Add CLI option for the number of threads to spawn

src/main.rs

@@ -23,6 +23,13 @@ fn main() {
                 .help("Depth to show")
                 .takes_value(true),
         )
+        .arg(
+            Arg::with_name("threads")
+                .short("t")
+                .long("threads")
+                .help("Number of threads to spawn simultaneously")
+                .takes_value(true),
+        )
         .arg(
             Arg::with_name("number_of_lines")
                 .short("n")
@@ -67,19 +74,20 @@ fn main() {
         }
     };
 
-    let depth = {
-        if options.is_present("depth") {
-            match value_t!(options.value_of("depth"), u64) {
-                Ok(v) => Some(v + 1),
-                Err(_) => {
-                    eprintln!("Ignoring bad value for depth");
-                    None
-                }
-            }
-        } else {
-            None
-        }
-    };
+    let threads = options.value_of("threads").and_then(|threads| {
+        threads
+            .parse::<usize>()
+            .map_err(|_| eprintln!("Ignoring bad value for threads: {:?}", threads))
+            .ok()
+    });
+
+    let depth = options.value_of("depth").and_then(|depth| {
+        depth
+            .parse::<u64>()
+            .map(|v| v + 1)
+            .map_err(|_| eprintln!("Ignoring bad value for depth"))
+            .ok()
+    });
     if options.is_present("depth") && number_of_lines != DEFAULT_NUMBER_OF_LINES {
         eprintln!("Use either -n or -d. Not both");
         return;
@@ -89,7 +97,7 @@ fn main() {
     let use_full_path = options.is_present("display_full_paths");
 
     let simplified_dirs = simplify_dir_names(target_dirs);
-    let (permissions, nodes) = get_dir_tree(&simplified_dirs, use_apparent_size);
+    let (permissions, nodes) = get_dir_tree(&simplified_dirs, use_apparent_size, threads);
     let sorted_data = sort(nodes);
     let biggest_ones = {
         match depth {

src/utils/mod.rs

@@ -44,13 +44,21 @@ pub fn simplify_dir_names(filenames: Vec<&str>) -> HashSet<String> {
 pub fn get_dir_tree(
     top_level_names: &HashSet<String>,
     apparent_size: bool,
+    threads: Option<usize>,
 ) -> (bool, HashMap<String, u64>) {
     let mut permissions = 0;
     let mut inodes: HashSet<(u64, u64)> = HashSet::new();
     let mut data: HashMap<String, u64> = HashMap::new();
 
     for b in top_level_names.iter() {
-        examine_dir(&b, apparent_size, &mut inodes, &mut data, &mut permissions);
+        examine_dir(
+            &b,
+            apparent_size,
+            &mut inodes,
+            &mut data,
+            &mut permissions,
+            threads,
+        );
     }
     (permissions == 0, data)
 }
@@ -76,11 +84,15 @@ fn examine_dir(
     inodes: &mut HashSet<(u64, u64)>,
     data: &mut HashMap<String, u64>,
     file_count_no_permission: &mut u64,
+    cpus: Option<usize>,
 ) {
-    for entry in WalkDir::new(top_dir)
+    let mut iter = WalkDir::new(top_dir)
         .preload_metadata(true)
-        .skip_hidden(false)
-    {
+        .skip_hidden(false);
+    if let Some(cpus) = cpus {
+        iter = iter.num_threads(cpus);
+    }
+    for entry in iter {
         if let Ok(e) = entry {
             let maybe_size_and_inode = get_metadata(&e, apparent_size);