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1: /* ThreadLocal -- a variable with a unique value per thread 2: Copyright (C) 2000, 2002, 2003, 2006 Free Software Foundation, Inc. 3: 4: This file is part of GNU Classpath. 5: 6: GNU Classpath is free software; you can redistribute it and/or modify 7: it under the terms of the GNU General Public License as published by 8: the Free Software Foundation; either version 2, or (at your option) 9: any later version. 10: 11: GNU Classpath is distributed in the hope that it will be useful, but 12: WITHOUT ANY WARRANTY; without even the implied warranty of 13: MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 14: General Public License for more details. 15: 16: You should have received a copy of the GNU General Public License 17: along with GNU Classpath; see the file COPYING. If not, write to the 18: Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 19: 02110-1301 USA. 20: 21: Linking this library statically or dynamically with other modules is 22: making a combined work based on this library. Thus, the terms and 23: conditions of the GNU General Public License cover the whole 24: combination. 25: 26: As a special exception, the copyright holders of this library give you 27: permission to link this library with independent modules to produce an 28: executable, regardless of the license terms of these independent 29: modules, and to copy and distribute the resulting executable under 30: terms of your choice, provided that you also meet, for each linked 31: independent module, the terms and conditions of the license of that 32: module. An independent module is a module which is not derived from 33: or based on this library. If you modify this library, you may extend 34: this exception to your version of the library, but you are not 35: obligated to do so. If you do not wish to do so, delete this 36: exception statement from your version. */ 37: 38: package java.lang; 39: 40: import java.util.Map; 41: 42: 43: /** 44: * ThreadLocal objects have a different state associated with every 45: * Thread that accesses them. Every access to the ThreadLocal object 46: * (through the <code>get()</code> and <code>set()</code> methods) 47: * only affects the state of the object as seen by the currently 48: * executing Thread. 49: * 50: * <p>The first time a ThreadLocal object is accessed on a particular 51: * Thread, the state for that Thread's copy of the local variable is set by 52: * executing the method <code>initialValue()</code>. 53: * </p> 54: * 55: * <p>An example how you can use this: 56: * </p> 57: * 58: * <pre> 59: * class Connection 60: * { 61: * private static ThreadLocal owner = new ThreadLocal() 62: * { 63: * public Object initialValue() 64: * { 65: * return("nobody"); 66: * } 67: * }; 68: * ... 69: * } 70: * </pre> 71: * 72: * <p>Now all instances of connection can see who the owner of the currently 73: * executing Thread is by calling <code>owner.get()</code>. By default any 74: * Thread would be associated with 'nobody'. But the Connection object could 75: * offer a method that changes the owner associated with the Thread on 76: * which the method was called by calling <code>owner.put("somebody")</code>. 77: * (Such an owner changing method should then be guarded by security checks.) 78: * </p> 79: * 80: * <p>When a Thread is garbage collected all references to values of 81: * the ThreadLocal objects associated with that Thread are removed. 82: * </p> 83: * 84: * @author Mark Wielaard (mark@klomp.org) 85: * @author Eric Blake (ebb9@email.byu.edu) 86: * @since 1.2 87: * @status updated to 1.5 88: */ 89: public class ThreadLocal<T> 90: { 91: /** 92: * Placeholder to distinguish between uninitialized and null set by the 93: * user. Do not expose this to the public. Package visible for use by 94: * InheritableThreadLocal 95: */ 96: static final Object sentinel = new Object(); 97: 98: /** 99: * The base for the computation of the next hash for a thread local. 100: */ 101: private static int nextHashBase = 1; 102: 103: /** 104: * Allocate a new hash. 105: */ 106: private synchronized int computeNextHash() 107: { 108: return nextHashBase++ * 6709; 109: } 110: 111: /** 112: * Hash code computed for ThreadLocalMap 113: */ 114: final int fastHash; 115: 116: /** 117: * Creates a ThreadLocal object without associating any value to it yet. 118: */ 119: public ThreadLocal() 120: { 121: constructNative(); 122: fastHash = computeNextHash(); 123: } 124: 125: /** 126: * Called once per thread on the first invocation of get(), if set() was 127: * not already called. The default implementation returns <code>null</code>. 128: * Often, this method is overridden to create the appropriate initial object 129: * for the current thread's view of the ThreadLocal. 130: * 131: * @return the initial value of the variable in this thread 132: */ 133: protected T initialValue() 134: { 135: return null; 136: } 137: 138: /** 139: * Gets the value associated with the ThreadLocal object for the currently 140: * executing Thread. If this is the first time the current thread has called 141: * get(), and it has not already called set(), the value is obtained by 142: * <code>initialValue()</code>. 143: * 144: * @return the value of the variable in this thread 145: */ 146: public native T get(); 147: 148: private final Object internalGet() 149: { 150: ThreadLocalMap map = Thread.getThreadLocals(); 151: // Note that we don't have to synchronize, as only this thread will 152: // ever modify the map. 153: T value = (T) map.get(this); 154: if (value == sentinel) 155: { 156: value = initialValue(); 157: map.set(this, value); 158: } 159: return value; 160: } 161: 162: /** 163: * Sets the value associated with the ThreadLocal object for the currently 164: * executing Thread. This overrides any existing value associated with the 165: * current Thread and prevents <code>initialValue()</code> from being 166: * called if this is the first access to this ThreadLocal in this Thread. 167: * 168: * @param value the value to set this thread's view of the variable to 169: */ 170: public native void set(T value); 171: 172: private final void internalSet(Object value) 173: { 174: ThreadLocalMap map = Thread.getThreadLocals(); 175: // Note that we don't have to synchronize, as only this thread will 176: // ever modify the map. 177: map.set(this, value); 178: } 179: 180: /** 181: * Removes the value associated with the ThreadLocal object for the 182: * currently executing Thread. 183: * @since 1.5 184: */ 185: public native void remove(); 186: 187: private final void internalRemove() 188: { 189: ThreadLocalMap map = Thread.getThreadLocals(); 190: map.remove(this); 191: } 192: 193: protected native void finalize () throws Throwable; 194: 195: private native void constructNative(); 196: 197: private gnu.gcj.RawData TLSPointer; 198: }