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QRegularExpression: fix optimizePattern, document the issue

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The studyData pointer is atomically set by the pointer assignment,
but another processor running a different thread might see the
new studyData value but not the memory it points to.

Therefore, the current studyData is returned from optimizePattern
and used by that thread.

Docs were added to optimizePattern to explain what's going on.

Change-Id: I4502c336077bb98a1751011aa93ffd4f585ed101
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
This commit is contained in:
Giuseppe D'Angelo 2012-02-16 23:49:27 +01:00 committed by Qt by Nokia
parent 6e58dd34ac
commit a47d974e19
1 changed files with 24 additions and 7 deletions
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31
src/corelib/tools/qregularexpression.cpp
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@ -773,7 +773,7 @@ struct QRegularExpressionPrivate : QSharedData
void cleanCompiledPattern();
void compilePattern();
void getPatternInfo();
void optimizePattern();
pcre16_extra *optimizePattern();
QRegularExpressionMatchPrivate *doMatch(const QString &subject,
int offset,
@ -1006,15 +1006,30 @@ static bool isJitEnabled()
/*!
\internal
The purpose of the function is to call pcre16_study (which allows some
optimizations to be performed, including JIT-compiling the pattern), and
setting the studyData member variable to the result of the study. It gets
called by doMatch() every time a match is performed. As of now, the
optimizations on the pattern are performed after a certain number of usages
(i.e. the OPTIMIZE_AFTER_USE_COUNT constant).
Notice that although the method is protected by a mutex, one thread may
invoke this function and return immediately (i.e. not study the pattern,
leaving studyData to NULL); but before calling pcre16_exec to perform the
match, another thread performs the studying and sets studyData to something
else. Although the assignment to studyData is itself atomic, the release of
the memory pointed by studyData isn't. Therefore, the current studyData
value is returned and used by doMatch.
*/
void QRegularExpressionPrivate::optimizePattern()
pcre16_extra *QRegularExpressionPrivate::optimizePattern()
{
Q_ASSERT(compiledPattern);
QMutexLocker lock(&mutex);
if (studyData || (++usedCount != OPTIMIZE_AFTER_USE_COUNT))
return;
return studyData;
static const bool enableJit = isJitEnabled();
@ -1027,6 +1042,8 @@ void QRegularExpressionPrivate::optimizePattern()
if (!studyData && err)
qWarning("QRegularExpressionPrivate::optimizePattern(): pcre_study failed: %s", err);
return studyData;
}
/*!
@ -1089,7 +1106,7 @@ QRegularExpressionMatchPrivate *QRegularExpressionPrivate::doMatch(const QString
capturingCount);
// this is mutex protected
const_cast<QRegularExpressionPrivate *>(this)->optimizePattern();
const pcre16_extra *currentStudyData = const_cast<QRegularExpressionPrivate *>(this)->optimizePattern();
int pcreOptions = convertToPcreOptions(matchOptions);
@ -1113,12 +1130,12 @@ QRegularExpressionMatchPrivate *QRegularExpressionPrivate::doMatch(const QString
int result;
if (!previousMatchWasEmpty) {
result = pcre16_exec(compiledPattern, studyData,
result = pcre16_exec(compiledPattern, currentStudyData,
subjectUtf16, subjectLength,
offset, pcreOptions,
captureOffsets, captureOffsetsCount);
} else {
result = pcre16_exec(compiledPattern, studyData,
result = pcre16_exec(compiledPattern, currentStudyData,
subjectUtf16, subjectLength,
offset, pcreOptions | PCRE_NOTEMPTY_ATSTART | PCRE_ANCHORED,
captureOffsets, captureOffsetsCount);
@ -1136,7 +1153,7 @@ QRegularExpressionMatchPrivate *QRegularExpressionPrivate::doMatch(const QString
++offset;
}
result = pcre16_exec(compiledPattern, studyData,
result = pcre16_exec(compiledPattern, currentStudyData,
subjectUtf16, subjectLength,
offset, pcreOptions,
captureOffsets, captureOffsetsCount);