'How can I use foreach and fork together to do something in parallel?
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
Solution 1:[1]
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
begin : foreach_fork
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 $finish
call. To enable raising of the objections in the sequences, I use the seq[j].starting_phase = phase;
construct.
Solution 2:[2]
The issue is each thread of the fork is pointing to the same static variable i
. Each thread needs its own unique copy and this can be achieved with the automatic
keyword.
foreach (env.agt[i])
begin
automatic int var_i = i;
fork
seq.start(env.agt[var_i].sqr);
join_none // non_blocking, allow next operation to start
end
wait fork;// wait for all forked threads in current scope to end
IEEE std 1800-2012 § 6.21 "Scope and lifetime" gives examples of the uses static and automatic. Also check out § 9.3.2 "Parallel blocks", the last example shows demonstrates parallel threads in a for-loop.
Use join_none
to create new threads; § 9.3.2 "Parallel blocks", Table 9-1—"fork-join control options".
Use fork wait
statement to wait for all threads in the current scope to complete; § 9.6.1 "Wait fork statement"
Example:
byte a[4];
initial begin
foreach(a[i]) begin
automatic int j =i;
fork
begin
a[j] = j;
#($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
Solution 3:[3]
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.
Solution 4:[4]
try with
int i = 0
foreach (env.agt)
begin
seq.start(env.agt[i].sqr);
i++;
end
Sources
This article follows the attribution requirements of Stack Overflow and is licensed under CC BY-SA 3.0.
Source: Stack Overflow
Solution | Source |
---|---|
Solution 1 | |
Solution 2 | |
Solution 3 | nguthrie |
Solution 4 | Mauro Midolo |