Replace read/write lock in JarResource to avoid virtual threads pinning

independent-projects/bootstrap/runner/src/main/java/io/quarkus/bootstrap/runner/JarFileReference.java

@@ -0,0 +1,143 @@
+package io.quarkus.bootstrap.runner;
+
+import java.io.IOException;
+import java.nio.file.Path;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.atomic.AtomicReference;
+import java.util.jar.JarFile;
+
+import io.smallrye.common.io.jar.JarFiles;
+
+public class JarFileReference {
+    // Guarded by an atomic reader counter that emulate the behaviour of a read/write lock.
+    // To enable virtual threads compatibility and avoid pinning it is not possible to use an explicit read/write lock
+    // because the jarFile access may happen inside a native call (for example triggered by the RunnerClassLoader)
+    // and then it is necessary to avoid blocking on it.
+    private final JarFile jarFile;
+
+    private final AtomicReference<JarFileReference> jarFileReference;
+
+    // The referenceCounter - 1 represents the number of effective readers (#aqcuire - #release), while the first
+    // reference is used to determine if a close has been required.
+    // The referenceCounter starts from 2 because a create always implies also a first acquire.
+    private final AtomicInteger referenceCounter = new AtomicInteger(2);
+
+    private JarFileReference(AtomicReference<JarFileReference> jarFileReference, JarFile jarFile) {
+        this.jarFileReference = jarFileReference;
+        this.jarFile = jarFile;
+    }
+
+    /**
+     * Increase the readers counter of the jarFile.
+     *
+     * @return true if the acquire succeeded: it's now safe to access and use the inner jarFile.
+     *         false if the jar reference is going to be closed and then no longer usable.
+     */
+    private boolean acquire() {
+        while (true) {
+            int count = referenceCounter.get();
+            if (count == 0) {
+                return false;
+            }
+            if (referenceCounter.compareAndSet(count, count + 1)) {
+                return true;
+            }
+        }
+    }
+
+    /**
+     * Decrease the readers counter of the jarFile.
+     * If the counter drops to 0 and a release has been requested also closes the jarFile.
+     *
+     * @return true if the release also closes the underlying jarFile.
+     */
+    private boolean release() {
+        while (true) {
+            int count = referenceCounter.get();
+            if (count <= 0) {
+                throw new IllegalStateException(
+                        "The reference counter cannot be negative, found: " + (referenceCounter.get() - 1));
+            }
+            if (referenceCounter.compareAndSet(count, count - 1)) {
+                if (count == 1) {
+                    try {
+                        jarFile.close();
+                    } catch (IOException e) {
+                        // ignore
+                    } finally {
+                        jarFileReference.compareAndSet(this, null);
+                    }
+                    return true;
+                }
+                return false;
+            }
+        }
+    }
+
+    /**
+     * Ask to close this reference.
+     * If there are no readers currently accessing the jarFile also close it, otherwise defer the closing when the last reader
+     * will leave.
+     */
+    void close() {
+        release();
+    }
+
+    @FunctionalInterface
+    interface JarFileConsumer<T> {
+        T apply(JarFile jarFile, Path jarPath, String resource);
+    }
+
+    static <T> T withJarFile(AtomicReference<JarFileReference> jarFileReference, Path jarPath, String resource,
+            JarFileConsumer<T> fileConsumer) {
+
+        // Happy path: the jar reference already exists and it's ready to be used
+        final var localJarFileRef = jarFileReference.get();
+        if (localJarFileRef != null && localJarFileRef.acquire()) {
+            return consumeSharedJarFile(jarPath, resource, fileConsumer, localJarFileRef);
+        }
+
+        // There's no valid jar reference, so load a new one
+        final var newJarFileRef = JarFileReference.loadAcquiredJarFile(jarFileReference, jarPath);
+        if (jarFileReference.compareAndSet(localJarFileRef, newJarFileRef) ||
+                jarFileReference.compareAndSet(null, newJarFileRef)) {
+            // The new file reference has been successfully published and can be used by the current and other threads
+            return consumeSharedJarFile(jarPath, resource, fileConsumer, newJarFileRef);
+        }
+
+        // The newly created file reference hasn't been published so it can be used exclusively by the current thread
+        return consumeUnsharedJarFile(jarFileReference, jarPath, resource, fileConsumer, newJarFileRef);
+    }
+
+    private static <T> T consumeSharedJarFile(Path jarPath, String resource, JarFileConsumer<T> fileConsumer,
+            JarFileReference jarFileRef) {
+        try {
+            return fileConsumer.apply(jarFileRef.jarFile, jarPath, resource);
+        } finally {
+            jarFileRef.release();
+        }
+    }
+
+    private static <T> T consumeUnsharedJarFile(AtomicReference<JarFileReference> jarFileReference, Path jarPath,
+            String resource, JarFileConsumer<T> fileConsumer, JarFileReference jarFileRef) {
+        try {
+            return fileConsumer.apply(jarFileRef.jarFile, jarPath, resource);
+        } finally {
+            boolean closed = jarFileRef.release();
+            assert !closed;
+            // Check one last time if the file reference can be published and reused by other threads, otherwise close it
+            if (!jarFileReference.compareAndSet(null, jarFileRef)) {
+                closed = jarFileRef.release();
+                assert closed;
+            }
+        }
+    }
+
+    private static JarFileReference loadAcquiredJarFile(AtomicReference<JarFileReference> jarFileReference, Path jarPath) {
+        try {
+            return new JarFileReference(jarFileReference, JarFiles.create(jarPath.toFile()));
+        } catch (IOException e) {
+            throw new RuntimeException("Failed to open " + jarPath, e);
+        }
+    }
+}

independent-projects/bootstrap/runner/src/main/java/io/quarkus/bootstrap/runner/JarResource.java

@@ -11,16 +11,12 @@
 import java.security.ProtectionDomain;
 import java.security.cert.Certificate;
 import java.util.Objects;
-import java.util.concurrent.locks.Lock;
-import java.util.concurrent.locks.ReadWriteLock;
-import java.util.concurrent.locks.ReentrantReadWriteLock;
+import java.util.concurrent.atomic.AtomicReference;
 import java.util.jar.JarEntry;
 import java.util.jar.JarFile;
 import java.util.zip.ZipEntry;
-import java.util.zip.ZipFile;
 
 import io.smallrye.common.io.jar.JarEntries;
-import io.smallrye.common.io.jar.JarFiles;
 
 /**
  * A jar resource
@@ -30,25 +26,13 @@ public class JarResource implements ClassLoadingResource {
     private final ManifestInfo manifestInfo;
     private final Path jarPath;
 
-    private final Lock readLock;
-    private final Lock writeLock;
-
     private volatile ProtectionDomain protectionDomain;
 
-    //Guarded by the read/write lock; open/close operations on the JarFile require the exclusive lock,
-    //while using an existing open reference can use the shared lock.
-    //If a lock is acquired, and as long as it's owned, we ensure that the zipFile reference
-    //points to an open JarFile instance, and read operations are valid.
-    //To close the jar, the exclusive lock must be owned, and reference will be set to null before releasing it.
-    //Likewise, opening a JarFile requires the exclusive lock.
-    private volatile JarFile zipFile;
+    private final AtomicReference<JarFileReference> jarFileReference = new AtomicReference<>();
 
     public JarResource(ManifestInfo manifestInfo, Path jarPath) {
         this.manifestInfo = manifestInfo;
         this.jarPath = jarPath;
-        final ReadWriteLock readWriteLock = new ReentrantReadWriteLock();
-        this.readLock = readWriteLock.readLock();
-        this.writeLock = readWriteLock.writeLock();
     }
 
     @Override
@@ -69,38 +53,48 @@ public void init() {
 
     @Override
     public byte[] getResourceData(String resource) {
-        final ZipFile zipFile = readLockAcquireAndGetJarReference();
-        try {
-            ZipEntry entry = zipFile.getEntry(resource);
+        return JarFileReference.withJarFile(jarFileReference, jarPath, resource, JarResourceDataProvider.INSTANCE);
+    }
+
+    private static class JarResourceDataProvider implements JarFileReference.JarFileConsumer<byte[]> {
+        private static final JarResourceDataProvider INSTANCE = new JarResourceDataProvider();
+
+        @Override
+        public byte[] apply(JarFile jarFile, Path path, String res) {
+            ZipEntry entry = jarFile.getEntry(res);
             if (entry == null) {
                 return null;
             }
-            try (InputStream is = zipFile.getInputStream(entry)) {
+            try (InputStream is = jarFile.getInputStream(entry)) {
                 byte[] data = new byte[(int) entry.getSize()];
                 int pos = 0;
                 int rem = data.length;
                 while (rem > 0) {
                     int read = is.read(data, pos, rem);
                     if (read == -1) {
-                        throw new RuntimeException("Failed to read all data for " + resource);
+                        throw new RuntimeException("Failed to read all data for " + res);
                     }
                     pos += read;
                     rem -= read;
                 }
                 return data;
             } catch (IOException e) {
-                throw new RuntimeException("Failed to read zip entry " + resource, e);
+                throw new RuntimeException("Failed to read zip entry " + res, e);
             }
-        } finally {
-            readLock.unlock();
         }
     }
 
     @Override
     public URL getResourceURL(String resource) {
-        final JarFile jarFile = readLockAcquireAndGetJarReference();
-        try {
-            JarEntry entry = jarFile.getJarEntry(resource);
+        return JarFileReference.withJarFile(jarFileReference, jarPath, resource, JarResourceURLProvider.INSTANCE);
+    }
+
+    private static class JarResourceURLProvider implements JarFileReference.JarFileConsumer<URL> {
+        private static final JarResourceURLProvider INSTANCE = new JarResourceURLProvider();
+
+        @Override
+        public URL apply(JarFile jarFile, Path path, String res) {
+            JarEntry entry = jarFile.getJarEntry(res);
             if (entry == null) {
                 return null;
             }
@@ -110,15 +104,7 @@ public URL getResourceURL(String resource) {
                 if (realName.endsWith("/")) {
                     realName = realName.substring(0, realName.length() - 1);
                 }
-                final URI jarUri = jarPath.toUri();
-                // first create a URI which includes both the jar file path and the relative resource name
-                // and then invoke a toURL on it. The URI reconstruction allows for any encoding to be done
-                // for the "path" which includes the "realName"
-                var ssp = new StringBuilder(jarUri.getPath().length() + realName.length() + 2);
-                ssp.append(jarUri.getPath());
-                ssp.append("!/");
-                ssp.append(realName);
-                final URL resUrl = new URI(jarUri.getScheme(), ssp.toString(), null).toURL();
+                final URL resUrl = getUrl(path, realName);
                 // wrap it up into a "jar" protocol URL
                 //horrible hack to deal with '?' characters in the URL
                 //seems to be the only way, the URI constructor just does not let you handle them in a sane way
@@ -136,8 +122,18 @@ public URL getResourceURL(String resource) {
             } catch (MalformedURLException | URISyntaxException e) {
                 throw new RuntimeException(e);
             }
-        } finally {
-            readLock.unlock();
+        }
+
+        private static URL getUrl(Path jarPath, String realName) throws MalformedURLException, URISyntaxException {
+            final URI jarUri = jarPath.toUri();
+            // first create a URI which includes both the jar file path and the relative resource name
+            // and then invoke a toURL on it. The URI reconstruction allows for any encoding to be done
+            // for the "path" which includes the "realName"
+            var ssp = new StringBuilder(jarUri.getPath().length() + realName.length() + 2);
+            ssp.append(jarUri.getPath());
+            ssp.append("!/");
+            ssp.append(realName);
+            return new URI(jarUri.getScheme(), ssp.toString(), null).toURL();
         }
     }
 
@@ -151,60 +147,11 @@ public ProtectionDomain getProtectionDomain() {
         return protectionDomain;
     }
 
-    private JarFile readLockAcquireAndGetJarReference() {
-        while (true) {
-            readLock.lock();
-            final JarFile zipFileLocal = this.zipFile;
-            if (zipFileLocal != null) {
-                //Expected fast path: returns a reference to the open JarFile while owning the readLock
-                return zipFileLocal;
-            } else {
-                //This Lock implementation doesn't allow upgrading a readLock to a writeLock, so release it
-                //as we're going to need the WriteLock.
-                readLock.unlock();
-                //trigger the JarFile being (re)opened.
-                ensureJarFileIsOpen();
-                //Now since we no longer own any lock, we need to try again to obtain the readLock
-                //and check for the reference still being valid.
-                //This exposes us to a race with closing the just-opened JarFile;
-                //however this should be extremely rare, so we can trust we won't loop much;
-                //A counter doesn't seem necessary, as in fact we know that methods close()
-                //and resetInternalCaches() are invoked each at most once, which limits the amount
-                //of loops here in practice.
-            }
-        }
-    }
-
-    private void ensureJarFileIsOpen() {
-        writeLock.lock();
-        try {
-            if (this.zipFile == null) {
-                try {
-                    this.zipFile = JarFiles.create(jarPath.toFile());
-                } catch (IOException e) {
-                    throw new RuntimeException("Failed to open " + jarPath, e);
-                }
-            }
-        } finally {
-            writeLock.unlock();
-        }
-    }
-
     @Override
     public void close() {
-        writeLock.lock();
-        try {
-            final JarFile zipFileLocal = this.zipFile;
-            if (zipFileLocal != null) {
-                try {
-                    this.zipFile = null;
-                    zipFileLocal.close();
-                } catch (Throwable e) {
-                    //ignore
-                }
-            }
-        } finally {
-            writeLock.unlock();
+        JarFileReference ref = jarFileReference.get();
+        if (ref != null) {
+            ref.close();
         }
     }