codeconsole commented on code in PR #16089:
URL: https://github.com/apache/grails-core/pull/16089#discussion_r3714814663
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grails-bootstrap/src/main/groovy/org/grails/io/watch/DirectoryWatcher.java:
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@@ -45,32 +45,57 @@ public class DirectoryWatcher extends Thread {
*/
public DirectoryWatcher() {
setDaemon(true);
- AbstractDirectoryWatcher directoryWatcherDelegate;
+ this.directoryWatcherDelegate = createDelegate();
+ }
+
+ /**
+ * Selects the best available watcher implementation.
+ *
+ * <p>On macOS the native FSEvents based watcher is preferred, but it
requires the optional
+ * {@code io.methvin:directory-watcher} dependency. When that isn't
available the JDK
+ * {@link java.nio.file.WatchService} is used instead. Polling is only a
last resort.</p>
+ *
+ * @return the watcher to delegate to
+ */
+ private static AbstractDirectoryWatcher createDelegate() {
+ if (System.getProperty("os.name").equals("Mac OS X")) {
+ AbstractDirectoryWatcher macOsWatcher = createMacOsWatcher();
+ if (macOsWatcher != null) {
+ return macOsWatcher;
+ }
+ }
try {
- if (System.getProperty("os.name").equals("Mac OS X")) {
- Boolean jnaAvailable = false;
- try {
- Class.forName("com.sun.jna.Pointer");
- jnaAvailable = true;
- } catch (ClassNotFoundException e) {
- if (LOG.isWarnEnabled()) {
- LOG.warn("Error Initializing Native OS X File Event
Watcher. Add JNA to classpath for Faster File Watching performance.");
- }
-
- }
- if (jnaAvailable) {
- directoryWatcherDelegate = (AbstractDirectoryWatcher)
Class.forName("org.grails.io.watch.MacOsWatchServiceDirectoryWatcher").getDeclaredConstructor().newInstance();
- } else {
- directoryWatcherDelegate = (AbstractDirectoryWatcher)
Class.forName("org.grails.io.watch.WatchServiceDirectoryWatcher").getDeclaredConstructor().newInstance();
- }
- } else {
- directoryWatcherDelegate = (AbstractDirectoryWatcher)
Class.forName("org.grails.io.watch.WatchServiceDirectoryWatcher").getDeclaredConstructor().newInstance();
+ return new WatchServiceDirectoryWatcher();
+ } catch (Throwable e) {
+ LOG.warn("Could not create a WatchService based directory watcher.
Falling back to PollingDirectoryWatcher.", e);
+ return new PollingDirectoryWatcher();
+ }
+ }
+
+ /**
+ * @return the native macOS watcher, or {@code null} if it is unavailable
+ */
+ private static AbstractDirectoryWatcher createMacOsWatcher() {
+ try {
+ // MacOsWatchServiceDirectoryWatcher delegates to io.methvin's
MacOSXListeningWatchService,
+ // an optional dependency of this module. Probe for that class
rather than for JNA: JNA is
+ // frequently present transitively (Testcontainers, docker-java,
...) without the watcher
+ // library, and using it as the signal sends those applications
down a load that can't succeed.
+ // A LinkageError means the class is present but its own
dependencies (JNA) are not, which is
+ // equally unusable, so treat both as simply unavailable.
+
Class.forName("io.methvin.watchservice.MacOSXListeningWatchService");
+ } catch (ClassNotFoundException | LinkageError e) {
+ if (LOG.isDebugEnabled()) {
+ LOG.debug("Native macOS file event watching is unavailable.
Add 'io.methvin:directory-watcher' to the classpath for faster file watching.",
e);
Review Comment:
Agreed — changed to warn in ab2b2afb3e.
Worth surfacing: the JDK supplies no native `WatchService` on macOS.
`FileSystems.getDefault().newWatchService()` returns
`sun.nio.fs.PollingWatchService`, and `WatchServiceDirectoryWatcher` registers
without a sensitivity modifier, so the fallback polls at the default 10s. That
is a real reload latency cost with a one dependency fix, so the message now
states the consequence as well as naming the dependency — and yes, adding the
library silences it.
The `ClassNotFoundException` stays at `LOG.debug` so the warn line remains a
single actionable sentence rather than a stack trace, which is what made the
message on `8.0.x` noisy.
`DirectoryWatcherSpec` now also covers that the advice is emitted on macOS
without the library, and that it stays off platforms it cannot help.
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