implement working solution

src/main.rs

@@ -240,37 +240,50 @@ fn main() {
     }
 
     // compute file hash in parallel
-    let magic = files_candidate.lock().unwrap().len() / num_cpus::get();
-    println!("Magic is : {}", magic);
+    let num_cpus = num_cpus::get();
+    let files_candidate_len = files_candidate.lock().unwrap().len();
+    let chunk_size = (files_candidate_len / num_cpus) + 1;
+    let modulus = files_candidate_len % num_cpus;
 
-    for i in 0..num_cpus::get()+1 {
-        let fc = files_candidate.clone();
-        let mut work = fc.lock().unwrap();
-        let end = if (i*magic)+(magic) > work.len() {
-            work.len()
-        } else {
-            (i*magic)+(magic)
-        };
-        // Example from :
-        // https://stackoverflow.com/questions/33818141/how-do-i-pass-disjoint-slices-from-a-vector-to-different-threads
-        // Scoped threads allow the compiler to prove that no threads will outlive
-        // table (which would be bad).
-        crossbeam::scope(|scope| {
+    println!("Calculate {} file(s)", files_candidate_len);
+    println!("Use {} chunk(s) of size {}", modulus, chunk_size);
+    println!("Use {} chunk(s) of size {}", num_cpus - modulus, chunk_size - 1);
+
+    let mut guards = vec![];
+    let fc = files_candidate.clone();
+    let mut work = fc.lock().unwrap();
+
+    // Example from :
+    // https://stackoverflow.com%2Fquestions/33818141/how-do-i-pass-disjoint-slices-from-a-vector-to-different-threads
+    // Scoped threads allow the compiler to prove that no threads will outlive
+    // table (which would be bad).
+    crossbeam::scope(|scope| {
+        let (split_a, split_b) = work.split_at_mut(chunk_size * modulus);
+        let chunk_a = split_a.chunks_mut(chunk_size);
+        let chunk_b = split_b.chunks_mut(chunk_size - 1);
+
+        for (i, slice) in chunk_a.chain(chunk_b).enumerate() {
             // Spawn a thread operating on that subslice.
-            scope.spawn(move ||
-                        for w in &mut work[i*magic .. end] {
-                            println!("[{}] Hashing : {}", i, w);
-                            if let Ok(mut file) = fs::File::open(&w.name) {
-                                w.hash::<Sha256, _>(&mut file);
-                            } else {
-                                panic!("Error opening file (name = {})!", w.name);
-                            }
-                        }
-            );
-        });
+            let guard = scope.spawn(move || {
+                for w in slice {
+                    println!("[{}] Hashing : {}", i, w);
+                    //thread::sleep(std::time::Duration::from_secs(2));
+                    if let Ok(mut file) = fs::File::open(&w.name) {
+                        w.hash::<Sha256, _>(&mut file);
+                    } else {
+                        panic!("Error opening file (name = {})!", w.name);
+                    }
+                }
+            });
+            guards.push(guard);
+        }
+    });
+
+    for guard in guards {
+        guard.join();
     }
 
-    for i in files_candidate.lock().unwrap().iter() {
+    for i in work.iter() {
         println!("{}", i);
     }