#ifndef IG_NOD_INCLUDE_NOD_HPP
#define IG_NOD_INCLUDE_NOD_HPP
#include <vector> // std::vector
#include <functional> // std::function
#include <mutex> // std::mutex, std::lock_guard
#include <memory> // std::shared_ptr, std::weak_ptr
#include <algorithm> // std::find_if()
#include <cassert> // assert()
#include <thread> // std::this_thread::yield()
#include <type_traits> // std::is_same
#include <iterator> // std::back_inserter
namespace nod {
// implementational details
namespace detail {
/// Interface for type erasure when disconnecting slots
struct disconnector {
virtual void operator()( std::size_t index ) const = 0;
};
/// Deleter that doesn't delete
inline void no_delete(disconnector*){
}
} // namespace detail
/// Base template for the signal class
template <class P, class T>
class signal_type;
/// Connection class.
///
/// This is used to be able to disconnect slots after they have been connected.
/// Used as return type for the connect method of the signals.
///
/// Connections are default constructible.
/// Connections are not copy constructible or copy assignable.
/// Connections are move constructible and move assignable.
///
class connection {
public:
/// Default constructor
connection() :
_index()
{}
// Connection are not copy constructible or copy assignable
connection( connection const& ) = delete;
connection& operator=( connection const& ) = delete;
/// Move constructor
/// @param other The instance to move from.
connection( connection&& other ) :
_weak_disconnector( std::move(other._weak_disconnector) ),
_index( other._index )
{}
/// Move assign operator.
/// @param other The instance to move from.
connection& operator=( connection&& other ) {
_weak_disconnector = std::move( other._weak_disconnector );
_index = other._index;
return *this;
}
/// @returns `true` if the connection is connected to a signal object,
/// and `false` otherwise.
bool connected() const {
return !_weak_disconnector.expired();
}
/// Disconnect the slot from the connection.
///
/// If the connection represents a slot that is connected to a signal object, calling
/// this method will disconnect the slot from that object. The result of this operation
/// is that the slot will stop receiving calls when the signal is invoked.
void disconnect();
private:
/// The signal template is a friend of the connection, since it is the
/// only one allowed to create instances using the meaningful constructor.
template<class P,class T> friend class signal_type;
/// Create a connection.
/// @param shared_disconnector Disconnector instance that will be used to disconnect
/// the connection when the time comes. A weak pointer
/// to the disconnector will be held within the connection
/// object.
/// @param index The slot index of the connection.
connection( std::shared_ptr<detail::disconnector> const& shared_disconnector, std::size_t index ) :
_weak_disconnector( shared_disconnector ),
_index( index )
{}
/// Weak pointer to the current disconnector functor.
std::weak_ptr<detail::disconnector> _weak_disconnector;
/// Slot index of the connected slot.
std::size_t _index;
};
/// Scoped connection class.
///
/// This type of connection is automatically disconnected when
/// the connection object is destructed.
///
class scoped_connection
{
public:
/// Scoped are default constructible
scoped_connection() = default;
/// Scoped connections are not copy constructible
scoped_connection( scoped_connection const& ) = delete;
/// Scoped connections are not copy assingable
scoped_connection& operator=( scoped_connection const& ) = delete;
/// Move constructor
scoped_connection( scoped_connection&& other ) :
_connection( std::move(other._connection) )
{}
/// Move assign operator.
/// @param other The instance to move from.
scoped_connection& operator=( scoped_connection&& other ) {
reset( std::move( other._connection ) );
return *this;
}
/// Construct a scoped connection from a connection object
/// @param connection The connection object to manage
scoped_connection( connection&& c ) :
_connection( std::forward<connection>(c) )
{}
/// destructor
~scoped_connection() {
disconnect();
}
/// Assignment operator moving a new connection into the instance.
/// @note If the scoped_connection instance already contains a
/// connection, that connection will be disconnected as if
/// the scoped_connection was destroyed.
/// @param c New connection to manage
scoped_connection& operator=( connection&& c ) {
reset( std::forward<connection>(c) );
return *this;
}
/// Reset the underlying connection to another connection.
/// @note The connection currently managed by the scoped_connection
/// instance will be disconnected when resetting.
/// @param c New connection to manage
void reset( connection&& c = {} ) {
disconnect();
_connection = std::move(c);
}
/// Release the underlying connection, without disconnecting it.
/// @returns The newly released connection instance is returned.
connection release() {
connection c = std::move(_connection);
_connection = connection{};
return c;
}
///
/// @returns `true` if the connection is connected to a signal object,
/// and `false` otherwise.
bool connected() const {
return _connection.connected();
}
/// Disconnect the slot from the connection.
///
/// If the connection represents a slot that is connected to a signal object, calling
/// this method will disconnect the slot from that object. The result of this operation
/// is that the slot will stop receiving calls when the signal is invoked.
void disconnect() {
_connection.disconnect();
}
private:
/// Underlying connection object
connection _connection;
};
/// Policy for multi threaded use of signals.
///
/// This policy provides mutex and lock types for use in
/// a multithreaded environment, where signals and slots
/// may exists in different threads.
///
/// This policy is used in the `nod::signal` type provided
/// by the library.
struct multithread_policy
{
using mutex_type = std::mutex;
using mutex_lock_type = std::unique_lock<mutex_type>;
/// Function that yields the current thread, allowing
/// the OS to reschedule.
static void yield_thread() {
std::this_thread::yield();
}
/// Function that defers a lock to a lock function that prevents deadlock
static mutex_lock_type defer_lock(mutex_type & m){
return mutex_lock_type{m, std::defer_lock};
}
/// Function that locks two mutexes and prevents deadlock
static void lock(mutex_lock_type & a,mutex_lock_type & b) {
std::lock(a,b);
}
};
/// Policy for single threaded use of signals.
///
/// This policy provides dummy implementations for mutex
/// and lock types, resulting in that no synchronization
/// will take place.
///
/// This policy is used in the `nod::unsafe_signal` type
/// provided by the library.
struct singlethread_policy
{
/// Dummy mutex type that doesn't do anything
struct mutex_type{};
/// Dummy lock type, that doesn't do any locking.
struct mutex_lock_type
{
/// A lock type must be constructible from a
/// mutex type from the same thread policy.
explicit mutex_lock_type( mutex_type const& ) {
}
};
/// Dummy implementation of thread yielding, that
/// doesn't do any actual yielding.
static void yield_thread() {
}
/// Dummy implemention of defer_lock that doesn't
/// do anything
static mutex_lock_type defer_lock(mutex_type &m){
return mutex_lock_type{m};
}
/// Dummy implemention of lock that doesn't
/// do anything
static void lock(mutex_lock_type &,mutex_lock_type &) {
}
};
/// Signal accumulator class template.
///
/// This acts sort of as a proxy for triggering a signal and
/// accumulating the slot return values.
///
/// This class is not really intended to instantiate by client code.
/// Instances are aquired as return values of the method `accumulate()`
/// called on signals.
///
/// @tparam S Type of signal. The signal_accumulator acts
/// as a type of proxy for a signal instance of
/// this type.
/// @tparam T Type of initial value of the accumulate algorithm.
/// This type must meet the requirements of `CopyAssignable`
/// and `CopyConstructible`
/// @tparam F Type of accumulation function.
/// @tparam A... Argument types of the underlying signal type.
///
template <class S, class T, class F, class...A>
class signal_accumulator
{
public:
/// Result type when calling the accumulating function operator.
#if (__cplusplus > 201703L)
using result_type = typename std::invoke_result<F, T, typename S::slot_type::result_type>::type;
#else
using result_type = typename std::result_of<F(T, typename S::slot_type::result_type)>::type;
#endif
/// Construct a signal_accumulator as a proxy to a given signal
//
/// @param signal Signal instance.
/// @param init Initial value of the accumulate algorithm.
/// @param func Binary operation function object that will be
/// applied to all slot return values.
/// The signature of the function should be
/// equivalent of the following:
/// `R func( T1 const& a, T2 const& b )`
/// - The signature does not need to have `const&`.
/// - The initial value, type `T`, must be implicitly
/// convertible to `R`
/// - The return type `R` must be implicitly convertible
/// to type `T1`.
/// - The type `R` must be `CopyAssignable`.
/// - The type `S::slot_type::result_type` (return type of
/// the signals slots) must be implicitly convertible to
/// type `T2`.
signal_accumulator( S const& signal, T init, F func ) :
_signal( signal ),
_init( init ),
_func( func )
{}
/// Function call operator.
///
/// Calling this will trigger the underlying signal and accumulate
/// all of the connected slots return values with the current
/// initial value and accumulator function.
///
/// When called, this will invoke the accumulator function will
/// be called for each return value of the slots. The semantics
/// are similar to the `std::accumulate` algorithm.
///
/// @param args Arguments to propagate to the slots of the
/// underlying when triggering the signal.
result_type operator()( A const& ... args ) const {
return _signal.trigger_with_accumulator( _init, _func, args... );
}
private:
/// Reference to the underlying signal to proxy.
S const& _signal;
/// Initial value of the accumulate algorithm.
T _init;
/// Accumulator function.
F _func;
};
/// Signal template specialization.
///
/// This is the main signal implementation, and it is used to
/// implement the observer pattern whithout the overhead
/// boilerplate code that typically comes with it.
///
/// Any function or function object is considered a slot, and
/// can be connected to a signal instance, as long as the signature
/// of the slot matches the signature of the signal.
///
/// @tparam P Threading policy for the signal.
/// A threading policy must provide two type definitions:
/// - P::mutex_type, this type will be used as a mutex
/// in the signal_type class template.
/// - P::mutex_lock_type, this type must implement a
/// constructor that takes a P::mutex_type as a parameter,
/// and it must have the semantics of a scoped mutex lock
/// like std::lock_guard, i.e. locking in the constructor
/// and unlocking in the destructor.
///
/// @tparam R Return value type of the slots connected to the signal.
/// @tparam A... Argument types of the slots connected to the signal.
template <class P, class R, class... A >
class signal_type<P,R(A...)>
{
public:
/// signals are not copy constructible
signal_type( signal_type const& ) = delete;
/// signals are not copy assignable
signal_type& operator=( signal_type const& ) = delete;
/// signals are move constructible
signal_type(signal_type&& other)
{
mutex_lock_type lock{other._mutex};
_slot_count = std::move(other._slot_count);
_slots = std::move(other._slots);
if(other._shared_disconnector != nullptr)
{
_disconnector = disconnector{ this };
_shared_disconnector = std::move(other._shared_disconnector);
// replace the disconnector with our own disconnector
*static_cast<disconnector*>(_shared_disconnector.get()) = _disconnector;
}
}
/// signals are move assignable
signal_type& operator=(signal_type&& other)
{
auto lock = thread_policy::defer_lock(_mutex);
auto other_lock = thread_policy::defer_lock(other._mutex);
thread_policy::lock(lock,other_lock);
_slot_count = std::move(other._slot_count);
_slots = std::move(other._slots);
if(other._shared_disconnector != nullptr)
{
_disconnector = disconnector{ this };
_shared_disconnector = std::move(other._shared_disconnector);
// replace the disconnector with our own disconnector
*static_cast<disconnector*>(_shared_disconnector.get()) = _disconnector;
}
return *this;
}
/// signals are default constructible
signal_type() :
_slot_count(0)
{}
// Destruct the signal object.
~signal_type() {
invalidate_disconnector();
}
/// Type that will be used to store the slots for this signal type.
using slot_type = std::function<R(A...)>;
/// Type that is used for counting the slots connected to this signal.
using size_type = typename std::vector<slot_type>::size_type;
/// Connect a new slot to the signal.
///
/// The connected slot will be called every time the signal
/// is triggered.
/// @param slot The slot to connect. This must be a callable with
/// the same signature as the signal itself.
/// @return A connection object is returned, and can be used to
/// disconnect the slot.
template <class T>
connection connect( T&& slot ) {
mutex_lock_type lock{ _mutex };
_slots.push_back( std::forward<T>(slot) );
std::size_t index = _slots.size()-1;
if( _shared_disconnector == nullptr ) {
_disconnector = disconnector{ this };
_shared_disconnector = std::shared_ptr<detail::disconnector>{&_disconnector, detail::no_delete};
}
++_slot_count;
return connection{ _shared_disconnector, index };
}
/// Function call operator.
///
/// Calling this is how the signal is triggered and the
/// connected slots are called.
///
/// @note The slots will be called in the order they were
/// connected to the signal.
///
/// @param args Arguments that will be propagated to the
/// connected slots when they are called.
void operator()( A const&... args ) const {
for( auto const& slot : copy_slots() ) {
if( slot ) {
slot( args... );
}
}
}
/// Construct a accumulator proxy object for the signal.
///
/// The intended purpose of this function is to create a function
/// object that can be used to trigger the signal and accumulate
/// all the slot return values.
///
/// The algorithm used to accumulate slot return values is similar
/// to `std::accumulate`. A given binary function is called for
/// each return value with the parameters consisting of the
/// return value of the accumulator function applied to the
/// previous slots return value, and the current slots return value.
/// A initial value must be provided for the first slot return type.
///
/// @note This can only be used on signals that have slots with
/// non-void return types, since we can't accumulate void
/// values.
///
/// @tparam T The type of the initial value given to the accumulator.
/// @tparam F The accumulator function type.
/// @param init Initial value given to the accumulator.
/// @param op Binary operator function object to apply by the accumulator.
/// The signature of the function should be
/// equivalent of the following:
/// `R func( T1 const& a, T2 const& b )`
/// - The signature does not need to have `const&`.
/// - The initial value, type `T`, must be implicitly
/// convertible to `R`
/// - The return type `R` must be implicitly convertible
/// to type `T1`.
/// - The type `R` must be `CopyAssignable`.
/// - The type `S::slot_type::result_type` (return type of
/// the signals slots) must be implicitly convertible to
/// type `T2`.
template <class T, class F>
signal_accumulator<signal_type, T, F, A...> accumulate( T init, F op ) const {
static_assert( std::is_same<R,void>::value == false, "Unable to accumulate slot return values with 'void' as return type." );
return { *this, init, op };
}
/// Trigger the signal, calling the slots and aggregate all
/// the slot return values into a container.
///
/// @tparam C The type of container. This type must be
/// `DefaultConstructible`, and usable with
/// `std::back_insert_iterator`. Additionally it
/// must be either copyable or moveable.
/// @param args The arguments to propagate to the slots.
template <class C>
C aggregate( A const&... args ) const {
static_assert( std::is_same<R,void>::value == false, "Unable to aggregate slot return values with 'void' as return type." );
C container;
auto iterator = std::back_inserter( container );
for( auto const& slot : copy_slots() ) {
if( slot ) {
(*iterator) = slot( args... );
}
}
return container;
}
/// Count the number of slots connected to this signal
/// @returns The number of connected slots
size_type slot_count() const {
return _slot_count;
}
/// Determine if the signal is empty, i.e. no slots are connected
/// to it.
/// @returns `true` is returned if the signal has no connected
/// slots, and `false` otherwise.
bool empty() const {
return slot_count() == 0;
}
/// Disconnects all slots
/// @note This operation invalidates all scoped_connection objects
void disconnect_all_slots() {
mutex_lock_type lock{ _mutex };
_slots.clear();
_slot_count = 0;
invalidate_disconnector();
}
private:
template<class, class, class, class...> friend class signal_accumulator;
/// Thread policy currently in use
using thread_policy = P;
/// Type of mutex, provided by threading policy
using mutex_type = typename thread_policy::mutex_type;
/// Type of mutex lock, provided by threading policy
using mutex_lock_type = typename thread_policy::mutex_lock_type;
/// Invalidate the internal disconnector object in a way
/// that is safe according to the current thread policy.
///
/// This will effectively make all current connection objects to
/// to this signal incapable of disconnecting, since they keep a
/// weak pointer to the shared disconnector object.
void invalidate_disconnector() {
// If we are unlucky, some of the connected slots
// might be in the process of disconnecting from other threads.
// If this happens, we are risking to destruct the disconnector
// object managed by our shared pointer before they are done
// disconnecting. This would be bad. To solve this problem, we
// discard the shared pointer (that is pointing to the disconnector
// object within our own instance), but keep a weak pointer to that
// instance. We then stall the destruction until all other weak
// pointers have released their "lock" (indicated by the fact that
// we will get a nullptr when locking our weak pointer).
std::weak_ptr<detail::disconnector> weak{_shared_disconnector};
_shared_disconnector.reset();
while( weak.lock() != nullptr ) {
// we just yield here, allowing the OS to reschedule. We do
// this until all threads has released the disconnector object.
thread_policy::yield_thread();
}
}
/// Retrieve a copy of the current slots
///
/// It's useful and necessary to copy the slots so we don't need
/// to hold the lock while calling the slots. If we hold the lock
/// we prevent the called slots from modifying the slots vector.
/// This simple "double buffering" will allow slots to disconnect
/// themself or other slots and connect new slots.
std::vector<slot_type> copy_slots() const
{
mutex_lock_type lock{ _mutex };
return _slots;
}
/// Implementation of the signal accumulator function call
template <class T, class F>
typename signal_accumulator<signal_type, T, F, A...>::result_type trigger_with_accumulator( T value, F& func, A const&... args ) const {
for( auto const& slot : copy_slots() ) {
if( slot ) {
value = func( value, slot( args... ) );
}
}
return value;
}
/// Implementation of the disconnection operation.
///
/// This is private, and only called by the connection
/// objects created when connecting slots to this signal.
/// @param index The slot index of the slot that should
/// be disconnected.
void disconnect( std::size_t index ) {
mutex_lock_type lock( _mutex );
assert( _slots.size() > index );
if( _slots[ index ] != nullptr ) {
--_slot_count;
}
_slots[ index ] = slot_type{};
while( _slots.size()>0 && !_slots.back() ) {
_slots.pop_back();
}
}
/// Implementation of the shared disconnection state
/// used by all connection created by signal instances.
///
/// This inherits the @ref detail::disconnector interface
/// for type erasure.
struct disconnector :
detail::disconnector
{
/// Default constructor, resulting in a no-op disconnector.
disconnector() :
_ptr(nullptr)
{}
/// Create a disconnector that works with a given signal instance.
/// @param ptr Pointer to the signal instance that the disconnector
/// should work with.
disconnector( signal_type<P,R(A...)>* ptr ) :
_ptr( ptr )
{}
/// Disconnect a given slot on the current signal instance.
/// @note If the instance is default constructed, or created
/// with `nullptr` as signal pointer this operation will
/// effectively be a no-op.
/// @param index The index of the slot to disconnect.
void operator()( std::size_t index ) const override {
if( _ptr ) {
_ptr->disconnect( index );
}
}
/// Pointer to the current signal.
signal_type<P,R(A...)>* _ptr;
};
/// Mutex to synchronize access to the slot vector
mutable mutex_type _mutex;
/// Vector of all connected slots
std::vector<slot_type> _slots;
/// Number of connected slots
size_type _slot_count;
/// Disconnector operation, used for executing disconnection in a
/// type erased manner.
disconnector _disconnector;
/// Shared pointer to the disconnector. All connection objects has a
/// weak pointer to this pointer for performing disconnections.
std::shared_ptr<detail::disconnector> _shared_disconnector;
};
// Implementation of the disconnect operation of the connection class
inline void connection::disconnect() {
auto ptr = _weak_disconnector.lock();
if( ptr ) {
(*ptr)( _index );
}
_weak_disconnector.reset();
}
/// Signal type that is safe to use in multithreaded environments,
/// where the signal and slots exists in different threads.
/// The multithreaded policy provides mutexes and locks to synchronize
/// access to the signals internals.
///
/// This is the recommended signal type, even for single threaded
/// environments.
template <class T> using signal = signal_type<multithread_policy, T>;
/// Signal type that is unsafe in multithreaded environments.
/// No synchronizations are provided to the signal_type for accessing
/// the internals.
///
/// Only use this signal type if you are sure that your environment is
/// single threaded and performance is of importance.
template <class T> using unsafe_signal = signal_type<singlethread_policy, T>;
} // namespace nod
#endif // IG_NOD_INCLUDE_NOD_HPP
