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Home » Modeling » TMF (Xtext) » How can i disable backtracking ?(I thought that using the code mentioned below in mwe2 code the backtracking will be disabled.)

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How can i disable backtracking ? [message #1801151]

Mon, 14 January 2019 16:52

kimi raikonnan is currently offline

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I thought that using the code mentioned below in mwe2 code the backtracking will be disabled.
But after debugging the InternalDSLParser class in antlr.internal package, i found that state.backtrack = 2
And i found this comment in RecognizerSharedState class :

/** If 0, no backtracking is going on. Safe to exec actions etc...
* If >0 then it's the level of backtracking.
*/
public int backtracking = 0;

so backtrack is enabled, right?
how can i disable it?

mew2 file :
fragment = parser.antlr.ex.rt.AntlrGeneratorFragment {
options = {
backtrack = false
classSplitting = true
fieldsPerClass = "500"
ignoreCase = true
//kAsString="1"
memoize=true
}
}

fragment = org.eclipse.xtext.generator.parser.antlr.ex.ca.ContentAssistParserGeneratorFragment {
options ={
backtrack = false
classSplitting = true
fieldsPerClass = "500"
memoize=true
ignoreCase = true
//kAsString="5"
}
}

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Re: How can i disable backtracking ? [message #1801153 is a reply to message #1801151]

Mon, 14 January 2019 16:55

Christian Dietrich is currently offline

Christian Dietrich

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0 = no backtracking

Twitter : @chrdietrich
Blog : https://www.dietrich-it.de

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Re: How can i disable backtracking ? [message #1801158 is a reply to message #1801153]

Mon, 14 January 2019 17:17

kimi raikonnan is currently offline

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by debugging in InternalDSLParser.java i found that state.backtracking = 2 not zero

so i think there is something i am missing in disabling the backtracking
I know that zero means no backtracking but the value is not equal to zero!!

public final EObject entryRuleprimary() throws RecognitionException {
EObject current = null;
int entryRuleprimary_StartIndex = input.index();
EObject iv_ruleprimary = null;

try {
if ( state.backtracking>0 && alreadyParsedRule(input, 409) ) { return current; }

[Updated on: Mon, 14 January 2019 17:18]

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Re: How can i disable backtracking ? [message #1801160 is a reply to message #1801158]

Mon, 14 January 2019 17:33

Christian Dietrich is currently offline

Christian Dietrich

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Maybe there is something in your grammar

Twitter : @chrdietrich
Blog : https://www.dietrich-it.de

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Re: How can i disable backtracking ? [message #1801162 is a reply to message #1801160]

Mon, 14 January 2019 18:11

kimi raikonnan is currently offline

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that what i am asking about, is there is something known in xtext that will enable the backtracking and i wrote it by mistake given that i disabled it in mwe2?
are you sure that if "state.backtracing" variable in InternalDSLParser class equals 2 means that backtracking is enabled?

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Re: How can i disable backtracking ? [message #1801164 is a reply to message #1801162]

Mon, 14 January 2019 18:15

Christian Dietrich is currently offline

Christian Dietrich

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yes this means backtracking. but i dont think its related to the global backtracking option for ambiguities.

is there any specific reason you ask?

Twitter : @chrdietrich
Blog : https://www.dietrich-it.de

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Re: How can i disable backtracking ? [message #1801170 is a reply to message #1801164]

Mon, 14 January 2019 20:02

kimi raikonnan is currently offline

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Yes i am suffering from performance problem, and i am really frustrated because i think i am disabling backtracking while its seems its enabled.

the comment in the code is clear,since backtracking variable is not equal zero so it means i am enabling backtracking.

Do you know how to disable it?

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Re: How can i disable backtracking ? [message #1801174 is a reply to message #1801170]

Mon, 14 January 2019 20:22

Christian Dietrich is currently offline

Christian Dietrich

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can you debug where it is set to != 0

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Re: How can i disable backtracking ? [message #1801175 is a reply to message #1801174]

Mon, 14 January 2019 20:26

kimi raikonnan is currently offline

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it was my next step, but i found that it's used widely in the code so i was looking for hints about the locations where its value got changed, if you have information about that

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Re: How can i disable backtracking ? [message #1801176 is a reply to message #1801175]

Mon, 14 January 2019 20:32

Christian Dietrich is currently offline

Christian Dietrich

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you know you can set a breakpoint on a field and configure it to match modifications

Twitter : @chrdietrich
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Re: How can i disable backtracking ? [message #1801177 is a reply to message #1801176]

Mon, 14 January 2019 20:39

kimi raikonnan is currently offline

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Thanks alot :)
I will check that and return back to this thread with the results

[Updated on: Mon, 14 January 2019 20:39]

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Re: How can i disable backtracking ? [message #1801224 is a reply to message #1801177]

Tue, 15 January 2019 15:46

kimi raikonnan is currently offline

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I found the modification in state.baacktracking happens in functions with this name

public final boolean synpred27_InternalDSLParser() {
state.backtracking++;
int start = input.mark();
try {
synpred27_InternalDSLParser_fragment(); // can never throw exception
} catch (RecognitionException re) {
System.err.println("impossible: "+re);
}
boolean success = !state.failed;
input.rewind(start);
state.backtracking--;
state.failed=false;
return success;
}

also it happens in many functions start with the same prefix "synpred".
Do you know what does it means?

[Updated on: Tue, 15 January 2019 15:50]

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Re: How can i disable backtracking ? [message #1801230 is a reply to message #1801224]

Tue, 15 January 2019 16:06

Christian Dietrich is currently offline

Christian Dietrich

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you you have a predicate in your grammar

=> or ->

Twitter : @chrdietrich
Blog : https://www.dietrich-it.de

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Re: How can i disable backtracking ? [message #1801231 is a reply to message #1801230]

Tue, 15 January 2019 16:11

kimi raikonnan is currently offline

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yes, does it enable backtracking?
and if it does, what can i do to avoid that?

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Re: How can i disable backtracking ? [message #1801239 is a reply to message #1801231]

Tue, 15 January 2019 17:12

Christian Dietrich is currently offline

Christian Dietrich

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semantic predicates do local backtracking and you cannot avoid it unless you dont use the predicate

Twitter : @chrdietrich
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Re: How can i disable backtracking ? [message #1861604 is a reply to message #1801239]

Sat, 21 October 2023 21:18

Mirko Raner is currently offline

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I don't know how this tale turned out in the end, but I just banged my head against a very similar problem where my backtracking setting had no effect.
After hours of debugging I realized that further down in my MWE2 configuration there was another parserGenerator = {debugGrammar=true} entry that overwrote the parser generator configuration that enabled the backtracking.
So keep in mind that there is no checking for duplicate entries, and that entries further down apparently overwrite earlier entries (so there is no merging of configurations either; this is as of Xtext 2.30/MWE2 2.14, not sure if this was fixed in the meantime).

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