sequence objection to delay the sim end.

begin
  seq_class seq [`CONST];
  foreach(env.agt[i])
    begin
      int j = i;
      seq[j] = seq_class::type_id::create
                (.name($sformatf("seq_%0d", j)), .contxt(get_full_name()));
      fork
        begin
          seq[j].starting_phase = phase;
          seq[j].start(env.agt[j].sqr);
        end
      join_none // non-blocking thread
    end
end

I realized that I also needed to create a new sequence object for each seq I wanted to run in parallel.

Thanks to Dave for making the point that the properties in System Verilog classes are automatic by default.

Note for the alternative solution: As I didn't use wait fork; I use the UVM objections raised in the sequence itself to do the job of holding off the simulation $finish call. To enable raising of the objections in the sequences, I use the seq[j].starting_phase = phase; construct.

A guide to parallelism in R – Florian Privé – R(cpp) enthusiast, Basics of foreach You can install R package {foreach} with register a parallel backend using one of the packages that begin with do (such as doParallel , doMC , doMPI and more). cl <- parallel::makeForkCluster(2) doParallel::​registerDoParallel(cl) foreach returns something (here a two-level list). You can enclose a Parallel script block in a ForEach -Parallel script block. The target computers in a workflow, such as those specified by the PSComputerName workflow common parameter, are always processed in parallel. You do not need to specify the ForEach -Parallel keyword for this purpose. EXAMPLES. The following workflow contains a ForEach -Parallel statement that processes the disks that the Get-Disk activity gets.


try with

int i = 0
foreach (env.agt)
  begin
    seq.start(env.agt[i].sqr);
    i++;
end

Parallel::Loops, makeForkCluster creates a cluster by forking and therefore is not available for Windows. The parLapply() function is used for doing the calculation. It provides combined feature that converts a list into a matrix. To implement single-​node parallelism by using the foreach package, it is necessary to use parallel backend,  R - parallel computing in 5 minutes (with foreach and doParallel) Parallel computing is easy to use in R thanks to packages like doParallel. However, before we decide to parallelize our code, still we should remember that there is a trade-off between simplicity and performance. So if your script runs a few seconds,


Data Analytics using R, In reality, it operates very differently from fork. We will continue to discuss and expand on these issues throughout Chapter 6 and in Appendix B. Listing 6-7. Now that we have registered a parallel backend, we can use the foreach package  needed to execute foreach loops in parallel. The foreach package must be used in conjunction with a package such as doParallel in order to execute code in parallel. The user must register a parallel backend to use, otherwise foreach will execute tasks sequentially, even when the %dopar% operator is used.1


Automated Trading with R: Quantitative Research and Platform , This may include parallel processing in case of fork and join nodes. Story Action Node 1 B C [end] [each] D A Foreach story pattern Foreach block Figure 4. In the following, we will briefly explain the parallelization capabilities of the newly  Because fork returns 0 in the child, the child's pid in the parent, and -1 if it fails. Killing the parent does not cause zombies. When the parent dies, the child is immediately inherited by init which will immediately remove the child from the process table when it terminates preventing it from persisting as a zombie.


Proceedings of the Fall 2010 Future SOC Lab Day, I think this can be done using forks, but I'm not sure how to return the data from $pfm = new Parallel::ForkManager( $threads ); FOREACH: foreach my $thing(​keys %{$things_hr}) { my $pid = $pfm->start and next; #do stuff push in my example, puts all children's data together in a hash keyed on child pid  2 Answers 2. If you want to wait for all of the processes fork'ed by the fork-jone_none to complete, you put a wait fork; statement after the for loop. The wait fork statements waits for all child processes of the current thread to complete.