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use polars_async::primitives::distributor_channel::distributor_channel;
use polars_async::primitives::wait_group::WaitGroup;
use polars_core::prelude::{AnyValue, Column, DataType, FillNullStrategy, Scalar};
use polars_error::PolarsResult;
use polars_utils::IdxSize;
use polars_utils::pl_str::PlSmallStr;
use super::compute_node_prelude::*;
use crate::DEFAULT_DISTRIBUTOR_BUFFER_SIZE;
pub struct ForwardFillNode {
dtype: DataType,
/// Last valid value seen. Equals `AnyValue::Null` i.f.f. no valid value has yet been seen.
last: AnyValue<'static>,
/// Maximum number of nulls to fill in until seeing a valid value.
limit: IdxSize,
/// Amount of nulls that have been filled in since seeing a valid value.
consecutive_nulls: IdxSize,
}
impl ForwardFillNode {
pub fn new(limit: Option<IdxSize>, dtype: DataType) -> Self {
Self {
limit: limit.unwrap_or(IdxSize::MAX),
dtype,
last: AnyValue::Null,
consecutive_nulls: 0,
}
}
}
impl ComputeNode for ForwardFillNode {
fn name(&self) -> &str {
"forward_fill"
}
fn update_state(
&mut self,
recv: &mut [PortState],
send: &mut [PortState],
_state: &StreamingExecutionState,
) -> PolarsResult<()> {
assert!(recv.len() == 1 && send.len() == 1);
recv.swap_with_slice(send);
Ok(())
}
fn spawn<'env, 's>(
&'env mut self,
scope: &'s TaskScope<'s, 'env>,
recv_ports: &mut [Option<RecvPort<'_>>],
send_ports: &mut [Option<SendPort<'_>>],
_state: &'s StreamingExecutionState,
join_handles: &mut Vec<JoinHandle<PolarsResult<()>>>,
) {
assert!(recv_ports.len() == 1 && send_ports.len() == 1);
let mut receiver = recv_ports[0].take().unwrap().serial();
let senders = send_ports[0].take().unwrap().parallel();
let (mut distributor, distr_receivers) =
distributor_channel(senders.len(), *DEFAULT_DISTRIBUTOR_BUFFER_SIZE);
let limit = self.limit;
let last = &mut self.last;
let consecutive_nulls = &mut self.consecutive_nulls;
// Serial receiver thread: determines the last non-null value and consecutive null
// count for each morsel, then distributes (morsel, last, consecutive_nulls) to workers.
join_handles.push(scope.spawn_task(TaskPriority::High, async move {
while let Ok(morsel) = receiver.recv().await {
if morsel.df().height() == 0 {
continue;
}
let column = &morsel.df()[0];
let height = column.len();
let null_count = column.null_count();
let morsel_last = last.clone();
let morsel_consecutive_nulls = *consecutive_nulls;
if null_count == height {
// All null.
*consecutive_nulls += height as IdxSize;
} else if let Some(idx) = column.last_non_null() {
// Some nulls.
*last = column.get(idx).unwrap().into_static();
*consecutive_nulls = (height - 1 - idx) as IdxSize;
} else {
// All valid.
*last = column.get(height - 1).unwrap().into_static();
*consecutive_nulls = 0;
}
*consecutive_nulls = IdxSize::min(*consecutive_nulls, limit);
if distributor
.send((morsel, morsel_last, morsel_consecutive_nulls))
.await
.is_err()
{
break;
}
}
Ok(())
}));
// Parallel worker threads: perform the actual fill / fast paths.
for (mut send, mut recv) in senders.into_iter().zip(distr_receivers) {
let dtype = self.dtype.clone();
join_handles.push(scope.spawn_task(TaskPriority::High, async move {
let wait_group = WaitGroup::default();
while let Ok((morsel, last, consecutive_nulls)) = recv.recv().await {
let mut morsel = morsel.try_map(|df| {
let column = &df[0];
let height = column.len();
let null_count = column.null_count();
let name = column.name().clone();
// Remaining fill limit for the start morsel.
let leading_limit = limit.saturating_sub(consecutive_nulls) as usize;
let out = if null_count == 0
|| (null_count == height && (last.is_null() || leading_limit == 0))
{
// Fast path: output = input.
column.clone()
} else if null_count == height {
// Fast path: input is all nulls.
let mut out = Column::new_scalar(
name,
Scalar::new(dtype.clone(), last),
height.min(leading_limit),
);
if leading_limit < height {
out.append_owned(Column::full_null(
PlSmallStr::EMPTY,
height - leading_limit,
&dtype,
))?;
}
out
} else if last.is_null()
|| leading_limit == 0
|| unsafe { !column.get_unchecked(0).is_null() }
{
// Faster path: result is equal to performing a normal `forward_fill` on
// the column.
column.fill_null(FillNullStrategy::Forward(Some(limit as IdxSize)))?
} else {
// Output = concat[
// repeat_n(last, min(leading, leading_limit)),
// repeat_n(NULL, leading - min(leading, leading_limit)),
// forward_fill(column[leading..]),
// ]
// @Performance. If you want to make this fully optimal (although it is
// likely overkill), you can implement a kernel of `forward_fill` with a
// `init` value. This would remove the need for these appends.
let leading = column.first_non_null().unwrap();
let fill_last_count = leading_limit.min(leading);
let mut out = Column::new_scalar(
name.clone(),
Scalar::new(dtype.clone(), last),
fill_last_count,
);
if fill_last_count < leading {
out.append_owned(Column::full_null(
name,
leading - fill_last_count,
&dtype,
))?;
}
let mut tail = column.slice(leading as i64, height - leading);
if tail.has_nulls() {
tail = tail
.fill_null(FillNullStrategy::Forward(Some(limit as IdxSize)))?;
}
out.append_owned(tail)?;
out
};
PolarsResult::Ok(out.into_frame())
})?;
morsel.set_consume_token(wait_group.token());
if send.send(morsel).await.is_err() {
break;
}
wait_group.wait().await;
}
Ok(())
}));
}
}
}