How Can I Implement Non-Blocking Copy and Rename Operations in Qt?

Non-Blocking Copy and Rename Operations in Qt

In situations where users are handling large files and need to interrupt copy or rename operations, the default Qt functions prove insufficient. This limitation stems from the blocking nature of these operations, leaving users waiting for potentially lengthy processes to complete even if they realize their error.

Copy Operation

Qt does not provide any inbuilt solution for non-blocking copy operations. To implement this functionality, a custom class with a fragmented copy approach is necessary. This class should allow the copying of files in chunks, utilizing a buffer to enable progress tracking and responsiveness to user cancelations.

Rename Operation

Similarly, Qt does not support non-blocking rename operations. As renaming is typically implemented as a copy-then-delete process, a custom class can also be used here. This class can perform the copy non-blockingly and then delete the original file once the copy is complete.

Implementation

Here is an example of a custom class that implements non-blocking copy operations:

class CopyHelper : public QObject {
    Q_OBJECT
    Q_PROPERTY(qreal progress READ progress WRITE setProgress NOTIFY progressChanged)
public:
    CopyHelper(QString sPath, QString dPath, quint64 bSize = 1024 * 1024) :
        isCancelled(false), bufferSize(bSize), prog(0.0), source(sPath), destination(dPath), position(0) { }
    ~CopyHelper() { free(buff); }

    qreal progress() const { return prog; }
    void setProgress(qreal p) {
        if (p != prog) {
            prog = p;
            emit progressChanged();
        }
    }

public slots:
    void begin() {
        // File opening, size checking, and buffer allocation
        QMetaObject::invokeMethod(this, "step", Qt::QueuedConnection);
    }
    void step() {
        // Read, write, and progress tracking
        if (isCancelled) {
            // Delete the copied portion and emit done signal
        }
        else if (position < fileSize) {
            QMetaObject::invokeMethod(this, "step", Qt::QueuedConnection);
        } else {
            // Emit done signal
        }
    }
    void cancel() { isCancelled = true; }

signals:
    void progressChanged();
    void done();

private:
    bool isCancelled;
    quint64 bufferSize;
    qreal prog;
    QFile source, destination;
    quint64 fileSize, position;
    char * buff;
};

This class allows you to initiate the copy process, track progress, and cancel it if necessary. It employs a non-blocking approach to prevent the main thread from being locked.

Conclusion

By implementing custom classes that leverage non-blocking techniques, developers can provide users with the ability to interrupt file copy and rename operations without sacrificing responsiveness. This enhanced user experience is particularly valuable when dealing with large files that can take significant time to process.

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