Core(Core&&) noexcept = delete;
Core& operator=(Core&&) = delete;
- // Core is assumed to be convertible only if the type is convertible
- // and the size is the same. This is a compromise for the complexity
- // of having to make Core truly have a conversion constructor which
- // would cause various other problems.
- // If we made Core move constructible then we would need to update the
- // Promise and Future with the location of the new Core. This is complex
- // and may be inefficient.
- // Core should only be modified so that for size(T) == size(U),
- // sizeof(Core<T>) == size(Core<U>).
- // This assumption is used as a proxy to make sure that
- // the members of Core<T> and Core<U> line up so that we can use a
- // reinterpret cast.
- template <
- class U,
- typename = typename std::enable_if<std::is_convertible<U, T>::value &&
- sizeof(U) == sizeof(T)>::type>
- static Core<T>* convert(Core<U>* from) {
- return reinterpret_cast<Core<T>*>(from);
- }
-
/// May call from any thread
- bool hasResult() const {
+ bool hasResult() const noexcept {
switch (fsm_.getState()) {
case State::OnlyResult:
case State::Armed:
}
/// May call from any thread
- bool ready() const {
+ bool ready() const noexcept {
return hasResult();
}
interruptLock_.lock();
}
if (!interrupt_ && !hasResult()) {
- interrupt_ = folly::make_unique<exception_wrapper>(std::move(e));
+ interrupt_ = std::make_unique<exception_wrapper>(std::move(e));
if (interruptHandler_) {
interruptHandler_(*interrupt_);
}
}
private:
- class CountedReference {
+ // Helper class that stores a pointer to the `Core` object and calls
+ // `derefCallback` and `detachOne` in the destructor.
+ class CoreAndCallbackReference {
public:
- ~CountedReference() {
- if (core_) {
- core_->detachOne();
- core_ = nullptr;
- }
- }
-
- explicit CountedReference(Core* core) noexcept : core_(core) {
- // do not construct a CountedReference from nullptr!
- DCHECK(core);
+ explicit CoreAndCallbackReference(Core* core) noexcept : core_(core) {}
- ++core_->attached_;
- }
-
- // CountedReference must be copy-constructable as long as
- // folly::Executor::add takes a std::function
- CountedReference(CountedReference const& o) noexcept : core_(o.core_) {
+ ~CoreAndCallbackReference() {
if (core_) {
- ++core_->attached_;
+ core_->derefCallback();
+ core_->detachOne();
}
}
- CountedReference& operator=(CountedReference const& o) noexcept {
- ~CountedReference();
- new (this) CountedReference(o);
- return *this;
- }
+ CoreAndCallbackReference(CoreAndCallbackReference const& o) = delete;
+ CoreAndCallbackReference& operator=(CoreAndCallbackReference const& o) =
+ delete;
- CountedReference(CountedReference&& o) noexcept {
+ CoreAndCallbackReference(CoreAndCallbackReference&& o) noexcept {
std::swap(core_, o.core_);
}
- CountedReference& operator=(CountedReference&& o) noexcept {
- ~CountedReference();
- new (this) CountedReference(std::move(o));
- return *this;
- }
-
Core* getCore() const noexcept {
return core_;
}
}
if (x) {
+ exception_wrapper ew;
+ // We need to reset `callback_` after it was executed (which can happen
+ // through the executor or, if `Executor::add` throws, below). The
+ // executor might discard the function without executing it (now or
+ // later), in which case `callback_` also needs to be reset.
+ // The `Core` has to be kept alive throughout that time, too. Hence we
+ // increment `attached_` and `callbackReferences_` by two, and construct
+ // exactly two `CoreAndCallbackReference` objects, which call
+ // `derefCallback` and `detachOne` in their destructor. One will guard
+ // this scope, the other one will guard the lambda passed to the executor.
+ attached_ += 2;
+ callbackReferences_ += 2;
+ CoreAndCallbackReference guard_local_scope(this);
+ CoreAndCallbackReference guard_lambda(this);
try {
if (LIKELY(x->getNumPriorities() == 1)) {
- x->add([core_ref = CountedReference(this)]() mutable {
+ x->add([core_ref = std::move(guard_lambda)]() mutable {
auto cr = std::move(core_ref);
Core* const core = cr.getCore();
RequestContextScopeGuard rctx(core->context_);
- SCOPE_EXIT { core->callback_ = {}; };
core->callback_(std::move(*core->result_));
});
} else {
- x->addWithPriority([core_ref = CountedReference(this)]() mutable {
- auto cr = std::move(core_ref);
- Core* const core = cr.getCore();
- RequestContextScopeGuard rctx(core->context_);
- SCOPE_EXIT { core->callback_ = {}; };
- core->callback_(std::move(*core->result_));
- }, priority);
+ x->addWithPriority(
+ [core_ref = std::move(guard_lambda)]() mutable {
+ auto cr = std::move(core_ref);
+ Core* const core = cr.getCore();
+ RequestContextScopeGuard rctx(core->context_);
+ core->callback_(std::move(*core->result_));
+ },
+ priority);
}
+ } catch (const std::exception& e) {
+ ew = exception_wrapper(std::current_exception(), e);
} catch (...) {
- CountedReference core_ref(this);
+ ew = exception_wrapper(std::current_exception());
+ }
+ if (ew) {
RequestContextScopeGuard rctx(context_);
- result_ = Try<T>(exception_wrapper(std::current_exception()));
- SCOPE_EXIT { callback_ = {}; };
+ result_ = Try<T>(std::move(ew));
callback_(std::move(*result_));
}
} else {
- CountedReference core_ref(this);
+ attached_++;
+ SCOPE_EXIT {
+ callback_ = {};
+ detachOne();
+ };
RequestContextScopeGuard rctx(context_);
- SCOPE_EXIT { callback_ = {}; };
callback_(std::move(*result_));
}
}
}
}
- // Core should only be modified so that for size(T) == size(U),
- // sizeof(Core<T>) == size(Core<U>).
- // See Core::convert for details.
+ void derefCallback() {
+ if (--callbackReferences_ == 0) {
+ callback_ = {};
+ }
+ }
folly::Function<void(Try<T>&&)> callback_;
// place result_ next to increase the likelihood that the value will be
folly::Optional<Try<T>> result_;
FSM<State> fsm_;
std::atomic<unsigned char> attached_;
+ std::atomic<unsigned char> callbackReferences_{0};
std::atomic<bool> active_ {true};
std::atomic<bool> interruptHandlerSet_ {false};
folly::MicroSpinLock interruptLock_ {0};
typename THead, typename... TTail>
void collectVariadicHelper(const std::shared_ptr<T<Ts...>>& ctx,
THead&& head, TTail&&... tail) {
- head.setCallback_([ctx](Try<typename THead::value_type>&& t) {
- ctx->template setPartialResult<typename THead::value_type,
- sizeof...(Ts) - sizeof...(TTail) - 1>(t);
+ using ValueType = typename std::decay<THead>::type::value_type;
+ std::forward<THead>(head).setCallback_([ctx](Try<ValueType>&& t) {
+ ctx->template setPartialResult<
+ ValueType,
+ sizeof...(Ts) - sizeof...(TTail)-1>(t);
});
// template tail-recursion
collectVariadicHelper(ctx, std::forward<TTail>(tail)...);
projects / folly.git / blobdiff