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From "Mohammed Alfallaj (JIRA)" <j...@apache.org>
Subject [jira] [Created] (LANG-1206) CharSetUtils.squeeze() Performance Issue
Date Wed, 24 Feb 2016 02:23:18 GMT
Mohammed Alfallaj created LANG-1206:
---------------------------------------

             Summary: CharSetUtils.squeeze() Performance Issue
                 Key: LANG-1206
                 URL: https://issues.apache.org/jira/browse/LANG-1206
             Project: Commons Lang
          Issue Type: Improvement
          Components: lang.*
    Affects Versions: 3.4
            Reporter: Mohammed Alfallaj
            Priority: Minor
             Fix For: 3.4


A readable form of the description is attached in Description_Squeeze.docx.

Below is a text format of the description (in case the .docx does not work):


***********************************************************************
Performance problems of current CharSetUtils.squeeze() algorithm:
***********************************************************************


************************************
FIRST PROBLEM: 
************************************
-Method org.apache.commons.lang3.CharSet.contains() is called in each character iteration
for a consecutive set of duplicated characters in str (starting from the second character
in the duplicated set). This large number of calls to contains() are determined to increase
the performance overhead for squeeze() calls given the high computing cost of executing contains()
method. Note that only one call to contains() is needed for the second character in this set
of duplicated characters. There is no need to repeat the calls to contains() method for the
same duplicated character that we have already checked in the second occurrence. For example,
if str=”abbbbbc” and set=”b”, then the algorithm should call contains() only once
for the second b character occurrence and prevent calling contains() again given that it has
already been called before for this block. The current algorithm adds high performance overhead
by calling contains() repetitively for each duplicated b character starting from the second
occurrence. For this example where str=”abbbbbc” and set=”b”, the suggested solution
will call contains() method only once instead of 4 times which will largely reduce the performance
overhead of squeeze() method. 

-Consider the following example, System.currentTimeMillis() testing shows a performance improvement
by around 83% if we run the suggested enhanced solution with the following sample input data

	str = “abbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbc”
	set = “b”

************************************
PROPOSED SOLUTION FOR FIRST PROBLEM:
************************************
-Using two character flags inChars and notInChars:
	inChars: flag to record the recent character that has been determined to be in chars CharSet
	notInChars: flag to record the recent character that has been determined to NOT be in chars
CharSet
-Adding the following conditions to prevent unnecessary/expensive calls to contains() method.
Only one call to contains() method is needed starting from the second character in the consecutive
set of duplicated characters:
	if ((inChars != null) && (ch == inChars))
		this if-statement checks if this ch char has recently been determined to be in chars CharSet,
this prevents calling contains() more than once for a consecutive set of duplicated characters
in str
		if one of these conditions fails, it means that the consecutive set of duplicated characters
for this ch character has not yet been checked for this block of duplicated characters (i.e.
has not been checked = we have not yet done the one-time call to contains method for this
particular set of duplicated characters)
	if ((notInChars == null) || (ch != notInChars))
		if both conditions are false, it means that ch has recently been determined to NOT be in
chars CharSet
	if (chars.contains(ch))
		here we call the expensive chars.contains() only once for this consecutive set of duplicated
characters.
-Note: this suggested solution does not break the functionality of org.apache.commons.lang3.CharSetUtils.squeeze(String
str, String… set). This suggested solution is executed against the latest UnitTest CharSetUtilsTest.java
written by Apache.




************************************
SECOND PROBLEM: 
************************************
the current algorithm starts the for-loop with i=0 which is not a necessary step. This adds
the overhead of executing the if condition (i != 0). In this logic, the algorithm will always
append the first character from str to the buffer. So there is no need to execute (i != 0)
for every character in the consecutive set of duplicated characters.

************************************
PROPOSED SOLUTION FOR SECOND PROBLEM: 
************************************
lastChar is assigned the first character in str and appended to buffer before executing the
for loop. Then the for loop begins with i=1 removing the unnecessary (i != 0) executions.




END OF DESCRIPTION



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