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ircd::ctx: Reorg / abstract / deinline promise related.

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This commit is contained in:
Jason Volk 2018-10-30 11:18:03 -07:00
parent 0ea1ba2968
commit a91cdeec0c
5 changed files with 528 additions and 465 deletions
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6
include/ircd/ctx/future.h
View file

@ -13,11 +13,13 @@
namespace ircd::ctx
{
IRCD_OVERLOAD(use_future)
template<class T = void> class future;
template<> class future<void>;
template<class... T> struct scoped_future;
IRCD_EXCEPTION(future_error, future_already_retrieved)
IRCD_OVERLOAD(use_future)
}
template<class T>

435
include/ircd/ctx/promise.h
View file

@ -13,369 +13,170 @@
namespace ircd::ctx
{
struct promise_base;
template<class T = void> class promise;
template<> class promise<void>;
template<class T> class future;
template<> class future<void>;
IRCD_EXCEPTION(ircd::ctx::error, future_error)
IRCD_EXCEPTION(future_error, no_state)
IRCD_EXCEPTION(future_error, broken_promise)
IRCD_EXCEPTION(future_error, future_already_retrieved)
IRCD_EXCEPTION(future_error, promise_already_satisfied)
}
template<class T>
struct ircd::ctx::promise
/// Abstract base type for ctx::promise. This dedupes most of the promissory
/// functionality with non-template definitions residing in ctx.cc.
///
/// In this system the promise is lightweight and maintains a pointer to the
/// shared_state object which generally resides within the future instance.
/// If the shared_state object moves or is destroyed the promise's pointer to
/// it must be updated. The shared_state object also has a pointer to the
/// promise; if the promise moves or is destroyed that pointer must be updated
/// as well. This is how the bi-directional relationship is maintained.
///
/// To further complicate things, this promise maintains a second pointer
/// to another instance of a promise implementing a linked-list semantic. All
/// of these promises are making the same promise to the same shared_state;
/// the list allows for copy semantics which are important for some callback
/// systems (like boost::asio). This solution is far more optimal than
/// allocating the promise in a shared_ptr and refcounting...
struct ircd::ctx::promise_base
{
shared_state<T> *st {nullptr}; // Reference to the state resident in future
mutable promise *next {nullptr}; // Promise fwdlist to support copy semantics
static void remove(shared_state_base &, promise_base &);
static void update(promise_base &new_, promise_base &old);
static void append(promise_base &new_, promise_base &old);
shared_state_base *st {nullptr};
mutable promise_base *next {nullptr};
template<class T> const shared_state<T> &state() const;
template<class T> shared_state<T> &state();
const shared_state_base &state() const;
shared_state_base &state();
void check_pending() const;
void make_ready();
public:
using value_type = typename shared_state<T>::value_type;
using pointer_type = typename shared_state<T>::pointer_type;
using reference_type = typename shared_state<T>::reference_type;
const shared_state<T> &state() const { assert(valid()); return *st; }
shared_state<T> &state() { assert(valid()); return *st; }
bool valid() const { return bool(st); }
bool operator!() const { return !valid(); }
operator bool() const { return valid(); }
bool valid() const;
operator bool() const;
bool operator!() const;
void set_exception(std::exception_ptr eptr);
protected:
promise_base() = default;
promise_base(const promise_base &);
promise_base(promise_base &&) noexcept;
promise_base &operator=(const promise_base &);
promise_base &operator=(promise_base &&) noexcept;
~promise_base() noexcept;
};
/// Value-oriented promise. The user creates an instance of this promise in
/// order to send a value to a future. After creating an instance of this
/// promise the user should construct a future with the matching template type
/// from this. The two will then be linked.
///
/// Space for the value will reside within the future instance and not the
/// promise instance. When the value is set it will be copied (or movied) there.
///
/// Full object semantics for this promise are supported; including copy
/// semantics. All copies of a promise are making the same promise thus
/// setting a value or exception for one invalidates all the copies.
///
/// Instances of this promise can safely destruct at any time. When all copies
/// of a promise destruct without setting a value or exception the future is
/// notified with a broken_promise exception.
template<class T>
struct ircd::ctx::promise
:promise_base
{
using value_type = typename shared_state<T>::value_type;
using pointer_type = typename shared_state<T>::pointer_type;
using reference_type = typename shared_state<T>::reference_type;
const shared_state<T> &state() const;
shared_state<T> &state();
public:
void set_value(const T &val);
void set_value(T&& val);
promise() = default;
promise(promise &&o) noexcept;
promise(const promise &);
promise &operator=(const promise &) = delete;
promise &operator=(promise &&) noexcept;
~promise() noexcept;
using promise_base::promise_base;
using promise_base::operator=;
};
/// Valueless promise. The user creates an instance of this promise in
/// order to notify a future of a success or set an exception for failure.
///
/// See docs for promise<T> for more information.
template<>
struct ircd::ctx::promise<void>
:promise_base
{
shared_state<void> *st {nullptr}; // Reference to the state resident in future
mutable promise *next {nullptr}; // Promise fwdlist to support copy semantics
using value_type = typename shared_state<void>::value_type;
const shared_state<void> &state() const;
shared_state<void> &state();
public:
using value_type = typename shared_state<void>::value_type;
const shared_state<void> &state() const { assert(valid()); return *st; }
shared_state<void> &state() { assert(valid()); return *st; }
bool valid() const { return bool(st); }
bool operator!() const { return !valid(); }
operator bool() const { return valid(); }
void set_exception(std::exception_ptr eptr);
void set_value();
promise() = default;
promise(promise &&o) noexcept;
promise(const promise &);
promise &operator=(const promise &) = delete;
promise &operator=(promise &&) noexcept;
~promise() noexcept;
using promise_base::promise_base;
using promise_base::operator=;
};
namespace ircd::ctx
{
template<class T> const shared_state<T> &state(const promise<T> &);
template<class T> shared_state<T> &state(promise<T> &);
template<class T> size_t refcount(const shared_state<T> &);
template<class T> void update(shared_state<T> &s);
template<class T> void invalidate(shared_state<T> &);
template<class T> void remove(shared_state<T> &, promise<T> &);
template<class T> void update(promise<T> &new_, promise<T> &old);
template<class T> void append(promise<T> &new_, promise<T> &old);
}
template<class T>
ircd::ctx::promise<T>::promise(promise<T> &&o)
noexcept
:st{std::move(o.st)}
,next{std::move(o.next)}
{
if(st)
{
update(*this, o);
o.st = nullptr;
}
}
inline
ircd::ctx::promise<void>::promise(promise<void> &&o)
noexcept
:st{std::move(o.st)}
,next{std::move(o.next)}
{
if(st)
{
update(*this, o);
o.st = nullptr;
}
}
template<class T>
ircd::ctx::promise<T>::promise(const promise<T> &o)
:st{o.st}
,next{nullptr}
{
append(*this, const_cast<promise<T> &>(o));
}
inline
ircd::ctx::promise<void>::promise(const promise<void> &o)
:st{o.st}
,next{nullptr}
{
append(*this, const_cast<promise<void> &>(o));
}
template<class T>
ircd::ctx::promise<T> &
ircd::ctx::promise<T>::operator=(promise<T> &&o)
noexcept
{
this->~promise();
st = std::move(o.st);
next = std::move(o.next);
if(!st)
return *this;
update(*this, o);
o.st = nullptr;
return *this;
}
inline
ircd::ctx::promise<void> &
ircd::ctx::promise<void>::operator=(promise<void> &&o)
noexcept
{
this->~promise();
st = std::move(o.st);
next = std::move(o.next);
if(!st)
return *this;
update(*this, o);
o.st = nullptr;
return *this;
}
template<class T>
ircd::ctx::promise<T>::~promise()
noexcept
{
if(!valid())
return;
if(refcount(state()) == 1)
set_exception(std::make_exception_ptr(broken_promise()));
else
remove(state(), *this);
}
inline
ircd::ctx::promise<void>::~promise()
noexcept
{
if(!valid())
return;
if(refcount(state()) == 1)
set_exception(std::make_exception_ptr(broken_promise()));
else
remove(state(), *this);
}
//
// promise<T>
//
template<class T>
void
ircd::ctx::promise<T>::set_value(T&& val)
{
assert(valid());
if(unlikely(!is(state(), future_state::PENDING)))
throw promise_already_satisfied{};
st->val = std::move(val);
auto *const st{this->st};
invalidate(*st);
set(*st, future_state::READY);
notify(*st);
assert(!valid());
check_pending();
state().val = std::move(val);
make_ready();
}
template<class T>
void
ircd::ctx::promise<T>::set_value(const T &val)
{
assert(valid());
if(unlikely(!is(state(), future_state::PENDING)))
throw promise_already_satisfied{};
st->val = val;
auto *const st{this->st};
invalidate(*st);
set(*st, future_state::READY);
notify(*st);
assert(!valid());
}
inline void
ircd::ctx::promise<void>::set_value()
{
assert(valid());
if(unlikely(!is(state(), future_state::PENDING)))
throw promise_already_satisfied{};
auto *const st{this->st};
invalidate(*st);
set(*st, future_state::READY);
notify(*st);
assert(!valid());
}
template<class T>
void
ircd::ctx::promise<T>::set_exception(std::exception_ptr eptr)
{
assert(valid());
if(unlikely(!is(state(), future_state::PENDING)))
throw promise_already_satisfied{};
st->eptr = std::move(eptr);
auto *const st{this->st};
invalidate(*st);
set(*st, future_state::READY);
notify(*st);
assert(!valid());
}
inline void
ircd::ctx::promise<void>::set_exception(std::exception_ptr eptr)
{
assert(valid());
if(unlikely(!is(state(), future_state::PENDING)))
throw promise_already_satisfied{};
st->eptr = std::move(eptr);
auto *const st{this->st};
invalidate(*st);
set(*st, future_state::READY);
notify(*st);
assert(!valid());
}
template<class T>
void
ircd::ctx::append(promise<T> &new_,
promise<T> &old)
{
if(!old.next)
{
old.next = &new_;
return;
}
promise<T> *next{old.next};
for(; next->next; next = next->next);
next->next = &new_;
}
template<class T>
void
ircd::ctx::update(promise<T> &new_,
promise<T> &old)
{
assert(old.st);
auto &st{*old.st};
if(!is(st, future_state::PENDING))
return;
if(st.p == &old)
{
st.p = &new_;
return;
}
promise<T> *last{st.p};
for(promise<T> *next{last->next}; next; last = next, next = last->next)
if(next == &old)
{
last->next = &new_;
break;
}
}
template<class T>
void
ircd::ctx::remove(shared_state<T> &st,
promise<T> &p)
{
if(!is(st, future_state::PENDING))
return;
if(st.p == &p)
{
st.p = p.next;
return;
}
promise<T> *last{st.p};
for(promise<T> *next{last->next}; next; last = next, next = last->next)
if(next == &p)
{
last->next = p.next;
break;
}
}
template<class T>
void
ircd::ctx::invalidate(shared_state<T> &st)
{
if(is(st, future_state::PENDING))
for(promise<T> *p{st.p}; p; p = p->next)
p->st = nullptr;
}
template<class T>
void
ircd::ctx::update(shared_state<T> &st)
{
if(is(st, future_state::PENDING))
for(promise<T> *p{st.p}; p; p = p->next)
p->st = &st;
}
template<class T>
size_t
ircd::ctx::refcount(const shared_state<T> &st)
{
size_t ret{0};
if(is(st, future_state::PENDING))
for(const promise<T> *p{st.p}; p; p = p->next)
++ret;
return ret;
check_pending();
state().val = val;
make_ready();
}
template<class T>
ircd::ctx::shared_state<T> &
ircd::ctx::state(promise<T> &promise)
ircd::ctx::promise<T>::state()
{
return promise.state();
return promise_base::state<T>();
}
template<class T>
const ircd::ctx::shared_state<T> &
ircd::ctx::state(const promise<T> &promise)
ircd::ctx::promise<T>::state()
const
{
return promise.state();
return promise_base::state<T>();
}
//
// promise_base
//
template<class T>
ircd::ctx::shared_state<T> &
ircd::ctx::promise_base::state()
{
return static_cast<shared_state<T> &>(state());
}
template<class T>
const ircd::ctx::shared_state<T> &
ircd::ctx::promise_base::state()
const
{
return static_cast<const shared_state<T> &>(state());
}

177
include/ircd/ctx/shared_state.h
View file

@ -13,18 +13,22 @@
namespace ircd::ctx
{
struct shared_state_base;
template<class T = void> struct shared_state;
template<> struct shared_state<void>;
template<class T> struct promise;
template<> struct promise<void>;
enum class future_state :uintptr_t;
struct shared_state_base;
struct promise_base;
template<class T> future_state state(const shared_state<T> &);
template<class T> bool is(const shared_state<T> &, const future_state &);
template<class T> void set(shared_state<T> &, const future_state &);
template<> void set(shared_state<void> &, const future_state &);
template<class T> void notify(shared_state<T> &);
template<class T> struct shared_state;
template<> struct shared_state<void>;
IRCD_EXCEPTION(ircd::ctx::error, future_error)
future_state state(const shared_state_base &);
bool is(const shared_state_base &, const future_state &);
void set(shared_state_base &, const future_state &);
size_t refcount(const shared_state_base &);
void invalidate(shared_state_base &);
void update(shared_state_base &);
void notify(shared_state_base &);
}
/// Internal state enumeration for the promise / future / related. These can
@ -33,11 +37,11 @@ namespace ircd::ctx
enum class ircd::ctx::future_state
:uintptr_t
{
INVALID = 0, ///< Null.
PENDING, ///< Promise is attached and busy.
READY, ///< Result ready; promise is gone.
OBSERVED, ///< Special case for when_*(); not a state; promise is gone.
RETRIEVED, ///< User retrieved future value; promise is gone.
INVALID = 0, ///< Null.
PENDING = 1, ///< Promise is attached and busy.
READY = 2, ///< Result ready; promise is gone.
OBSERVED = 3, ///< Special case for when_*(); not a state; promise is gone.
RETRIEVED = 4, ///< User retrieved future value; promise is gone.
};
/// Internal Non-template base of the state object shared by promise and
@ -48,8 +52,14 @@ struct ircd::ctx::shared_state_base
mutable dock cond;
std::exception_ptr eptr;
std::function<void (shared_state_base &)> then;
union
{
promise_base *p {nullptr};
future_state st;
};
shared_state_base();
shared_state_base(promise_base &p);
shared_state_base() = default;
shared_state_base(shared_state_base &&) = default;
shared_state_base(const shared_state_base &) = delete;
shared_state_base &operator=(shared_state_base &&) = default;
@ -62,22 +72,14 @@ template<class T>
struct ircd::ctx::shared_state
:shared_state_base
{
using value_type = T;
using pointer_type = T *;
using reference_type = T &;
using value_type = T;
using pointer_type = T *;
using reference_type = T &;
union
{
promise<T> *p {nullptr};
future_state st;
};
T val;
shared_state(promise<T> &p)
:p{&p}
{}
shared_state() = default;
using shared_state_base::shared_state_base;
using shared_state_base::operator=;
};
/// Internal shared state between future and promise when there is no future
@ -86,119 +88,8 @@ template<>
struct ircd::ctx::shared_state<void>
:shared_state_base
{
using value_type = void;
using value_type = void;
union
{
promise<void> *p {nullptr};
future_state st;
};
shared_state(promise<void> &p)
:p{&p}
{}
shared_state() = default;
using shared_state_base::shared_state_base;
using shared_state_base::operator=;
};
/// Internal use
template<class T>
void
ircd::ctx::notify(shared_state<T> &st)
{
if(!st.then)
{
st.cond.notify_all();
return;
}
if(!current)
{
st.cond.notify_all();
assert(bool(st.then));
st.then(st);
return;
}
const stack_usage_assertion sua;
st.cond.notify_all();
assert(bool(st.then));
st.then(st);
}
/// Internal use
template<class T>
void
ircd::ctx::set(shared_state<T> &st,
const future_state &state)
{
switch(state)
{
case future_state::INVALID: assert(0); return;
case future_state::PENDING: assert(0); return;
case future_state::OBSERVED:
case future_state::READY:
case future_state::RETRIEVED:
default:
st.st = state;
return;
}
}
/// Internal use
template<>
inline void
ircd::ctx::set(shared_state<void> &st,
const future_state &state)
{
switch(state)
{
case future_state::INVALID: assert(0); return;
case future_state::PENDING: assert(0); return;
case future_state::READY:
case future_state::OBSERVED:
case future_state::RETRIEVED:
default:
st.st = state;
return;
}
}
/// Internal; check if the current state is something; safe but unnecessary
/// for public use.
template<class T>
bool
ircd::ctx::is(const shared_state<T> &st,
const future_state &state_)
{
switch(st.st)
{
case future_state::READY:
case future_state::OBSERVED:
case future_state::RETRIEVED:
return state_ == st.st;
default: switch(state_)
{
case future_state::INVALID:
return st.p == nullptr;
case future_state::PENDING:
return uintptr_t(st.p) >= 0x1000;
default:
return false;
}
}
}
/// Internal; get the current state of the shared_state; safe but unnecessary
/// for public use.
template<class T>
ircd::ctx::future_state
ircd::ctx::state(const shared_state<T> &st)
{
return uintptr_t(st.p) >= 0x1000?
future_state::PENDING:
st.st;
}

2
include/ircd/ctx/when.h
View file

@ -129,7 +129,7 @@ ircd::ctx::when::all_then(promise<void> &p)
if(refcount(p.state()) < 2)
return p.set_value();
return remove(p.state(), p);
return p.remove(p.state(), p);
}
/// In order for this template to be reusable with std::set iterations we

373
ircd/ctx.cc
View file

@ -1478,13 +1478,382 @@ ircd::ctx::ole::pop()
return std::move(c);
}
///////////////////////////////////////////////////////////////////////////////
//
// ctx/promise.h
//
//
// promise<void>
//
void
ircd::ctx::promise<void>::set_value()
{
check_pending();
make_ready();
}
ircd::ctx::shared_state<void> &
ircd::ctx::promise<void>::state()
{
return promise_base::state<void>();
}
const ircd::ctx::shared_state<void> &
ircd::ctx::promise<void>::state()
const
{
return promise_base::state<void>();
}
//
// promise_base::promise_base
//
ircd::ctx::promise_base::promise_base(promise_base &&o)
noexcept
:st{std::move(o.st)}
,next{std::move(o.next)}
{
if(st)
{
update(*this, o);
o.st = nullptr;
}
}
ircd::ctx::promise_base::promise_base(const promise_base &o)
:st{o.st}
,next{nullptr}
{
append(*this, const_cast<promise_base &>(o));
}
ircd::ctx::promise_base &
ircd::ctx::promise_base::operator=(promise_base &&o)
noexcept
{
this->~promise_base();
st = std::move(o.st);
next = std::move(o.next);
if(!st)
return *this;
update(*this, o);
o.st = nullptr;
return *this;
}
ircd::ctx::promise_base::~promise_base()
noexcept
{
if(!valid())
return;
if(refcount(state()) == 1)
set_exception(std::make_exception_ptr(broken_promise()));
else
remove(state(), *this);
}
void
ircd::ctx::promise_base::set_exception(std::exception_ptr eptr)
{
check_pending();
state().eptr = std::move(eptr);
make_ready();
}
void
ircd::ctx::promise_base::make_ready()
{
auto &st(state());
// First we have to chase the linked list of promises reachable
// from this shared_state. invalidate() will null their pointer
// to the shared_state indicating the promise was already satisfied.
// This is done first because the set() to the READY writes to the
// same union as the promise pointer (see shared_state.h).
invalidate(st);
// Now set the shared_state to READY. We know the location of the
// shared state by saving it in this frame earlier, otherwise invalidate()
// would have nulled it.
set(st, future_state::READY);
// Finally call the notify() routine which will tell the future the promise
// was satisfied and the value/exception is ready for them. This call may
// notify an ircd::ctx and/or post a function to the ircd::ios for a then()
// callback etc.
notify(st);
// At this point the future should not longer be considered valid; no longer
// referring to the shared_state.
assert(!valid());
}
void
ircd::ctx::promise_base::check_pending()
const
{
assert(valid());
if(unlikely(!is(state(), future_state::PENDING)))
throw promise_already_satisfied{};
}
bool
ircd::ctx::promise_base::operator!()
const
{
return !valid();
}
ircd::ctx::promise_base::operator bool()
const
{
return valid();
}
bool
ircd::ctx::promise_base::valid()
const
{
return bool(st);
}
ircd::ctx::shared_state_base &
ircd::ctx::promise_base::state()
{
assert(valid());
return *st;
}
const ircd::ctx::shared_state_base &
ircd::ctx::promise_base::state()
const
{
assert(valid());
return *st;
}
/// Internal semantics; chases the linked list of promises and adds a reference
/// to a new copy at the end (for copy semantic).
void
ircd::ctx::promise_base::append(promise_base &new_,
promise_base &old)
{
if(!old.next)
{
old.next = &new_;
return;
}
promise_base *next{old.next};
for(; next->next; next = next->next);
next->next = &new_;
}
/// Internal semantics; updates the location of a promise within the linked
/// list of related promises (for move semantic).
void
ircd::ctx::promise_base::update(promise_base &new_,
promise_base &old)
{
assert(old.st);
auto &st{*old.st};
if(!is(st, future_state::PENDING))
return;
if(st.p == &old)
{
st.p = &new_;
return;
}
promise_base *last{st.p};
for(promise_base *next{last->next}; next; last = next, next = last->next)
if(next == &old)
{
last->next = &new_;
break;
}
}
/// Internal semantics; removes the promise from the linked list of promises.
/// Because the linked list of promises is a forward singly-linked list this
/// operation requires a reference to the list's head in shared_state_base
/// (for dtor semantic).
void
ircd::ctx::promise_base::remove(shared_state_base &st,
promise_base &p)
{
if(!is(st, future_state::PENDING))
return;
if(st.p == &p)
{
st.p = p.next;
return;
}
promise_base *last{st.p};
for(promise_base *next{last->next}; next; last = next, next = last->next)
if(next == &p)
{
last->next = p.next;
break;
}
}
///////////////////////////////////////////////////////////////////////////////
//
// ctx/shared_shared.h
//
// Linkage
ircd::ctx::shared_state_base::shared_state_base()
/// Internal use
void
ircd::ctx::notify(shared_state_base &st)
{
if(!st.then)
{
st.cond.notify_all();
return;
}
if(!current)
{
st.cond.notify_all();
assert(bool(st.then));
st.then(st);
return;
}
const stack_usage_assertion sua;
st.cond.notify_all();
assert(bool(st.then));
st.then(st);
}
/// Internal use; chases the linked list of promises starting from the head
/// in the shared_state and invalidates all of their references to the shared
/// state. This will cause the promise to no longer be valid().
///
void
ircd::ctx::invalidate(shared_state_base &st)
{
if(is(st, future_state::PENDING))
for(promise_base *p{st.p}; p; p = p->next)
p->st = nullptr;
}
/// Internal use; chases the linked list of promises starting from the head in
/// the shared_state and updates the location of the shared_state within each
/// promise. This is used to tell the promises when the shared_state itself
/// has relocated.
///
void
ircd::ctx::update(shared_state_base &st)
{
if(is(st, future_state::PENDING))
for(promise_base *p{st.p}; p; p = p->next)
p->st = &st;
}
/// Internal use; returns the number of copies of the promise reachable from
/// the linked list headed by the shared state. This is used to indicate when
/// the last copy has destructed which may result in a broken_promise exception
/// being sent to the future.
size_t
ircd::ctx::refcount(const shared_state_base &st)
{
size_t ret{0};
if(is(st, future_state::PENDING))
for(const promise_base *p{st.p}; p; p = p->next)
++ret;
return ret;
}
/// Internal use; sets the state indicator within the shared_state object. Take
/// special note that this data is unionized. Setting a state here will clobber
/// the shared_state's reference to its promise.
void
ircd::ctx::set(shared_state_base &st,
const future_state &state)
{
switch(state)
{
case future_state::INVALID: assert(0); return;
case future_state::PENDING: assert(0); return;
case future_state::OBSERVED:
case future_state::READY:
case future_state::RETRIEVED:
default:
st.st = state;
return;
}
}
/// Internal; check if the current state is something; safe but unnecessary
/// for public use. Take special note here that the state value is unionized.
///
/// A PENDING state returned here does not mean the state contains the
/// enumerated PENDING value itself, but instead contains a valid pointer
/// to a promise.
///
/// An INVALID state shares a zero/null value in the unionized data.
bool
ircd::ctx::is(const shared_state_base &st,
const future_state &state_)
{
switch(st.st)
{
case future_state::READY:
case future_state::OBSERVED:
case future_state::RETRIEVED:
return state_ == st.st;
default: switch(state_)
{
case future_state::INVALID:
return st.p == nullptr;
case future_state::PENDING:
return uintptr_t(st.p) >= 0x1000;
default:
return false;
}
}
}
/// Internal; get the current state of the shared_state; safe but unnecessary
/// for public use.
///
/// NOTE: This operates over a union of a pointer and an enum class. The
/// way we determine whether the data is a pointer or an enum value is
/// with a test of the value being >= the system's page size. This assumes
/// the system does not use the first page of a process's address space
/// to fault on null pointer dereference. This assumption may not hold on
/// all systems or in all environments.
///
/// Alternatively, we can switch this to checking whether the value is simply
/// above the few low-numbered enum values.
ircd::ctx::future_state
ircd::ctx::state(const shared_state_base &st)
{
return uintptr_t(st.p) >= ircd::info::page_size?
future_state::PENDING:
st.st;
}
//
// shared_state_base::shared_state_base
//
ircd::ctx::shared_state_base::shared_state_base(promise_base &p)
:p{&p}
{
}