vnote/src/vsingleinstanceguard.h

#ifndef VSINGLEINSTANCEGUARD_H
#define VSINGLEINSTANCEGUARD_H

#include <QString>
#include <QSharedMemory>
#include <QStringList>

class VSingleInstanceGuard
{
public:
    VSingleInstanceGuard();

    // Return ture if this is the only instance of VNote.
    bool tryRun();

    // There is already another instance running.
    // Call this to ask that instance to open external files passed in
    // via command line arguments.
    void openExternalFiles(const QStringList &p_files);

    // Ask another instance to show itself.
    void showInstance();

    // Fetch files from shared memory to open.
    // Will clear the shared memory.
    QStringList fetchFilesToOpen();

    // Whether this instance is asked to show itself.
    bool fetchAskedToShow();

    // A running instance requests to exit.
    void exit();

private:
    // The count of the entries in the buffer to hold the path of the files to open.
    enum { FilesBufCount = 1024 };

    struct SharedStruct {
        // A magic number to identify if this struct is initialized
        int m_magic;

        // Next empty entry in m_filesBuf.
        int m_filesBufIdx;

        // File paths to be opened.
        // Encoded in this way with 2 bytes for each size part.
        // [size of file1][file1][size of file2][file 2]
        // Unicode representation of QString.
        ushort m_filesBuf[FilesBufCount];

        // Whether other instances ask to show the legal instance.
        bool m_askedToShow;
    };

    // Append @p_file to the shared struct files buffer.
    // Returns true if succeeds or false if there is no enough space.
    bool appendFileToBuffer(SharedStruct *p_str, const QString &p_file);

    bool m_online;

    QSharedMemory m_sharedMemory;

    static const QString c_memKey;
    static const int c_magic;
};

#endif // VSINGLEINSTANCEGUARD_H