#include <atomic>
#include <mutex>
#include <stdexcept>
+#include <utility>
#include <vector>
#include <folly/Executor.h>
#include <folly/Optional.h>
#include <folly/ScopeGuard.h>
#include <folly/Try.h>
-#include <folly/futures/Future.h>
-#include <folly/futures/Promise.h>
+#include <folly/Utility.h>
+#include <folly/futures/FutureException.h>
#include <folly/futures/detail/FSM.h>
+#include <folly/portability/BitsFunctexcept.h>
#include <folly/io/async/Request.h>
-namespace folly { namespace detail {
+namespace folly {
+namespace futures {
+namespace detail {
/*
OnlyCallback
/// first blush, but it's the same principle. In general, as long as the user
/// doesn't access a Future or Promise object from more than one thread at a
/// time there won't be any problems.
-template<typename T>
+template <typename T>
class Core final {
static_assert(!std::is_void<T>::value,
"void futures are not supported. Use Unit instead.");
fsm_(State::OnlyResult),
attached_(1) {}
+ template <typename... Args>
+ explicit Core(in_place_t, Args&&... args) noexcept(
+ std::is_nothrow_constructible<T, Args&&...>::value)
+ : result_(in_place, in_place, std::forward<Args>(args)...),
+ fsm_(State::OnlyResult),
+ attached_(1) {}
+
~Core() {
DCHECK(attached_ == 0);
}
Core& operator=(Core&&) = delete;
/// 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();
}
if (ready()) {
return *result_;
} else {
- throw FutureNotReady();
+ throwFutureNotReady();
}
}
case State::OnlyCallback:
case State::Armed:
case State::Done:
- throw std::logic_error("setCallback called twice");
+ std::__throw_logic_error("setCallback called twice");
FSM_END
// we could always call this, it is an optimization to only call it when
case State::OnlyResult:
case State::Armed:
case State::Done:
- throw std::logic_error("setResult called twice");
+ std::__throw_logic_error("setResult called twice");
FSM_END
if (transitionToArmed) {
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);
-
- ++core_->attached_;
- }
+ explicit CoreAndCallbackReference(Core* core) noexcept : core_(core) {}
- // 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_;
}
void doCallback() {
Executor* x = executor_;
- int8_t priority;
+ // initialize, solely to appease clang's -Wconditional-uninitialized
+ int8_t priority = 0;
if (x) {
if (!executorLock_.try_lock()) {
executorLock_.lock();
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);
ew = exception_wrapper(std::current_exception());
}
if (ew) {
- CountedReference core_ref(this);
RequestContextScopeGuard rctx(context_);
result_ = Try<T>(std::move(ew));
- SCOPE_EXIT { callback_ = {}; };
callback_(std::move(*result_));
}
} else {
- CountedReference core_ref(this);
+ attached_++;
+ SCOPE_EXIT {
+ callback_ = {};
+ detachOne();
+ };
RequestContextScopeGuard rctx(context_);
- SCOPE_EXIT { callback_ = {}; };
callback_(std::move(*result_));
}
}
}
}
+ 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};
std::function<void(exception_wrapper const&)> interruptHandler_ {nullptr};
};
-template <typename... Ts>
-struct CollectAllVariadicContext {
- CollectAllVariadicContext() {}
- template <typename T, size_t I>
- inline void setPartialResult(Try<T>& t) {
- std::get<I>(results) = std::move(t);
- }
- ~CollectAllVariadicContext() {
- p.setValue(std::move(results));
- }
- Promise<std::tuple<Try<Ts>...>> p;
- std::tuple<Try<Ts>...> results;
- typedef Future<std::tuple<Try<Ts>...>> type;
-};
-
-template <typename... Ts>
-struct CollectVariadicContext {
- CollectVariadicContext() {}
- template <typename T, size_t I>
- inline void setPartialResult(Try<T>& t) {
- if (t.hasException()) {
- if (!threw.exchange(true)) {
- p.setException(std::move(t.exception()));
- }
- } else if (!threw) {
- std::get<I>(results) = std::move(t);
- }
- }
- ~CollectVariadicContext() noexcept {
- if (!threw.exchange(true)) {
- p.setValue(unwrapTryTuple(std::move(results)));
- }
- }
- Promise<std::tuple<Ts...>> p;
- std::tuple<folly::Try<Ts>...> results;
- std::atomic<bool> threw {false};
- typedef Future<std::tuple<Ts...>> type;
-};
-
template <template <typename...> class T, typename... Ts>
void collectVariadicHelper(const std::shared_ptr<T<Ts...>>& /* ctx */) {
// base case
}
-template <template <typename ...> class T, typename... Ts,
- typename THead, typename... TTail>
+template <
+ template <typename...> class T,
+ typename... Ts,
+ 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)...);
}
-}} // folly::detail
+} // namespace detail
+} // namespace futures
+} // namespace folly
projects / folly.git / blobdiff