--- /dev/null
+/*
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation. Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * This file is available under and governed by the GNU General Public
+ * License version 2 only, as published by the Free Software Foundation.
+ * However, the following notice accompanied the original version of this
+ * file:
+ *
+ * Written by Doug Lea with assistance from members of JCP JSR-166
+ * Expert Group and released to the public domain, as explained at
+ * http://creativecommons.org/licenses/publicdomain
+ */
+
+package edu.tamu.aser.internaljuc;
+import sun.misc.Unsafe;
+
+
+/**
+ * Basic thread blocking primitives for creating locks and other
+ * synchronization classes.
+ *
+ * <p>This class associates, with each thread that uses it, a permit
+ * (in the sense of the {@link java.util.concurrent.Semaphore
+ * Semaphore} class). A call to {@code park} will return immediately
+ * if the permit is available, consuming it in the process; otherwise
+ * it <em>may</em> block. A call to {@code unpark} makes the permit
+ * available, if it was not already available. (Unlike with Semaphores
+ * though, permits do not accumulate. There is at most one.)
+ *
+ * <p>Methods {@code park} and {@code unpark} provide efficient
+ * means of blocking and unblocking threads that do not encounter the
+ * problems that cause the deprecated methods {@code Thread.suspend}
+ * and {@code Thread.resume} to be unusable for such purposes: Races
+ * between one thread invoking {@code park} and another thread trying
+ * to {@code unpark} it will preserve liveness, due to the
+ * permit. Additionally, {@code park} will return if the caller's
+ * thread was interrupted, and timeout versions are supported. The
+ * {@code park} method may also return at any other time, for "no
+ * reason", so in general must be invoked within a loop that rechecks
+ * conditions upon return. In this sense {@code park} serves as an
+ * optimization of a "busy wait" that does not waste as much time
+ * spinning, but must be paired with an {@code unpark} to be
+ * effective.
+ *
+ * <p>The three forms of {@code park} each also support a
+ * {@code blocker} object parameter. This object is recorded while
+ * the thread is blocked to permit monitoring and diagnostic tools to
+ * identify the reasons that threads are blocked. (Such tools may
+ * access blockers using method {@link #getBlocker}.) The use of these
+ * forms rather than the original forms without this parameter is
+ * strongly encouraged. The normal argument to supply as a
+ * {@code blocker} within a lock implementation is {@code this}.
+ *
+ * <p>These methods are designed to be used as tools for creating
+ * higher-level synchronization utilities, and are not in themselves
+ * useful for most concurrency control applications. The {@code park}
+ * method is designed for use only in constructions of the form:
+ * <pre>while (!canProceed()) { ... LockSupport.park(this); }</pre>
+ * where neither {@code canProceed} nor any other actions prior to the
+ * call to {@code park} entail locking or blocking. Because only one
+ * permit is associated with each thread, any intermediary uses of
+ * {@code park} could interfere with its intended effects.
+ *
+ * <p><b>Sample Usage.</b> Here is a sketch of a first-in-first-out
+ * non-reentrant lock class:
+ * <pre>{@code
+ * class FIFOMutex {
+ * private final AtomicBoolean locked = new AtomicBoolean(false);
+ * private final Queue<Thread> waiters
+ * = new ConcurrentLinkedQueue<Thread>();
+ *
+ * public void lock() {
+ * boolean wasInterrupted = false;
+ * Thread current = Thread.currentThread();
+ * waiters.add(current);
+ *
+ * // Block while not first in queue or cannot acquire lock
+ * while (waiters.peek() != current ||
+ * !locked.compareAndSet(false, true)) {
+ * LockSupport.park(this);
+ * if (Thread.interrupted()) // ignore interrupts while waiting
+ * wasInterrupted = true;
+ * }
+ *
+ * waiters.remove();
+ * if (wasInterrupted) // reassert interrupt status on exit
+ * current.interrupt();
+ * }
+ *
+ * public void unlock() {
+ * locked.set(false);
+ * LockSupport.unpark(waiters.peek());
+ * }
+ * }}</pre>
+ */
+
+public class Reex_LockSupport {
+ private Reex_LockSupport() {} // Cannot be instantiated.
+
+ // Hotspot implementation via intrinsics API
+ private static final Unsafe unsafe = MyUnsafe.getUnsafe();
+ private static final long parkBlockerOffset;
+
+ static {
+ try {
+ parkBlockerOffset = unsafe.objectFieldOffset
+ (java.lang.Thread.class.getDeclaredField("parkBlocker"));
+ } catch (Exception ex) { throw new Error(ex); }
+ }
+
+ private static void setBlocker(Thread t, Object arg) {
+ // Even though volatile, hotspot doesn't need a write barrier here.
+ unsafe.putObject(t, parkBlockerOffset, arg);
+ }
+
+ /**
+ * Makes available the permit for the given thread, if it
+ * was not already available. If the thread was blocked on
+ * {@code park} then it will unblock. Otherwise, its next call
+ * to {@code park} is guaranteed not to block. This operation
+ * is not guaranteed to have any effect at all if the given
+ * thread has not been started.
+ *
+ * @param thread the thread to unpark, or {@code null}, in which case
+ * this operation has no effect
+ */
+ public static void unpark(Thread thread) {
+ if (thread != null)
+ unsafe.unpark(thread);
+ }
+
+ /**
+ * Disables the current thread for thread scheduling purposes unless the
+ * permit is available.
+ *
+ * <p>If the permit is available then it is consumed and the call returns
+ * immediately; otherwise
+ * the current thread becomes disabled for thread scheduling
+ * purposes and lies dormant until one of three things happens:
+ *
+ * <ul>
+ * <li>Some other thread invokes {@link #unpark unpark} with the
+ * current thread as the target; or
+ *
+ * <li>Some other thread {@linkplain Thread#interrupt interrupts}
+ * the current thread; or
+ *
+ * <li>The call spuriously (that is, for no reason) returns.
+ * </ul>
+ *
+ * <p>This method does <em>not</em> report which of these caused the
+ * method to return. Callers should re-check the conditions which caused
+ * the thread to park in the first place. Callers may also determine,
+ * for example, the interrupt status of the thread upon return.
+ *
+ * @param blocker the synchronization object responsible for this
+ * thread parking
+ * @since 1.6
+ */
+ public static void park(Object blocker) {
+ Thread t = Thread.currentThread();
+ setBlocker(t, blocker);
+ unsafe.park(false, 0L);
+ setBlocker(t, null);
+ }
+
+ /**
+ * Disables the current thread for thread scheduling purposes, for up to
+ * the specified waiting time, unless the permit is available.
+ *
+ * <p>If the permit is available then it is consumed and the call
+ * returns immediately; otherwise the current thread becomes disabled
+ * for thread scheduling purposes and lies dormant until one of four
+ * things happens:
+ *
+ * <ul>
+ * <li>Some other thread invokes {@link #unpark unpark} with the
+ * current thread as the target; or
+ *
+ * <li>Some other thread {@linkplain Thread#interrupt interrupts} the current
+ * thread; or
+ *
+ * <li>The specified waiting time elapses; or
+ *
+ * <li>The call spuriously (that is, for no reason) returns.
+ * </ul>
+ *
+ * <p>This method does <em>not</em> report which of these caused the
+ * method to return. Callers should re-check the conditions which caused
+ * the thread to park in the first place. Callers may also determine,
+ * for example, the interrupt status of the thread, or the elapsed time
+ * upon return.
+ *
+ * @param blocker the synchronization object responsible for this
+ * thread parking
+ * @param nanos the maximum number of nanoseconds to wait
+ * @since 1.6
+ */
+ public static void parkNanos(Object blocker, long nanos) {
+ if (nanos > 0) {
+ Thread t = Thread.currentThread();
+ setBlocker(t, blocker);
+ unsafe.park(false, nanos);
+ setBlocker(t, null);
+ }
+ }
+
+ /**
+ * Disables the current thread for thread scheduling purposes, until
+ * the specified deadline, unless the permit is available.
+ *
+ * <p>If the permit is available then it is consumed and the call
+ * returns immediately; otherwise the current thread becomes disabled
+ * for thread scheduling purposes and lies dormant until one of four
+ * things happens:
+ *
+ * <ul>
+ * <li>Some other thread invokes {@link #unpark unpark} with the
+ * current thread as the target; or
+ *
+ * <li>Some other thread {@linkplain Thread#interrupt interrupts} the
+ * current thread; or
+ *
+ * <li>The specified deadline passes; or
+ *
+ * <li>The call spuriously (that is, for no reason) returns.
+ * </ul>
+ *
+ * <p>This method does <em>not</em> report which of these caused the
+ * method to return. Callers should re-check the conditions which caused
+ * the thread to park in the first place. Callers may also determine,
+ * for example, the interrupt status of the thread, or the current time
+ * upon return.
+ *
+ * @param blocker the synchronization object responsible for this
+ * thread parking
+ * @param deadline the absolute time, in milliseconds from the Epoch,
+ * to wait until
+ * @since 1.6
+ */
+ public static void parkUntil(Object blocker, long deadline) {
+ Thread t = Thread.currentThread();
+ setBlocker(t, blocker);
+ unsafe.park(true, deadline);
+ setBlocker(t, null);
+ }
+
+ /**
+ * Returns the blocker object supplied to the most recent
+ * invocation of a park method that has not yet unblocked, or null
+ * if not blocked. The value returned is just a momentary
+ * snapshot -- the thread may have since unblocked or blocked on a
+ * different blocker object.
+ *
+ * @return the blocker
+ * @since 1.6
+ */
+ public static Object getBlocker(Thread t) {
+ return unsafe.getObjectVolatile(t, parkBlockerOffset);
+ }
+
+ /**
+ * Disables the current thread for thread scheduling purposes unless the
+ * permit is available.
+ *
+ * <p>If the permit is available then it is consumed and the call
+ * returns immediately; otherwise the current thread becomes disabled
+ * for thread scheduling purposes and lies dormant until one of three
+ * things happens:
+ *
+ * <ul>
+ *
+ * <li>Some other thread invokes {@link #unpark unpark} with the
+ * current thread as the target; or
+ *
+ * <li>Some other thread {@linkplain Thread#interrupt interrupts}
+ * the current thread; or
+ *
+ * <li>The call spuriously (that is, for no reason) returns.
+ * </ul>
+ *
+ * <p>This method does <em>not</em> report which of these caused the
+ * method to return. Callers should re-check the conditions which caused
+ * the thread to park in the first place. Callers may also determine,
+ * for example, the interrupt status of the thread upon return.
+ */
+ public static void park() {
+ unsafe.park(false, 0L);
+ }
+
+ /**
+ * Disables the current thread for thread scheduling purposes, for up to
+ * the specified waiting time, unless the permit is available.
+ *
+ * <p>If the permit is available then it is consumed and the call
+ * returns immediately; otherwise the current thread becomes disabled
+ * for thread scheduling purposes and lies dormant until one of four
+ * things happens:
+ *
+ * <ul>
+ * <li>Some other thread invokes {@link #unpark unpark} with the
+ * current thread as the target; or
+ *
+ * <li>Some other thread {@linkplain Thread#interrupt interrupts}
+ * the current thread; or
+ *
+ * <li>The specified waiting time elapses; or
+ *
+ * <li>The call spuriously (that is, for no reason) returns.
+ * </ul>
+ *
+ * <p>This method does <em>not</em> report which of these caused the
+ * method to return. Callers should re-check the conditions which caused
+ * the thread to park in the first place. Callers may also determine,
+ * for example, the interrupt status of the thread, or the elapsed time
+ * upon return.
+ *
+ * @param nanos the maximum number of nanoseconds to wait
+ */
+ public static void parkNanos(long nanos) {
+ if (nanos > 0)
+ unsafe.park(false, nanos);
+ }
+
+ /**
+ * Disables the current thread for thread scheduling purposes, until
+ * the specified deadline, unless the permit is available.
+ *
+ * <p>If the permit is available then it is consumed and the call
+ * returns immediately; otherwise the current thread becomes disabled
+ * for thread scheduling purposes and lies dormant until one of four
+ * things happens:
+ *
+ * <ul>
+ * <li>Some other thread invokes {@link #unpark unpark} with the
+ * current thread as the target; or
+ *
+ * <li>Some other thread {@linkplain Thread#interrupt interrupts}
+ * the current thread; or
+ *
+ * <li>The specified deadline passes; or
+ *
+ * <li>The call spuriously (that is, for no reason) returns.
+ * </ul>
+ *
+ * <p>This method does <em>not</em> report which of these caused the
+ * method to return. Callers should re-check the conditions which caused
+ * the thread to park in the first place. Callers may also determine,
+ * for example, the interrupt status of the thread, or the current time
+ * upon return.
+ *
+ * @param deadline the absolute time, in milliseconds from the Epoch,
+ * to wait until
+ */
+ public static void parkUntil(long deadline) {
+ unsafe.park(true, deadline);
+ }
+}
projects / Benchmarks_CSolver.git / blobdiff