pick

pick is the HDB for condition-guarded parallel branches. Unlike a conditional, pick does not select one branch — it is all-match: every pif(cond) block whose condition holds runs, as siblings. And pick does not wait for all branches to complete before exiting — it exits as branches resolve. pickDef provides a default for the case where no condition matched.

#define pick for(auto kathrynBlock = new FlowBlockPick(); kathrynBlock->doPrePostFunction(); kathrynBlock->step())
#define pickDef kathrynBlock->setReqAutoExit();
#define pif(expr) for(auto kathrynBlock = new FlowBlockPickCond(expr); kathrynBlock->doPrePostFunction(); kathrynBlock->step())

From autoSim simAutoTest38, a pick inside a cwhile:

seq{
    cwhile(r1 < 20){
        r1 = r1 + 1;
        pick{
            pif(r1 == 8){
                a <<= 48;
            }
            pif(r1 == 16){
                a <<= 24;
            }
            pickDef
        }
    }
    rend <<= 48;
}

All-match semantics

Each pif branch is joined to the pick’s entry through a node gated by that branch’s own condition (pick.cpp gives every pif sub-block a dependency on the shared joint node, qualified by its condition). So every pif whose condition is true launches — several branches may fire at once. Matched branches run as siblings, in the manner of the pick master block, and the pick exits as they resolve rather than waiting for all of them. If you need strict one-of-N behavior, write mutually exclusive pif conditions yourself — or use a cif/sif chain.

flowchart TD
    ENTER["pick entry (joint node)"] --> P1{"pif condition 1"}
    ENTER --> P2{"pif condition 2"}
    ENTER --> ALLF{"all conditions false?"}
    P1 -->|true| B1["branch 1 runs"]
    P2 -->|true| B2["branch 2 runs<br/>(both may fire at once)"]
    ALLF -->|yes| DEF["pickDef branch runs"]
    B1 --> EXIT["pick exits<br/>(no wait-for-all)"]
    B2 --> EXIT
    DEF --> EXIT

pickDef and setReqAutoExit

pickDef is not a block — it calls setReqAutoExit() on the current pick. That builds an auto-exit node whose condition is the AND of the negations of every pif condition, so it triggers exactly when none of the branches matched, giving the pick a clean exit in the no-match case.

When to use pick

Use pick when zero or more independent conditions may each trigger their own work in the same step, and you do not want the block to stall until every branch finishes. For strictly one-of-N selection where later branches must not fire once an earlier one matches, prefer a cif/sif chain or the structural ztate/zcase selector.