src/obikmer/src/cli.rs

@@ -1,5 +1,6 @@
 use std::io;
 use std::path::PathBuf;
+use std::sync::{Arc, Condvar, Mutex};
 
 use clap::Args;
 use obikrope::Rope;
@@ -43,7 +44,7 @@ pub struct CommonArgs {
     )]
     pub threads: usize,
 
-    /// Maximum number of input files open simultaneously during scatter
+    /// Maximum number of input files open simultaneously
     #[arg(long, default_value_t = 20)]
     pub max_open_files: usize,
 }
@@ -61,10 +62,54 @@ impl CommonArgs {
     }
 }
 
+// ── Open-file throttling ──────────────────────────────────────────────────────
+
+struct FileSlots {
+    count:   Mutex<usize>,
+    condvar: Condvar,
+    max:     usize,
+}
+
+impl FileSlots {
+    fn new(max: usize) -> Self {
+        Self { count: Mutex::new(0), condvar: Condvar::new(), max }
+    }
+
+    fn acquire(&self) {
+        let mut count = self.count.lock().unwrap();
+        while *count >= self.max {
+            count = self.condvar.wait(count).unwrap();
+        }
+        *count += 1;
+    }
+
+    fn release(&self) {
+        let mut count = self.count.lock().unwrap();
+        *count -= 1;
+        self.condvar.notify_one();
+    }
+}
+
+struct SlotsGuard(Arc<FileSlots>);
+
+impl Drop for SlotsGuard {
+    fn drop(&mut self) {
+        self.0.release();
+    }
+}
+
 // ── Pipeline data carrier ─────────────────────────────────────────────────────
 
+/// A path bundled with an opaque guard token.
+/// The guard is acquired in the source thread and dropped by the flat worker
+/// once the file is fully read, releasing the open-file slot.
+pub struct PathWithSlot {
+    pub path:   PathBuf,
+    pub _guard: Box<dyn Send + 'static>,
+}
+
 pub enum PipelineData {
-    Path(PathBuf),
+    Path(PathWithSlot),
     RawChunk(Rope),
     NormChunk(Rope),
     Batch(Vec<RoutableSuperKmer>),
@@ -75,6 +120,23 @@ pub enum PipelineData {
 unsafe impl Send for PipelineData {}
 unsafe impl Sync for PipelineData {}
 
+/// Wrap a path iterator so that at most `max_open` files are open simultaneously.
+/// Acquisition happens in the caller's thread (the pipeline source thread),
+/// never inside a worker, preventing deadlocks.
+pub fn throttle_paths(
+    source: impl Iterator<Item = PathBuf> + Send + 'static,
+    max_open: usize,
+) -> impl Iterator<Item = PathWithSlot> + Send + 'static {
+    let slots = Arc::new(FileSlots::new(max_open));
+    source.map(move |path| {
+        slots.acquire();
+        PathWithSlot {
+            path,
+            _guard: Box::new(SlotsGuard(Arc::clone(&slots))),
+        }
+    })
+}
+
 // ── I/O plumbing ──────────────────────────────────────────────────────────────
 
 pub fn open_chunks(path: PathBuf) -> io::Result<impl Iterator<Item = Rope>> {

src/obikmer/src/cmd/superkmer.rs

@@ -1,11 +1,10 @@
 use std::io::{self, BufWriter, Write};
-use std::path::PathBuf;
 
 use clap::Args;
 use obifastwrite::write_scatter;
 use obikseq::{RoutableSuperKmer, set_k, set_m};
 
-use crate::cli::{CommonArgs, PipelineData, open_chunks, partitions_to_bits};
+use crate::cli::{CommonArgs, PipelineData, PathWithSlot, open_chunks, partitions_to_bits, throttle_paths};
 
 #[derive(Args)]
 pub struct SuperkmerArgs {
@@ -40,17 +39,18 @@ pub fn run(args: SuperkmerArgs) {
     let level_max = args.common.level_max;
     let partition_bits = partitions_to_bits(args.common.partitions);
     let n_workers = args.common.threads.max(1);
+    let max_open = args.common.max_open_files.max(1);
 
     set_k(k);
     set_m(m);
 
-    let path_source = args.common.seqfile_paths();
+    let path_source = throttle_paths(args.common.seqfile_paths(), max_open);
 
     let pipe = obipipeline::make_pipe! {
-        PipelineData : PathBuf => Vec<RoutableSuperKmer>,
+        PipelineData : PathWithSlot => Vec<RoutableSuperKmer>,
-        ||? { |path| open_chunks(path) }                                               : Path     => RawChunk,
+        ||? { |pw: PathWithSlot| open_chunks(pw.path) }                                : Path     => RawChunk,
         |?  { move |rope| obiread::normalize_sequence_chunk(rope, k) }                 : RawChunk => NormChunk,
-        |   { move |rope| obiskbuilder::build_superkmers(rope, k, level_max, theta) }: NormChunk => Batch,
+        |   { move |rope| obiskbuilder::build_superkmers(rope, k, level_max, theta) }  : NormChunk => Batch,
     };
 
     let mut out = BufWriter::new(io::stdout());

src/obikmer/src/steps/scatter.rs

@@ -1,52 +1,30 @@
 use std::path::PathBuf;
-use std::sync::{Arc, Condvar, Mutex};
 use std::time::{Duration, Instant};
 
 use indicatif::{ProgressBar, ProgressStyle};
 use obikpartitionner::KmerPartition;
+use obikrope::Rope;
 use obisys::{Reporter, Stage};
 use tracing::info;
 
-use crate::cli::{PipelineData, open_chunks};
+use crate::cli::{PipelineData, PathWithSlot, open_chunks, throttle_paths};
 
-// ── Counting semaphore ────────────────────────────────────────────────────────
+// ── Iterator that keeps the slot guard alive until the file is exhausted ──────
 
-struct Semaphore {
-    state: Mutex<usize>,
-    cvar:  Condvar,
-}
-
-impl Semaphore {
-    fn new(n: usize) -> Arc<Self> {
-        Arc::new(Self { state: Mutex::new(n), cvar: Condvar::new() })
-    }
-    fn acquire(self: &Arc<Self>) {
-        let mut n = self.state.lock().unwrap();
-        while *n == 0 { n = self.cvar.wait(n).unwrap(); }
-        *n -= 1;
-    }
-    fn release(self: &Arc<Self>) {
-        *self.state.lock().unwrap() += 1;
-        self.cvar.notify_one();
-    }
-}
-
-struct SemGuard(Arc<Semaphore>);
-impl Drop for SemGuard {
-    fn drop(&mut self) { self.0.release(); }
-}
-
-/// Iterator wrapper that holds a semaphore permit for its lifetime.
-/// The permit is released when the iterator is exhausted or dropped.
 struct GuardedIter<I> {
     inner:  I,
-    _guard: SemGuard,
+    _guard: Box<dyn Send + 'static>,
 }
-impl<I: Iterator> Iterator for GuardedIter<I> {
+
-    type Item = I::Item;
+impl<I: Iterator<Item = Rope>> Iterator for GuardedIter<I> {
-    fn next(&mut self) -> Option<Self::Item> { self.inner.next() }
+    type Item = Rope;
+    fn next(&mut self) -> Option<Rope> {
+        self.inner.next()
+    }
 }
 
+// ── scatter ───────────────────────────────────────────────────────────────────
+
 /// Run scatter: normalise → build superkmers → route to partition → close.
 /// Reports the "scatter" stage to `rep`.
 pub fn scatter(
@@ -61,18 +39,20 @@ pub fn scatter(
 ) {
     use obikseq::RoutableSuperKmer;
 
-    let sem = Semaphore::new(max_open);
+    // Throttle in the source thread — never in a worker — to prevent deadlock.
+    let throttled = throttle_paths(path_source, max_open);
 
     let t = Stage::start("scatter");
     let pipe = obipipeline::make_pipe! {
-        PipelineData : PathBuf => Vec<RoutableSuperKmer>,
+        PipelineData : PathWithSlot => Vec<RoutableSuperKmer>,
-        ||? { move |path: PathBuf| {
+        ||? { move |pw: PathWithSlot| {
-            sem.acquire();
+            let PathWithSlot { path, _guard } = pw;
             info!("indexing: {}", path.display());
-            open_chunks(path).map(|iter| GuardedIter { inner: iter, _guard: SemGuard(Arc::clone(&sem)) })
+            // _guard travels into GuardedIter; released when all chunks are read
+            open_chunks(path).map(|iter| GuardedIter { inner: iter, _guard })
         }} : Path => RawChunk,
         |?  { move |rope| obiread::normalize_sequence_chunk(rope, k) }                 : RawChunk => NormChunk,
-        |   { move |rope| obiskbuilder::build_superkmers(rope, k, level_max, theta) }: NormChunk => Batch,
+        |   { move |rope| obiskbuilder::build_superkmers(rope, k, level_max, theta) }  : NormChunk => Batch,
     };
 
     let pb = ProgressBar::new_spinner();
@@ -89,7 +69,7 @@ pub fn scatter(
     let mut last_bases: u64 = 0;
     const ALPHA: f64 = 0.15;
 
-    for batch in pipe.apply(path_source, n_workers, 1) {
+    for batch in pipe.apply(throttled, n_workers, 1) {
         total_bases += batch.iter().map(|sk| sk.seql() as u64).sum::<u64>();
         let now = Instant::now();
         let dt = now.duration_since(last_t).as_secs_f64();
@@ -115,4 +95,3 @@ pub fn scatter(
     kp.close().expect("close error");
     rep.push(t.stop());
 }
-