Avoid memory leaks

This commit replaces the `threadpool` crate with a handcrafted
solution based on scoped threads. This leaves `valgrind` much
happier than before. We also lose some dependency baggage.

CHANGELOG.md

@@ -5,6 +5,9 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
+- Replace dependency on threadpool crate with a custom solution built on the
+  standard library only, and only using scoped threads
+  -> fixes memory leaks observed when running under valgrind
 
 ## [0.7.3] - 2024-05-10
 - Default to single-threaded tests for WebAssembly (thanks @alexcrichton) in [#41](https://github.com/LukasKalbertodt/libtest-mimic/pull/41)

Cargo.toml

@@ -20,7 +20,6 @@ exclude = [".github"]
 
 [dependencies]
 clap = { version = "4.0.8", features = ["derive"] }
-threadpool = "1.8.1"
 escape8259 = "0.5.2"
 anstream = "0.6.14"
 anstyle = "1.0.7"

src/lib.rs

@@ -71,13 +71,19 @@
 
 #![forbid(unsafe_code)]
 
-use std::{borrow::Cow, fmt, process::{self, ExitCode}, sync::mpsc, time::Instant};
+use std::{
+    borrow::Cow,
+    fmt,
+    process::{self, ExitCode},
+    sync::{mpsc, Mutex},
+    thread,
+    time::Instant,
+};
 
 mod args;
 mod printer;
 
 use printer::Printer;
-use threadpool::ThreadPool;
 
 pub use crate::args::{Arguments, ColorSetting, FormatSetting};
 
@@ -481,7 +487,14 @@ pub fn run(args: &Arguments, mut tests: Vec<Trial>) -> Conclusion {
 
     // Execute all tests.
     let test_mode = !args.bench;
-    if platform_defaults_to_one_thread() || args.test_threads == Some(1) {
+
+    let num_threads = platform_defaults_to_one_thread()
+        .then_some(1)
+        .or(args.test_threads)
+        .or_else(|| std::thread::available_parallelism().ok().map(Into::into))
+        .unwrap_or(1);
+
+    if num_threads == 1 {
         // Run test sequentially in main thread
         for test in tests {
             // Print `test foo    ...`, run the test, then print the outcome in
@@ -496,35 +509,45 @@ pub fn run(args: &Arguments, mut tests: Vec<Trial>) -> Conclusion {
         }
     } else {
         // Run test in thread pool.
-        let pool = match args.test_threads {
-            Some(num_threads) => ThreadPool::new(num_threads),
-            None => ThreadPool::default()
-        };
         let (sender, receiver) = mpsc::channel();
 
         let num_tests = tests.len();
-        for test in tests {
-            if args.is_ignored(&test) {
-                sender.send((Outcome::Ignored, test.info)).unwrap();
-            } else {
-                let sender = sender.clone();
-                pool.execute(move || {
-                    // It's fine to ignore the result of sending. If the
-                    // receiver has hung up, everything will wind down soon
-                    // anyway.
-                    let outcome = run_single(test.runner, test_mode);
-                    let _ = sender.send((outcome, test.info));
+        // TODO: this should use a mpmc channel, once that's stabilized in std.
+        let iter = Mutex::new(tests.into_iter());
+        thread::scope(|scope| {
+            // Start worker threads
+            for _ in 0..num_threads {
+                scope.spawn(|| {
+                    // Get next test to process from the iterator. We have the
+                    // extra `let` binding as otherwise, the mutex would be
+                    // locked for the whole `if` body.
+                    let next_trial = iter.lock().unwrap().next();
+                    if let Some(trial) = next_trial {
+                        let payload = if args.is_ignored(&trial) {
+                            (Outcome::Ignored, trial.info)
+                        } else {
+                            let outcome = run_single(trial.runner, test_mode);
+                            (outcome, trial.info)
+                        };
+
+                        // It's fine to ignore the result of sending. If the
+                        // receiver has hung up, everything will wind down soon
+                        // anyway.
+                        let _ = sender.send(payload);
+                    }
                 });
             }
-        }
 
-        for (outcome, test_info) in receiver.iter().take(num_tests) {
-            // In multithreaded mode, we do only print the start of the line
-            // after the test ran, as otherwise it would lead to terribly
-            // interleaved output.
-            printer.print_test(&test_info);
-            handle_outcome(outcome, test_info, &mut printer);
-        }
+            // Print results of tests that already dinished
+            for (outcome, test_info) in receiver.iter().take(num_tests) {
+                // In multithreaded mode, we do only print the start of the line
+                // after the test ran, as otherwise it would lead to terribly
+                // interleaved output.
+                printer.print_test(&test_info);
+                handle_outcome(outcome, test_info, &mut printer);
+            }
+        });
+
     }
 
     // Print failures if there were any, and the final summary.