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// Licensed under the MIT License:
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
// This file contains extended inline implementation details that are required along with async.h.
// We move this all into a separate file to make async.h more readable.
//
// Non-inline declarations here are defined in async.c++.
#ifndef KJ_ASYNC_H_
#error "Do not include this directly; include kj/async.h."
#include "async.h" // help IDE parse this file
#endif
#ifndef KJ_ASYNC_INL_H_
#define KJ_ASYNC_INL_H_
#if defined(__GNUC__) && !KJ_HEADER_WARNINGS
#pragma GCC system_header
#endif
namespace kj {
namespace _ { // private
template <typename T>
class ExceptionOr;
class ExceptionOrValue {
public:
ExceptionOrValue(bool, Exception&& exception): exception(kj::mv(exception)) {}
KJ_DISALLOW_COPY(ExceptionOrValue);
void addException(Exception&& exception) {
if (this->exception == nullptr) {
this->exception = kj::mv(exception);
}
}
template <typename T>
ExceptionOr<T>& as() { return *static_cast<ExceptionOr<T>*>(this); }
template <typename T>
const ExceptionOr<T>& as() const { return *static_cast<const ExceptionOr<T>*>(this); }
Maybe<Exception> exception;
protected:
// Allow subclasses to have move constructor / assignment.
ExceptionOrValue() = default;
ExceptionOrValue(ExceptionOrValue&& other) = default;
ExceptionOrValue& operator=(ExceptionOrValue&& other) = default;
};
template <typename T>
class ExceptionOr: public ExceptionOrValue {
public:
ExceptionOr() = default;
ExceptionOr(T&& value): value(kj::mv(value)) {}
ExceptionOr(bool, Exception&& exception): ExceptionOrValue(false, kj::mv(exception)) {}
ExceptionOr(ExceptionOr&&) = default;
ExceptionOr& operator=(ExceptionOr&&) = default;
Maybe<T> value;
};
class Event {
// An event waiting to be executed. Not for direct use by applications -- promises use this
// internally.
public:
Event();
~Event() noexcept(false);
KJ_DISALLOW_COPY(Event);
void armDepthFirst();
// Enqueue this event so that `fire()` will be called from the event loop soon.
//
// Events scheduled in this way are executed in depth-first order: if an event callback arms
// more events, those events are placed at the front of the queue (in the order in which they
// were armed), so that they run immediately after the first event's callback returns.
//
// Depth-first event scheduling is appropriate for events that represent simple continuations
// of a previous event that should be globbed together for performance. Depth-first scheduling
// can lead to starvation, so any long-running task must occasionally yield with
// `armBreadthFirst()`. (Promise::then() uses depth-first whereas evalLater() uses
// breadth-first.)
//
// To use breadth-first scheduling instead, use `armBreadthFirst()`.
void armBreadthFirst();
// Like `armDepthFirst()` except that the event is placed at the end of the queue.
kj::String trace();
// Dump debug info about this event.
virtual _::PromiseNode* getInnerForTrace();
// If this event wraps a PromiseNode, get that node. Used for debug tracing.
// Default implementation returns nullptr.
protected:
virtual Maybe<Own<Event>> fire() = 0;
// Fire the event. Possibly returns a pointer to itself, which will be discarded by the
// caller. This is the only way that an event can delete itself as a result of firing, as
// doing so from within fire() will throw an exception.
private:
friend class kj::EventLoop;
EventLoop& loop;
Event* next;
Event** prev;
bool firing = false;
};
class PromiseNode {
// A Promise<T> contains a chain of PromiseNodes tracking the pending transformations.
//
// To reduce generated code bloat, PromiseNode is not a template. Instead, it makes very hacky
// use of pointers to ExceptionOrValue which actually point to ExceptionOr<T>, but are only
// so down-cast in the few places that really need to be templated. Luckily this is all
// internal implementation details.
public:
virtual void onReady(Event& event) noexcept = 0;
// Arms the given event when ready.
virtual void setSelfPointer(Own<PromiseNode>* selfPtr) noexcept;
// Tells the node that `selfPtr` is the pointer that owns this node, and will continue to own
// this node until it is destroyed or setSelfPointer() is called again. ChainPromiseNode uses
// this to shorten redundant chains. The default implementation does nothing; only
// ChainPromiseNode should implement this.
virtual void get(ExceptionOrValue& output) noexcept = 0;
// Get the result. `output` points to an ExceptionOr<T> into which the result will be written.
// Can only be called once, and only after the node is ready. Must be called directly from the
// event loop, with no application code on the stack.
virtual PromiseNode* getInnerForTrace();
// If this node wraps some other PromiseNode, get the wrapped node. Used for debug tracing.
// Default implementation returns nullptr.
protected:
class OnReadyEvent {
// Helper class for implementing onReady().
public:
void init(Event& newEvent);
// Returns true if arm() was already called.
void arm();
// Arms the event if init() has already been called and makes future calls to init() return
// true.
private:
Event* event = nullptr;
};
};
// -------------------------------------------------------------------
class ImmediatePromiseNodeBase: public PromiseNode {
public:
ImmediatePromiseNodeBase();
~ImmediatePromiseNodeBase() noexcept(false);
void onReady(Event& event) noexcept override;
};
template <typename T>
class ImmediatePromiseNode final: public ImmediatePromiseNodeBase {
// A promise that has already been resolved to an immediate value or exception.
public:
ImmediatePromiseNode(ExceptionOr<T>&& result): result(kj::mv(result)) {}
void get(ExceptionOrValue& output) noexcept override {
output.as<T>() = kj::mv(result);
}
private:
ExceptionOr<T> result;
};
class ImmediateBrokenPromiseNode final: public ImmediatePromiseNodeBase {
public:
ImmediateBrokenPromiseNode(Exception&& exception);
void get(ExceptionOrValue& output) noexcept override;
private:
Exception exception;
};
// -------------------------------------------------------------------
class AttachmentPromiseNodeBase: public PromiseNode {
public:
AttachmentPromiseNodeBase(Own<PromiseNode>&& dependency);
void onReady(Event& event) noexcept override;
void get(ExceptionOrValue& output) noexcept override;
PromiseNode* getInnerForTrace() override;
private:
Own<PromiseNode> dependency;
void dropDependency();
template <typename>
friend class AttachmentPromiseNode;
};
template <typename Attachment>
class AttachmentPromiseNode final: public AttachmentPromiseNodeBase {
// A PromiseNode that holds on to some object (usually, an Own<T>, but could be any movable
// object) until the promise resolves.
public:
AttachmentPromiseNode(Own<PromiseNode>&& dependency, Attachment&& attachment)
: AttachmentPromiseNodeBase(kj::mv(dependency)),
attachment(kj::mv<Attachment>(attachment)) {}
~AttachmentPromiseNode() noexcept(false) {
// We need to make sure the dependency is deleted before we delete the attachment because the
// dependency may be using the attachment.
dropDependency();
}
private:
Attachment attachment;
};
// -------------------------------------------------------------------
class PtmfHelper {
// This class is a private helper for GetFunctorStartAddress. The class represents the internal
// representation of a pointer-to-member-function.
template <typename... ParamTypes>
friend struct GetFunctorStartAddress;
#if __GNUG__
void* ptr;
ptrdiff_t adj;
// Layout of a pointer-to-member-function used by GCC and compatible compilers.
void* apply(void* obj) {
#if defined(__arm__) || defined(__mips__) || defined(__aarch64__)
if (adj & 1) {
ptrdiff_t voff = (ptrdiff_t)ptr;
#else
ptrdiff_t voff = (ptrdiff_t)ptr;
if (voff & 1) {
voff &= ~1;
#endif
return *(void**)(*(char**)obj + voff);
} else {
return ptr;
}
}
#define BODY \
PtmfHelper result; \
static_assert(sizeof(p) == sizeof(result), "unknown ptmf layout"); \
memcpy(&result, &p, sizeof(result)); \
return result
#else // __GNUG__
void* apply(void* obj) { return nullptr; }
// TODO(port): PTMF instruction address extraction
#define BODY return PtmfHelper{}
#endif // __GNUG__, else
template <typename R, typename C, typename... P, typename F>
static PtmfHelper from(F p) { BODY; }
// Create a PtmfHelper from some arbitrary pointer-to-member-function which is not
// overloaded nor a template. In this case the compiler is able to deduce the full function
// signature directly given the name since there is only one function with that name.
template <typename R, typename C, typename... P>
static PtmfHelper from(R (C::*p)(NoInfer<P>...)) { BODY; }
template <typename R, typename C, typename... P>
static PtmfHelper from(R (C::*p)(NoInfer<P>...) const) { BODY; }
// Create a PtmfHelper from some poniter-to-member-function which is a template. In this case
// the function must match exactly the containing type C, return type R, and parameter types P...
// GetFunctorStartAddress normally specifies exactly the correct C and R, but can only make a
// guess at P. Luckily, if the function parameters are template parameters then it's not
// necessary to be precise about P.
#undef BODY
};
template <typename... ParamTypes>
struct GetFunctorStartAddress {
// Given a functor (any object defining operator()), return the start address of the function,
// suitable for passing to addr2line to obtain a source file/line for debugging purposes.
//
// This turns out to be incredibly hard to implement in the presence of overloaded or templated
// functors. Therefore, we impose these specific restrictions, specific to our use case:
// - Overloading is not allowed, but templating is. (Generally we only intend to support lambdas
// anyway.)
// - The template parameters to GetFunctorStartAddress specify a hint as to the expected
// parameter types. If the functor is templated, its parameters must match exactly these types.
// (If it's not templated, ParamTypes are ignored.)
template <typename Func>
static void* apply(Func&& func) {
typedef decltype(func(instance<ParamTypes>()...)) ReturnType;
return PtmfHelper::from<ReturnType, Decay<Func>, ParamTypes...>(
&Decay<Func>::operator()).apply(&func);
}
};
template <>
struct GetFunctorStartAddress<Void&&>: public GetFunctorStartAddress<> {};
// Hack for TransformPromiseNode use case: an input type of `Void` indicates that the function
// actually has no parameters.
class TransformPromiseNodeBase: public PromiseNode {
public:
TransformPromiseNodeBase(Own<PromiseNode>&& dependency, void* continuationTracePtr);
void onReady(Event& event) noexcept override;
void get(ExceptionOrValue& output) noexcept override;
PromiseNode* getInnerForTrace() override;
private:
Own<PromiseNode> dependency;
void* continuationTracePtr;
void dropDependency();
void getDepResult(ExceptionOrValue& output);
virtual void getImpl(ExceptionOrValue& output) = 0;
template <typename, typename, typename, typename>
friend class TransformPromiseNode;
};
template <typename T, typename DepT, typename Func, typename ErrorFunc>
class TransformPromiseNode final: public TransformPromiseNodeBase {
// A PromiseNode that transforms the result of another PromiseNode through an application-provided
// function (implements `then()`).
public:
TransformPromiseNode(Own<PromiseNode>&& dependency, Func&& func, ErrorFunc&& errorHandler)
: TransformPromiseNodeBase(kj::mv(dependency),
GetFunctorStartAddress<DepT&&>::apply(func)),
func(kj::fwd<Func>(func)), errorHandler(kj::fwd<ErrorFunc>(errorHandler)) {}
~TransformPromiseNode() noexcept(false) {
// We need to make sure the dependency is deleted before we delete the continuations because it
// is a common pattern for the continuations to hold ownership of objects that might be in-use
// by the dependency.
dropDependency();
}
private:
Func func;
ErrorFunc errorHandler;
void getImpl(ExceptionOrValue& output) override {
ExceptionOr<DepT> depResult;
getDepResult(depResult);
KJ_IF_MAYBE(depException, depResult.exception) {
output.as<T>() = handle(
MaybeVoidCaller<Exception, FixVoid<ReturnType<ErrorFunc, Exception>>>::apply(
errorHandler, kj::mv(*depException)));
} else KJ_IF_MAYBE(depValue, depResult.value) {
output.as<T>() = handle(MaybeVoidCaller<DepT, T>::apply(func, kj::mv(*depValue)));
}
}
ExceptionOr<T> handle(T&& value) {
return kj::mv(value);
}
ExceptionOr<T> handle(PropagateException::Bottom&& value) {
return ExceptionOr<T>(false, value.asException());
}
};
// -------------------------------------------------------------------
class ForkHubBase;
class ForkBranchBase: public PromiseNode {
public:
ForkBranchBase(Own<ForkHubBase>&& hub);
~ForkBranchBase() noexcept(false);
void hubReady() noexcept;
// Called by the hub to indicate that it is ready.
// implements PromiseNode ------------------------------------------
void onReady(Event& event) noexcept override;
PromiseNode* getInnerForTrace() override;
protected:
inline ExceptionOrValue& getHubResultRef();
void releaseHub(ExceptionOrValue& output);
// Release the hub. If an exception is thrown, add it to `output`.
private:
OnReadyEvent onReadyEvent;
Own<ForkHubBase> hub;
ForkBranchBase* next = nullptr;
ForkBranchBase** prevPtr = nullptr;
friend class ForkHubBase;
};
template <typename T> T copyOrAddRef(T& t) { return t; }
template <typename T> Own<T> copyOrAddRef(Own<T>& t) { return t->addRef(); }
template <typename T>
class ForkBranch final: public ForkBranchBase {
// A PromiseNode that implements one branch of a fork -- i.e. one of the branches that receives
// a const reference.
public:
ForkBranch(Own<ForkHubBase>&& hub): ForkBranchBase(kj::mv(hub)) {}
void get(ExceptionOrValue& output) noexcept override {
ExceptionOr<T>& hubResult = getHubResultRef().template as<T>();
KJ_IF_MAYBE(value, hubResult.value) {
output.as<T>().value = copyOrAddRef(*value);
} else {
output.as<T>().value = nullptr;
}
output.exception = hubResult.exception;
releaseHub(output);
}
};
template <typename T, size_t index>
class SplitBranch final: public ForkBranchBase {
// A PromiseNode that implements one branch of a fork -- i.e. one of the branches that receives
// a const reference.
public:
SplitBranch(Own<ForkHubBase>&& hub): ForkBranchBase(kj::mv(hub)) {}
typedef kj::Decay<decltype(kj::get<index>(kj::instance<T>()))> Element;
void get(ExceptionOrValue& output) noexcept override {
ExceptionOr<T>& hubResult = getHubResultRef().template as<T>();
KJ_IF_MAYBE(value, hubResult.value) {
output.as<Element>().value = kj::mv(kj::get<index>(*value));
} else {
output.as<Element>().value = nullptr;
}
output.exception = hubResult.exception;
releaseHub(output);
}
};
// -------------------------------------------------------------------
class ForkHubBase: public Refcounted, protected Event {
public:
ForkHubBase(Own<PromiseNode>&& inner, ExceptionOrValue& resultRef);
inline ExceptionOrValue& getResultRef() { return resultRef; }
private:
Own<PromiseNode> inner;
ExceptionOrValue& resultRef;
ForkBranchBase* headBranch = nullptr;
ForkBranchBase** tailBranch = &headBranch;
// Tail becomes null once the inner promise is ready and all branches have been notified.
Maybe<Own<Event>> fire() override;
_::PromiseNode* getInnerForTrace() override;
friend class ForkBranchBase;
};
template <typename T>
class ForkHub final: public ForkHubBase {
// A PromiseNode that implements the hub of a fork. The first call to Promise::fork() replaces
// the promise's outer node with a ForkHub, and subsequent calls add branches to that hub (if
// possible).
public:
ForkHub(Own<PromiseNode>&& inner): ForkHubBase(kj::mv(inner), result) {}
Promise<_::UnfixVoid<T>> addBranch() {
return Promise<_::UnfixVoid<T>>(false, kj::heap<ForkBranch<T>>(addRef(*this)));
}
_::SplitTuplePromise<T> split() {
return splitImpl(MakeIndexes<tupleSize<T>()>());
}
private:
ExceptionOr<T> result;
template <size_t... indexes>
_::SplitTuplePromise<T> splitImpl(Indexes<indexes...>) {
return kj::tuple(addSplit<indexes>()...);
}
template <size_t index>
Promise<JoinPromises<typename SplitBranch<T, index>::Element>> addSplit() {
return Promise<JoinPromises<typename SplitBranch<T, index>::Element>>(
false, maybeChain(kj::heap<SplitBranch<T, index>>(addRef(*this)),
implicitCast<typename SplitBranch<T, index>::Element*>(nullptr)));
}
};
inline ExceptionOrValue& ForkBranchBase::getHubResultRef() {
return hub->getResultRef();
}
// -------------------------------------------------------------------
class ChainPromiseNode final: public PromiseNode, public Event {
// Promise node which reduces Promise<Promise<T>> to Promise<T>.
//
// `Event` is only a public base class because otherwise we can't cast Own<ChainPromiseNode> to
// Own<Event>. Ugh, templates and private...
public:
explicit ChainPromiseNode(Own<PromiseNode> inner);
~ChainPromiseNode() noexcept(false);
void onReady(Event& event) noexcept override;
void setSelfPointer(Own<PromiseNode>* selfPtr) noexcept override;
void get(ExceptionOrValue& output) noexcept override;
PromiseNode* getInnerForTrace() override;
private:
enum State {
STEP1,
STEP2
};
State state;
Own<PromiseNode> inner;
// In STEP1, a PromiseNode for a Promise<T>.
// In STEP2, a PromiseNode for a T.
Event* onReadyEvent = nullptr;
Own<PromiseNode>* selfPtr = nullptr;
Maybe<Own<Event>> fire() override;
};
template <typename T>
Own<PromiseNode> maybeChain(Own<PromiseNode>&& node, Promise<T>*) {
return heap<ChainPromiseNode>(kj::mv(node));
}
template <typename T>
Own<PromiseNode>&& maybeChain(Own<PromiseNode>&& node, T*) {
return kj::mv(node);
}
// -------------------------------------------------------------------
class ExclusiveJoinPromiseNode final: public PromiseNode {
public:
ExclusiveJoinPromiseNode(Own<PromiseNode> left, Own<PromiseNode> right);
~ExclusiveJoinPromiseNode() noexcept(false);
void onReady(Event& event) noexcept override;
void get(ExceptionOrValue& output) noexcept override;
PromiseNode* getInnerForTrace() override;
private:
class Branch: public Event {
public:
Branch(ExclusiveJoinPromiseNode& joinNode, Own<PromiseNode> dependency);
~Branch() noexcept(false);
bool get(ExceptionOrValue& output);
// Returns true if this is the side that finished.
Maybe<Own<Event>> fire() override;
_::PromiseNode* getInnerForTrace() override;
private:
ExclusiveJoinPromiseNode& joinNode;
Own<PromiseNode> dependency;
};
Branch left;
Branch right;
OnReadyEvent onReadyEvent;
};
// -------------------------------------------------------------------
class ArrayJoinPromiseNodeBase: public PromiseNode {
public:
ArrayJoinPromiseNodeBase(Array<Own<PromiseNode>> promises,
ExceptionOrValue* resultParts, size_t partSize);
~ArrayJoinPromiseNodeBase() noexcept(false);
void onReady(Event& event) noexcept override final;
void get(ExceptionOrValue& output) noexcept override final;
PromiseNode* getInnerForTrace() override final;
protected:
virtual void getNoError(ExceptionOrValue& output) noexcept = 0;
// Called to compile the result only in the case where there were no errors.
private:
uint countLeft;
OnReadyEvent onReadyEvent;
class Branch final: public Event {
public:
Branch(ArrayJoinPromiseNodeBase& joinNode, Own<PromiseNode> dependency,
ExceptionOrValue& output);
~Branch() noexcept(false);
Maybe<Own<Event>> fire() override;
_::PromiseNode* getInnerForTrace() override;
Maybe<Exception> getPart();
// Calls dependency->get(output). If there was an exception, return it.
private:
ArrayJoinPromiseNodeBase& joinNode;
Own<PromiseNode> dependency;
ExceptionOrValue& output;
};
Array<Branch> branches;
};
template <typename T>
class ArrayJoinPromiseNode final: public ArrayJoinPromiseNodeBase {
public:
ArrayJoinPromiseNode(Array<Own<PromiseNode>> promises,
Array<ExceptionOr<T>> resultParts)
: ArrayJoinPromiseNodeBase(kj::mv(promises), resultParts.begin(), sizeof(ExceptionOr<T>)),
resultParts(kj::mv(resultParts)) {}
protected:
void getNoError(ExceptionOrValue& output) noexcept override {
auto builder = heapArrayBuilder<T>(resultParts.size());
for (auto& part: resultParts) {
KJ_IASSERT(part.value != nullptr,
"Bug in KJ promise framework: Promise result had neither value no exception.");
builder.add(kj::mv(*_::readMaybe(part.value)));
}
output.as<Array<T>>() = builder.finish();
}
private:
Array<ExceptionOr<T>> resultParts;
};
template <>
class ArrayJoinPromiseNode<void> final: public ArrayJoinPromiseNodeBase {
public:
ArrayJoinPromiseNode(Array<Own<PromiseNode>> promises,
Array<ExceptionOr<_::Void>> resultParts);
~ArrayJoinPromiseNode();
protected:
void getNoError(ExceptionOrValue& output) noexcept override;
private:
Array<ExceptionOr<_::Void>> resultParts;
};
// -------------------------------------------------------------------
class EagerPromiseNodeBase: public PromiseNode, protected Event {
// A PromiseNode that eagerly evaluates its dependency even if its dependent does not eagerly
// evaluate it.
public:
EagerPromiseNodeBase(Own<PromiseNode>&& dependency, ExceptionOrValue& resultRef);
void onReady(Event& event) noexcept override;
PromiseNode* getInnerForTrace() override;
private:
Own<PromiseNode> dependency;
OnReadyEvent onReadyEvent;
ExceptionOrValue& resultRef;
Maybe<Own<Event>> fire() override;
};
template <typename T>
class EagerPromiseNode final: public EagerPromiseNodeBase {
public:
EagerPromiseNode(Own<PromiseNode>&& dependency)
: EagerPromiseNodeBase(kj::mv(dependency), result) {}
void get(ExceptionOrValue& output) noexcept override {
output.as<T>() = kj::mv(result);
}
private:
ExceptionOr<T> result;
};
template <typename T>
Own<PromiseNode> spark(Own<PromiseNode>&& node) {
// Forces evaluation of the given node to begin as soon as possible, even if no one is waiting
// on it.
return heap<EagerPromiseNode<T>>(kj::mv(node));
}
// -------------------------------------------------------------------
class AdapterPromiseNodeBase: public PromiseNode {
public:
void onReady(Event& event) noexcept override;
protected:
inline void setReady() {
onReadyEvent.arm();
}
private:
OnReadyEvent onReadyEvent;
};
template <typename T, typename Adapter>
class AdapterPromiseNode final: public AdapterPromiseNodeBase,
private PromiseFulfiller<UnfixVoid<T>> {
// A PromiseNode that wraps a PromiseAdapter.
public:
template <typename... Params>
AdapterPromiseNode(Params&&... params)
: adapter(static_cast<PromiseFulfiller<UnfixVoid<T>>&>(*this), kj::fwd<Params>(params)...) {}
void get(ExceptionOrValue& output) noexcept override {
KJ_IREQUIRE(!isWaiting());
output.as<T>() = kj::mv(result);
}
private:
ExceptionOr<T> result;
bool waiting = true;
Adapter adapter;
void fulfill(T&& value) override {
if (waiting) {
waiting = false;
result = ExceptionOr<T>(kj::mv(value));
setReady();
}
}
void reject(Exception&& exception) override {
if (waiting) {
waiting = false;
result = ExceptionOr<T>(false, kj::mv(exception));
setReady();
}
}
bool isWaiting() override {
return waiting;
}
};
} // namespace _ (private)
// =======================================================================================
template <typename T>
Promise<T>::Promise(_::FixVoid<T> value)
: PromiseBase(heap<_::ImmediatePromiseNode<_::FixVoid<T>>>(kj::mv(value))) {}
template <typename T>
Promise<T>::Promise(kj::Exception&& exception)
: PromiseBase(heap<_::ImmediateBrokenPromiseNode>(kj::mv(exception))) {}
template <typename T>
template <typename Func, typename ErrorFunc>
PromiseForResult<Func, T> Promise<T>::then(Func&& func, ErrorFunc&& errorHandler) {
typedef _::FixVoid<_::ReturnType<Func, T>> ResultT;
Own<_::PromiseNode> intermediate =
heap<_::TransformPromiseNode<ResultT, _::FixVoid<T>, Func, ErrorFunc>>(
kj::mv(node), kj::fwd<Func>(func), kj::fwd<ErrorFunc>(errorHandler));
return PromiseForResult<Func, T>(false,
_::maybeChain(kj::mv(intermediate), implicitCast<ResultT*>(nullptr)));
}
namespace _ { // private
template <typename T>
struct IdentityFunc {
inline T operator()(T&& value) const {
return kj::mv(value);
}
};
template <typename T>
struct IdentityFunc<Promise<T>> {
inline Promise<T> operator()(T&& value) const {
return kj::mv(value);
}
};
template <>
struct IdentityFunc<void> {
inline void operator()() const {}
};
template <>
struct IdentityFunc<Promise<void>> {
Promise<void> operator()() const;
// This can't be inline because it will make the translation unit depend on kj-async. Awkwardly,
// Cap'n Proto relies on being able to include this header without creating such a link-time
// dependency.
};
} // namespace _ (private)
template <typename T>
template <typename ErrorFunc>
Promise<T> Promise<T>::catch_(ErrorFunc&& errorHandler) {
// then()'s ErrorFunc can only return a Promise if Func also returns a Promise. In this case,
// Func is being filled in automatically. We want to make sure ErrorFunc can return a Promise,
// but we don't want the extra overhead of promise chaining if ErrorFunc doesn't actually
// return a promise. So we make our Func return match ErrorFunc.
return then(_::IdentityFunc<decltype(errorHandler(instance<Exception&&>()))>(),
kj::fwd<ErrorFunc>(errorHandler));
}
template <typename T>
T Promise<T>::wait(WaitScope& waitScope) {
_::ExceptionOr<_::FixVoid<T>> result;
waitImpl(kj::mv(node), result, waitScope);
KJ_IF_MAYBE(value, result.value) {
KJ_IF_MAYBE(exception, result.exception) {
throwRecoverableException(kj::mv(*exception));
}
return _::returnMaybeVoid(kj::mv(*value));
} else KJ_IF_MAYBE(exception, result.exception) {
throwFatalException(kj::mv(*exception));
} else {
// Result contained neither a value nor an exception?
KJ_UNREACHABLE;
}
}
template <>
inline void Promise<void>::wait(WaitScope& waitScope) {
// Override <void> case to use throwRecoverableException().
_::ExceptionOr<_::Void> result;
waitImpl(kj::mv(node), result, waitScope);
if (result.value != nullptr) {
KJ_IF_MAYBE(exception, result.exception) {
throwRecoverableException(kj::mv(*exception));
}
} else KJ_IF_MAYBE(exception, result.exception) {
throwRecoverableException(kj::mv(*exception));
} else {
// Result contained neither a value nor an exception?
KJ_UNREACHABLE;
}
}
template <typename T>
ForkedPromise<T> Promise<T>::fork() {
return ForkedPromise<T>(false, refcounted<_::ForkHub<_::FixVoid<T>>>(kj::mv(node)));
}
template <typename T>
Promise<T> ForkedPromise<T>::addBranch() {
return hub->addBranch();
}
template <typename T>
_::SplitTuplePromise<T> Promise<T>::split() {
return refcounted<_::ForkHub<_::FixVoid<T>>>(kj::mv(node))->split();
}
template <typename T>
Promise<T> Promise<T>::exclusiveJoin(Promise<T>&& other) {
return Promise(false, heap<_::ExclusiveJoinPromiseNode>(kj::mv(node), kj::mv(other.node)));
}
template <typename T>
template <typename... Attachments>
Promise<T> Promise<T>::attach(Attachments&&... attachments) {
return Promise(false, kj::heap<_::AttachmentPromiseNode<Tuple<Attachments...>>>(
kj::mv(node), kj::tuple(kj::fwd<Attachments>(attachments)...)));
}
template <typename T>
template <typename ErrorFunc>
Promise<T> Promise<T>::eagerlyEvaluate(ErrorFunc&& errorHandler) {
// See catch_() for commentary.
return Promise(false, _::spark<_::FixVoid<T>>(then(
_::IdentityFunc<decltype(errorHandler(instance<Exception&&>()))>(),
kj::fwd<ErrorFunc>(errorHandler)).node));
}
template <typename T>
Promise<T> Promise<T>::eagerlyEvaluate(decltype(nullptr)) {
return Promise(false, _::spark<_::FixVoid<T>>(kj::mv(node)));
}
template <typename T>
kj::String Promise<T>::trace() {
return PromiseBase::trace();
}
template <typename Func>
inline PromiseForResult<Func, void> evalLater(Func&& func) {
return _::yield().then(kj::fwd<Func>(func), _::PropagateException());
}
template <typename Func>
inline PromiseForResult<Func, void> evalNow(Func&& func) {
PromiseForResult<Func, void> result = nullptr;
KJ_IF_MAYBE(e, kj::runCatchingExceptions([&]() {
result = func();
})) {
result = kj::mv(*e);
}
return result;
}
template <typename T>
template <typename ErrorFunc>
void Promise<T>::detach(ErrorFunc&& errorHandler) {
return _::detach(then([](T&&) {}, kj::fwd<ErrorFunc>(errorHandler)));
}
template <>
template <typename ErrorFunc>
void Promise<void>::detach(ErrorFunc&& errorHandler) {
return _::detach(then([]() {}, kj::fwd<ErrorFunc>(errorHandler)));
}
template <typename T>
Promise<Array<T>> joinPromises(Array<Promise<T>>&& promises) {
return Promise<Array<T>>(false, kj::heap<_::ArrayJoinPromiseNode<T>>(
KJ_MAP(p, promises) { return kj::mv(p.node); },
heapArray<_::ExceptionOr<T>>(promises.size())));
}
// =======================================================================================
namespace _ { // private
template <typename T>
class WeakFulfiller final: public PromiseFulfiller<T>, private kj::Disposer {
// A wrapper around PromiseFulfiller which can be detached.
//
// There are a couple non-trivialities here:
// - If the WeakFulfiller is discarded, we want the promise it fulfills to be implicitly
// rejected.
// - We cannot destroy the WeakFulfiller until the application has discarded it *and* it has been
// detached from the underlying fulfiller, because otherwise the later detach() call will go
// to a dangling pointer. Essentially, WeakFulfiller is reference counted, although the
// refcount never goes over 2 and we manually implement the refcounting because we need to do
// other special things when each side detaches anyway. To this end, WeakFulfiller is its own
// Disposer -- dispose() is called when the application discards its owned pointer to the
// fulfiller and detach() is called when the promise is destroyed.
public:
KJ_DISALLOW_COPY(WeakFulfiller);
static kj::Own<WeakFulfiller> make() {
WeakFulfiller* ptr = new WeakFulfiller;
return Own<WeakFulfiller>(ptr, *ptr);
}
void fulfill(FixVoid<T>&& value) override {
if (inner != nullptr) {
inner->fulfill(kj::mv(value));
}
}
void reject(Exception&& exception) override {
if (inner != nullptr) {
inner->reject(kj::mv(exception));
}
}
bool isWaiting() override {
return inner != nullptr && inner->isWaiting();
}
void attach(PromiseFulfiller<T>& newInner) {
inner = &newInner;
}
void detach(PromiseFulfiller<T>& from) {
if (inner == nullptr) {
// Already disposed.
delete this;
} else {
KJ_IREQUIRE(inner == &from);
inner = nullptr;
}
}
private:
mutable PromiseFulfiller<T>* inner;
WeakFulfiller(): inner(nullptr) {}
void disposeImpl(void* pointer) const override {
// TODO(perf): Factor some of this out so it isn't regenerated for every fulfiller type?
if (inner == nullptr) {
// Already detached.
delete this;
} else {
if (inner->isWaiting()) {
inner->reject(kj::Exception(kj::Exception::Type::FAILED, __FILE__, __LINE__,
kj::heapString("PromiseFulfiller was destroyed without fulfilling the promise.")));
}
inner = nullptr;
}
}
};
template <typename T>
class PromiseAndFulfillerAdapter {
public:
PromiseAndFulfillerAdapter(PromiseFulfiller<T>& fulfiller,
WeakFulfiller<T>& wrapper)
: fulfiller(fulfiller), wrapper(wrapper) {
wrapper.attach(fulfiller);
}
~PromiseAndFulfillerAdapter() noexcept(false) {
wrapper.detach(fulfiller);
}
private:
PromiseFulfiller<T>& fulfiller;
WeakFulfiller<T>& wrapper;
};
} // namespace _ (private)
template <typename T>
template <typename Func>
bool PromiseFulfiller<T>::rejectIfThrows(Func&& func) {
KJ_IF_MAYBE(exception, kj::runCatchingExceptions(kj::mv(func))) {
reject(kj::mv(*exception));
return false;
} else {
return true;
}
}
template <typename Func>
bool PromiseFulfiller<void>::rejectIfThrows(Func&& func) {
KJ_IF_MAYBE(exception, kj::runCatchingExceptions(kj::mv(func))) {
reject(kj::mv(*exception));
return false;
} else {
return true;
}
}
template <typename T, typename Adapter, typename... Params>
Promise<T> newAdaptedPromise(Params&&... adapterConstructorParams) {
return Promise<T>(false, heap<_::AdapterPromiseNode<_::FixVoid<T>, Adapter>>(
kj::fwd<Params>(adapterConstructorParams)...));
}
template <typename T>
PromiseFulfillerPair<T> newPromiseAndFulfiller() {
auto wrapper = _::WeakFulfiller<T>::make();
Own<_::PromiseNode> intermediate(
heap<_::AdapterPromiseNode<_::FixVoid<T>, _::PromiseAndFulfillerAdapter<T>>>(*wrapper));
Promise<_::JoinPromises<T>> promise(false,
_::maybeChain(kj::mv(intermediate), implicitCast<T*>(nullptr)));
return PromiseFulfillerPair<T> { kj::mv(promise), kj::mv(wrapper) };
}
} // namespace kj
#endif // KJ_ASYNC_INL_H_
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