parallelize hash_to_kmer update

src/lib.rs

@@ -3,7 +3,10 @@ use std::collections::hash_map::IntoIter;
 use std::collections::{HashMap, HashSet};
 use std::fs::File;
 use std::io::{BufReader, BufWriter, Write};
-use std::sync::atomic::{AtomicU64, Ordering};
+use std::sync::{
+    atomic::{AtomicU64, Ordering},
+    Mutex,
+};
 //use std::path::Path;
 
 // External crate imports
@@ -774,9 +777,18 @@ impl KmerCountTable {
     ///
     /// Returns a PyResult with a tuple containing:
     /// * The number of k-mer counts added
-    /// * The number of new keys added to hash_to_kmer (if store_kmers is true)
+    /// * The number of new keys added
     #[pyo3(signature = (other))]
     pub fn add(&mut self, other: &KmerCountTable) -> PyResult<(u64, u64)> {
+        // TODO: Borrow error raised when initialising "&mut self, other: &KmerCountTable"
+        // on same object. Below doesn't get a chance to run.
+        // Check if the other table is the same object as self
+        //if std::ptr::eq(self, other) {
+        //    return Err(PyValueError::new_err(
+        //        "Cannot add KmerCountTable to itself.",
+        //    ));
+        //}
+
         // Check if ksizes match
         if self.ksize != other.ksize {
             return Err(PyValueError::new_err(
@@ -813,21 +825,19 @@ impl KmerCountTable {
         if self.store_kmers {
             if other.store_kmers {
                 // Both tables have store_kmers = true, so we can import
-                let new_kmers: Vec<_> = other
+                let hash_to_kmer_mutex = Mutex::new(self.hash_to_kmer.as_mut().unwrap());
+
+                other
                     .hash_to_kmer
                     .as_ref()
                     .unwrap()
                     .par_iter()
-                    .map(|(&hash, kmer)| (hash, kmer.clone()))
-                    .collect();
-
-                for (hash, kmer) in new_kmers {
-                    self.hash_to_kmer
-                        .as_mut()
-                        .unwrap()
-                        .entry(hash)
-                        .or_insert(kmer);
-                }
+                    .for_each(|(&hash, kmer)| {
+                        let mut hash_to_kmer_lock = hash_to_kmer_mutex.lock().unwrap();
+                        hash_to_kmer_lock
+                            .entry(hash)
+                            .or_insert_with(|| kmer.clone());
+                    });
             } else {
                 // Warning: incoming table doesn't store kmers
                 eprintln!("Warning: Incoming table does not store k-mers, but target table does. K-mer information for new hashes will be missing.");
@@ -843,7 +853,7 @@ impl KmerCountTable {
         println!("Added {} new keys to the table", new_keys);
 
         Ok((total_added, new_keys))
-        }
+    }
 }
 
 #[pyclass]