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par_sort_pairs: Fix panic when rdst is multi-threaded #151

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Merged
merged 1 commit into from
Oct 10, 2025
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par_sort_pairs: Fix panic when rdst is multi-threaded #151

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20 changes: 18 additions & 2 deletions webgraph/src/utils/par_sort_pairs.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,7 @@ use anyhow::{ensure, Context, Result};
use dsi_bitstream::traits::NE;
use dsi_progress_logger::{concurrent_progress_logger, ProgressLog};
use rayon::prelude::*;
use rayon::Yield;
use rdst::RadixSort;
use thread_local::ThreadLocal;

Expand Down Expand Up @@ -292,7 +293,8 @@ impl<L> ParSortPairs<L> {
|| {
(
pl.clone(),
sorter_thread_states
loop {
if let Ok(state) = sorter_thread_states
.get_or(|| {
RefCell::new(SorterThreadState {
worker_id: worker_id.fetch_add(1, Ordering::Relaxed),
Expand All @@ -302,7 +304,21 @@ impl<L> ParSortPairs<L> {
sorted_pairs: (0..num_partitions).map(|_| Vec::new()).collect(),
})
})
.borrow_mut(),
.try_borrow_mut() {
// usually succeeds in the first attempt
break state;
}
// This thread is already borrowing its state higher in the call stack,
// but rayon is calling us again because of work stealing.
// But we cannot work right now (without allocating a new state, that is)
// so we yield back to rayon so it can resume the task that is already
// running in this thread.
match rayon::yield_now() {
None => panic!("rayon::yield_now() claims we are not running in a thread pool"),
Some(Yield::Idle) => panic!("Thread state is already borrowed, but there are no other tasks running"),
Some(Yield::Executed) => (),
}
}
)
},
|(pl, thread_state), pair| -> Result<_> {
Expand Down