/*
- * Copyright 2015 Facebook, Inc.
+ * Copyright 2017 Facebook, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
#include <stdexcept>
#include <vector>
+#include <folly/Executor.h>
+#include <folly/Function.h>
+#include <folly/MicroSpinLock.h>
#include <folly/Optional.h>
-#include <folly/SmallLocks.h>
-
-#include <folly/futures/Try.h>
-#include <folly/futures/Promise.h>
+#include <folly/ScopeGuard.h>
+#include <folly/Try.h>
#include <folly/futures/Future.h>
-#include <folly/Executor.h>
+#include <folly/futures/Promise.h>
#include <folly/futures/detail/FSM.h>
#include <folly/io/async/Request.h>
/// 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>
-class Core {
+class Core final {
+ static_assert(!std::is_void<T>::value,
+ "void futures are not supported. Use Unit instead.");
public:
/// This must be heap-constructed. There's probably a way to enforce that in
/// code but since this is just internal detail code and I don't know how
/// off-hand, I'm punting.
- Core() {}
+ Core() : result_(), fsm_(State::Start), attached_(2) {}
+
+ explicit Core(Try<T>&& t)
+ : result_(std::move(t)),
+ fsm_(State::OnlyResult),
+ attached_(1) {}
+
~Core() {
- assert(attached_ == 0);
+ DCHECK(attached_ == 0);
}
// not copyable
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();
}
}
}
- template <typename F>
- class LambdaBufHelper {
- public:
- explicit LambdaBufHelper(F&& func) : func_(std::forward<F>(func)) {}
- void operator()(Try<T>&& t) {
- SCOPE_EXIT { this->~LambdaBufHelper(); };
- func_(std::move(t));
- }
- private:
- F func_;
- };
-
/// Call only from Future thread.
template <typename F>
- void setCallback(F func) {
+ void setCallback(F&& func) {
bool transitionToArmed = false;
auto setCallback_ = [&]{
context_ = RequestContext::saveContext();
-
- // Move the lambda into the Core if it fits
- if (sizeof(LambdaBufHelper<F>) <= lambdaBufSize) {
- auto funcLoc = static_cast<LambdaBufHelper<F>*>((void*)lambdaBuf_);
- new (funcLoc) LambdaBufHelper<F>(std::forward<F>(func));
- callback_ = std::ref(*funcLoc);
- } else {
- callback_ = std::move(func);
- }
+ callback_ = std::forward<F>(func);
};
FSM_START(fsm_)
void detachPromise() {
// detachPromise() and setResult() should never be called in parallel
// so we don't need to protect this.
- if (!result_) {
- setResult(Try<T>(exception_wrapper(BrokenPromise())));
+ if (UNLIKELY(!result_)) {
+ setResult(Try<T>(exception_wrapper(BrokenPromise(typeid(T).name()))));
}
detachOne();
}
/// May call from any thread
void deactivate() {
- active_ = false;
+ active_.store(false, std::memory_order_release);
}
/// May call from any thread
void activate() {
- active_ = true;
+ active_.store(true, std::memory_order_release);
maybeCallback();
}
/// May call from any thread
- bool isActive() { return active_; }
+ bool isActive() { return active_.load(std::memory_order_acquire); }
/// Call only from Future thread
- void setExecutor(Executor* x) {
+ void setExecutor(Executor* x, int8_t priority = Executor::MID_PRI) {
+ if (!executorLock_.try_lock()) {
+ executorLock_.lock();
+ }
+ executor_ = x;
+ priority_ = priority;
+ executorLock_.unlock();
+ }
+
+ void setExecutorNoLock(Executor* x, int8_t priority = Executor::MID_PRI) {
executor_ = x;
+ priority_ = priority;
}
Executor* getExecutor() {
/// Call only from Future thread
void raise(exception_wrapper e) {
- std::lock_guard<decltype(interruptLock_)> guard(interruptLock_);
+ if (!interruptLock_.try_lock()) {
+ 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_);
}
}
+ interruptLock_.unlock();
+ }
+
+ std::function<void(exception_wrapper const&)> getInterruptHandler() {
+ if (!interruptHandlerSet_.load(std::memory_order_acquire)) {
+ return nullptr;
+ }
+ if (!interruptLock_.try_lock()) {
+ interruptLock_.lock();
+ }
+ auto handler = interruptHandler_;
+ interruptLock_.unlock();
+ return handler;
}
/// Call only from Promise thread
void setInterruptHandler(std::function<void(exception_wrapper const&)> fn) {
- std::lock_guard<decltype(interruptLock_)> guard(interruptLock_);
+ if (!interruptLock_.try_lock()) {
+ interruptLock_.lock();
+ }
if (!hasResult()) {
if (interrupt_) {
fn(*interrupt_);
} else {
- interruptHandler_ = std::move(fn);
+ setInterruptHandlerNoLock(std::move(fn));
}
}
+ interruptLock_.unlock();
}
- protected:
+ void setInterruptHandlerNoLock(
+ std::function<void(exception_wrapper const&)> fn) {
+ interruptHandlerSet_.store(true, std::memory_order_relaxed);
+ interruptHandler_ = std::move(fn);
+ }
+
+ private:
+ // Helper class that stores a pointer to the `Core` object and calls
+ // `derefCallback` and `detachOne` in the destructor.
+ class CoreAndCallbackReference {
+ public:
+ explicit CoreAndCallbackReference(Core* core) noexcept : core_(core) {}
+
+ ~CoreAndCallbackReference() {
+ if (core_) {
+ core_->derefCallback();
+ core_->detachOne();
+ }
+ }
+
+ CoreAndCallbackReference(CoreAndCallbackReference const& o) = delete;
+ CoreAndCallbackReference& operator=(CoreAndCallbackReference const& o) =
+ delete;
+
+ CoreAndCallbackReference(CoreAndCallbackReference&& o) noexcept {
+ std::swap(core_, o.core_);
+ }
+
+ Core* getCore() const noexcept {
+ return core_;
+ }
+
+ private:
+ Core* core_{nullptr};
+ };
+
void maybeCallback() {
FSM_START(fsm_)
case State::Armed:
- if (active_) {
- FSM_UPDATE2(fsm_, State::Done, []{},
- std::bind(&Core::doCallback, this));
+ if (active_.load(std::memory_order_acquire)) {
+ FSM_UPDATE2(fsm_, State::Done, []{}, [this]{ this->doCallback(); });
}
FSM_BREAK
}
void doCallback() {
- RequestContext::setContext(context_);
-
- // TODO(6115514) semantic race on reading executor_ and setExecutor()
Executor* x = executor_;
+ int8_t priority;
if (x) {
- ++attached_; // keep Core alive until executor did its thing
+ if (!executorLock_.try_lock()) {
+ executorLock_.lock();
+ }
+ x = executor_;
+ priority = priority_;
+ executorLock_.unlock();
+ }
+
+ 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 {
- x->add([this]() mutable {
- SCOPE_EXIT { detachOne(); };
- callback_(std::move(*result_));
- });
+ if (LIKELY(x->getNumPriorities() == 1)) {
+ x->add([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_));
+ });
+ } else {
+ 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 (...) {
- result_ = Try<T>(exception_wrapper(std::current_exception()));
+ ew = exception_wrapper(std::current_exception());
+ }
+ if (ew) {
+ RequestContextScopeGuard rctx(context_);
+ result_ = Try<T>(std::move(ew));
callback_(std::move(*result_));
}
} else {
+ attached_++;
+ SCOPE_EXIT {
+ callback_ = {};
+ detachOne();
+ };
+ RequestContextScopeGuard rctx(context_);
callback_(std::move(*result_));
}
}
void detachOne() {
- auto a = --attached_;
- assert(a >= 0);
- assert(a <= 2);
- if (a == 0) {
+ auto a = attached_--;
+ assert(a >= 1);
+ if (a == 1) {
delete this;
}
}
- FSM<State> fsm_ {State::Start};
- std::atomic<unsigned char> attached_ {2};
+ void derefCallback() {
+ if (--callbackReferences_ == 0) {
+ callback_ = {};
+ }
+ }
+
+ folly::Function<void(Try<T>&&)> callback_;
+ // place result_ next to increase the likelihood that the value will be
+ // contained entirely in one cache line
+ 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};
- folly::Optional<Try<T>> result_ {};
- std::function<void(Try<T>&&)> callback_ {nullptr};
- static constexpr size_t lambdaBufSize = 8 * sizeof(void*);
- char lambdaBuf_[lambdaBufSize];
+ folly::MicroSpinLock executorLock_ {0};
+ int8_t priority_ {-1};
+ Executor* executor_ {nullptr};
std::shared_ptr<RequestContext> context_ {nullptr};
- std::atomic<Executor*> executor_ {nullptr};
std::unique_ptr<exception_wrapper> interrupt_ {};
std::function<void(exception_wrapper const&)> interruptHandler_ {nullptr};
};
template <typename... Ts>
-struct VariadicContext {
- VariadicContext() {}
- ~VariadicContext() {
+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;
+ Promise<std::tuple<Try<Ts>...>> p;
+ std::tuple<Try<Ts>...> results;
typedef Future<std::tuple<Try<Ts>...>> type;
};
-template <typename... Ts, typename THead, typename... Fs>
-typename std::enable_if<sizeof...(Fs) == 0, void>::type
-collectAllVariadicHelper(std::shared_ptr<VariadicContext<Ts...>> ctx,
- THead&& head, Fs&&... tail) {
- head.setCallback_([ctx](Try<typename THead::value_type>&& t) {
- std::get<sizeof...(Ts) - sizeof...(Fs) - 1>(ctx->results) = std::move(t);
- });
+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 <typename... Ts, typename THead, typename... Fs>
-typename std::enable_if<sizeof...(Fs) != 0, void>::type
-collectAllVariadicHelper(std::shared_ptr<VariadicContext<Ts...>> ctx,
- THead&& head, Fs&&... tail) {
- head.setCallback_([ctx](Try<typename THead::value_type>&& t) {
- std::get<sizeof...(Ts) - sizeof...(Fs) - 1>(ctx->results) = std::move(t);
+template <template <typename ...> class T, typename... Ts,
+ typename THead, typename... TTail>
+void collectVariadicHelper(const std::shared_ptr<T<Ts...>>& ctx,
+ THead&& head, TTail&&... tail) {
+ 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
- collectAllVariadicHelper(ctx, std::forward<Fs>(tail)...);
+ collectVariadicHelper(ctx, std::forward<TTail>(tail)...);
}
}} // folly::detail
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