Add option for changing number of threads at runtime

Closes #39

CHANGELOG.md

@@ -2,6 +2,7 @@
  - Minor compression improvement on interlaced images
  - Performance optimizations
  - [SEMVER_MINOR] Move default Options into a Default impl
+ - [SEMVER_MINOR] Add option for setting number of threads ([#39](https://github.com/shssoichiro/oxipng/issues/39))
 
 **Version 0.6.0**
  - Fix issue where output directory would not be created if it did not exist

src/lib.rs

@@ -79,6 +79,8 @@ pub struct Options {
     /// Whether to use heuristics to pick the best filter and compression
     /// Intended for use with `-o 1` from the CLI interface
     pub use_heuristics: bool,
+    /// Number of threads to use, defaults to 1.5x CPU cores, rounded down
+    pub threads: usize,
 }
 
 impl Default for Options {
@@ -96,6 +98,10 @@ impl Default for Options {
             strategies.insert(i);
         }
 
+        // Default to 1 thread on single-core, otherwise use threads = 1.5x CPU cores
+        let num_cpus = num_cpus::get();
+        let thread_count = num_cpus + (num_cpus >> 1);
+
         Options {
             backup: false,
             out_file: PathBuf::new(),
@@ -121,6 +127,7 @@ impl Default for Options {
             idat_recoding: true,
             strip: png::Headers::None,
             use_heuristics: false,
+            threads: thread_count,
         }
     }
 }
@@ -200,9 +207,7 @@ pub fn optimize(filepath: &Path, opts: &Options) -> Result<(), String> {
     let something_changed = perform_reductions(&mut png, &opts);
 
     if opts.idat_recoding || something_changed {
-        // Use 1 thread on single-core, otherwise use threads = 1.5x CPU cores
-        let num_cpus = num_cpus::get();
-        let thread_count = num_cpus + (num_cpus >> 1);
+        let thread_count = opts.threads;
         let pool = Pool::new(thread_count);
         // Go through selected permutations and determine the best
         let best: Arc<Mutex<Option<TrialWithData>>> = Arc::new(Mutex::new(None));

src/main.rs

@@ -172,6 +172,23 @@ fn main() {
                      .help("Strip safely-removable metadata objects")
                      .short("s")
                      .conflicts_with("strip"))
+            .arg(Arg::with_name("threads")
+                     .help("Set number of threads to use - default 1.5x CPU cores")
+                     .long("threads")
+                     .short("t")
+                     .takes_value(true)
+                     .validator(|x| {
+                         match x.parse::<usize>() {
+                             Ok(val) => {
+                                 if val > 0 {
+                                     Ok(())
+                                 } else {
+                                     Err("Thread count must be >= 1".to_owned())
+                                 }
+                             }
+                             Err(_) => Err("Thread count must be >= 1".to_owned()),
+                         }
+                     }))
             .after_help("Optimization levels:
     -o 0		=>	--zc 3 --nz				(0 or 1 trials)
     -o 1		=>	--zc 9					(1 trial, determined heuristically)
@@ -478,6 +495,10 @@ fn parse_opts_into_struct(matches: &ArgMatches, opts: &mut oxipng::Options) -> R
         opts.strip = png::Headers::Safe;
     }
 
+    if let Some(x) = matches.value_of("threads") {
+        opts.threads = x.parse::<usize>().unwrap();
+    }
+
     Ok(())
 }
 

tests/filters.rs

@@ -10,43 +10,15 @@ use std::path::Path;
 use std::path::PathBuf;
 
 fn get_opts(input: &Path) -> oxipng::Options {
+    let mut options = oxipng::Options::default();
+    options.out_file = input.with_extension("out.png").to_owned();
+    options.verbosity = None;
+    options.force = true;
     let mut filter = HashSet::new();
     filter.insert(0);
-    let mut compression = HashSet::new();
-    compression.insert(9);
-    let mut memory = HashSet::new();
-    memory.insert(9);
-    let mut strategies = HashSet::new();
-    for i in 0..4 {
-        strategies.insert(i);
-    }
-
-    oxipng::Options {
-        backup: false,
-        out_file: input.with_extension("out.png").to_owned(),
-        out_dir: None,
-        stdout: false,
-        pretend: false,
-        recursive: false,
-        fix_errors: false,
-        force: true,
-        clobber: true,
-        create: true,
-        preserve_attrs: false,
-        verbosity: None,
-        filter: filter,
-        interlace: None,
-        compression: compression,
-        memory: memory,
-        strategies: strategies,
-        window: 15,
-        bit_depth_reduction: true,
-        color_type_reduction: true,
-        palette_reduction: true,
-        idat_recoding: true,
-        strip: png::Headers::None,
-        use_heuristics: false,
-    }
+    options.filter = filter;
+
+    options
 }
 
 fn test_it_converts(input: &Path,

tests/flags.rs

@@ -10,43 +10,15 @@ use std::path::Path;
 use std::path::PathBuf;
 
 fn get_opts(input: &Path) -> oxipng::Options {
+    let mut options = oxipng::Options::default();
+    options.out_file = input.with_extension("out.png").to_owned();
+    options.verbosity = None;
+    options.force = true;
     let mut filter = HashSet::new();
     filter.insert(0);
-    let mut compression = HashSet::new();
-    compression.insert(9);
-    let mut memory = HashSet::new();
-    memory.insert(9);
-    let mut strategies = HashSet::new();
-    for i in 0..4 {
-        strategies.insert(i);
-    }
-
-    oxipng::Options {
-        backup: false,
-        out_file: input.with_extension("out.png").to_owned(),
-        out_dir: None,
-        stdout: false,
-        pretend: false,
-        recursive: false,
-        fix_errors: false,
-        force: true,
-        clobber: true,
-        create: true,
-        preserve_attrs: false,
-        verbosity: None,
-        filter: filter,
-        interlace: None,
-        compression: compression,
-        memory: memory,
-        strategies: strategies,
-        window: 15,
-        bit_depth_reduction: true,
-        color_type_reduction: true,
-        palette_reduction: true,
-        idat_recoding: true,
-        strip: png::Headers::None,
-        use_heuristics: false,
-    }
+    options.filter = filter;
+
+    options
 }
 
 fn test_it_converts(input: &Path,

tests/interlaced.rs

@@ -10,43 +10,15 @@ use std::path::Path;
 use std::path::PathBuf;
 
 fn get_opts(input: &Path) -> oxipng::Options {
+    let mut options = oxipng::Options::default();
+    options.out_file = input.with_extension("out.png").to_owned();
+    options.verbosity = None;
+    options.force = true;
     let mut filter = HashSet::new();
     filter.insert(0);
-    let mut compression = HashSet::new();
-    compression.insert(9);
-    let mut memory = HashSet::new();
-    memory.insert(9);
-    let mut strategies = HashSet::new();
-    for i in 0..4 {
-        strategies.insert(i);
-    }
-
-    oxipng::Options {
-        backup: false,
-        out_file: input.with_extension("out.png").to_owned(),
-        out_dir: None,
-        stdout: false,
-        pretend: false,
-        recursive: false,
-        fix_errors: false,
-        force: true,
-        clobber: true,
-        create: true,
-        preserve_attrs: false,
-        verbosity: None,
-        filter: filter,
-        interlace: None,
-        compression: compression,
-        memory: memory,
-        strategies: strategies,
-        window: 15,
-        bit_depth_reduction: true,
-        color_type_reduction: true,
-        palette_reduction: true,
-        idat_recoding: true,
-        strip: png::Headers::None,
-        use_heuristics: false,
-    }
+    options.filter = filter;
+
+    options
 }
 
 fn test_it_converts(input: &Path,

tests/reduction.rs

@@ -10,43 +10,15 @@ use std::path::Path;
 use std::path::PathBuf;
 
 fn get_opts(input: &Path) -> oxipng::Options {
+    let mut options = oxipng::Options::default();
+    options.out_file = input.with_extension("out.png").to_owned();
+    options.verbosity = None;
+    options.force = true;
     let mut filter = HashSet::new();
     filter.insert(0);
-    let mut compression = HashSet::new();
-    compression.insert(9);
-    let mut memory = HashSet::new();
-    memory.insert(9);
-    let mut strategies = HashSet::new();
-    for i in 0..4 {
-        strategies.insert(i);
-    }
-
-    oxipng::Options {
-        backup: false,
-        out_file: input.with_extension("out.png").to_owned(),
-        out_dir: None,
-        stdout: false,
-        pretend: false,
-        recursive: false,
-        fix_errors: false,
-        force: true,
-        clobber: true,
-        create: true,
-        preserve_attrs: false,
-        verbosity: None,
-        filter: filter,
-        interlace: None,
-        compression: compression,
-        memory: memory,
-        strategies: strategies,
-        window: 15,
-        bit_depth_reduction: true,
-        color_type_reduction: true,
-        palette_reduction: true,
-        idat_recoding: true,
-        strip: png::Headers::None,
-        use_heuristics: false,
-    }
+    options.filter = filter;
+
+    options
 }
 
 fn test_it_converts(input: &Path,