| Clover coverage report - PLT Utilities Test Coverage (plt-20120304-r5436) |
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| Source file | Conditionals | Statements | Methods | TOTAL | |||||||||||||||
| CachedThunk.java | 50% | 73.3% | 71.4% | 69.2% |
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| 1 | /*BEGIN_COPYRIGHT_BLOCK* | |
| 2 | ||
| 3 | PLT Utilities BSD License | |
| 4 | ||
| 5 | Copyright (c) 2007-2010 JavaPLT group at Rice University | |
| 6 | All rights reserved. | |
| 7 | ||
| 8 | Developed by: Java Programming Languages Team | |
| 9 | Rice University | |
| 10 | http://www.cs.rice.edu/~javaplt/ | |
| 11 | ||
| 12 | Redistribution and use in source and binary forms, with or without modification, are permitted | |
| 13 | provided that the following conditions are met: | |
| 14 | ||
| 15 | - Redistributions of source code must retain the above copyright notice, this list of conditions | |
| 16 | and the following disclaimer. | |
| 17 | - Redistributions in binary form must reproduce the above copyright notice, this list of | |
| 18 | conditions and the following disclaimer in the documentation and/or other materials provided | |
| 19 | with the distribution. | |
| 20 | - Neither the name of the JavaPLT group, Rice University, nor the names of the library's | |
| 21 | contributors may be used to endorse or promote products derived from this software without | |
| 22 | specific prior written permission. | |
| 23 | ||
| 24 | THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR | |
| 25 | IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND | |
| 26 | FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS AND | |
| 27 | CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL | |
| 28 | DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, | |
| 29 | DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER | |
| 30 | IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT | |
| 31 | OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. | |
| 32 | ||
| 33 | *END_COPYRIGHT_BLOCK*/ | |
| 34 | ||
| 35 | package edu.rice.cs.plt.lambda; | |
| 36 | ||
| 37 | import edu.rice.cs.plt.tuple.Option; | |
| 38 | ||
| 39 | /** | |
| 40 | * <p>A thunk that caches the result of a nested thunk on the first invocation of {@code value()}. | |
| 41 | * Unlike {@link LazyThunk}, the cached result can be invalidated by invoking {@link #reset}; the | |
| 42 | * next invocation of {@code value()} will again delegate to the nested thunk (the trade-off for | |
| 43 | * this behavior is that the wrapped thunk cannot be discarded for the life of this object). | |
| 44 | * If an exception occurs during evaluation, no result is cached.</p> | |
| 45 | * | |
| 46 | * <p>Evaluation is thread-safe: locking guarantees that the nested thunk will never be evaluated (and | |
| 47 | * terminate normally) twice without an intervening {@code reset()} invocation. Thus, if two threads | |
| 48 | * invoke {@code value()} simultaneously (and a result is not cached), one will block until | |
| 49 | * the other resolves the nested thunk.</p> | |
| 50 | * | |
| 51 | * @see LazyThunk | |
| 52 | * @see DelayedThunk | |
| 53 | * @see LazyRunnable | |
| 54 | */ | |
| 55 | public class CachedThunk<R> implements ResolvingThunk<R> { | |
| 56 | ||
| 57 | private final Thunk<? extends R> _thunk; | |
| 58 | private volatile Option<R> _val; | |
| 59 | ||
| 60 | 12 | public CachedThunk(Thunk<? extends R> value) { |
| 61 | 12 | _thunk = value; |
| 62 | 12 | _val = Option.none(); |
| 63 | } | |
| 64 | ||
| 65 | 9 | public R value() { |
| 66 | 9 | Option<R> v = _val; // get a local copy in case there's a concurrent reset |
| 67 | 9 | if (v.isNone()) { return resolve(); } |
| 68 | 0 | else { return v.unwrap(); } |
| 69 | } | |
| 70 | ||
| 71 | 9 | public synchronized void reset() { |
| 72 | // *must* synchronize -- if we try to reset while resolve() is half-done, the reset may appear | |
| 73 | // to have never happened | |
| 74 | 9 | _val = Option.none(); |
| 75 | } | |
| 76 | ||
| 77 | 0 | public boolean isResolved() { return _val.isSome(); } |
| 78 | ||
| 79 | /** | |
| 80 | * Combines {@link #isResolved} and {@link #value} in an atomic operation (avoiding inconsistencies | |
| 81 | * due to a concurrent {@link #reset}): if a value is cached, return it; otherwise, return "none". | |
| 82 | */ | |
| 83 | 0 | public Option<R> cachedValue() { return _val; } |
| 84 | ||
| 85 | 9 | private synchronized R resolve() { |
| 86 | 9 | if (_val.isNone()) { // verify that the result is still unresolved now that we have a lock |
| 87 | 9 | R result = _thunk.value(); |
| 88 | 9 | _val = Option.some(result); |
| 89 | 9 | return result; |
| 90 | } | |
| 91 | 0 | else { return _val.unwrap(); } |
| 92 | } | |
| 93 | ||
| 94 | 12 | public static <R> CachedThunk<R> make(Thunk<? extends R> value) { return new CachedThunk<R>(value); } |
| 95 | ||
| 96 | } |
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