The QSharedMemory class provides access to a shared memory segment. More...

Inheritance diagram for QSharedMemory:

Public Types
enum	AccessMode

enum	SharedMemoryError

Public Methods
	QSharedMemory (const QString &key, QObject *parent=nullptr)

	QSharedMemory (QObject *parent=nullptr)

	~QSharedMemory ()

bool	attach (AccessMode mode=ReadWrite)

const void *	constData () const

bool	create (int size, AccessMode mode=ReadWrite)

void *	data ()

const void *	data () const

bool	detach ()

SharedMemoryError	error () const

QString	errorString () const

bool	isAttached () const

QString	key () const

bool	lock ()

QString	nativeKey () const

void	setKey (const QString &key)

void	setNativeKey (const QString &key)

int	size () const

bool	unlock ()

Public Methods inherited from QObject
	QObject (QObject *parent=nullptr)

	~QObject ()

bool	blockSignals (bool block)

const QList< QObject * > &	children () const

bool	connect (const QObject *sender, const QString &signalMethod, const QString &location, const QString &slotMethod, Qt::ConnectionType type=Qt::AutoConnection)

bool	connect (const QObject *sender, const QString &signalMethod, const QString &slotMethod, Qt::ConnectionType type=Qt::AutoConnection)

bool	disconnect (const QObject *receiver, const QString &slotMethod=QString ()) const

bool	disconnect (const QString &signalMethod, const QString &location, const QObject *receiver=nullptr, const QString &slotMethod=QString ()) const

bool	disconnect (const QString &signalMethod=QString (), const QObject *receiver=nullptr, const QString &slotMethod=QString ()) const

void	dumpObjectInfo ()

void	dumpObjectTree ()

QList< QString >	dynamicPropertyNames () const

virtual bool	event (QEvent *event)

virtual bool	eventFilter (QObject watched, QEvent event)

template<typename T >
T	findChild (const QString &childName=QString ()) const

template<class T >
QList< T >	findChildren (const QRegularExpression &regExp, Qt::FindChildOptions options=Qt::FindChildrenRecursively) const

template<class T >
QList< T >	findChildren (const QString &childName=QString (), Qt::FindChildOptions options=Qt::FindChildrenRecursively) const

bool	inherits (const QString &className) const

void	installEventFilter (QObject *filterObj)

bool	isWidgetType () const

bool	isWindowType () const

void	killTimer (int id)

const QMetaObject *	metaObject () const

void	moveToThread (QThread *targetThread)

QString	objectName () const

QObject *	parent () const

template<class T = QVariant>
T	property (const QString &name) const

void	removeEventFilter (QObject *obj)

void	setObjectName (const QString &name)

void	setParent (QObject *parent)

bool	setProperty (const QString &name, const QVariant &value)

bool	signalsBlocked () const

int	startTimer (int interval, Qt::TimerType timerType=Qt::CoarseTimer)

QThread *	thread () const

Additional Inherited Members
Public Signals inherited from QObject
void	destroyed (QObject *obj=nullptr)

void	objectNameChanged (const QString &objectName)

Public Slots inherited from QObject
void	deleteLater ()

Static Public Methods inherited from QObject
static bool	connect (const QObject sender, const QMetaMethod &signalMethod, const QObject receiver, const QMetaMethod &slotMethod, Qt::ConnectionType type=Qt::AutoConnection)

static bool	connect (const QObject sender, const QString &signalMethod, const QObject receiver, const QString &slotMethod, Qt::ConnectionType type=Qt::AutoConnection, const QString &location=QString ())

static bool	connect (const QObject sender, const QString &signalMethod, const QString &location, const QObject receiver, const QString &slotMethod, Qt::ConnectionType type=Qt::AutoConnection)

template<class Sender , class SignalClass , class... SignalArgs, class Receiver , class SlotClass , class... SlotArgs, class SlotReturn >
static bool	connect (const Sender sender, void (SignalClass::signalMethod)(SignalArgs...), const Receiver receiver, SlotReturn (SlotClass::slotMethod)(SlotArgs...), Qt::ConnectionType type=Qt::AutoConnection)

template<class Sender , class SignalClass , class... SignalArgs, class Receiver , class T >
static bool	connect (const Sender sender, void (SignalClass::signalMethod)(SignalArgs...), const Receiver *receiver, T slotLambda, Qt::ConnectionType type=Qt::AutoConnection)

static bool	disconnect (const QObject sender, const QMetaMethod &signalMethod, const QObject receiver, const QMetaMethod &slotMethod)

static bool	disconnect (const QObject sender, const QString &signalMethod, const QObject receiver, const QString &slotMethod)

static bool	disconnect (const QObject sender, const QString &signalMethod, const QString &location, const QObject receiver, const QString &slotMethod)

static bool	disconnect (const QObject sender, std::nullptr_t, const QObject receiver, std::nullptr_t)

template<class Sender , class SignalClass , class... SignalArgs, class Receiver , class SlotClass , class... SlotArgs, class SlotReturn >
static bool	disconnect (const Sender sender, void (SignalClass::signalMethod)(SignalArgs...), const Receiver receiver, SlotReturn (SlotClass::slotMethod)(SlotArgs...))

template<class Sender , class SignalClass , class... SignalArgs, class Receiver >
static bool	disconnect (const Sender sender, void (SignalClass::signalMethod)(SignalArgs...), const Receiver *receiver, std::nullptr_t slotMethod=nullptr)

template<class Sender , class SignalClass , class... SignalArgs, class Receiver , class T >
static bool	disconnect (const Sender sender, void (SignalClass::signalMethod)(SignalArgs...), const Receiver *receiver, T slotMethod)

static QMetaObject &	staticMetaObject ()

static QString	tr (const char text, const char comment=nullptr, std::optional< int > numArg=std::optional< int >())

Protected Methods inherited from QObject
virtual void	childEvent (QChildEvent *event)

virtual void	connectNotify (const QMetaMethod &signalMethod) const

virtual void	customEvent (QEvent *event)

virtual void	disconnectNotify (const QMetaMethod &signalMethod) const

bool	isSignalConnected (const QMetaMethod &signalMethod) const

int	receivers (const QString &signal) const

QObject *	sender () const

int	senderSignalIndex () const

virtual void	timerEvent (QTimerEvent *event)

Properties inherited from QObject
	objectName

Related Functions inherited from QObject
T	qobject_cast (QObject *object)

	QObjectList

Detailed Description

The QSharedMemory class provides access to a shared memory segment.

QSharedMemory provides access to a shared memory segment by multiple threads and processes. It also provides a way for a single thread or process to lock the memory for exclusive access.

When using this class be aware of the following platform differences:

Windows: QSharedMemory does not "own" the shared memory segment. When all threads or processes that have an instance of QSharedMemory attached to a particular shared memory segment have either destroyed their instance of QSharedMemory or exited, the Windows kernel releases the shared memory segment automatically.
Unix: QSharedMemory "owns" the shared memory segment. When the last thread or process that has an instance of QSharedMemory attached to a particular shared memory segment detaches from the segment by destroying its instance of QSharedMemory, the Unix kernel release the shared memory segment. But if that last thread or process crashes without running the QSharedMemory destructor, the shared memory segment survives the crash.
HP-UX: Only one attach to a shared memory segment is allowed per process. This means that QSharedMemory should not be used across multiple threads in the same process in HP-UX.

Remember to lock the shared memory with lock() before reading from or writing to the shared memory, and remember to release the lock with unlock() after you are done.

Unlike QtSharedMemory, QSharedMemory automatically destroys the shared memory segment when the last instance of QSharedMemory is detached from the segment, and no references to the segment remain. Do not mix using QtSharedMemory and QSharedMemory. Port everything to QSharedMemory.

Warning: QSharedMemory changes the key in a CopperSpice specific way, unless otherwise specified. Interoperation with non-CopperSpice applications is achieved by first creating a default shared memory with QSharedMemory() and then setting a native key with setNativeKey(). When using native keys, shared memory is not protected against multiple accesses on it (e.g. unable to lock()) and a user-defined mechanism should be used to achieve a such protection.

See also: setKey(), create(), attach()

Member Enumeration Documentation

enum QSharedMemory::AccessMode

Constant	Value	Description
`QSharedMemory::ReadOnly`	`0`	The shared memory segment is read only. Writing to the shared memory segment is not allowed. An attempt to write to a shared memory segment created with ReadOnly causes the program to abort.
`QSharedMemory::ReadWrite`	`1`	Reading and writing the shared memory segment are both allowed.

enum QSharedMemory::SharedMemoryError

Constant	Value	Description
`QSharedMemory::NoError`	`0`	No error occurred.
`QSharedMemory::PermissionDenied`	`1`	The operation failed because the caller did not have the required permissions.
`QSharedMemory::InvalidSize`	`2`	A create operation failed because the requested size was invalid.
`QSharedMemory::KeyError`	`3`	The operation failed because of an invalid key.
`QSharedMemory::AlreadyExists`	`4`	A create() operation failed because a shared memory segment with the specified key already existed.
`QSharedMemory::NotFound`	`5`	An attach() failed because a shared memory segment with the specified key could not be found.
`QSharedMemory::LockError`	`6`	The attempt to lock() the shared memory segment failed because create() or attach() failed and returned false, or because a system error occurred in QSystemSemaphore::acquire().
`QSharedMemory::OutOfResources`	`7`	A create() operation failed because there was not enough memory available to fill the request.
`QSharedMemory::UnknownError`	`8`	Something else happened and it was bad.

Constructor & Destructor Documentation

QSharedMemory::QSharedMemory ( QObject * parent = nullptr )

Constructs a shared memory object with the given parent. The shared memory object's key is not set by the constructor, so the shared memory object does not have an underlying shared memory segment attached. The key must be set with setKey() or setNativeKey() before create() or attach() can be used.

See also: setKey()

QSharedMemory::QSharedMemory	(	const QString &	key,
		QObject *	parent = `nullptr`
	)

Constructs a shared memory object with the given parent and with its key set to key. Because its key is set, its create() and attach() functions can be called.

See also: setKey(), create(), attach()

QSharedMemory::~QSharedMemory ( )

The destructor clears the key, which forces the shared memory object to detach from its underlying shared memory segment. If this shared memory object is the last one connected to the shared memory segment, the detach() operation destroys the shared memory segment.

See also: detach(), isAttached()

Method Documentation

bool QSharedMemory::attach ( AccessMode mode = ReadWrite )

Attempts to attach the process to the shared memory segment identified by the key that was passed to the constructor or to a call to setKey() or setNativeKey(). The access mode is ReadWrite by default. It can also be ReadOnly. Returns true if the attach operation is successful. If false is returned, call error() to determine which error occurred. After attaching the shared memory segment, a pointer to the shared memory can be obtained by calling data().

See also: isAttached(), detach(), create()

const void * QSharedMemory::constData ( ) const

Returns a const pointer to the contents of the shared memory segment, if one is attached. Otherwise it returns null. Remember to lock the shared memory with lock() before reading from or writing to the shared memory, and remember to release the lock with unlock() after you are done.

See also: attach(), create()

bool QSharedMemory::create	(	int	size,
		AccessMode	mode = `ReadWrite`
	)

Creates a shared memory segment of size bytes with the key passed to the constructor, set with setKey() or set with setNativeKey(), then attaches to the new shared memory segment with the given access mode and returns true. If a shared memory segment identified by the key already exists, the attach operation is not performed and false is returned. When the return value is false, call error() to determine which error occurred.

See also: error()

void * QSharedMemory::data ( )

Returns a pointer to the contents of the shared memory segment, if one is attached. Otherwise it returns null. Remember to lock the shared memory with lock() before reading from or writing to the shared memory, and remember to release the lock with unlock() after you are done.

See also: attach()

const void * QSharedMemory::data ( ) const

Returns a const pointer to the contents of the shared memory segment, if one is attached.

bool QSharedMemory::detach ( )

Detaches the process from the shared memory segment. If this was the last process attached to the shared memory segment, then the shared memory segment is released by the system, i.e., the contents are destroyed. The function returns true if it detaches the shared memory segment. If it returns false, it usually means the segment either is not attached, or it is locked by another process.

See also: attach(), isAttached()

SharedMemoryError QSharedMemory::error ( ) const

Returns a value indicating whether an error occurred, and, if so, which error it was.

See also: errorString()

QString QSharedMemory::errorString ( ) const

Returns a text description of the last error that occurred. If error() returns an error value, call this function to get a text string that describes the error.

See also: error()

bool QSharedMemory::isAttached ( ) const

Returns true if this process is attached to the shared memory segment.

See also: attach(), detach()

QString QSharedMemory::key ( ) const

Returns the key assigned with setKey() to this shared memory, or a null key if no key has been assigned, or if the segment is using a nativeKey(). The key is the identifier used by CopperSpice applications to identify the shared memory segment.

You can find the native, platform specific, key used by the operating system by calling nativeKey().

See also: setKey(), setNativeKey()

bool QSharedMemory::lock ( )

This is a semaphore that locks the shared memory segment for access by this process and returns true. If another process has locked the segment, this function blocks until the lock is released. Then it acquires the lock and returns true. If this function returns false, it means that you have ignored a false return from create() or attach(), that you have set the key with setNativeKey() or that QSystemSemaphore::acquire() failed due to an unknown system error.

See also: unlock(), data(), QSystemSemaphore::acquire()

QString QSharedMemory::nativeKey ( ) const

Returns the native, platform specific, key for this shared memory object. The native key is the identifier used by the operating system to identify the shared memory segment.

You can use the native key to access shared memory segments that have not been created by CopperSpice, or to grant shared memory access to non-CopperSpice applications.

See also: setKey(), setNativeKey()

void QSharedMemory::setKey ( const QString & key )

Sets the platform independent key for this shared memory object. If key is the same as the current key, the function returns without doing anything.

You can call key() to retrieve the platform independent key. Internally, QSharedMemory converts this key into a platform specific key. If you instead call nativeKey(), you will get the platform specific, converted key.

If the shared memory object is attached to an underlying shared memory segment, it will detach from it before setting the new key. This function does not do an attach().

See also: key(), nativeKey(), isAttached()

void QSharedMemory::setNativeKey ( const QString & key )

Sets the native, platform specific, key for this shared memory object. If key is the same as the current native key, the function returns without doing anything. If all you want is to assign a key to a segment, you should call setKey() instead.

You can call nativeKey() to retrieve the native key. If a native key has been assigned, calling key() will return a null string.

If the shared memory object is attached to an underlying shared memory segment, it will detach from it before setting the new key. This function does not do an attach().

The application will not be portable if you set a native key.

See also: nativeKey(), key(), isAttached()

int QSharedMemory::size ( ) const

Returns the size of the attached shared memory segment. If no shared memory segment is attached, 0 is returned.

See also: create(), attach()

bool QSharedMemory::unlock ( )

Releases the lock on the shared memory segment and returns true, if the lock is currently held by this process. If the segment is not locked, or if the lock is held by another process, nothing happens and false is returned.

See also: lock()

Public Types

Public Methods

Additional Inherited Members

Detailed Description

Member Enumeration Documentation

Constructor & Destructor Documentation

Method Documentation