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Mojo function
pjoin
def pjoin[State: ReduceOp, params: ContextParams, //](mut state: State, mut ctx: Context[params])
Cross-thread join for a single monoid state, tier-appropriately.
Called by the body after rowwise.reduce, once per state. The
cooperative tiers (warp, block) emit a hardware-backed warp/block
reduce; the tiled and serial tiers no-op (one thread per output).
Split-K does a within-block reduce then a cross-block
partials-buffer join, setting ctx._is_last_block so
rowwise.once gates emission.
This is a separate call rather than a parameter to
rowwise.reduce because a mut *states: *States variadic copies
arguments into the pack at the call site, so mutations inside
reduce wouldn't propagate back. Single mut state: State passes
by mut reference cleanly.
Parameters:
- State (
ReduceOp): The monoid type being joined. - params (
ContextParams): The comptime dispatch parameters.
Args:
- state (
State): The body's monoid accumulator. On return, holds the cross-thread-joined value on every thread (cooperative tiers) or its own value (tiled/serial tiers). - ctx (
Context[params]): The dispatch bundle. Mutated for the split-K case sorowwise.onceknows which block is the canonical writer.