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future.h
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future.h
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/*
This file is part of MADNESS.
Copyright (C) 2007,2010 Oak Ridge National Laboratory
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
For more information please contact:
Robert J. Harrison
Oak Ridge National Laboratory
One Bethel Valley Road
P.O. Box 2008, MS-6367
email: harrisonrj@ornl.gov
tel: 865-241-3937
fax: 865-572-0680
*/
/**
\file future.h
\brief Implements \c Future and related items.
\ingroup futures
*/
#ifndef MADNESS_WORLD_FUTURE_H__INCLUDED
#define MADNESS_WORLD_FUTURE_H__INCLUDED
#include <vector>
#include <stack>
#include <new>
#include <madness/world/nodefaults.h>
#include <madness/world/dependency_interface.h>
#include <madness/world/stack.h>
#include <madness/world/worldref.h>
#include <madness/world/world.h>
/// \addtogroup futures
/// @{
namespace madness {
//extern SharedCounter future_count; // For tracking memory leak
// forward decl
template <typename T> class Future;
/// Boost-type-trait-like test if a type is a future.
/// \tparam T The type to test.
template <typename T>
struct is_future : public std::false_type { };
/// Boost-type-trait-like test if a type is a future.
/// \tparam T The type to test.
template <typename T>
struct is_future< Future<T> > : public std::true_type { };
/// Boost-type-trait-like mapping of type \c T to \c Future<T>.
/// \tparam T The type to have future added.
template <typename T>
struct add_future {
/// Type with \c Future added.
typedef Future<T> type;
};
/// Boost-type-trait-like mapping of \c Future<T> to \c Future<T>.
/// Specialization of \c add_future<T> that properly forbids the type
/// \c Future< Future<T> >.
/// \tparam T The underlying data type.
template <typename T>
struct add_future< Future<T> > {
/// Type with \c Future added.
typedef Future<T> type;
};
/// Boost-type-trait-like mapping of \c Future<T> to \c T.
/// \tparam T The type to have future removed; in this case, do nothing.
template <typename T>
struct remove_future {
/// Type with \c Future removed.
typedef T type;
};
/// This metafunction maps \c Future<T> to \c T.
/// \internal Future is a wrapper for T (it acts like an Identity monad), so this
/// unwraps T. It makes sense that the result should preserve the access traits
/// of the Future, i.e. const Future<T> should map to const T, etc.
/// Specialization of \c remove_future for \c Future<T>
/// \tparam T The type to have future removed.
template <typename T>
struct remove_future< Future<T> > {
/// Type with \c Future removed.
typedef T type;
};
/// Specialization of \c remove_future for \c Future<T>
/// \tparam T The type to have future removed.
template <typename T>
struct remove_future< const Future<T> > {
/// Type with \c Future removed.
typedef const T type;
};
/// Specialization of \c remove_future for \c Future<T>&
/// \tparam T The type to have future removed.
template <typename T>
struct remove_future< Future<T>& > {
/// Type with \c Future removed.
typedef T& type;
};
/// Specialization of \c remove_future for \c Future<T>&&
/// \tparam T The type to have future removed.
template <typename T>
struct remove_future< Future<T>&& > {
/// Type with \c Future removed.
typedef T&& type;
};
/// Specialization of \c remove_future for \c const \c Future<T>&
/// \tparam T The type to have future removed.
template <typename T>
struct remove_future< const Future<T>& > {
/// Type with \c Future removed.
typedef const T& type;
};
/// Macro to determine type of future (by removing wrapping \c Future template).
/// \param T The type (possibly with \c Future).
#define REMFUTURE(T) typename remove_future< T >::type
/// C++11 version of REMFUTURE
template <typename T>
using remove_future_t = typename remove_future< T >::type;
/// Similar to remove_future , but future_to_ref<Future<T>> evaluates to T& ,whereas
/// remove_future<Future<T>> evaluates to T .
/// \tparam T The type to have future removed; in this case, do nothing.
template <typename T>
struct future_to_ref {
typedef T type;
};
template <typename T>
struct future_to_ref<Future<T>> {
typedef T& type;
};
template <typename T>
struct future_to_ref<Future<T>&> {
typedef T& type;
};
template <typename T>
struct future_to_ref<const Future<T>&> {
typedef const T& type;
};
template <typename T>
using future_to_ref_t = typename future_to_ref< T >::type;
/// Human readable printing of a \c Future to a stream.
/// \tparam T The type of future.
/// \param[in,out] out The output stream.
/// \param[in] f The future.
/// \return The output stream.
template <typename T>
std::ostream& operator<<(std::ostream& out, const Future<T>& f);
/// Implements the functionality of futures.
/// \tparam T The type of future.
template <typename T>
class FutureImpl : private Spinlock {
friend class Future<T>;
friend std::ostream& operator<< <T>(std::ostream& out, const Future<T>& f);
private:
/// The static stack size used for callbacks and future assignment used
/// for small stack size optimizations.
static const int MAXCALLBACKS = 4;
typedef Stack<CallbackInterface*, MAXCALLBACKS> callbackT; ///< Callback type.
typedef Stack<std::shared_ptr<FutureImpl<T> >,MAXCALLBACKS> assignmentT; ///< Assignment type.
/// A stack that stores callbacks that are invoked once the future has
/// been assigned.
volatile callbackT callbacks;
/// A stack that stores future objects that are set to the same value
/// as this future, once it has been set.
volatile mutable assignmentT assignments;
/// A flag indicating if the future has been set.
volatile bool assigned;
/// Reference to a remote future pimpl.
RemoteReference< FutureImpl<T> > remote_ref;
volatile T t; ///< The future data.
/// AM handler for remote set operations.
/// \todo Description needed.
/// \param[in] arg Description needed.
static void set_handler(const AmArg& arg) {
RemoteReference< FutureImpl<T> > ref;
archive::BufferInputArchive input_arch = arg & ref;
// The remote reference holds a copy of the shared_ptr, so no need
// to take another.
{
FutureImpl<T>* pimpl = ref.get();
ScopedMutex<Spinlock> fred(pimpl);
if(pimpl->remote_ref) {
// Unarchive the value to a temporary since it is going to
// be forwarded to another node.
T value;
input_arch & value;
// Copy world and owner from remote_ref since sending remote_ref
// will invalidate it.
World& world = pimpl->remote_ref.get_world();
const ProcessID owner = pimpl->remote_ref.owner();
world.am.send(owner, FutureImpl<T>::set_handler,
new_am_arg(pimpl->remote_ref, value));
pimpl->set_assigned(value);
} else {
// Unarchive the value of the future
input_arch & const_cast<T&>(pimpl->t);
pimpl->set_assigned(const_cast<const T&>(pimpl->t));
}
}
ref.reset();
}
/// \todo Brief description needed.
/// Invoked locally by set routine after assignment.
/// \todo Description needed.
/// \param[in] value Description needed.
inline void set_assigned(const T& value) {
// Assume that whoever is invoking this routine is holding
// a copy of our shared pointer on its *stack* so that
// if this future is destroyed as a result of a callback
// the destructor of this object is not invoked until
// we return.
//
// Also assume that the caller either has the lock
// or is sure that we are single threaded.
MADNESS_ASSERT(!assigned);
assigned = true;
assignmentT& as = const_cast<assignmentT&>(assignments);
callbackT& cb = const_cast<callbackT&>(callbacks);
while (!as.empty()) {
MADNESS_ASSERT(as.top());
as.top()->set(value);
as.pop();
}
while (!cb.empty()) {
MADNESS_ASSERT(cb.top());
cb.top()->notify();
cb.pop();
}
as.reset();
cb.reset();
}
/// Pass by value with implied copy to manage lifetime of \c f.
/// \todo Description needed.
/// \param[in] f Description needed.
inline void add_to_assignments(const std::shared_ptr< FutureImpl<T> > f) {
// ASSUME lock is already acquired
if (assigned) {
f->set(const_cast<T&>(t));
}
else {
assignmentT* as = const_cast<assignmentT*>(&assignments);
as->push(f);
}
}
public:
/// Constructor that uses a local unassigned value.
FutureImpl()
: callbacks()
, assignments()
, assigned(false)
, remote_ref()
, t()
{ }
/// Constructor that uses a wrapper for a remote future.
/// \todo Description needed.
/// \param[in] remote_ref Description needed.
FutureImpl(const RemoteReference< FutureImpl<T> >& remote_ref)
: callbacks()
, assignments()
, assigned(false)
, remote_ref(remote_ref)
, t()
{ }
/// Checks if the value has been assigned.
/// \return True if the value has been assigned; false otherwise.
inline bool probe() const {
return assigned;
}
/// Registers a function to be invoked when future is assigned.
/// Callbacks are invoked in the order registered. If the
/// future is already assigned, the callback is immediately
/// invoked.
/// \todo Description needed.
/// \param callback Description needed.
inline void register_callback(CallbackInterface* callback) {
ScopedMutex<Spinlock> fred(this);
if (assigned) callback->notify();
else const_cast<callbackT&>(callbacks).push(callback);
}
/// Sets the value of the future (assignment).
/// \todo Descriptions needed.
/// \tparam U Description needed.
/// \param[in] value Description needed.
template <typename U>
void set(const U& value) {
ScopedMutex<Spinlock> fred(this);
if(remote_ref) {
// Copy world and owner from remote_ref since sending remote_ref
// will invalidate it.
World& world = remote_ref.get_world();
const ProcessID owner = remote_ref.owner();
world.am.send(owner, FutureImpl<T>::set_handler,
new_am_arg(remote_ref, value));
set_assigned(value);
} else {
set_assigned((const_cast<T&>(t) = value));
}
}
/// \todo Brief description needed.
/// \todo Descriptions needed.
/// \param[in] input_arch Description needed.
void set(const archive::BufferInputArchive& input_arch) {
ScopedMutex<Spinlock> fred(this);
MADNESS_ASSERT(! remote_ref);
input_arch & const_cast<T&>(t);
set_assigned(const_cast<T&>(t));
}
/// Gets/forces the value, waiting if necessary.
/// \attention Throws an error if not local.
/// \todo Description needed.
/// \return Description needed.
T& get() {
MADNESS_ASSERT(! remote_ref); // Only for local futures
World::await([this] () -> bool { return this->probe(); });
return *const_cast<T*>(&t);
}
/// Gets/forces the value, waiting if necessary.
/// \attention Throws an error if not local.
/// \todo Description needed.
/// \return Description needed.
const T& get() const {
MADNESS_ASSERT(! remote_ref); // Only for local futures
World::await([this] () -> bool { return this->probe(); });
return *const_cast<const T*>(&t);
}
/// \todo Brief description needed.
/// \todo Description needed.
/// \return Description needed.
bool is_local() const {
return ! remote_ref;
}
/// \todo Brief description needed.
/// \todo Is this function needed?
/// \todo Details needed.
/// \param f Description needed.
/// \return Description needed.
bool replace_with(FutureImpl<T>* f) {
MADNESS_EXCEPTION("IS THIS WORKING? maybe now we have the mutex", 0);
// ScopedMutex<Spinlock> fred(this);
// MADNESS_ASSERT(!world); // was return false;
// MADNESS_ASSERT(!assigned || f->assigned);
// if (f->world) {
// world = f->world;
// remote_ref = f->remote_ref;
// f->world = 0;
// }
// while(f->callbacks.size()) callbacks.push(f->callbacks.pop());
// while(f->assignments.size()) assignments.push(f->assignments.pop());
return true;
}
/// Destructor.
/// \todo Perhaps a comment about its behavior.
virtual ~FutureImpl() {
if (const_cast<callbackT&>(callbacks).size()) {
print("Future: uninvoked callbacks being destroyed?", assigned);
abort();
}
if (const_cast<assignmentT&>(assignments).size()) {
print("Future: uninvoked assignment being destroyed?", assigned);
abort();
}
}
}; // class FutureImpl
/// A future is a possibly yet unevaluated value.
/// Uses delegation to \c FutureImpl to provide desired copy/assignment
/// semantics, as well as safe reference counting for remote futures.
///
/// Since we are using futures a lot to store local values coming
/// from containers and inside task wrappers for messages, we
/// included in this class a value. If a future is assigned
/// before a copy/remote-reference is taken, the shared pointer is
/// never made. The point of this is to eliminate the two `malloc`s
/// that must be peformed for every new \c shared_ptr.
/// \tparam T The type of future.
/// \todo Can this detailed description be made clearer?
template <typename T>
class Future {
friend std::ostream& operator<< <T>(std::ostream& out, const Future<T>& f);
private:
/// Pointer to the implementation object.
std::shared_ptr< FutureImpl<T> > f;
char buffer[sizeof(T)]; ///< Buffer to hold a single \c T object.
T* const value; ///< Pointer to buffer when it holds a \c T object.
/// \todo Has something to do with the "Gotchas" section in \ref futures. More detail needed.
/// \todo Perhaps more detail here, too... At the very least, can we give it a better name?
class dddd {};
/// \todo Constructor for ...
/// \todo Description needed.
/// \param[in] blah Description needed.
explicit Future(const dddd& blah) : f(), value(nullptr) { }
public:
/// \todo Brief description needed.
typedef RemoteReference< FutureImpl<T> > remote_refT;
/// Makes an unassigned future.
Future() :
f(new FutureImpl<T>()), value(nullptr)
{ }
/// Makes an assigned future.
/// \todo Description needed.
/// \param[in] t Description needed.
explicit Future(const T& t) :
f(), value(new(static_cast<void*>(buffer)) T(t))
{ }
/// Makes a future wrapping a remote reference.
/// \param[in] remote_ref The remote reference.
explicit Future(const remote_refT& remote_ref) :
f(remote_ref.is_local() ?
remote_ref.get_shared() :
std::make_shared<FutureImpl<T> >(remote_ref)),
// std::shared_ptr<FutureImpl<T> >(new FutureImpl<T>(remote_ref))),
value(nullptr)
{ }
/// Makes an assigned future from an input archive.
/// \param[in] input_arch The input archive.
explicit Future(const archive::BufferInputArchive& input_arch) :
f(), value(new(static_cast<void*>(buffer)) T())
{
input_arch & (*value);
}
/// Shallow copy constructor.
/// \param[in] other The future to copy.
Future(const Future<T>& other) :
f(other.f),
value(other.value ?
new(static_cast<void*>(buffer)) T(* other.value) :
nullptr)
{
if(other.is_default_initialized())
f.reset(new FutureImpl<T>()); // Other was default constructed so make a new f
}
/// Destructor.
~Future() {
if(value)
value->~T();
}
/// \todo Informative description needed.
/// See "Gotchas" on \ref futures about why this exists and how to use it.
static const Future<T> default_initializer() {
return Future<T>(dddd());
}
/// Check if the future is default initialized.
/// \return True if this future was constructed with
/// \c default_initializer(); false otherwise.
bool is_default_initialized() const {
return ! (f || value);
}
/// Shallow assignment operator.
/// \param[in] other The future to copy.
/// \return This.
Future<T>& operator=(const Future<T>& other) {
if(this != &other) {
MADNESS_ASSERT(!probe());
if(f && other.value)
set(other);
else
f = other.f;
}
return *this;
}
/// \brief `A.set(B)`, where `A` and `B` are futures ensures `A`
/// has/will have the same value as `B`.
/// An exception is thrown if `A` is already assigned since a
/// \c Future is a single assignment variable. We don't yet
/// track multiple assignments from unassigned futures.
///
/// If `B` is already assigned, this is the same as `A.set(B.get())`,
/// which sets `A` to the value of `B`.
///
/// If `B` has not yet been assigned, the behavior is to ensure
/// that, when `B` is assigned, both `A` and `B` will be assigned
/// and have the same value (though they may/may not refer to
/// the same underlying copy of the data and indeed may even
/// be in different processes).
/// \todo Verification needed in the param statement.
/// \param[in] other The future `B` described above. `*this` is `A`.
void set(const Future<T>& other) {
MADNESS_ASSERT(f);
if(f != other.f) {
MADNESS_ASSERT(! f->probe());
if (other.probe()) {
set(other.get()); // The easy case
} else {
// Assignment is supposed to happen just once so
// safe to assume that this is not being messed
// with ... also other might invoke the assignment
// callback since it could have been assigned
// between the test above and now (and this does
// happen)
std::shared_ptr< FutureImpl<T> > ff = f; // manage lifetime of me
std::shared_ptr< FutureImpl<T> > of = other.f; // manage lifetime of other
{ // BEGIN CRITICAL SECTION
ScopedMutex<Spinlock> fred(of.get());
of->add_to_assignments(ff); // Recheck of assigned is performed in here
} // END CRITICAL SECTION
}
}
}
/// Assigns the value.
/// The value can only be set \em once.
/// \param[in] value The value to be assigned.
inline void set(const T& value) {
MADNESS_ASSERT(f);
std::shared_ptr< FutureImpl<T> > ff = f; // manage life time of f
ff->set(value);
}
/// Assigns the value.
/// The value can only be set \em once.
/// \todo Description needed.
/// \param[in] input_arch Description needed.
inline void set(const archive::BufferInputArchive& input_arch) {
MADNESS_ASSERT(f);
std::shared_ptr< FutureImpl<T> > ff = f; // manage life time of f
ff->set(input_arch);
}
/// Gets the value, waiting if necessary.
/// \attention Throws an error if this is not a local future.
/// \return The value.
inline T& get() {
MADNESS_ASSERT(f || value); // Check that future is not default initialized
return (f ? f->get() : *value);
}
/// Gets the value, waiting if necessary.
/// \attention Throws an error if this is not a local future.
/// \return The value.
inline const T& get() const {
MADNESS_ASSERT(f || value); // Check that future is not default initialized
return (f ? f->get() : *value);
}
/// Check whether this future has been assigned.
/// \return True if the future has been assigned; false otherwise.
inline bool probe() const {
return (f ? f->probe() : bool(value));
}
/// Same as \c get().
/// \return An lvalue reference to the value.
inline operator T&() & {
return get();
}
/// Same as `get() const`.
/// \return An const lvalue reference to the value.
inline operator const T&() const& {
return get();
}
/// An rvalue analog of \c get().
/// \return An rvalue reference to the value.
/// \internal Rationale: the conversion operators unwrap the
/// Future object (see also \c remove_future
/// metafunction), hence the result should maintain
/// the traits of the Future object. The rvalue conversion
/// is made explicit to avoid accidents (perhaps this should
/// be revisited to make easier moving Future objects into
/// functions).
inline explicit operator T&&() && {
return std::move(get());
}
/// An rvalue analog of \c get().
/// \return An rvalue reference to the value.
/// \internal Rationale: this makes possible to move the value from a mutable assigned future.
inline explicit operator T&&() & {
return std::move(get());
}
/// Returns a structure used to pass references to another process.
/// This is used for passing pointers/references to another
/// process. To make remote references completely safe, the
/// \c RemoteReference increments the internal reference count of
/// the \c Future. The counter is decremented by either
/// assigning to the remote \c Future or its destructor if it is
/// never assigned. The remote \c Future is \em only useful for
/// setting the future. It will \em not be notified if the value
/// is set elsewhere.
///
/// If this is already a reference to a remote future, the
/// actual remote reference is returned; that is, \em not a
/// a reference to the local future. Therefore, the local
/// future will not be notified when the result is set
/// (i.e., the communication is short circuited).
/// \param[in,out] world The communication world.
/// \todo Verify the return comment.
/// \return The remote reference.
inline remote_refT remote_ref(World& world) const {
MADNESS_ASSERT(!probe());
if (f->remote_ref)
return f->remote_ref;
else
return RemoteReference< FutureImpl<T> >(world, f);
}
/// \todo Brief description needed.
/// \todo Description needed.
/// \return Description needed.
inline bool is_local() const {
return (f && f->is_local()) || value;
}
/// \todo Brief description needed.
/// \todo Description needed.
/// \return Description needed.
inline bool is_remote() const {
return !is_local();
}
/// Registers an object to be called when future is assigned.
/// Callbacks are invoked in the order registered. If the
/// future is already assigned, the callback is immediately
/// invoked.
/// \param[in] callback The callback to be invoked.
inline void register_callback(CallbackInterface* callback) {
if(probe()) {
callback->notify();
} else {
MADNESS_ASSERT(f);
f->register_callback(callback);
}
}
}; // class Future
/// A future of a future is forbidden (by deleted constructor).
/// \tparam T The type of future.
template <typename T>
class Future< Future<T> > {
Future() = delete;
};
/// \brief Specialization of \c FutureImpl<void> for internal convenience.
/// This does nothing useful!
template <>
class FutureImpl<void> {};
/// \brief Specialization of \c Future<void> for internal convenience.
/// This does nothing useful!
template <> class
Future<void> {
public:
/// \todo Brief description needed.
typedef RemoteReference< FutureImpl<void> > remote_refT;
/// \todo Brief description needed.
static const Future<void> value;
/// \todo Brief description needed.
/// \todo Descriptions needed.
/// \param[in,out] world Description needed.
/// \return Description needed.
static remote_refT remote_ref(World& world) {
return remote_refT();
}
Future() {}
/// \todo Brief description needed.
/// \todo Description needed.
/// \param[in] remote_ref Description needed.
Future(const RemoteReference< FutureImpl<void> >& remote_ref) {}
/// Construct from an input archive.
/// \param[in] input_arch The input archive.
Future(const archive::BufferInputArchive& input_arch) {
input_arch & *this;
}
/// Assignment operator.
/// \param[in] other The future to copy.
/// \return This.
inline Future<void>& operator=(const Future<void>& other) {
return *this;
}
/// Set the future from another \c void future.
/// In this specialization, do nothing.
/// \param[in] f The other future.
static void set(const Future<void>& f) { }
/// Set the future.
/// In this specialization, do nothing.
static void set() { }
/// Check if this future has been assigned.
/// \return True (in this specialization).
static bool probe() {
return true;
}
}; // class Future<void>
/// Specialization of \c Future for a vector of `Future`s.
/// Enables passing a vector of futures into a task and having the
/// dependencies correctly tracked. Does not directly support most
/// operations that other futures do; these are the responsibility of the
/// individual futures in the vector.
/// \tparam T The type of future.
template <typename T>
class Future< std::vector< Future<T> > > : public DependencyInterface, private NO_DEFAULTS {
private:
/// Alias for a vector of futures.
typedef typename std::vector< Future<T> > vectorT;
/// The vector of futures.
vectorT v;
public:
Future() : v() { }
/// \todo Brief description needed.
/// \todo Description needed.
/// \param[in] v Vector of something...
Future(const vectorT& v) : DependencyInterface(v.size()), v(v) {
for (int i=0; i<(int)v.size(); ++i) {
this->v[i].register_callback(this);
}
}
/// \todo Brief description needed.
/// \todo Description needed.
/// \param[in] input_arch Description needed.
///
/// \todo Not implemented. If this is deliberate, specify why and change the tag to \\attention.
explicit Future(const archive::BufferInputArchive& input_arch) {
input_arch & v;
}
/// Access the vector of futures.
/// \return The vector of futures.
vectorT& get() {
return v;
}
/// Access the const vector of futures.
/// \return The vector of futures.
const vectorT& get() const {
return v;
}
/// Access the vector of futures.
/// \return The vector of futures.
operator vectorT& () {
return get();
}
/// Access the const vector of futures.
/// \return The vector of futures.
operator const vectorT& () const {
return get();
}
/// Check if all of the futures in the vector have been assigned.
/// \return True if all futures have been assigned; false otherwise.
bool probe() const {
return DependencyInterface::probe();
}
}; // class Future< std::vector< Future<T> > >
/// Factory for a vectors of futures.
/// Rationale for this function can be found in \ref futures.
/// \tparam T The type of future in the vector.
/// \param[in] n The size of the vector to create.
/// \return A vector of futures, as described in \ref futures.
template <typename T>
std::vector< Future<T> > future_vector_factory(std::size_t n) {
return std::vector< Future<T> >(n, Future<T>::default_initializer());
}
namespace archive {
/// Serialize an assigned future.
/// \tparam Archive Archive type.
/// \tparam T Future type.
template <class Archive, typename T>
struct ArchiveStoreImpl< Archive, Future<T> > {
/// Store the assigned future in an archive.
/// \param[in,out] ar The archive.
/// \param[in] f The future.
static inline void store(const Archive& ar, const Future<T>& f) {
MAD_ARCHIVE_DEBUG(std::cout << "serializing future" << std::endl);
MADNESS_ASSERT(f.probe());
ar & f.get();
}
};
/// Deserialize a future into an unassigned future.
/// \tparam Archive Archive type.
/// \tparam T Future type.
template <class Archive, typename T>
struct ArchiveLoadImpl< Archive, Future<T> > {
/// Read into an unassigned future.
/// \param[in,out] ar The archive.
/// \param[out] f The future.
static inline void load(const Archive& ar, Future<T>& f) {
MAD_ARCHIVE_DEBUG(std::cout << "deserializing future" << std::endl);
MADNESS_ASSERT(!f.probe());
T value;
ar & value;
f.set(value);
}
};