Purge caches and build directories when nothing is running

This prevents deleting files that Cargo is trying to read out from under
it.

Author: Mark-Simulacrum

src/runner/mod.rs

@@ -10,6 +10,7 @@ use crate::prelude::*;
 use crate::results::TestResult;
 use crate::runner::worker::{DiskSpaceWatcher, Worker};
 use rustwide::Workspace;
+use std::sync::Arc;
 use std::thread::scope;
 use std::time::Duration;
 pub use worker::RecordProgress;
@@ -95,9 +96,19 @@ pub fn run_ex(
     let disk_watcher = DiskSpaceWatcher::new(
         DISK_SPACE_WATCHER_INTERVAL,
         DISK_SPACE_WATCHER_THRESHOLD,
-        &workers,
+        workers.len(),
     );
 
+    for worker in workers.iter() {
+        let disk_watcher = Arc::clone(&disk_watcher);
+        assert!(worker
+            .between_crates
+            .set(Box::new(move || {
+                disk_watcher.worker_idle();
+            }))
+            .is_ok());
+    }
+
     scope(|scope1| {
         std::thread::Builder::new()
             .name("disk-space-watcher".into())

src/runner/worker.rs

@@ -11,11 +11,8 @@ use crate::utils;
 use rustwide::logging::{self, LogStorage};
 use rustwide::{BuildDirectory, Workspace};
 use std::collections::HashMap;
-use std::sync::Condvar;
-use std::sync::{
-    atomic::{AtomicBool, Ordering},
-    Mutex,
-};
+use std::sync::Mutex;
+use std::sync::{Arc, Condvar, OnceLock};
 use std::time::Duration;
 
 pub trait RecordProgress: Send + Sync {
@@ -51,8 +48,10 @@ pub(super) struct Worker<'a> {
     ex: &'a Experiment,
     config: &'a crate::config::Config,
     api: &'a dyn RecordProgress,
-    target_dir_cleanup: AtomicBool,
     next_crate: &'a (dyn Fn() -> Fallible<Option<Crate>> + Send + Sync),
+
+    // Called by the worker thread between crates, when no global state (namely caches) is in use.
+    pub(super) between_crates: OnceLock<Box<dyn Fn() + Send + Sync + 'a>>,
 }
 
 impl<'a> Worker<'a> {
@@ -81,7 +80,8 @@ impl<'a> Worker<'a> {
             config,
             next_crate,
             api,
-            target_dir_cleanup: AtomicBool::new(false),
+
+            between_crates: OnceLock::new(),
         }
     }
 
@@ -167,10 +167,12 @@ impl<'a> Worker<'a> {
                 return Ok(());
             };
 
-            self.maybe_cleanup_target_dir()?;
-
             info!("{} processing crate {}", self.name, krate);
 
+            if let Some(cb) = self.between_crates.get() {
+                cb();
+            }
+
             if !self.ex.ignore_blacklist && self.config.should_skip(&krate) {
                 for tc in &self.ex.toolchains {
                     // If a skipped crate is somehow sent to the agent (for example, when a crate was
@@ -338,41 +340,36 @@ impl<'a> Worker<'a> {
             }
         }
     }
-
-    fn maybe_cleanup_target_dir(&self) -> Fallible<()> {
-        if !self.target_dir_cleanup.swap(false, Ordering::SeqCst) {
-            return Ok(());
-        }
-        info!("purging target dir for {}", self.name);
-        for dir in self.build_dir.values() {
-            dir.lock().unwrap().purge()?;
-        }
-
-        Ok(())
-    }
-
-    fn schedule_target_dir_cleanup(&self) {
-        self.target_dir_cleanup.store(true, Ordering::SeqCst);
-    }
 }
 
-pub(super) struct DiskSpaceWatcher<'a> {
+pub(super) struct DiskSpaceWatcher {
     interval: Duration,
     threshold: f32,
-    workers: &'a [Worker<'a>],
     should_stop: Mutex<bool>,
     waiter: Condvar,
+
+    worker_count: usize,
+
+    // If the bool is true, that means we're waiting for the cache to reach zero, in which case
+    // workers will wait for it to be false before starting. This gives us a global 'is the cache
+    // in use' synchronization point.
+    cache_in_use: Mutex<(usize, bool)>,
+    cache_waiter: Condvar,
 }
 
-impl<'a> DiskSpaceWatcher<'a> {
-    pub(super) fn new(interval: Duration, threshold: f32, workers: &'a [Worker<'a>]) -> Self {
-        DiskSpaceWatcher {
+impl DiskSpaceWatcher {
+    pub(super) fn new(interval: Duration, threshold: f32, worker_count: usize) -> Arc<Self> {
+        Arc::new(DiskSpaceWatcher {
             interval,
             threshold,
-            workers,
             should_stop: Mutex::new(false),
             waiter: Condvar::new(),
-        }
+
+            worker_count,
+
+            cache_in_use: Mutex::new((0, false)),
+            cache_waiter: Condvar::new(),
+        })
     }
 
     pub(super) fn stop(&self) {
@@ -406,14 +403,66 @@ impl<'a> DiskSpaceWatcher<'a> {
         };
 
         if usage.is_threshold_reached(self.threshold) {
-            warn!("running the scheduled thread cleanup");
-            for worker in self.workers {
-                worker.schedule_target_dir_cleanup();
-            }
+            self.clean(workspace);
+        }
+    }
 
-            if let Err(e) = workspace.purge_all_caches() {
-                warn!("failed to purge caches: {:?}", e);
-            }
+    fn clean(&self, workspace: &dyn ToClean) {
+        warn!("declaring interest in worker idle");
+
+        // Set interest in cleaning caches and then wait for cache use to drain to zero.
+        let mut guard = self.cache_in_use.lock().unwrap();
+        guard.1 = true;
+
+        self.cache_waiter.notify_all();
+
+        warn!("declared interest in workers, waiting for everyone to idle");
+
+        let mut guard = self
+            .cache_waiter
+            .wait_while(guard, |c| dbg!(c.0, "clean waiter").0 != self.worker_count)
+            .unwrap();
+
+        // OK, purging caches, clear interest.
+        guard.1 = false;
+
+        self.cache_waiter.notify_all();
+
+        warn!("purging all build dirs and caches");
+
+        workspace.purge();
+    }
+
+    pub(super) fn worker_idle(&self) {
+        log::trace!("worker at idle point");
+        let mut guard = self.cache_in_use.lock().unwrap();
+        log::trace!("worker declared idle");
+        // note that we're not running right now.
+        guard.0 += 1;
+        self.cache_waiter.notify_all();
+        let mut guard = self.cache_waiter.wait_while(guard, |c| c.1).unwrap();
+        info!("worker resuming from idle");
+        // Then set ourselves as running.
+        guard.0 -= 1;
+        self.cache_waiter.notify_all();
+    }
+}
+
+trait ToClean {
+    fn purge(&self);
+}
+
+impl ToClean for Workspace {
+    fn purge(&self) {
+        if let Err(e) = self.purge_all_caches() {
+            warn!("failed to purge caches: {:?}", e);
+        }
+
+        if let Err(e) = self.purge_all_build_dirs() {
+            warn!("failed to purge build directories: {:?}", e);
         }
     }
 }
+
+#[cfg(test)]
+mod test;

src/runner/worker/test.rs

@@ -0,0 +1,89 @@
+use std::sync::atomic::AtomicBool;
+use std::sync::atomic::Ordering;
+use std::sync::Arc;
+use std::sync::Condvar;
+use std::sync::Mutex;
+use std::time::Duration;
+
+use crate::runner::DiskSpaceWatcher;
+
+#[derive(Default, Debug)]
+struct PurgeTracker {
+    count: Mutex<usize>,
+    wait: Condvar,
+}
+
+impl PurgeTracker {
+    #[track_caller]
+    fn assert_count_eq(&self, count: usize) {
+        let guard = self.count.lock().unwrap();
+        let (g, timer) = self
+            .wait
+            .wait_timeout_while(guard, Duration::from_secs(10), |g| *g != count)
+            .unwrap();
+        assert!(
+            !timer.timed_out(),
+            "timed out while waiting for {} to equal {}",
+            *g,
+            count
+        );
+        assert_eq!(*g, count);
+    }
+}
+
+impl super::ToClean for PurgeTracker {
+    fn purge(&self) {
+        *self.count.lock().unwrap() += 1;
+        self.wait.notify_all();
+    }
+}
+
+#[test]
+fn check_cleanup_single_worker() {
+    let _ = env_logger::try_init();
+    let tracker = Arc::new(PurgeTracker::default());
+    let watcher = DiskSpaceWatcher::new(Duration::from_secs(60), 0.8, 1);
+    let done = &AtomicBool::new(false);
+    std::thread::scope(|s| {
+        s.spawn(|| {
+            for _ in 0..3 {
+                watcher.clean(&*tracker);
+            }
+            done.store(true, Ordering::Relaxed);
+        });
+
+        s.spawn(|| {
+            while !done.load(Ordering::Relaxed) {
+                watcher.worker_idle();
+            }
+        });
+    });
+
+    tracker.assert_count_eq(3);
+}
+
+#[test]
+fn check_cleanup_multi_worker() {
+    let _ = env_logger::try_init();
+    let tracker = Arc::new(PurgeTracker::default());
+    let watcher = DiskSpaceWatcher::new(Duration::from_secs(60), 0.8, 3);
+    let done = &AtomicBool::new(false);
+    std::thread::scope(|s| {
+        s.spawn(|| {
+            for _ in 0..5 {
+                watcher.clean(&*tracker);
+            }
+            done.store(true, Ordering::Relaxed);
+        });
+
+        for _ in 0..3 {
+            s.spawn(|| {
+                while !done.load(Ordering::Relaxed) {
+                    watcher.worker_idle();
+                }
+            });
+        }
+    });
+
+    tracker.assert_count_eq(5);
+}