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QTemporaryFile: document rename() differences from QFile

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We will not do a copy+delete if the destination is on another mount
point (in fact, QFile uses QTemporaryFile for the latter). In my
opinion, that's a misfeature in QFile, because such an operation may
need to display a progress bar to the user so they won't think the
application has frozen. But it's too late to change now.

I don't know why QTemporaryFile is different. It might be because it was
used for the atomic materialization of a file before QSaveFile existed
(5.1) but I didn't research to confirm. It's still useful even in the
presence of that class if the file is really temporary (meant to be
removed when the QTemporaryFile is destroyed).

Fixes: QTBUG-103740
Change-Id: Iba16e8ea451b444ab213fffd16f4461f3f972d8c
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
(cherry picked from commit 612f5cf9a1c708a18d6488f2b25d85716a899d99)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
This commit is contained in:
Thiago Macieira 2022-05-31 12:07:43 -07:00 committed by Qt Cherry-pick Bot
parent 8727d61475
commit 185f3c26d4
1 changed files with 31 additions and 7 deletions
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38
src/corelib/io/qtemporaryfile.cpp
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@ -620,6 +620,9 @@ QString QTemporaryFilePrivate::defaultTemplateName()
be placed into the temporary path as returned by QDir::tempPath().
If you specify your own filename, a relative file path will not be placed in the
temporary directory by default, but be relative to the current working directory.
It is important to specify the correct directory if the rename() function will be
called, as QTemporaryFile can only rename files within the same volume / filesystem
as the temporary file itself was created on.
Specified filenames can contain the following template \c XXXXXX
(six upper case "X" characters), which will be replaced by the
@ -671,7 +674,11 @@ QTemporaryFile::QTemporaryFile()
If \a templateName is a relative path, the path will be relative to the
current working directory. You can use QDir::tempPath() to construct \a
templateName if you want use the system's temporary directory.
templateName if you want use the system's temporary directory. It is
important to specify the correct directory if the rename() function will be
called, as QTemporaryFile can only rename files within the same volume /
filesystem as the temporary file itself was created on.
\sa open(), fileTemplate()
*/
@ -704,7 +711,10 @@ QTemporaryFile::QTemporaryFile(QObject *parent)
If \a templateName is a relative path, the path will be relative to the
current working directory. You can use QDir::tempPath() to construct \a
templateName if you want use the system's temporary directory.
templateName if you want use the system's temporary directory. It is
important to specify the correct directory if the rename() function will be
called, as QTemporaryFile can only rename files within the same volume /
filesystem as the temporary file itself was created on.
\sa open(), fileTemplate()
*/
@ -823,7 +833,10 @@ QString QTemporaryFile::fileTemplate() const
If \a name contains a relative file path, the path will be relative to the
current working directory. You can use QDir::tempPath() to construct \a
name if you want use the system's temporary directory.
name if you want use the system's temporary directory. It is important to
specify the correct directory if the rename() function will be called, as
QTemporaryFile can only rename files within the same volume / filesystem as
the temporary file itself was created on.
\sa fileTemplate()
*/
@ -834,11 +847,22 @@ void QTemporaryFile::setFileTemplate(const QString &name)
}
/*!
\internal
Renames the current temporary file to \a newName and returns true if it
succeeded.
This is just a simplified version of QFile::rename() because we know a few
extra details about what kind of file we have. The documentation is hidden
from the user because QFile::rename() should be enough.
This function has an important difference compared to QFile::rename(): it
will not perform a copy+delete if the low-level system call to rename the
file fails, something that could happen if \a newName specifies a file in a
different volume or filesystem than the temporary file was created on. In
other words, QTemporaryFile only supports atomic file renaming.
This functionality is intended to support materializing the destination
file with all contents already present, so another process cannot see an
incomplete file in the process of being written. The \l QSaveFile class can
be used for a similar purpose too, particularly if the destination file is
not temporary.
\sa QSaveFile, QSaveFile::commit(), QFile::rename()
*/
bool QTemporaryFile::rename(const QString &newName)
{