QMimeDatabase::mimeTypeForFile: don't create QFileInfo on UNIX

When mode != MatchExtension is passed to
QMimeDatabase::mimeTypeForFile(const QString &fileName, MatchMode mode) const
a QFileInfo object is always created and used to check
QFileInfo::isDir(). Replace this expensive approach with a very cheap
(bitmask) S_ISDIR check under Q_OS_UNIX. QT_STAT is already called for
other reasons, so we just reuse its result in the S_ISDIR check.

Extract almost all code from
QMimeDatabase::mimeTypeForFile(const QString &, MatchMode) const;
QMimeDatabase::mimeTypeForData(QIODevice *) const;
QMimeDatabase::mimeTypeForFile(const QFileInfo &, MatchMode) const
into
QMimeDatabasePrivate::mimeTypeForFileExtension(const QString &);
QMimeDatabasePrivate::mimeTypeForData(QIODevice *);
QMimeDatabasePrivate::mimeTypeForFile(const QString &, const QFileInfo *, QMimeDatabase::MatchMode)
respectively. This refactoring is a less convoluted and more efficient
alternative to adding more mutex-unlocking hacks. The existing
QMutexLocker::unlock() calls are thereby eliminated.

The following table contains the average results of the benchmark
tst_QMimeDatabase::benchMimeTypeForFile() on my GNU/Linux system before
and at this commit. The numbers denote milliseconds per iteration.
This commit does not measurably affect performance when
mode == MatchExtension, therefore the MatchExtension section contains a
single column with results common to both commits (it is interesting to
compare benchmark results across match modes).

        data row tag                        before  at
MatchDefault:
        archive                             0.012   0.010
        OpenDocument Text                   0.012   0.010
        existent archive with extension     0.022   0.018
        existent C with extension           0.016   0.012
        existent text file with extension   0.017   0.012
        existent C w/o extension            0.072   0.067
        existent patch w/o extension        0.10    0.10
        existent archive w/o extension      0.064   0.060
MatchExtension:
        archive                                 0.0081
        OpenDocument Text                       0.0076
        existent archive with extension         0.012
        existent C with extension               0.0075
        existent text file with extension       0.0076
        existent C w/o extension                0.0122
        existent patch w/o extension            0.0091
        existent archive w/o extension          0.0091
MatchContent:
        archive                             0.0098  0.0078
        OpenDocument Text                   0.0098  0.0078
        existent archive with extension     0.051   0.047
        existent C with extension           0.051   0.047
        existent text file with extension   0.053   0.049
        existent C w/o extension            0.058   0.054
        existent patch w/o extension        0.099   0.095
        existent archive w/o extension      0.054   0.050

Change-Id: I01b37c9645f0d8d35fd1a6ea1c7a99be2faeeb73
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: David Faure <david.faure@kdab.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/src/corelib/mimetypes/qmimedatabase_p.h b/src/corelib/mimetypes/qmimedatabase_p.h
index e6af23e7ed..d5ed61b0b9 100644
--- a/src/corelib/mimetypes/qmimedatabase_p.h
+++ b/src/corelib/mimetypes/qmimedatabase_p.h
@@ -52,6 +52,7 @@
 // We mean it.
 //
 
+#include "qmimedatabase.h"
 #include "qmimetype.h"
 
 QT_REQUIRE_CONFIG(mimetype);
@@ -68,6 +69,7 @@ QT_REQUIRE_CONFIG(mimetype);
 
 QT_BEGIN_NAMESPACE
 
+class QFileInfo;
 class QIODevice;
 class QMimeDatabase;
 class QMimeProviderBase;
@@ -92,6 +94,9 @@ public:
     QStringList parents(const QString &mimeName);
     QMimeType mimeTypeForName(const QString &nameOrAlias);
     QMimeType mimeTypeForFileNameAndData(const QString &fileName, QIODevice *device, int *priorityPtr);
+    QMimeType mimeTypeForFileExtension(const QString &fileName);
+    QMimeType mimeTypeForData(QIODevice *device);
+    QMimeType mimeTypeForFile(const QString &fileName, const QFileInfo *fileInfo, QMimeDatabase::MatchMode mode);
     QMimeType findByData(const QByteArray &data, int *priorityPtr);
     QStringList mimeTypeForFileName(const QString &fileName);
     QMimeGlobMatchResult findByFileName(const QString &fileName);