QString::utf8() - is it re-entrant or not?

blex

In accordance with the Qt documentation for QString class

bq. All functions in this class are reentrant, except for ascii(), latin1(), utf8(), and local8Bit(), which are non-reentrant.

But the implementation of QString::utf8() is the following:

@ inline QT3_SUPPORT QByteArray utf8() const{ return toUtf8(); }
@

So, the toUtf8() should be also non-reentrant.

The same situation with local8Bit().

My current understanding is that the documentation is incorrect. utf8() (and local8Bit()) should be removed from the list of non-reentrant functions.

Please confirm or provide additional clarifications.

Thanks

dangelog

Right -- did you try to download the sources for Qt 4.0 or similar and see if the implementation was different? (Maybe it used a global, non locked cache).

goetz

The warning has been introduced with "Qt 4.2.0":http://doc.qt.nokia.com/4.2/qstring.html. Both in "Qt 4.0.x":http://doc.qt.nokia.com/4.0/qstring-qt3.html and "4.1.x":http://doc.qt.nokia.com/4.1/qstring.html no method was marked as being not reentrant. I don't know the reason, the change logs for the release do not mention the change and I do not have a git log or something similar that could give a comment on it.

dangelog

Ok, point settled down -- utf8() is reentrant, ascii is not(). Documentation bug.

(Thanks to Thiago for telling :) )

goetz

@peppe
Did you check the other methods with Thiago too?

I would expect the following situation to be true:

@
// NOT reentrant:
inline QT3_SUPPORT const char *ascii() const { return ascii_helper(); }
inline QT3_SUPPORT const char *latin1() const { return latin1_helper(); }

// actually reentrant but wrong in the docs
// these are just aliases for reentrant Qt4 methods
inline QT3_SUPPORT QByteArray utf8() const { return toUtf8(); }
inline QT3_SUPPORT QByteArray local8Bit() const{ return toLocal8Bit(); }
@

dangelog

That's exactly the case -- notice that the helper()s methods store stuff in a non-locked, global hash.

goetz

Thanx for clarifying. I've added a "DocNote":/doc/qt-4.7/qstring.html#note-104 to [[Doc:QString]]'s online docs.