1 /* 2 * Copyright 2016 The gRPC Authors 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 package io.grpc; 18 19 import java.util.logging.Level; 20 import java.util.logging.Logger; 21 22 /** 23 * A {@link ThreadLocal}-based context storage implementation. Used by default. 24 */ 25 final class ThreadLocalContextStorage extends Context.Storage { 26 private static final Logger log = Logger.getLogger(ThreadLocalContextStorage.class.getName()); 27 28 /** 29 * Currently bound context. 30 */ 31 // VisibleForTesting 32 static final ThreadLocal<Context> localContext = new ThreadLocal<>(); 33 34 @Override doAttach(Context toAttach)35 public Context doAttach(Context toAttach) { 36 Context current = current(); 37 localContext.set(toAttach); 38 return current; 39 } 40 41 @Override detach(Context toDetach, Context toRestore)42 public void detach(Context toDetach, Context toRestore) { 43 if (current() != toDetach) { 44 // Log a severe message instead of throwing an exception as the context to attach is assumed 45 // to be the correct one and the unbalanced state represents a coding mistake in a lower 46 // layer in the stack that cannot be recovered from here. 47 log.log(Level.SEVERE, "Context was not attached when detaching", 48 new Throwable().fillInStackTrace()); 49 } 50 if (toRestore != Context.ROOT) { 51 localContext.set(toRestore); 52 } else { 53 // Avoid leaking our ClassLoader via ROOT if this Thread is reused across multiple 54 // ClassLoaders, as is common for Servlet Containers. The ThreadLocal is weakly referenced by 55 // the Thread, but its current value is strongly referenced and only lazily collected as new 56 // ThreadLocals are created. 57 // 58 // Use set(null) instead of remove() since remove() deletes the entry which is then re-created 59 // on the next get() (because of initialValue() handling). set(null) has same performance as 60 // set(toRestore). 61 localContext.set(null); 62 } 63 } 64 65 @Override current()66 public Context current() { 67 Context current = localContext.get(); 68 if (current == null) { 69 return Context.ROOT; 70 } 71 return current; 72 } 73 } 74