antlr.v4.runtime.atn.ATNSimulator source code

1 /*
2  * Copyright (c) 2012-2019 The ANTLR Project. All rights reserved.
3  * Use of this file is governed by the BSD 3-clause license that
4  * can be found in the LICENSE.txt file in the project root.
5  */
6 
7 module antlr.v4.runtime.atn.ATNSimulator;
8 
9 import antlr.v4.runtime.UnsupportedOperationException;
10 import antlr.v4.runtime.atn.ATN;
11 import antlr.v4.runtime.atn.ATNDeserializer;
12 import antlr.v4.runtime.atn.InterfaceATNSimulator;
13 import antlr.v4.runtime.atn.PredictionContext;
14 import antlr.v4.runtime.atn.PredictionContextCache;
15 import antlr.v4.runtime.dfa.DFAState;
16 import std.uuid;
17 
18 /**
19  * ATN simulator base class
20  */
21 abstract class ATNSimulator : InterfaceATNSimulator
22 {
23 
24     public static int SERIALIZED_VERSION;
25 
26     /**
27      * This is the current serialized UUID.
28      * deprecated Use {@link ATNDeserializer#checkCondition(boolean)} instead.
29      */
30     public static UUID SERIALIZED_UUID;
31 
32     /**
33      * Must distinguish between missing edge and edge we know leads nowhere
34      */
35     public static DFAState ERROR;
36 
37     public ATN atn;
38 
39     /**
40      * The context cache maps all PredictionContext objects that are equals()
41      * to a single cached copy. This cache is shared across all contexts
42      * in all ATNConfigs in all DFA states.  We rebuild each ATNConfigSet
43      * to use only cached nodes/graphs in addDFAState(). We don't want to
44      * fill this during closure() since there are lots of contexts that
45      * pop up but are not used ever again. It also greatly slows down closure().
46      *
47      * <p>This cache makes a huge difference in memory and a little bit in speed.
48      * For the Java grammar on java.*, it dropped the memory requirements
49      * at the end from 25M to 16M. We don't store any of the full context
50      * graphs in the DFA because they are limited to local context only,
51      * but apparently there's a lot of repetition there as well. We optimize
52      * the config contexts before storing the config set in the DFA states
53      * by literally rebuilding them with cached subgraphs only.</p>
54      *
55      * <p>I tried a cache for use during closure operations, that was
56      * whacked after each adaptivePredict(). It cost a little bit
57      * more time I think and doesn't save on the overall footprint
58      * so it's not worth the complexity.</p>
59      */
60     public PredictionContextCache sharedContextCache;
61 
62     public static this()
63     {
64         SERIALIZED_VERSION = ATNDeserializer.SERIALIZED_VERSION;
65         SERIALIZED_UUID = ATNDeserializer.SERIALIZED_UUID;
66     }
67 
68     public this(ATN atn, PredictionContextCache sharedContextCache)
69     {
70         this.atn = atn;
71         this.sharedContextCache = sharedContextCache;
72     }
73 
74     abstract public void reset();
75 
76     /**
77      * Clear the DFA cache used by the current instance. Since the DFA cache may
78      * be shared by multiple ATN simulators, this method may affect the
79      * performance (but not accuracy) of other parsers which are being used
80      * concurrently.
81      *
82      *  @throws UnsupportedOperationException if the current instance does not
83      * support clearing the DFA.
84      */
85     public void clearDFA()
86     {
87         throw new UnsupportedOperationException("This ATN simulator does not support clearing the DFA.");
88     }
89 
90     public PredictionContextCache getSharedContextCache()
91     {
92         return sharedContextCache;
93     }
94 
95     public PredictionContext getCachedContext(PredictionContext context)
96     {
97         if (sharedContextCache is null)
98             return context;
99         PredictionContext[PredictionContext] visited;
100         return PredictionContext.getCachedContext(context,
101                                                   sharedContextCache,
102                                                   visited);
103     }
104 
105 }