7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.lang;
27 import java.lang.ref.*;
28 import java.util.Objects;
29 import java.util.concurrent.atomic.AtomicInteger;
30 import java.util.function.Supplier;
31
32 /**
33 * This class provides thread-local variables. These variables differ from
34 * their normal counterparts in that each thread that accesses one (via its
35 * {@code get} or {@code set} method) has its own, independently initialized
36 * copy of the variable. {@code ThreadLocal} instances are typically private
37 * static fields in classes that wish to associate state with a thread (e.g.,
38 * a user ID or Transaction ID).
39 *
40 * <p>For example, the class below generates unique identifiers local to each
41 * thread.
42 * A thread's id is assigned the first time it invokes {@code ThreadId.get()}
43 * and remains unchanged on subsequent calls.
44 * <pre>
45 * import java.util.concurrent.atomic.AtomicInteger;
46 *
154 * current thread, it is first initialized to the value returned
155 * by an invocation of the {@link #initialValue} method.
156 *
157 * @return the current thread's value of this thread-local
158 */
159 public T get() {
160 Thread t = Thread.currentThread();
161 ThreadLocalMap map = getMap(t);
162 if (map != null) {
163 ThreadLocalMap.Entry e = map.getEntry(this);
164 if (e != null) {
165 @SuppressWarnings("unchecked")
166 T result = (T)e.value;
167 return result;
168 }
169 }
170 return setInitialValue();
171 }
172
173 /**
174 * Variant of set() to establish initialValue. Used instead
175 * of set() in case user has overridden the set() method.
176 *
177 * @return the initial value
178 */
179 private T setInitialValue() {
180 T value = initialValue();
181 Thread t = Thread.currentThread();
182 ThreadLocalMap map = getMap(t);
183 if (map != null)
184 map.set(this, value);
185 else
186 createMap(t, value);
187 return value;
188 }
189
190 /**
191 * Sets the current thread's copy of this thread-local variable
192 * to the specified value. Most subclasses will have no need to
193 * override this method, relying solely on the {@link #initialValue}
194 * method to set the values of thread-locals.
195 *
196 * @param value the value to be stored in the current thread's copy of
197 * this thread-local.
198 */
199 public void set(T value) {
200 Thread t = Thread.currentThread();
201 ThreadLocalMap map = getMap(t);
202 if (map != null)
203 map.set(this, value);
204 else
205 createMap(t, value);
206 }
|
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.lang;
27 import jdk.internal.misc.TerminatingThreadLocal;
28
29 import java.lang.ref.*;
30 import java.util.Objects;
31 import java.util.concurrent.atomic.AtomicInteger;
32 import java.util.function.Supplier;
33
34 /**
35 * This class provides thread-local variables. These variables differ from
36 * their normal counterparts in that each thread that accesses one (via its
37 * {@code get} or {@code set} method) has its own, independently initialized
38 * copy of the variable. {@code ThreadLocal} instances are typically private
39 * static fields in classes that wish to associate state with a thread (e.g.,
40 * a user ID or Transaction ID).
41 *
42 * <p>For example, the class below generates unique identifiers local to each
43 * thread.
44 * A thread's id is assigned the first time it invokes {@code ThreadId.get()}
45 * and remains unchanged on subsequent calls.
46 * <pre>
47 * import java.util.concurrent.atomic.AtomicInteger;
48 *
156 * current thread, it is first initialized to the value returned
157 * by an invocation of the {@link #initialValue} method.
158 *
159 * @return the current thread's value of this thread-local
160 */
161 public T get() {
162 Thread t = Thread.currentThread();
163 ThreadLocalMap map = getMap(t);
164 if (map != null) {
165 ThreadLocalMap.Entry e = map.getEntry(this);
166 if (e != null) {
167 @SuppressWarnings("unchecked")
168 T result = (T)e.value;
169 return result;
170 }
171 }
172 return setInitialValue();
173 }
174
175 /**
176 * Returns {@code true} if there is a value in the current thread's copy of
177 * this thread-local variable, even if that values is {@code null}.
178 *
179 * @return {@code true} if current thread has associated value in this
180 * thread-local variable; {@code false} if not
181 */
182 boolean isPresent() {
183 Thread t = Thread.currentThread();
184 ThreadLocalMap map = getMap(t);
185 return map != null && map.getEntry(this) != null;
186 }
187
188 /**
189 * Variant of set() to establish initialValue. Used instead
190 * of set() in case user has overridden the set() method.
191 *
192 * @return the initial value
193 */
194 private T setInitialValue() {
195 T value = initialValue();
196 Thread t = Thread.currentThread();
197 ThreadLocalMap map = getMap(t);
198 if (map != null)
199 map.set(this, value);
200 else
201 createMap(t, value);
202 TerminatingThreadLocal.register(this);
203 return value;
204 }
205
206 /**
207 * Sets the current thread's copy of this thread-local variable
208 * to the specified value. Most subclasses will have no need to
209 * override this method, relying solely on the {@link #initialValue}
210 * method to set the values of thread-locals.
211 *
212 * @param value the value to be stored in the current thread's copy of
213 * this thread-local.
214 */
215 public void set(T value) {
216 Thread t = Thread.currentThread();
217 ThreadLocalMap map = getMap(t);
218 if (map != null)
219 map.set(this, value);
220 else
221 createMap(t, value);
222 }
|