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/* SPDX-License-Identifier: LGPL-2.1-or-later */
/*
* Copyright (C) 2019, Google Inc.
*
* Base object
*/
#include <libcamera/base/object.h>
#include <algorithm>
#include <libcamera/base/log.h>
#include <libcamera/base/message.h>
#include <libcamera/base/semaphore.h>
#include <libcamera/base/signal.h>
#include <libcamera/base/thread.h>
#include <libcamera/base/utils.h>
/**
* \file base/object.h
* \brief Base object to support automatic signal disconnection
*/
namespace libcamera {
LOG_DEFINE_CATEGORY(Object)
/**
* \class Object
* \brief Base object to support automatic signal disconnection
*
* The Object class simplifies signal/slot handling for classes implementing
* slots. By inheriting from Object, an object is automatically disconnected
* from all connected signals when it gets destroyed.
*
* Object instances are bound to the thread of their parent, or the thread in
* which they're created when they have no parent. When a message is posted to
* an object, its handler will run in the object's thread. This allows
* implementing easy message passing between threads by inheriting from the
* Object class.
*
* Deleting an object from a thread other than the one the object is bound to is
* unsafe, unless the caller ensures that the object's thread is stopped and no
* parent or child of the object gets deleted concurrently. See
* Object::~Object() for more information.
*
* Object slots connected to signals will also run in the context of the
* object's thread, regardless of whether the signal is emitted in the same or
* in another thread.
*
* Objects can be connected to multiple signals, but they can only be connected
* to each signal once. Attempting to create multiple concurrent connections
* between the same signal and the same Object (to either the same or differents
* slots of the object) will cause an assertion failure. While it would be
* possible to allow the implementation to let objects connect to the same
* signal multiple times, there are no expected use cases for this in libcamera
* and this behaviour is restricted to favour defensive programming.
*
* \sa Message, Signal, Thread
*/
/**
* \brief Construct an Object instance
* \param[in] parent The object parent
*
* The new Object instance is bound to the thread of its \a parent, or to the
* current thread if the \a parent is nullptr.
*/
Object::Object(Object *parent)
: parent_(parent), pendingMessages_(0)
{
thread_ = parent ? parent->thread() : Thread::current();
if (parent)
parent->children_.push_back(this);
}
/**
* \brief Destroy an Object instance
*
* Deleting an Object automatically disconnects all signals from the Object's
* slots. All the Object's children are made orphan, but stay bound to their
* current thread.
*
* Object instances shall be destroyed from the thread they are bound to,
* otherwise undefined behaviour may occur. If deletion of an Object needs to
* be scheduled from a different thread, deleteLater() shall be used.
*
* As an exception to this rule, Object instances may be deleted from a
* different thread if the thread the instance is bound to is stopped through
* the whole duration of the object's destruction, *and* the parent and children
* of the object do not get deleted concurrently. The caller is responsible for
* fulfilling those requirements.
*
* In all cases Object instances shall be deleted before the Thread they are
* bound to.
*/
Object::~Object()
{
ASSERT(Thread::current() == thread_ || !thread_->isRunning());
/*
* Move signals to a private list to avoid concurrent iteration and
* deletion of items from Signal::disconnect().
*/
std::list<SignalBase *> signals(std::move(signals_));
for (SignalBase *signal : signals)
signal->disconnect(this);
if (pendingMessages_)
thread()->removeMessages(this);
if (parent_) {
auto it = std::find(parent_->children_.begin(),
parent_->children_.end(), this);
ASSERT(it != parent_->children_.end());
parent_->children_.erase(it);
}
for (auto child : children_)
child->parent_ = nullptr;
}
/**
* \brief Schedule deletion of the instance in the thread it belongs to
*
* This function schedules deletion of the Object when control returns to the
* event loop that the object belongs to. This ensures the object is destroyed
* from the right context, as required by the libcamera threading model.
*
* If this function is called before the thread's event loop is started or after
* it has stopped, the object will be deleted when the event loop (re)starts. If
* this never occurs, the object will be leaked.
*
* Deferred deletion can be used to control the destruction context with shared
* pointers. An object managed with shared pointers is deleted when the last
* reference is destroyed, which makes difficult to ensure through software
* design which context the deletion will take place in. With a custom deleter
* for the shared pointer using deleteLater(), the deletion can be guaranteed to
* happen in the thread the object is bound to.
*
* \code{.cpp}
* std::shared_ptr<MyObject> createObject()
* {
* struct Deleter : std::default_delete<MyObject> {
* void operator()(MyObject *obj)
* {
* obj->deleteLater();
* }
* };
*
* MyObject *obj = new MyObject();
*
* return std::shared_ptr<MyObject>(obj, Deleter());
* }
* \endcode
*
* \context This function is \threadsafe.
*/
void Object::deleteLater()
{
postMessage(std::make_unique<Message>(Message::DeferredDelete));
}
/**
* \brief Post a message to the object's thread
* \param[in] msg The message
*
* This function posts the message \a msg to the message queue of the object's
* thread, to be delivered to the object through the message() function in the
* context of its thread. Message ownership is passed to the thread, and the
* message will be deleted after being delivered.
*
* Messages are delivered through the thread's event loop. If the thread is not
* running its event loop the message will not be delivered until the event
* loop gets started.
*
* Due to their asynchronous nature, threads do not provide any guarantee that
* all posted messages are delivered before the thread is stopped. See
* \ref thread-stop for additional information.
*
* \context This function is \threadsafe.
*/
void Object::postMessage(std::unique_ptr<Message> msg)
{
thread()->postMessage(std::move(msg), this);
}
/**
* \brief Message handler for the object
* \param[in] msg The message
*
* This virtual function receives messages for the object. It is called in the
* context of the object's thread, and can be overridden to process custom
* messages. The parent Object::message() function shall be called for any
* message not handled by the override function.
*
* The message \a msg is valid only for the duration of the call, no reference
* to it shall be kept after this function returns.
*/
void Object::message(Message *msg)
{
switch (msg->type()) {
case Message::InvokeMessage: {
/*
* A static_cast should be enough, but gcc 10 and 11 choke on
* it in release mode (with -O2 or -O3).
*/
InvokeMessage *iMsg = dynamic_cast<InvokeMessage *>(msg);
Semaphore *semaphore = iMsg->semaphore();
iMsg->invoke();
if (semaphore)
semaphore->release();
break;
}
case Message::DeferredDelete:
delete this;
break;
default:
break;
}
}
/**
* \fn Object::assertThreadBound()
* \brief Check if the caller complies with thread-bound constraints
* \param[in] message The message to be printed on error
*
* This function verifies the calling constraints required by the \threadbound
* definition. It shall be called at the beginning of member functions of an
* Object subclass that are explicitly marked as thread-bound in their
* documentation.
*
* If the thread-bound constraints are not met, the function prints \a message
* as an error message. For debug builds, it additionally causes an assertion
* error.
*
* \todo Verify the thread-bound requirements for functions marked as
* thread-bound at the class level.
*
* \return True if the call is thread-bound compliant, false otherwise
*/
bool Object::assertThreadBound(const char *message)
{
if (Thread::current() == thread_)
return true;
LOG(Object, Error) << message;
ASSERT(false);
return false;
}
/**
* \fn R Object::invokeMethod()
* \brief Invoke a method asynchronously on an Object instance
* \param[in] func The object method to invoke
* \param[in] type Connection type for method invocation
* \param[in] args The method arguments
*
* This function invokes the member method \a func with arguments \a args, based
* on the connection \a type. Depending on the type, the method will be called
* synchronously in the same thread or asynchronously in the object's thread.
*
* Arguments \a args passed by value or reference are copied, while pointers
* are passed untouched. The caller shall ensure that any pointer argument
* remains valid until the method is invoked.
*
* Due to the asynchronous nature of threads, functions invoked asynchronously
* with the ConnectionTypeQueued type are not guaranteed to be called before
* the thread is stopped. See \ref thread-stop for additional information.
*
* \context This function is \threadsafe.
*
* \return For connection types ConnectionTypeDirect and
* ConnectionTypeBlocking, return the return value of the invoked method. For
* connection type ConnectionTypeQueued, return a default-constructed R value.
*/
/**
* \fn Object::thread()
* \brief Retrieve the thread the object is bound to
* \context This function is \threadsafe.
* \return The thread the object is bound to
*/
/**
* \brief Move the object and all its children to a different thread
* \param[in] thread The target thread
*
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