连接形式
connect有好几种形式
static QMetaObject::Connection connect(const QObject *sender, const char *signal, const QObject *receiver, const char *member, Qt::ConnectionType = Qt::AutoConnection);
static QMetaObject::Connection connect(const QObject *sender, const QMetaMethod &signal, const QObject *receiver, const QMetaMethod &method, Qt::ConnectionType type = Qt::AutoConnection);
inline QMetaObject::Connection connect(const QObject *sender, const char *signal, const char *member, Qt::ConnectionType type = Qt::AutoConnection) const;
连接方式有
连接类型 | 说明 |
---|---|
Qt::AutoConnection | 如果发送者和接收者在同一线程,使用Qt::DirectConnection,否则使用Qt::QueuedConnection |
Qt::DirectConnection | 信号被发射时立即执行,信号和槽函数在同一线程 |
Qt::QueuedConnection | 在事件循环回到接收者线程后执行槽函数,信号和槽函数不在同一线程 |
Qt::BlockingQueuedConnection | 信号线程会阻塞直到槽函数执行完毕,当信号与槽函数在同一线程时,不能使用这种方式 |
Qt::UniqueConnection | 表示不能重复连接信号和槽 |
涉及到的宏
# define SLOT(a) "1"#a
# define SIGNAL(a) "2"#a
connect底层到底做了什么呢?
其实际上添加发送者对应信号索引的监听器列表中
QObjectPrivate::Connection *QMetaObjectPrivate::connect(const QObject *sender,
int signal_index, const QMetaObject *smeta,
const QObject *receiver, int method_index,
const QMetaObject *rmeta, int type, int *types)
{
QObject *s = const_cast<QObject *>(sender);
QObject *r = const_cast<QObject *>(receiver);
int method_offset = rmeta ? rmeta->methodOffset() : 0;
Q_ASSERT(!rmeta || QMetaObjectPrivate::get(rmeta)->revision >= 6);
QObjectPrivate::StaticMetaCallFunction callFunction = rmeta ? rmeta->d.static_metacall : nullptr;
QOrderedMutexLocker locker(signalSlotLock(sender),
signalSlotLock(receiver));
QObjectPrivate::ConnectionData *scd = QObjectPrivate::get(s)->connections.loadRelaxed();
if (type & Qt::UniqueConnection && scd) {
if (scd->signalVectorCount() > signal_index) {
const QObjectPrivate::Connection *c2 = scd->signalVector.loadRelaxed()->at(signal_index).first.loadRelaxed();
int method_index_absolute = method_index + method_offset;
while (c2) {
if (!c2->isSlotObject && c2->receiver.loadRelaxed() == receiver && c2->method() == method_index_absolute)
return nullptr;
c2 = c2->nextConnectionList.loadRelaxed();
}
}
type &= Qt::UniqueConnection - 1;
}
std::unique_ptr<QObjectPrivate::Connection> c{new QObjectPrivate::Connection};
c->sender = s;
c->signal_index = signal_index;
c->receiver.storeRelaxed(r);
QThreadData *td = r->d_func()->threadData;
td->ref();
c->receiverThreadData.storeRelaxed(td);
c->method_relative = method_index;
c->method_offset = method_offset;
c->connectionType = type;
c->isSlotObject = false;
c->argumentTypes.storeRelaxed(types);
c->callFunction = callFunction;
QObjectPrivate::get(s)->addConnection(signal_index, c.get());
locker.unlock();
QMetaMethod smethod = QMetaObjectPrivate::signal(smeta, signal_index);
if (smethod.isValid())
s->connectNotify(smethod);
return c.release();
}
void QObjectPrivate::addConnection(int signal, Connection *c)
{
Q_ASSERT(c->sender == q_ptr);
ensureConnectionData();
ConnectionData *cd = connections.loadRelaxed();
cd->resizeSignalVector(signal + 1);
ConnectionList &connectionList = cd->connectionsForSignal(signal);
if (connectionList.last.loadRelaxed()) {
Q_ASSERT(connectionList.last.loadRelaxed()->receiver.loadRelaxed());
connectionList.last.loadRelaxed()->nextConnectionList.storeRelaxed(c);
} else {
connectionList.first.storeRelaxed(c);
}
c->id = ++cd->currentConnectionId;
c->prevConnectionList = connectionList.last.loadRelaxed();
connectionList.last.storeRelaxed(c);
QObjectPrivate *rd = QObjectPrivate::get(c->receiver.loadRelaxed());
rd->ensureConnectionData();
c->prev = &(rd->connections.loadRelaxed()->senders);
c->next = *c->prev;
*c->prev = c;
if (c->next)
c->next->prev = &c->next;
}
在添加连接设置连接对象时,将isSlotObject设置为false,callFunction设置为接收对象元对象的static_metacall
QObjectPrivate::StaticMetaCallFunction callFunction = rmeta ? rmeta->d.static_metacall : nullptr;
在doActivate调用时就会走callFunction分支
什么时候会触发接收者的调用
在emit 触发信号时。
moc(元对象编译器)在处理定义有SIGNALS的类时,会针对定义的信号生成对应的处理函数,在内部会调用QMetaObject::active方法,其定义为文章来源:https://www.toymoban.com/news/detail-465009.html
void QMetaObject::activate(QObject *sender, const QMetaObject *m, int local_signal_index,
void **argv)
{
int signal_index = local_signal_index + QMetaObjectPrivate::signalOffset(m);
if (Q_UNLIKELY(qt_signal_spy_callback_set.loadRelaxed()))
doActivate<true>(sender, signal_index, argv);
else
doActivate<false>(sender, signal_index, argv);
}
doActivate会从发送者的信号索引取出连接列表,调用处理函数
对于 Qt::AutoConnection,会判断发送线程和接收处理线程是否在同一线程,如果在同一线程,QMetaObject::metacall作同步调用,否则生成QMetaCallEvent发送qt的事件处理线程中
对于 Qt::DirectConnection, QMetaObject::metacall作同步调用
对于Qt::QueuedConnection,直接生成QMetaCallEvent发送qt的事件处理线程中
对于Qt::BlockingQueuedConnection,如果发现发送线程和接收处理线程是在同一线程,输出告警日志,会使用信号量QSemaphore,生成QMetaCallEvent发送qt的事件处理线程中等待处理结果文章来源地址https://www.toymoban.com/news/detail-465009.html
template <bool callbacks_enabled>
void doActivate(QObject *sender, int signal_index, void **argv)
{
QObjectPrivate *sp = QObjectPrivate::get(sender);
if (sp->blockSig)
return;
if (sp->isDeclarativeSignalConnected(signal_index)
&& QAbstractDeclarativeData::signalEmitted) {
Q_TRACE_SCOPE(QMetaObject_activate_declarative_signal, sender, signal_index);
QAbstractDeclarativeData::signalEmitted(sp->declarativeData, sender,
signal_index, argv);
}
const QSignalSpyCallbackSet *signal_spy_set = callbacks_enabled ? qt_signal_spy_callback_set.loadAcquire() : nullptr;
void *empty_argv[] = { nullptr };
if (!argv)
argv = empty_argv;
if (!sp->maybeSignalConnected(signal_index)) {
// The possible declarative connection is done, and nothing else is connected
if (callbacks_enabled && signal_spy_set->signal_begin_callback != nullptr)
signal_spy_set->signal_begin_callback(sender, signal_index, argv);
if (callbacks_enabled && signal_spy_set->signal_end_callback != nullptr)
signal_spy_set->signal_end_callback(sender, signal_index);
return;
}
if (callbacks_enabled && signal_spy_set->signal_begin_callback != nullptr)
signal_spy_set->signal_begin_callback(sender, signal_index, argv);
bool senderDeleted = false;
{
Q_ASSERT(sp->connections.loadAcquire());
QObjectPrivate::ConnectionDataPointer connections(sp->connections.loadRelaxed());
QObjectPrivate::SignalVector *signalVector = connections->signalVector.loadRelaxed();
const QObjectPrivate::ConnectionList *list;
if (signal_index < signalVector->count())
list = &signalVector->at(signal_index);
else
list = &signalVector->at(-1);
Qt::HANDLE currentThreadId = QThread::currentThreadId();
bool inSenderThread = currentThreadId == QObjectPrivate::get(sender)->threadData->threadId.loadRelaxed();
// We need to check against the highest connection id to ensure that signals added
// during the signal emission are not emitted in this emission.
uint highestConnectionId = connections->currentConnectionId.loadRelaxed();
do {
QObjectPrivate::Connection *c = list->first.loadRelaxed();
if (!c)
continue;
do {
QObject * const receiver = c->receiver.loadRelaxed();
if (!receiver)
continue;
QThreadData *td = c->receiverThreadData.loadRelaxed();
if (!td)
continue;
bool receiverInSameThread;
if (inSenderThread) {
receiverInSameThread = currentThreadId == td->threadId.loadRelaxed();
} else {
// need to lock before reading the threadId, because moveToThread() could interfere
QMutexLocker lock(signalSlotLock(receiver));
receiverInSameThread = currentThreadId == td->threadId.loadRelaxed();
}
// determine if this connection should be sent immediately or
// put into the event queue
if ((c->connectionType == Qt::AutoConnection && !receiverInSameThread)
|| (c->connectionType == Qt::QueuedConnection)) {
queued_activate(sender, signal_index, c, argv);
continue;
#if QT_CONFIG(thread)
} else if (c->connectionType == Qt::BlockingQueuedConnection) {
if (receiverInSameThread) {
qWarning("Qt: Dead lock detected while activating a BlockingQueuedConnection: "
"Sender is %s(%p), receiver is %s(%p)",
sender->metaObject()->className(), sender,
receiver->metaObject()->className(), receiver);
}
QSemaphore semaphore;
{
QBasicMutexLocker locker(signalSlotLock(sender));
if (!c->receiver.loadAcquire())
continue;
QMetaCallEvent *ev = c->isSlotObject ?
new QMetaCallEvent(c->slotObj, sender, signal_index, argv, &semaphore) :
new QMetaCallEvent(c->method_offset, c->method_relative, c->callFunction,
sender, signal_index, argv, &semaphore);
QCoreApplication::postEvent(receiver, ev);
}
semaphore.acquire();
continue;
#endif
}
QObjectPrivate::Sender senderData(receiverInSameThread ? receiver : nullptr, sender, signal_index);
if (c->isSlotObject) {
c->slotObj->ref();
struct Deleter {
void operator()(QtPrivate::QSlotObjectBase *slot) const {
if (slot) slot->destroyIfLastRef();
}
};
const std::unique_ptr<QtPrivate::QSlotObjectBase, Deleter> obj{c->slotObj};
{
Q_TRACE_SCOPE(QMetaObject_activate_slot_functor, obj.get());
obj->call(receiver, argv);
}
} else if (c->callFunction && c->method_offset <= receiver->metaObject()->methodOffset()) {
//we compare the vtable to make sure we are not in the destructor of the object.
const int method_relative = c->method_relative;
const auto callFunction = c->callFunction;
const int methodIndex = (Q_HAS_TRACEPOINTS || callbacks_enabled) ? c->method() : 0;
if (callbacks_enabled && signal_spy_set->slot_begin_callback != nullptr)
signal_spy_set->slot_begin_callback(receiver, methodIndex, argv);
{
Q_TRACE_SCOPE(QMetaObject_activate_slot, receiver, methodIndex);
callFunction(receiver, QMetaObject::InvokeMetaMethod, method_relative, argv);
}
if (callbacks_enabled && signal_spy_set->slot_end_callback != nullptr)
signal_spy_set->slot_end_callback(receiver, methodIndex);
} else {
const int method = c->method_relative + c->method_offset;
if (callbacks_enabled && signal_spy_set->slot_begin_callback != nullptr) {
signal_spy_set->slot_begin_callback(receiver, method, argv);
}
{
Q_TRACE_SCOPE(QMetaObject_activate_slot, receiver, method);
QMetaObject::metacall(receiver, QMetaObject::InvokeMetaMethod, method, argv);
}
if (callbacks_enabled && signal_spy_set->slot_end_callback != nullptr)
signal_spy_set->slot_end_callback(receiver, method);
}
} while ((c = c->nextConnectionList.loadRelaxed()) != nullptr && c->id <= highestConnectionId);
} while (list != &signalVector->at(-1) &&
//start over for all signals;
((list = &signalVector->at(-1)), true));
if (connections->currentConnectionId.loadRelaxed() == 0)
senderDeleted = true;
}
if (!senderDeleted) {
sp->connections.loadRelaxed()->cleanOrphanedConnections(sender);
if (callbacks_enabled && signal_spy_set->signal_end_callback != nullptr)
signal_spy_set->signal_end_callback(sender, signal_index);
}
}
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