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/* SPDX-License-Identifier: LGPL-2.1-or-later */
/*
* Copyright (C) 2019, Google Inc.
*
* signal.cpp - Signal & slot implementation
*/
#include <libcamera/base/signal.h>
#include <libcamera/base/thread.h>
/**
* \file base/signal.h
* \brief Signal & slot implementation
*/
namespace libcamera {
namespace {
/*
* Mutex to protect the SignalBase::slots_ and Object::signals_ lists. If lock
* contention needs to be decreased, this could be replaced with locks in
* Object and SignalBase, or with a mutex pool.
*/
Mutex signalsLock;
} /* namespace */
void SignalBase::connect(BoundMethodBase *slot)
{
MutexLocker locker(signalsLock);
Object *object = slot->object();
if (object)
object->connect(this);
slots_.push_back(slot);
}
void SignalBase::disconnect(Object *object)
{
disconnect([object](SlotList::iterator &iter) {
return (*iter)->match(object);
});
}
void SignalBase::disconnect(std::function<bool(SlotList::iterator &)> match)
{
MutexLocker locker(signalsLock);
for (auto iter = slots_.begin(); iter != slots_.end(); ) {
if (match(iter)) {
Object *object = (*iter)->object();
if (object)
object->disconnect(this);
delete *iter;
iter = slots_.erase(iter);
} else {
++iter;
}
}
}
SignalBase::SlotList SignalBase::slots()
{
MutexLocker locker(signalsLock);
return slots_;
}
/**
* \class Signal
* \brief Generic signal and slot communication mechanism
*
* Signals and slots are a language construct aimed at communication between
* objects through the observer pattern without the need for boilerplate code.
* See http://doc.qt.io/qt-5/signalsandslots.html for more information.
*
* Signals model events that can be observed from objects unrelated to the event
* source. Slots are functions that are called in response to a signal. Signals
* can be connected to and disconnected from slots dynamically at runtime. When
* a signal is emitted, all connected slots are called sequentially in the order
* they have been connected.
*
* Signals are defined with zero, one or more typed parameters. They are emitted
* with a value for each of the parameters, and those values are passed to the
* connected slots.
*
* Slots are normal static or class member functions. In order to be connected
* to a signal, their signature must match the signal type (taking the same
* arguments as the signal and returning void).
*
* Connecting a signal to a slot results in the slot being called with the
* arguments passed to the emit() function when the signal is emitted. Multiple
* slots can be connected to the same signal, and multiple signals can connected
* to the same slot. Duplicate connections between a signal and a slot are
* allowed and result in the slot being called multiple times for the same
* signal emission.
*
* When a slot belongs to an instance of the Object class, the slot is called
* in the context of the thread that the object is bound to. If the signal is
* emitted from the same thread, the slot will be called synchronously, before
* Signal::emit() returns. If the signal is emitted from a different thread,
* the slot will be called asynchronously from the object's thread's event
* loop, after the Signal::emit() method returns, with a copy of the signal's
* arguments. The emitter shall thus ensure that any pointer or reference
* passed through the signal will remain valid after the signal is emitted.
*/
/**
* \fn Signal::connect(T *object, R (T::*func)(Args...))
* \brief Connect the signal to a member function slot
* \param[in] object The slot object pointer
* \param[in] func The slot member function
*
* If the typename T inherits from Object, the signal will be automatically
* disconnected from the \a func slot of \a object when \a object is destroyed.
* Otherwise the caller shall disconnect signals manually before destroying \a
* object.
*
* \context This function is \threadsafe.
*/
/**
* \fn Signal::connect(R (*func)(Args...))
* \brief Connect the signal to a static function slot
* \param[in] func The slot static function
*
* \context This function is \threadsafe.
*/
/**
* \fn Signal::disconnect()
* \brief Disconnect the signal from all slots
*
* \context This function is \threadsafe.
*/
/**
* \fn Signal::disconnect(T *object)
* \brief Disconnect the signal from all slots of the \a object
* \param[in] object The object pointer whose slots to disconnect
*
* \context This function is \threadsafe.
*/
/**
* \fn Signal::disconnect(T *object, R (T::*func)(Args...))
* \brief Disconnect the signal from the \a object slot member function \a func
* \param[in] object The object pointer whose slots to disconnect
* \param[in] func The slot member function to disconnect
*
* \context This function is \threadsafe.
*/
/**
* \fn Signal::disconnect(R (*func)(Args...))
* \brief Disconnect the signal from the slot static function \a func
* \param[in] func The slot static function to disconnect
*
* \context This function is \threadsafe.
*/
/**
* \fn Signal::emit(Args... args)
* \brief Emit the signal and call all connected slots
* \param args The arguments passed to the connected slots
*
* Emitting a signal calls all connected slots synchronously and sequentially in
* the order the slots have been connected. The arguments passed to the emit()
* function are passed to the slot functions unchanged. If a slot modifies one
* of the arguments (when passed by pointer or reference), the modification is
* thus visible to all subsequently called slots.
*
* This function is not \threadsafe, but thread-safety is guaranteed against
* concurrent connect() and disconnect() calls.
*/
} /* namespace libcamera */
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