Optimize QMimeDatabase::mimeTypeForFile(f, MatchDefault)

Open the file only if matching on content is needed.

Use QFileInfo::filePath() instead of QFileInfo::absoluteFilePath() in
QMimeDatabase::mimeTypeForFile(). filePath() does much less work, and so
is faster. Thiago Macieira helpfully explained in a review comment why
the absolute path is not useful for correctness here: "Nothing needs
absolute paths within the same application that would resolve the
relative path to absolute. You only need an absolute path if you're
communicating with another application that may be in a different
directory."

QMimeDatabase::mimeTypeForFile() checks fileInfo.isDir(), so the
fileName.endsWith(QLatin1Char('/')) check in
QMimeDatabasePrivate::mimeTypeForFileNameAndData() was redundant when
called from this function. The other two callers of that function now
check this condition before opening IO devices. This improves
performance of the two QMimeDatabase::mimeTypeForFileNameAndData()
overloads in the corner case.

Refactor and optimize QMimeDatabasePrivate::findByFileName() and its
usages. Previously each caller constructed a QFileInfo object and passed
QFileInfo::fileName() into this function. Now the callers simply pass an
absolute or relative path to a file into this function, which then uses
QFileSystemEntry::fileName() to exclude the path. Constructing QFileInfo
is relatively expensive, so this change slightly improves performance.

Optimize QMimeDatabasePrivate::loadProviders() by calling static
QFileInfo::exists() instead of constructing a QFileInfo object and
calling the non-static QFileInfo::exists() overload. Note that the
QFileInfo object was always created, even if QFileInfo::exists() under
an `if` and an `#if` was never called.

The following table contains the average results of the added benchmark
tst_QMimeDatabase::benchMimeTypeForFile() on my GNU/Linux system before
and at this commit. The numbers denote milliseconds per iteration.

        data row tag                        before  at
MatchDefault:
        archive                             0.029   0.016
        OpenDocument Text                   0.029   0.015
        existent archive with extension     0.039   0.025
        existent C with extension           0.033   0.020
        existent text file with extension   0.033   0.020
        existent C w/o extension            0.076   0.074
        existent patch w/o extension        0.11    0.105
        existent archive w/o extension      0.069   0.066
MatchExtension:
        archive                             0.012   0.0115
        OpenDocument Text                   0.0115  0.011
        existent archive with extension     0.017   0.016
        existent C with extension           0.011   0.011
        existent text file with extension   0.011   0.011
        existent C w/o extension            0.016   0.0155
        existent patch w/o extension        0.013   0.012
        existent archive w/o extension      0.013   0.012
MatchContent:
        archive                             0.019   0.012
        OpenDocument Text                   0.019   0.012
        existent archive with extension     0.053   0.051
        existent C with extension           0.056   0.0545
        existent text file with extension   0.058   0.056
        existent C w/o extension            0.0605  0.059
        existent patch w/o extension        0.10    0.099
        existent archive w/o extension      0.057   0.054

Change-Id: Idb541656e073a2c4822ace3f4da412f29f2351f8
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: David Faure <david.faure@kdab.com>

0 files changed, 0 insertions, 0 deletions