[LOGMGR-180] Add a new LogContextSelector that short-circuits after t…

src/main/java/org/jboss/logmanager/CallerClassLoaderLogContextSelector.java

@@ -0,0 +1,216 @@
+/*
+ * JBoss, Home of Professional Open Source.
+ *
+ * Copyright 2017 Red Hat, Inc., and individual contributors
+ * as indicated by the @author tags.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.jboss.logmanager;
+
+import java.security.AccessController;
+import java.security.Permission;
+import java.security.PrivilegedAction;
+import java.util.Collections;
+import java.util.Set;
+import java.util.concurrent.ConcurrentMap;
+
+/**
+ * A log context selector which chooses a log context based on the caller's classloader. The first caller that is not
+ * a {@linkplain #addLogApiClassLoader(ClassLoader) log API} or does not have a {@code null} classloader will be the
+ * class loader used.
+ */
+@SuppressWarnings({"WeakerAccess", "unused"})
+public final class CallerClassLoaderLogContextSelector implements LogContextSelector {
+
+    private static final Permission REGISTER_LOG_CONTEXT_PERMISSION = new RuntimePermission("registerLogContext", null);
+    private static final Permission UNREGISTER_LOG_CONTEXT_PERMISSION = new RuntimePermission("unregisterLogContext", null);
+    private static final Permission LOG_API_PERMISSION = new RuntimePermission("logApiPermission", null);
+
+    /**
+     * Construct a new instance.  If no matching log context is found, the provided default selector is consulted.
+     *
+     * @param defaultSelector the selector to consult if no matching log context is found
+     */
+    public CallerClassLoaderLogContextSelector(final LogContextSelector defaultSelector) {
+        this(defaultSelector, false);
+    }
+
+    /**
+     * Construct a new instance.  If no matching log context is found, the provided default selector is consulted.
+     * <p>
+     * If the {@code checkParentClassLoaders} is set to {@code true} this selector recursively searches the class loader
+     * parents until a match is found or a {@code null} parent is found.
+     * </p>
+     *
+     * @param defaultSelector         the selector to consult if no matching log context is found
+     * @param checkParentClassLoaders {@code true} if the {@link LogContext log context} could not
+     *                                found for the class loader and the {@link ClassLoader#getParent() parent class
+     *                                loader} should be checked
+     */
+    public CallerClassLoaderLogContextSelector(final LogContextSelector defaultSelector, final boolean checkParentClassLoaders) {
+        this.defaultSelector = defaultSelector == null ? LogContext.DEFAULT_LOG_CONTEXT_SELECTOR : defaultSelector;
+        this.checkParentClassLoaders = checkParentClassLoaders;
+    }
+
+    /**
+     * Construct a new instance.  If no matching log context is found, the system context is used.
+     */
+    public CallerClassLoaderLogContextSelector() {
+        this(false);
+    }
+
+    /**
+     * Construct a new instance.  If no matching log context is found, the system context is used.
+     * <p>
+     * If the {@code checkParentClassLoaders} is set to {@code true} this selector recursively searches the class loader
+     * parents until a match is found or a {@code null} parent is found.
+     * </p>
+     *
+     * @param checkParentClassLoaders {@code true} if the {@link LogContext log context} could not
+     *                                found for the class loader and the {@link ClassLoader#getParent() parent class
+     *                                loader} should be checked
+     */
+    public CallerClassLoaderLogContextSelector(final boolean checkParentClassLoaders) {
+        this(LogContext.DEFAULT_LOG_CONTEXT_SELECTOR, checkParentClassLoaders);
+    }
+
+    private static final class Gateway extends SecurityManager {
+        protected Class[] getClassContext() {
+            return super.getClassContext();
+        }
+    }
+
+    private static final Gateway GATEWAY;
+
+    static {
+        GATEWAY = AccessController.doPrivileged(new PrivilegedAction<Gateway>() {
+            public Gateway run() {
+                return new Gateway();
+            }
+        });
+    }
+
+    private final LogContextSelector defaultSelector;
+
+    private final ConcurrentMap<ClassLoader, LogContext> contextMap = new CopyOnWriteMap<ClassLoader, LogContext>();
+    private final Set<ClassLoader> logApiClassLoaders = Collections.newSetFromMap(new CopyOnWriteMap<ClassLoader, Boolean>());
+    private final boolean checkParentClassLoaders;
+
+    private final PrivilegedAction<LogContext> logContextAction = new PrivilegedAction<LogContext>() {
+        public LogContext run() {
+            for (Class<?> caller : GATEWAY.getClassContext()) {
+                final ClassLoader classLoader = caller.getClassLoader();
+                // If the class loader is a log API class loader or null (bootstrap class loader), keep checking
+                if (classLoader == null || logApiClassLoaders.contains(classLoader)) {
+                    continue;
+                }
+                final LogContext result = check(classLoader);
+                if (result != null) {
+                    return result;
+                }
+                break;
+            }
+            return defaultSelector.getLogContext();
+        }
+
+        private LogContext check(final ClassLoader classLoader) {
+            if (classLoader != null && !logApiClassLoaders.contains(classLoader)) {
+                final LogContext context = contextMap.get(classLoader);
+                if (context != null) {
+                    return context;
+                }
+                if (checkParentClassLoaders) {
+                    return check(classLoader.getParent());
+                }
+            }
+            return null;
+        }
+    };
+
+    /**
+     * {@inheritDoc} This instance will consult the call stack to see if the first callers classloader is associated
+     * with a log context. The first caller is determined by the first class loader that is not registered as a
+     * {@linkplain #addLogApiClassLoader(ClassLoader) log API}.
+     */
+    @Override
+    public LogContext getLogContext() {
+        return AccessController.doPrivileged(logContextAction);
+    }
+
+    /**
+     * Register a class loader which is a known log API, and thus should be skipped over when searching for the
+     * log context to use for the caller class.
+     *
+     * @param apiClassLoader the API class loader
+     *
+     * @return {@code true} if this class loader was previously unknown, or {@code false} if it was already registered
+     */
+    public boolean addLogApiClassLoader(ClassLoader apiClassLoader) {
+        final SecurityManager sm = System.getSecurityManager();
+        if (sm != null) {
+            sm.checkPermission(LOG_API_PERMISSION);
+        }
+        return logApiClassLoaders.add(apiClassLoader);
+    }
+
+    /**
+     * Remove a class loader from the known log APIs set.
+     *
+     * @param apiClassLoader the API class loader
+     *
+     * @return {@code true} if the class loader was removed, or {@code false} if it was not known to this selector
+     */
+    public boolean removeLogApiClassLoader(ClassLoader apiClassLoader) {
+        final SecurityManager sm = System.getSecurityManager();
+        if (sm != null) {
+            sm.checkPermission(LOG_API_PERMISSION);
+        }
+        return logApiClassLoaders.remove(apiClassLoader);
+    }
+
+    /**
+     * Register a class loader with a log context.  This method requires the {@code registerLogContext} {@link RuntimePermission}.
+     *
+     * @param classLoader the classloader
+     * @param logContext  the log context
+     *
+     * @throws IllegalArgumentException if the classloader is already associated with a log context
+     */
+    public void registerLogContext(ClassLoader classLoader, LogContext logContext) throws IllegalArgumentException {
+        final SecurityManager sm = System.getSecurityManager();
+        if (sm != null) {
+            sm.checkPermission(REGISTER_LOG_CONTEXT_PERMISSION);
+        }
+        if (contextMap.putIfAbsent(classLoader, logContext) != null) {
+            throw new IllegalArgumentException("ClassLoader instance is already registered to a log context (" + classLoader + ")");
+        }
+    }
+
+    /**
+     * Unregister a class loader/log context association.  This method requires the {@code unregisterLogContext} {@link RuntimePermission}.
+     *
+     * @param classLoader the classloader
+     * @param logContext  the log context
+     *
+     * @return {@code true} if the association exists and was removed, {@code false} otherwise
+     */
+    public boolean unregisterLogContext(ClassLoader classLoader, LogContext logContext) {
+        final SecurityManager sm = System.getSecurityManager();
+        if (sm != null) {
+            sm.checkPermission(UNREGISTER_LOG_CONTEXT_PERMISSION);
+        }
+        return contextMap.remove(classLoader, logContext);
+    }
+}