desruisseaux commented on code in PR #347:
URL:
https://github.com/apache/maven-clean-plugin/pull/347#discussion_r4110874605
##########
src/main/java/org/apache/maven/plugins/clean/BackgroundCleaner.java:
##########
@@ -98,57 +169,114 @@ final class BackgroundCleaner extends Cleaner implements
Listener, Runnable {
*/
private IOException errors;
- /**
- * Whether at least one deletion task has been queued.
- */
- private boolean started;
-
/**
* Whether to disable the deletion of files in background threads.
* This is used for avoiding to repeat the same warning many times
* when the {@link #fastDir} directory does not exist.
+ *
+ * <p>This field is written by {@link #fastDeleteError(IOException)}
without holding any lock
+ * (to avoid a lock-ordering risk), and read by the synchronized {@link
#fastDelete} method.
+ * Declaring it {@code volatile} ensures that the write is immediately
visible to all threads
+ * without requiring the reader to hold the same monitor as the writer.</p>
*/
- private boolean disabled;
+ private volatile boolean disabled;
/**
- * Creates a new cleaner to be executed in a background thread.
+ * Creates a new background cleaner service.
+ * Use {@link #getOrCreate} to obtain a session-scoped instance.
*
- * @param session the Maven session to be used
- * @param matcherFactory the service to use for creating include and
exclude filters.
- * @param logger the logger to use
- * @param verbose whether to perform verbose logging
- * @param fastDir the explicit configured directory or to be
deleted in fast mode
- * @param fastMode the fast deletion mode
- * @param followSymlinks whether to follow symlinks
- * @param force whether to force the deletion of read-only files
- * @param failOnError whether to abort with an exception in case a
selected file/directory could not be deleted
- * @param retryOnError whether to undertake additional delete attempts
in case the first attempt failed
+ * @param session the Maven session to be used
+ * @param logger the logger to use
+ * @param fastDir the directory where to temporarily move the files to
delete
+ * @param fastMode the fast deletion mode
*/
- @SuppressWarnings("checkstyle:ParameterNumber")
- BackgroundCleaner(
- @Nonnull Session session,
- @Nonnull PathMatcherFactory matcherFactory,
- @Nonnull Log logger,
- boolean verbose,
- @Nonnull Path fastDir,
- @Nonnull FastMode fastMode,
- boolean followSymlinks,
- boolean force,
- boolean failOnError,
- boolean retryOnError) {
- super(matcherFactory, logger, verbose, followSymlinks, force,
failOnError, retryOnError);
+ private BackgroundCleaner(
+ @Nonnull Session session, @Nonnull Log logger, @Nonnull Path
fastDir, @Nonnull FastMode fastMode) {
this.session = session;
+ this.logger = logger;
this.fastDir = fastDir;
this.fastMode = fastMode;
filesToDeleteAtEnd = (fastMode != FastMode.BACKGROUND) ? new
ArrayList<>() : null;
directoriesToDeleteIfEmpty = new LinkedHashSet<>(); // Will need to
delete in order.
executor = Executors.newSingleThreadExecutor((task) -> new
Thread(task, "mvn-background-cleaner"));
+ // Note: registerListener() and scanForLeftovers() are called by
getOrCreate() AFTER
+ // computeIfAbsent() returns, to avoid re-entrant ConcurrentHashMap
access and to
+ // prevent `this` from escaping the constructor.
+ }
+
+ /**
+ * Initializes the background cleaner by registering the session listener
and scanning
+ * for leftover directories. This method must be called exactly once,
immediately after
+ * the instance is created by {@link #getOrCreate}, but outside the
+ * {@link java.util.concurrent.ConcurrentHashMap#computeIfAbsent} mapping
function
+ * to avoid re-entrant deadlock.
+ */
+ private void init() {
+ session.registerListener(this);
+ scanForLeftovers();
+ }
+
+ /**
+ * Returns the session-scoped {@code BackgroundCleaner}, creating it on
first access.
+ * The instance is stored in {@link SessionData} so that all subprojects
in a reactor
+ * share the same background thread and session listener.
+ *
+ * @param session the Maven session to be used
+ * @param logger the logger to use
+ * @param fastDir the directory where to temporarily move the files to
delete
+ * @param fastMode the fast deletion mode
+ * @return the shared background cleaner instance for the session
+ */
+ static BackgroundCleaner getOrCreate(
+ @Nonnull Session session, @Nonnull Log logger, @Nonnull Path
fastDir, @Nonnull FastMode fastMode) {
+ boolean[] created = {false};
+ BackgroundCleaner bc = session.getData().computeIfAbsent(KEY, () -> {
+ created[0] = true;
+ return new BackgroundCleaner(session, logger, fastDir, fastMode);
+ });
+ if (created[0]) {
+ // Initialization is deferred to here (outside computeIfAbsent) to
avoid
+ // re-entrant ConcurrentHashMap access and `this` escaping the
constructor.
+ bc.init();
+ }
+ if (!bc.fastDir.equals(fastDir) || bc.fastMode != fastMode) {
+ logger.warn("BackgroundCleaner already initialized with fastDir="
+ bc.fastDir
+ + ", fastMode=" + bc.fastMode + "; ignoring fastDir=" +
fastDir
+ + ", fastMode=" + fastMode + " from this subproject.");
+ }
+ return bc;
+ }
+
+ /**
+ * Scans the fast directory for leftover directories from previous
(possibly killed) builds
+ * and queues them for background deletion. This restores the cleanup
behavior that was
+ * present in the singleton pattern of version 3.5.0 but was lost when
switching to
+ * per-subproject instances.
+ *
+ * <p><b>Limitation:</b> leftovers are always deleted with {@code
force=false}.
+ * Because the previous build's configuration is not persisted, we cannot
know
+ * whether it used {@code force=true}. As a consequence, read-only files
that
+ * survived a killed build will not be force-deleted here; they will
remain until
+ * the user runs a new clean with {@code force=true}.</p>
+ */
+ private void scanForLeftovers() {
+ if (Files.isDirectory(fastDir)) {
+ try (DirectoryStream<Path> stream =
Files.newDirectoryStream(fastDir)) {
+ for (Path child : stream) {
+ if (Files.isDirectory(child)) {
+ logger.debug("Cleaning leftover directory from
previous build: " + child);
+ executor.submit(() -> deleteInBackground(child, false,
true));
+ }
+ }
+ } catch (IOException e) {
+ logger.debug("Failed to scan for leftover directories in " +
fastDir + ": " + e);
Review Comment:
Replace `+ ": " + e` by `+ '.', e` in order to report the exception in the
log.
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