GNU Classpath (0.97.2) | |
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1: /* 2: * Written by Doug Lea with assistance from members of JCP JSR-166 3: * Expert Group and released to the public domain, as explained at 4: * http://creativecommons.org/licenses/publicdomain 5: */ 6: 7: package java.util.concurrent.atomic; 8: import sun.misc.Unsafe; 9: 10: /** 11: * An <tt>int</tt> value that may be updated atomically. See the 12: * {@link java.util.concurrent.atomic} package specification for 13: * description of the properties of atomic variables. An 14: * <tt>AtomicInteger</tt> is used in applications such as atomically 15: * incremented counters, and cannot be used as a replacement for an 16: * {@link java.lang.Integer}. However, this class does extend 17: * <tt>Number</tt> to allow uniform access by tools and utilities that 18: * deal with numerically-based classes. 19: * 20: * @since 1.5 21: * @author Doug Lea 22: */ 23: public class AtomicInteger extends Number implements java.io.Serializable { 24: private static final long serialVersionUID = 6214790243416807050L; 25: 26: // setup to use Unsafe.compareAndSwapInt for updates 27: private static final Unsafe unsafe = Unsafe.getUnsafe(); 28: private static final long valueOffset; 29: 30: static { 31: try { 32: valueOffset = unsafe.objectFieldOffset 33: (AtomicInteger.class.getDeclaredField("value")); 34: } catch (Exception ex) { throw new Error(ex); } 35: } 36: 37: private volatile int value; 38: 39: /** 40: * Creates a new AtomicInteger with the given initial value. 41: * 42: * @param initialValue the initial value 43: */ 44: public AtomicInteger(int initialValue) { 45: value = initialValue; 46: } 47: 48: /** 49: * Creates a new AtomicInteger with initial value <tt>0</tt>. 50: */ 51: public AtomicInteger() { 52: } 53: 54: /** 55: * Gets the current value. 56: * 57: * @return the current value 58: */ 59: public final int get() { 60: return value; 61: } 62: 63: /** 64: * Sets to the given value. 65: * 66: * @param newValue the new value 67: */ 68: public final void set(int newValue) { 69: value = newValue; 70: } 71: 72: /** 73: * Eventually sets to the given value. 74: * 75: * @param newValue the new value 76: * @since 1.6 77: */ 78: public final void lazySet(int newValue) { 79: unsafe.putOrderedInt(this, valueOffset, newValue); 80: } 81: 82: /** 83: * Atomically sets to the given value and returns the old value. 84: * 85: * @param newValue the new value 86: * @return the previous value 87: */ 88: public final int getAndSet(int newValue) { 89: for (;;) { 90: int current = get(); 91: if (compareAndSet(current, newValue)) 92: return current; 93: } 94: } 95: 96: /** 97: * Atomically sets the value to the given updated value 98: * if the current value <tt>==</tt> the expected value. 99: * 100: * @param expect the expected value 101: * @param update the new value 102: * @return true if successful. False return indicates that 103: * the actual value was not equal to the expected value. 104: */ 105: public final boolean compareAndSet(int expect, int update) { 106: return unsafe.compareAndSwapInt(this, valueOffset, expect, update); 107: } 108: 109: /** 110: * Atomically sets the value to the given updated value 111: * if the current value <tt>==</tt> the expected value. 112: * May fail spuriously and does not provide ordering guarantees, 113: * so is only rarely an appropriate alternative to <tt>compareAndSet</tt>. 114: * 115: * @param expect the expected value 116: * @param update the new value 117: * @return true if successful. 118: */ 119: public final boolean weakCompareAndSet(int expect, int update) { 120: return unsafe.compareAndSwapInt(this, valueOffset, expect, update); 121: } 122: 123: /** 124: * Atomically increments by one the current value. 125: * 126: * @return the previous value 127: */ 128: public final int getAndIncrement() { 129: for (;;) { 130: int current = get(); 131: int next = current + 1; 132: if (compareAndSet(current, next)) 133: return current; 134: } 135: } 136: 137: /** 138: * Atomically decrements by one the current value. 139: * 140: * @return the previous value 141: */ 142: public final int getAndDecrement() { 143: for (;;) { 144: int current = get(); 145: int next = current - 1; 146: if (compareAndSet(current, next)) 147: return current; 148: } 149: } 150: 151: /** 152: * Atomically adds the given value to the current value. 153: * 154: * @param delta the value to add 155: * @return the previous value 156: */ 157: public final int getAndAdd(int delta) { 158: for (;;) { 159: int current = get(); 160: int next = current + delta; 161: if (compareAndSet(current, next)) 162: return current; 163: } 164: } 165: 166: /** 167: * Atomically increments by one the current value. 168: * 169: * @return the updated value 170: */ 171: public final int incrementAndGet() { 172: for (;;) { 173: int current = get(); 174: int next = current + 1; 175: if (compareAndSet(current, next)) 176: return next; 177: } 178: } 179: 180: /** 181: * Atomically decrements by one the current value. 182: * 183: * @return the updated value 184: */ 185: public final int decrementAndGet() { 186: for (;;) { 187: int current = get(); 188: int next = current - 1; 189: if (compareAndSet(current, next)) 190: return next; 191: } 192: } 193: 194: /** 195: * Atomically adds the given value to the current value. 196: * 197: * @param delta the value to add 198: * @return the updated value 199: */ 200: public final int addAndGet(int delta) { 201: for (;;) { 202: int current = get(); 203: int next = current + delta; 204: if (compareAndSet(current, next)) 205: return next; 206: } 207: } 208: 209: /** 210: * Returns the String representation of the current value. 211: * @return the String representation of the current value. 212: */ 213: public String toString() { 214: return Integer.toString(get()); 215: } 216: 217: 218: public int intValue() { 219: return get(); 220: } 221: 222: public long longValue() { 223: return (long)get(); 224: } 225: 226: public float floatValue() { 227: return (float)get(); 228: } 229: 230: public double doubleValue() { 231: return (double)get(); 232: } 233: 234: }
GNU Classpath (0.97.2) |