feat: limit thread number to 1 when HDD is detected

On HDD, multi-threaded du won't provide any performance benefit over
the single-threaded one. Therefore, when HDD is detected on one of
the files, limit the thread number to 1.

This PR fixes issue KSXGitHub#257.

Cargo.toml

@@ -65,6 +65,7 @@ clap_complete = { version = "^4.5.36", optional = true }
 clap-utilities = { version = "^0.2.0", optional = true }
 serde = { version = "^1.0.214", optional = true }
 serde_json = { version = "^1.0.132", optional = true }
+sysinfo = "0.32.0"
 
 [dev-dependencies]
 build-fs-tree = "^0.7.1"

src/app/sub.rs

@@ -12,7 +12,14 @@ use crate::{
     visualizer::{BarAlignment, ColumnWidthDistribution, Direction, Visualizer},
 };
 use serde::Serialize;
-use std::{io::stdout, iter::once, num::NonZeroUsize, path::PathBuf};
+use std::{
+    fs,
+    io::stdout,
+    iter::once,
+    num::NonZeroUsize,
+    path::{Path, PathBuf},
+};
+use sysinfo::{DiskKind, Disks};
 
 /// The sub program of the main application.
 pub struct Sub<Size, SizeGetter, Report>
@@ -69,6 +76,29 @@ where
             no_sort,
         } = self;
 
+        // If one of the files is on HDD, set thread number to 1
+        let disks = Disks::new_with_refreshed_list();
+
+        if files
+            .iter()
+            .filter_map(|file| fs::canonicalize(&file).ok())
+            .any(|path| {
+                let mount_points: Vec<_> = disks.iter().map(|disk| disk.mount_point()).collect();
+                if let Some(mount_point) = find_mountpoint(&path, &mount_points) {
+                    disks.iter().any(|disk| {
+                        matches!(disk.kind(), DiskKind::HDD) && disk.mount_point() == mount_point
+                    })
+                } else {
+                    false
+                }
+            })
+        {
+            rayon::ThreadPoolBuilder::new()
+                .num_threads(1)
+                .build_global()
+                .unwrap();
+        }
+
         let mut iter = files
             .into_iter()
             .map(|root| -> DataTree<OsStringDisplay, Size> {
@@ -149,3 +179,13 @@ where
         Ok(())
     }
 }
+
+pub fn find_mountpoint(path: &Path, mount_points: &[&Path]) -> Option<PathBuf> {
+    let path = path.to_string_lossy();
+
+    mount_points
+        .iter()
+        .filter(|mnt| path.starts_with(&*mnt.to_string_lossy()))
+        .max_by_key(|mnt| mnt.to_string_lossy().len())
+        .map(|mnt| mnt.to_path_buf())
+}

tests/find_mountpoint.rs

@@ -0,0 +1,26 @@
+use parallel_disk_usage::app::sub::find_mountpoint;
+use std::path::Path;
+
+#[test]
+fn test_mountpoint() {
+    let mount_points = &[
+        Path::new("/"),
+        Path::new("/home"),
+        Path::new("/mnt/data"),
+        Path::new("/mnt/data/repo"),
+        Path::new("/mnt/repo"),
+    ];
+
+    for (path, mount_point) in &[
+        ("/etc/fstab", "/"),
+        ("/home/user", "/home"),
+        ("/mnt/data/repo/test", "/mnt/data/repo"),
+        ("/mnt/data/test/test", "/mnt/data/"),
+        ("/mnt/repo/test/test", "/mnt/repo/"),
+    ] {
+        assert_eq!(
+            find_mountpoint(Path::new(path), mount_points).unwrap(),
+            Path::new(mount_point)
+        );
+    }
+}