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gecko-dev/xpcom/threads/MozPromise.h

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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
#if !defined(MozPromise_h_)
#define MozPromise_h_
#include "mozilla/Logging.h"
#include "mozilla/Maybe.h"
#include "mozilla/Mutex.h"
#include "mozilla/Monitor.h"
#include "mozilla/RefPtr.h"
#include "mozilla/Tuple.h"
#include "mozilla/TypeTraits.h"
#include "mozilla/Variant.h"
#include "nsISerialEventTarget.h"
#include "nsTArray.h"
#include "nsThreadUtils.h"
#if MOZ_DIAGNOSTIC_ASSERT_ENABLED
#define PROMISE_DEBUG
#endif
#ifdef PROMISE_DEBUG
#define PROMISE_ASSERT MOZ_RELEASE_ASSERT
#else
#define PROMISE_ASSERT(...) do { } while (0)
#endif
namespace mozilla {
extern LazyLogModule gMozPromiseLog;
#define PROMISE_LOG(x, ...) \
MOZ_LOG(gMozPromiseLog, mozilla::LogLevel::Debug, (x, ##__VA_ARGS__))
namespace detail {
template <typename F>
struct MethodTraitsHelper : MethodTraitsHelper<decltype(&F::operator())>
{
};
template <typename ThisType, typename Ret, typename... ArgTypes>
struct MethodTraitsHelper<Ret(ThisType::*)(ArgTypes...)>
{
using ReturnType = Ret;
static const size_t ArgSize = sizeof...(ArgTypes);
};
template <typename ThisType, typename Ret, typename... ArgTypes>
struct MethodTraitsHelper<Ret(ThisType::*)(ArgTypes...) const>
{
using ReturnType = Ret;
static const size_t ArgSize = sizeof...(ArgTypes);
};
template <typename ThisType, typename Ret, typename... ArgTypes>
struct MethodTraitsHelper<Ret(ThisType::*)(ArgTypes...) volatile>
{
using ReturnType = Ret;
static const size_t ArgSize = sizeof...(ArgTypes);
};
template <typename ThisType, typename Ret, typename... ArgTypes>
struct MethodTraitsHelper<Ret(ThisType::*)(ArgTypes...) const volatile>
{
using ReturnType = Ret;
static const size_t ArgSize = sizeof...(ArgTypes);
};
template <typename T>
struct MethodTrait : MethodTraitsHelper<typename RemoveReference<T>::Type>
{
};
} // namespace detail
template<typename MethodType>
using TakesArgument =
IntegralConstant<bool, detail::MethodTrait<MethodType>::ArgSize != 0>;
template<typename MethodType, typename TargetType>
using ReturnTypeIs =
IsConvertible<typename detail::MethodTrait<MethodType>::ReturnType, TargetType>;
template<typename ResolveValueT, typename RejectValueT, bool IsExclusive>
class MozPromise;
template<typename Return>
struct IsMozPromise : FalseType
{
};
template<typename ResolveValueT, typename RejectValueT, bool IsExclusive>
struct IsMozPromise<MozPromise<ResolveValueT, RejectValueT, IsExclusive>>
: TrueType
{
};
/*
* A promise manages an asynchronous request that may or may not be able to be
* fulfilled immediately. When an API returns a promise, the consumer may attach
* callbacks to be invoked (asynchronously, on a specified thread) when the
* request is either completed (resolved) or cannot be completed (rejected).
* Whereas JS promise callbacks are dispatched from Microtask checkpoints,
* MozPromises resolution/rejection make a normal round-trip through the event
* loop, which simplifies their ordering semantics relative to other native code.
*
* MozPromises attempt to mirror the spirit of JS Promises to the extent that
* is possible (and desirable) in C++. While the intent is that MozPromises
* feel familiar to programmers who are accustomed to their JS-implemented cousin,
* we don't shy away from imposing restrictions and adding features that make
* sense for the use cases we encounter.
*
* A MozPromise is ThreadSafe, and may be ->Then()ed on any thread. The Then()
* call accepts resolve and reject callbacks, and returns a magic object which
* will be implicitly converted to a MozPromise::Request or a MozPromise object
* depending on how the return value is used. The magic object serves several
* purposes for the consumer.
*
* (1) When converting to a MozPromise::Request, it allows the caller to
* cancel the delivery of the resolve/reject value if it has not already
* occurred, via Disconnect() (this must be done on the target thread to
* avoid racing).
*
* (2) When converting to a MozPromise (which is called a completion promise),
* it allows promise chaining so ->Then() can be called again to attach
* more resolve and reject callbacks. If the resolve/reject callback
* returns a new MozPromise, that promise is chained to the completion
* promise, such that its resolve/reject value will be forwarded along
* when it arrives. If the resolve/reject callback returns void, the
* completion promise is resolved/rejected with the same value that was
* passed to the callback.
*
* The MozPromise APIs skirt traditional XPCOM convention by returning nsRefPtrs
* (rather than already_AddRefed) from various methods. This is done to allow elegant
* chaining of calls without cluttering up the code with intermediate variables, and
* without introducing separate API variants for callers that want a return value
* (from, say, ->Then()) from those that don't.
*
* When IsExclusive is true, the MozPromise does a release-mode assertion that
* there is at most one call to either Then(...) or ChainTo(...).
*/
class MozPromiseRefcountable
{
public:
NS_INLINE_DECL_THREADSAFE_REFCOUNTING(MozPromiseRefcountable)
protected:
virtual ~MozPromiseRefcountable() {}
};
class MozPromiseBase : public MozPromiseRefcountable
{
public:
virtual void AssertIsDead() = 0;
};
template<typename T> class MozPromiseHolder;
template<typename T> class MozPromiseRequestHolder;
template<typename ResolveValueT, typename RejectValueT, bool IsExclusive>
class MozPromise : public MozPromiseBase
{
static const uint32_t sMagic = 0xcecace11;
// Return a |T&&| to enable move when IsExclusive is true or
// a |const T&| to enforce copy otherwise.
template <typename T,
typename R = typename Conditional<IsExclusive, T&&, const T&>::Type>
static R MaybeMove(T& aX)
{
return static_cast<R>(aX);
}
public:
typedef ResolveValueT ResolveValueType;
typedef RejectValueT RejectValueType;
class ResolveOrRejectValue
{
public:
template<typename ResolveValueType_>
void SetResolve(ResolveValueType_&& aResolveValue)
{
MOZ_ASSERT(IsNothing());
mValue = Storage(VariantIndex<ResolveIndex>{},
std::forward<ResolveValueType_>(aResolveValue));
}
template<typename RejectValueType_>
void SetReject(RejectValueType_&& aRejectValue)
{
MOZ_ASSERT(IsNothing());
mValue = Storage(VariantIndex<RejectIndex>{},
std::forward<RejectValueType_>(aRejectValue));
}
template<typename ResolveValueType_>
static ResolveOrRejectValue MakeResolve(ResolveValueType_&& aResolveValue)
{
ResolveOrRejectValue val;
val.SetResolve(std::forward<ResolveValueType_>(aResolveValue));
return val;
}
template<typename RejectValueType_>
static ResolveOrRejectValue MakeReject(RejectValueType_&& aRejectValue)
{
ResolveOrRejectValue val;
val.SetReject(std::forward<RejectValueType_>(aRejectValue));
return val;
}
bool IsResolve() const { return mValue.template is<ResolveIndex>(); }
bool IsReject() const { return mValue.template is<RejectIndex>(); }
bool IsNothing() const { return mValue.template is<NothingIndex>(); }
const ResolveValueType& ResolveValue() const
{
return mValue.template as<ResolveIndex>();
}
ResolveValueType& ResolveValue()
{
return mValue.template as<ResolveIndex>();
}
const RejectValueType& RejectValue() const
{
return mValue.template as<RejectIndex>();
}
RejectValueType& RejectValue()
{
return mValue.template as<RejectIndex>();
}
private:
enum { NothingIndex, ResolveIndex, RejectIndex };
using Storage = Variant<Nothing, ResolveValueType, RejectValueType>;
Storage mValue = Storage(VariantIndex<NothingIndex>{});
};
protected:
// MozPromise is the public type, and never constructed directly. Construct
// a MozPromise::Private, defined below.
MozPromise(const char* aCreationSite, bool aIsCompletionPromise)
: mCreationSite(aCreationSite)
, mMutex("MozPromise Mutex")
, mHaveRequest(false)
, mIsCompletionPromise(aIsCompletionPromise)
#ifdef PROMISE_DEBUG
, mMagic4(&mMutex)
#endif
{
PROMISE_LOG("%s creating MozPromise (%p)", mCreationSite, this);
}
public:
// MozPromise::Private allows us to separate the public interface (upon which
// consumers of the promise may invoke methods like Then()) from the private
// interface (upon which the creator of the promise may invoke Resolve() or
// Reject()). APIs should create and store a MozPromise::Private (usually
// via a MozPromiseHolder), and return a MozPromise to consumers.
//
// NB: We can include the definition of this class inline once B2G ICS is gone.
class Private;
template<typename ResolveValueType_>
static RefPtr<MozPromise>
CreateAndResolve(ResolveValueType_&& aResolveValue, const char* aResolveSite)
{
RefPtr<typename MozPromise::Private> p = new MozPromise::Private(aResolveSite);
p->Resolve(std::forward<ResolveValueType_>(aResolveValue), aResolveSite);
return p.forget();
}
template<typename RejectValueType_>
static RefPtr<MozPromise>
CreateAndReject(RejectValueType_&& aRejectValue, const char* aRejectSite)
{
RefPtr<typename MozPromise::Private> p = new MozPromise::Private(aRejectSite);
p->Reject(std::forward<RejectValueType_>(aRejectValue), aRejectSite);
return p.forget();
}
template<typename ResolveOrRejectValueType_>
static RefPtr<MozPromise>
CreateAndResolveOrReject(ResolveOrRejectValueType_&& aValue, const char* aSite)
{
RefPtr<typename MozPromise::Private> p = new MozPromise::Private(aSite);
p->ResolveOrReject(std::forward<ResolveOrRejectValueType_>(aValue), aSite);
return p.forget();
}
typedef MozPromise<nsTArray<ResolveValueType>, RejectValueType, IsExclusive> AllPromiseType;
private:
class AllPromiseHolder : public MozPromiseRefcountable
{
public:
explicit AllPromiseHolder(size_t aDependentPromises)
: mPromise(new typename AllPromiseType::Private(__func__))
, mOutstandingPromises(aDependentPromises)
{
MOZ_ASSERT(aDependentPromises > 0);
mResolveValues.SetLength(aDependentPromises);
}
void Resolve(size_t aIndex, ResolveValueType&& aResolveValue)
{
if (!mPromise) {
// Already rejected.
return;
}
mResolveValues[aIndex].emplace(std::move(aResolveValue));
if (--mOutstandingPromises == 0) {
nsTArray<ResolveValueType> resolveValues;
resolveValues.SetCapacity(mResolveValues.Length());
for (auto&& resolveValue : mResolveValues) {
resolveValues.AppendElement(std::move(resolveValue.ref()));
}
mPromise->Resolve(std::move(resolveValues), __func__);
mPromise = nullptr;
mResolveValues.Clear();
}
}
void Reject(RejectValueType&& aRejectValue)
{
if (!mPromise) {
// Already rejected.
return;
}
mPromise->Reject(std::move(aRejectValue), __func__);
mPromise = nullptr;
mResolveValues.Clear();
}
AllPromiseType* Promise() { return mPromise; }
private:
nsTArray<Maybe<ResolveValueType>> mResolveValues;
RefPtr<typename AllPromiseType::Private> mPromise;
size_t mOutstandingPromises;
};
public:
static RefPtr<AllPromiseType> All(nsISerialEventTarget* aProcessingTarget, nsTArray<RefPtr<MozPromise>>& aPromises)
{
if (aPromises.Length() == 0) {
return AllPromiseType::CreateAndResolve(nsTArray<ResolveValueType>(), __func__);
}
RefPtr<AllPromiseHolder> holder = new AllPromiseHolder(aPromises.Length());
RefPtr<AllPromiseType> promise = holder->Promise();
for (size_t i = 0; i < aPromises.Length(); ++i) {
aPromises[i]->Then(aProcessingTarget, __func__,
[holder, i] (ResolveValueType aResolveValue) -> void { holder->Resolve(i, std::move(aResolveValue)); },
[holder] (RejectValueType aRejectValue) -> void { holder->Reject(std::move(aRejectValue)); }
);
}
return promise;
}
class Request : public MozPromiseRefcountable
{
public:
virtual void Disconnect() = 0;
protected:
Request() : mComplete(false), mDisconnected(false) {}
virtual ~Request() {}
bool mComplete;
bool mDisconnected;
};
protected:
/*
* A ThenValue tracks a single consumer waiting on the promise. When a consumer
* invokes promise->Then(...), a ThenValue is created. Once the Promise is
* resolved or rejected, a {Resolve,Reject}Runnable is dispatched, which
* invokes the resolve/reject method and then deletes the ThenValue.
*/
class ThenValueBase : public Request
{
friend class MozPromise;
static const uint32_t sMagic = 0xfadece11;
public:
class ResolveOrRejectRunnable : public CancelableRunnable
{
public:
ResolveOrRejectRunnable(ThenValueBase* aThenValue, MozPromise* aPromise)
: CancelableRunnable(
"MozPromise::ThenValueBase::ResolveOrRejectRunnable")
, mThenValue(aThenValue)
, mPromise(aPromise)
{
MOZ_DIAGNOSTIC_ASSERT(!mPromise->IsPending());
}
~ResolveOrRejectRunnable()
{
if (mThenValue) {
mThenValue->AssertIsDead();
}
}
NS_IMETHOD Run() override
{
PROMISE_LOG("ResolveOrRejectRunnable::Run() [this=%p]", this);
mThenValue->DoResolveOrReject(mPromise->Value());
mThenValue = nullptr;
mPromise = nullptr;
return NS_OK;
}
nsresult Cancel() override
{
return Run();
}
private:
RefPtr<ThenValueBase> mThenValue;
RefPtr<MozPromise> mPromise;
};
ThenValueBase(nsISerialEventTarget* aResponseTarget,
const char* aCallSite)
: mResponseTarget(aResponseTarget)
, mCallSite(aCallSite)
{
MOZ_ASSERT(aResponseTarget);
}
#ifdef PROMISE_DEBUG
~ThenValueBase()
{
mMagic1 = 0;
mMagic2 = 0;
}
#endif
void AssertIsDead()
{
PROMISE_ASSERT(mMagic1 == sMagic && mMagic2 == sMagic);
// We want to assert that this ThenValues is dead - that is to say, that
// there are no consumers waiting for the result. In the case of a normal
// ThenValue, we check that it has been disconnected, which is the way
// that the consumer signals that it no longer wishes to hear about the
// result. If this ThenValue has a completion promise (which is mutually
// exclusive with being disconnectable), we recursively assert that every
// ThenValue associated with the completion promise is dead.
if (MozPromiseBase* p = CompletionPromise()) {
p->AssertIsDead();
} else {
MOZ_DIAGNOSTIC_ASSERT(Request::mDisconnected);
}
}
void Dispatch(MozPromise *aPromise)
{
PROMISE_ASSERT(mMagic1 == sMagic && mMagic2 == sMagic);
aPromise->mMutex.AssertCurrentThreadOwns();
MOZ_ASSERT(!aPromise->IsPending());
nsCOMPtr<nsIRunnable> r = new ResolveOrRejectRunnable(this, aPromise);
PROMISE_LOG("%s Then() call made from %s [Runnable=%p, Promise=%p, ThenValue=%p]",
aPromise->mValue.IsResolve() ? "Resolving" : "Rejecting", mCallSite,
r.get(), aPromise, this);
// Promise consumers are allowed to disconnect the Request object and
// then shut down the thread or task queue that the promise result would
// be dispatched on. So we unfortunately can't assert that promise
// dispatch succeeds. :-(
mResponseTarget->Dispatch(r.forget());
}
void Disconnect() override
{
MOZ_DIAGNOSTIC_ASSERT(mResponseTarget->IsOnCurrentThread());
MOZ_DIAGNOSTIC_ASSERT(!Request::mComplete);
Request::mDisconnected = true;
// We could support rejecting the completion promise on disconnection, but
// then we'd need to have some sort of default reject value. The use cases
// of disconnection and completion promise chaining seem pretty orthogonal,
// so let's use assert against it.
MOZ_DIAGNOSTIC_ASSERT(!CompletionPromise());
}
protected:
virtual MozPromiseBase* CompletionPromise() const = 0;
virtual void DoResolveOrRejectInternal(ResolveOrRejectValue& aValue) = 0;
void DoResolveOrReject(ResolveOrRejectValue& aValue)
{
PROMISE_ASSERT(mMagic1 == sMagic && mMagic2 == sMagic);
MOZ_DIAGNOSTIC_ASSERT(mResponseTarget->IsOnCurrentThread());
Request::mComplete = true;
if (Request::mDisconnected) {
PROMISE_LOG("ThenValue::DoResolveOrReject disconnected - bailing out [this=%p]", this);
return;
}
// Invoke the resolve or reject method.
DoResolveOrRejectInternal(aValue);
}
nsCOMPtr<nsISerialEventTarget> mResponseTarget; // May be released on any thread.
#ifdef PROMISE_DEBUG
uint32_t mMagic1 = sMagic;
#endif
const char* mCallSite;
#ifdef PROMISE_DEBUG
uint32_t mMagic2 = sMagic;
#endif
};
/*
* We create two overloads for invoking Resolve/Reject Methods so as to
* make the resolve/reject value argument "optional".
*/
template<typename ThisType, typename MethodType, typename ValueType>
static typename EnableIf<
TakesArgument<MethodType>::value,
typename detail::MethodTrait<MethodType>::ReturnType>::Type
InvokeMethod(ThisType* aThisVal, MethodType aMethod, ValueType&& aValue)
{
return (aThisVal->*aMethod)(std::forward<ValueType>(aValue));
}
template<typename ThisType, typename MethodType, typename ValueType>
static typename EnableIf<
!TakesArgument<MethodType>::value,
typename detail::MethodTrait<MethodType>::ReturnType>::Type
InvokeMethod(ThisType* aThisVal, MethodType aMethod, ValueType&& aValue)
{
return (aThisVal->*aMethod)();
}
// Called when promise chaining is supported.
template<bool SupportChaining,
typename ThisType,
typename MethodType,
typename ValueType,
typename CompletionPromiseType>
static typename EnableIf<SupportChaining, void>::Type InvokeCallbackMethod(
ThisType* aThisVal,
MethodType aMethod,
ValueType&& aValue,
CompletionPromiseType&& aCompletionPromise)
{
auto p = InvokeMethod(aThisVal, aMethod, std::forward<ValueType>(aValue));
if (aCompletionPromise) {
p->ChainTo(aCompletionPromise.forget(), "<chained completion promise>");
}
}
// Called when promise chaining is not supported.
template<bool SupportChaining,
typename ThisType,
typename MethodType,
typename ValueType,
typename CompletionPromiseType>
static typename EnableIf<!SupportChaining, void>::Type InvokeCallbackMethod(
ThisType* aThisVal,
MethodType aMethod,
ValueType&& aValue,
CompletionPromiseType&& aCompletionPromise)
{
MOZ_DIAGNOSTIC_ASSERT(
!aCompletionPromise,
"Can't do promise chaining for a non-promise-returning method.");
InvokeMethod(aThisVal, aMethod, std::forward<ValueType>(aValue));
}
template<typename>
class ThenCommand;
template<typename...>
class ThenValue;
template<typename ThisType,
typename ResolveMethodType,
typename RejectMethodType>
class ThenValue<ThisType*, ResolveMethodType, RejectMethodType>
: public ThenValueBase
{
friend class ThenCommand<ThenValue>;
using R1 = typename RemoveSmartPointer<
typename detail::MethodTrait<ResolveMethodType>::ReturnType>::Type;
using R2 = typename RemoveSmartPointer<
typename detail::MethodTrait<RejectMethodType>::ReturnType>::Type;
using SupportChaining =
IntegralConstant<bool, IsMozPromise<R1>::value && IsSame<R1, R2>::value>;
// Fall back to MozPromise when promise chaining is not supported to make code compile.
using PromiseType =
typename Conditional<SupportChaining::value, R1, MozPromise>::Type;
public:
ThenValue(nsISerialEventTarget* aResponseTarget,
ThisType* aThisVal,
ResolveMethodType aResolveMethod,
RejectMethodType aRejectMethod,
const char* aCallSite)
: ThenValueBase(aResponseTarget, aCallSite)
, mThisVal(aThisVal)
, mResolveMethod(aResolveMethod)
, mRejectMethod(aRejectMethod)
{
}
void Disconnect() override
{
ThenValueBase::Disconnect();
// If a Request has been disconnected, we don't guarantee that the
// resolve/reject runnable will be dispatched. Null out our refcounted
// this-value now so that it's released predictably on the dispatch thread.
mThisVal = nullptr;
}
protected:
MozPromiseBase* CompletionPromise() const override
{
return mCompletionPromise;
}
void DoResolveOrRejectInternal(ResolveOrRejectValue& aValue) override
{
if (aValue.IsResolve()) {
InvokeCallbackMethod<SupportChaining::value>(
mThisVal.get(),
mResolveMethod,
MaybeMove(aValue.ResolveValue()),
std::move(mCompletionPromise));
} else {
InvokeCallbackMethod<SupportChaining::value>(
mThisVal.get(),
mRejectMethod,
MaybeMove(aValue.RejectValue()),
std::move(mCompletionPromise));
}
// Null out mThisVal after invoking the callback so that any references are
// released predictably on the dispatch thread. Otherwise, it would be
// released on whatever thread last drops its reference to the ThenValue,
// which may or may not be ok.
mThisVal = nullptr;
}
private:
RefPtr<ThisType> mThisVal; // Only accessed and refcounted on dispatch thread.
ResolveMethodType mResolveMethod;
RejectMethodType mRejectMethod;
RefPtr<typename PromiseType::Private> mCompletionPromise;
};
template<typename ThisType, typename ResolveRejectMethodType>
class ThenValue<ThisType*, ResolveRejectMethodType> : public ThenValueBase
{
friend class ThenCommand<ThenValue>;
using R1 = typename RemoveSmartPointer<
typename detail::MethodTrait<ResolveRejectMethodType>::ReturnType>::Type;
using SupportChaining = IntegralConstant<bool, IsMozPromise<R1>::value>;
// Fall back to MozPromise when promise chaining is not supported to make code compile.
using PromiseType =
typename Conditional<SupportChaining::value, R1, MozPromise>::Type;
public:
ThenValue(nsISerialEventTarget* aResponseTarget,
ThisType* aThisVal,
ResolveRejectMethodType aResolveRejectMethod,
const char* aCallSite)
: ThenValueBase(aResponseTarget, aCallSite)
, mThisVal(aThisVal)
, mResolveRejectMethod(aResolveRejectMethod)
{}
void Disconnect() override
{
ThenValueBase::Disconnect();
// If a Request has been disconnected, we don't guarantee that the
// resolve/reject runnable will be dispatched. Null out our refcounted
// this-value now so that it's released predictably on the dispatch thread.
mThisVal = nullptr;
}
protected:
MozPromiseBase* CompletionPromise() const override
{
return mCompletionPromise;
}
void DoResolveOrRejectInternal(ResolveOrRejectValue& aValue) override
{
InvokeCallbackMethod<SupportChaining::value>(mThisVal.get(),
mResolveRejectMethod,
MaybeMove(aValue),
std::move(mCompletionPromise));
// Null out mThisVal after invoking the callback so that any references are
// released predictably on the dispatch thread. Otherwise, it would be
// released on whatever thread last drops its reference to the ThenValue,
// which may or may not be ok.
mThisVal = nullptr;
}
private:
RefPtr<ThisType> mThisVal; // Only accessed and refcounted on dispatch thread.
ResolveRejectMethodType mResolveRejectMethod;
RefPtr<typename PromiseType::Private> mCompletionPromise;
};
// NB: We could use std::function here instead of a template if it were supported. :-(
template<typename ResolveFunction, typename RejectFunction>
class ThenValue<ResolveFunction, RejectFunction> : public ThenValueBase
{
friend class ThenCommand<ThenValue>;
using R1 = typename RemoveSmartPointer<
typename detail::MethodTrait<ResolveFunction>::ReturnType>::Type;
using R2 = typename RemoveSmartPointer<
typename detail::MethodTrait<RejectFunction>::ReturnType>::Type;
using SupportChaining =
IntegralConstant<bool, IsMozPromise<R1>::value && IsSame<R1, R2>::value>;
// Fall back to MozPromise when promise chaining is not supported to make code compile.
using PromiseType =
typename Conditional<SupportChaining::value, R1, MozPromise>::Type;
public:
ThenValue(nsISerialEventTarget* aResponseTarget,
ResolveFunction&& aResolveFunction,
RejectFunction&& aRejectFunction,
const char* aCallSite)
: ThenValueBase(aResponseTarget, aCallSite)
{
mResolveFunction.emplace(std::move(aResolveFunction));
mRejectFunction.emplace(std::move(aRejectFunction));
}
void Disconnect() override
{
ThenValueBase::Disconnect();
// If a Request has been disconnected, we don't guarantee that the
// resolve/reject runnable will be dispatched. Destroy our callbacks
// now so that any references in closures are released predictable on
// the dispatch thread.
mResolveFunction.reset();
mRejectFunction.reset();
}
protected:
MozPromiseBase* CompletionPromise() const override
{
return mCompletionPromise;
}
void DoResolveOrRejectInternal(ResolveOrRejectValue& aValue) override
{
// Note: The usage of InvokeCallbackMethod here requires that
// ResolveFunction/RejectFunction are capture-lambdas (i.e. anonymous
// classes with ::operator()), since it allows us to share code more easily.
// We could fix this if need be, though it's quite easy to work around by
// just capturing something.
if (aValue.IsResolve()) {
InvokeCallbackMethod<SupportChaining::value>(
mResolveFunction.ptr(),
&ResolveFunction::operator(),
MaybeMove(aValue.ResolveValue()),
std::move(mCompletionPromise));
} else {
InvokeCallbackMethod<SupportChaining::value>(
mRejectFunction.ptr(),
&RejectFunction::operator(),
MaybeMove(aValue.RejectValue()),
std::move(mCompletionPromise));
}
// Destroy callbacks after invocation so that any references in closures are
// released predictably on the dispatch thread. Otherwise, they would be
// released on whatever thread last drops its reference to the ThenValue,
// which may or may not be ok.
mResolveFunction.reset();
mRejectFunction.reset();
}
private:
Maybe<ResolveFunction> mResolveFunction; // Only accessed and deleted on dispatch thread.
Maybe<RejectFunction> mRejectFunction; // Only accessed and deleted on dispatch thread.
RefPtr<typename PromiseType::Private> mCompletionPromise;
};
template<typename ResolveRejectFunction>
class ThenValue<ResolveRejectFunction> : public ThenValueBase
{
friend class ThenCommand<ThenValue>;
using R1 = typename RemoveSmartPointer<
typename detail::MethodTrait<ResolveRejectFunction>::ReturnType>::Type;
using SupportChaining = IntegralConstant<bool, IsMozPromise<R1>::value>;
// Fall back to MozPromise when promise chaining is not supported to make code compile.
using PromiseType =
typename Conditional<SupportChaining::value, R1, MozPromise>::Type;
public:
ThenValue(nsISerialEventTarget* aResponseTarget,
ResolveRejectFunction&& aResolveRejectFunction,
const char* aCallSite)
: ThenValueBase(aResponseTarget, aCallSite)
{
mResolveRejectFunction.emplace(std::move(aResolveRejectFunction));
}
void Disconnect() override
{
ThenValueBase::Disconnect();
// If a Request has been disconnected, we don't guarantee that the
// resolve/reject runnable will be dispatched. Destroy our callbacks
// now so that any references in closures are released predictable on
// the dispatch thread.
mResolveRejectFunction.reset();
}
protected:
MozPromiseBase* CompletionPromise() const override
{
return mCompletionPromise;
}
void DoResolveOrRejectInternal(ResolveOrRejectValue& aValue) override
{
// Note: The usage of InvokeCallbackMethod here requires that
// ResolveRejectFunction is capture-lambdas (i.e. anonymous
// classes with ::operator()), since it allows us to share code more easily.
// We could fix this if need be, though it's quite easy to work around by
// just capturing something.
InvokeCallbackMethod<SupportChaining::value>(
mResolveRejectFunction.ptr(),
&ResolveRejectFunction::operator(),
MaybeMove(aValue),
std::move(mCompletionPromise));
// Destroy callbacks after invocation so that any references in closures are
// released predictably on the dispatch thread. Otherwise, they would be
// released on whatever thread last drops its reference to the ThenValue,
// which may or may not be ok.
mResolveRejectFunction.reset();
}
private:
Maybe<ResolveRejectFunction> mResolveRejectFunction; // Only accessed and deleted on dispatch thread.
RefPtr<typename PromiseType::Private> mCompletionPromise;
};
public:
void ThenInternal(already_AddRefed<ThenValueBase> aThenValue,
const char* aCallSite)
{
PROMISE_ASSERT(mMagic1 == sMagic && mMagic2 == sMagic && mMagic3 == sMagic && mMagic4 == &mMutex);
RefPtr<ThenValueBase> thenValue = aThenValue;
MutexAutoLock lock(mMutex);
MOZ_DIAGNOSTIC_ASSERT(!IsExclusive || !mHaveRequest);
mHaveRequest = true;
PROMISE_LOG("%s invoking Then() [this=%p, aThenValue=%p, isPending=%d]",
aCallSite,
this,
thenValue.get(),
(int)IsPending());
if (!IsPending()) {
thenValue->Dispatch(this);
} else {
mThenValues.AppendElement(thenValue.forget());
}
}
protected:
/*
* A command object to store all information needed to make a request to
* the promise. This allows us to delay the request until further use is
* known (whether it is ->Then() again for more promise chaining or ->Track()
* to terminate chaining and issue the request).
*
* This allows a unified syntax for promise chaining and disconnection
* and feels more like its JS counterpart.
*/
template<typename ThenValueType>
class ThenCommand
{
// Allow Promise1::ThenCommand to access the private constructor,
// Promise2::ThenCommand(ThenCommand&&).
template<typename, typename, bool>
friend class MozPromise;
using PromiseType = typename ThenValueType::PromiseType;
using Private = typename PromiseType::Private;
ThenCommand(const char* aCallSite,
already_AddRefed<ThenValueType> aThenValue,
MozPromise* aReceiver)
: mCallSite(aCallSite)
, mThenValue(aThenValue)
, mReceiver(aReceiver)
{
}
ThenCommand(ThenCommand&& aOther) = default;
public:
~ThenCommand()
{
// Issue the request now if the return value of Then() is not used.
if (mThenValue) {
mReceiver->ThenInternal(mThenValue.forget(), mCallSite);
}
}
// Allow RefPtr<MozPromise> p = somePromise->Then();
// p->Then(thread1, ...);
// p->Then(thread2, ...);
operator RefPtr<PromiseType>()
{
static_assert(
ThenValueType::SupportChaining::value,
"The resolve/reject callback needs to return a RefPtr<MozPromise> "
"in order to do promise chaining.");
// mCompletionPromise must be created before ThenInternal() to avoid race.
RefPtr<Private> p =
new Private("<completion promise>", true /* aIsCompletionPromise */);
mThenValue->mCompletionPromise = p;
// Note ThenInternal() might nullify mCompletionPromise before return.
// So we need to return p instead of mCompletionPromise.
mReceiver->ThenInternal(mThenValue.forget(), mCallSite);
return p;
}
template<typename... Ts>
auto Then(Ts&&... aArgs)
-> decltype(DeclVal<PromiseType>().Then(std::forward<Ts>(aArgs)...))
{
return static_cast<RefPtr<PromiseType>>(*this)->Then(
std::forward<Ts>(aArgs)...);
}
void Track(MozPromiseRequestHolder<MozPromise>& aRequestHolder)
{
aRequestHolder.Track(do_AddRef(mThenValue));
mReceiver->ThenInternal(mThenValue.forget(), mCallSite);
}
// Allow calling ->Then() again for more promise chaining or ->Track() to
// end chaining and track the request for future disconnection.
ThenCommand* operator->()
{
return this;
}
private:
const char* mCallSite;
RefPtr<ThenValueType> mThenValue;
RefPtr<MozPromise> mReceiver;
};
public:
template<typename ThisType,
typename... Methods,
typename ThenValueType = ThenValue<ThisType*, Methods...>,
typename ReturnType = ThenCommand<ThenValueType>>
ReturnType Then(nsISerialEventTarget* aResponseTarget,
const char* aCallSite,
ThisType* aThisVal,
Methods... aMethods)
{
RefPtr<ThenValueType> thenValue =
new ThenValueType(aResponseTarget, aThisVal, aMethods..., aCallSite);
return ReturnType(aCallSite, thenValue.forget(), this);
}
template<typename... Functions,
typename ThenValueType = ThenValue<Functions...>,
typename ReturnType = ThenCommand<ThenValueType>>
ReturnType Then(nsISerialEventTarget* aResponseTarget,
const char* aCallSite,
Functions&&... aFunctions)
{
RefPtr<ThenValueType> thenValue =
new ThenValueType(aResponseTarget, std::move(aFunctions)..., aCallSite);
return ReturnType(aCallSite, thenValue.forget(), this);
}
void ChainTo(already_AddRefed<Private> aChainedPromise, const char* aCallSite)
{
MutexAutoLock lock(mMutex);
MOZ_DIAGNOSTIC_ASSERT(!IsExclusive || !mHaveRequest);
mHaveRequest = true;
RefPtr<Private> chainedPromise = aChainedPromise;
PROMISE_LOG("%s invoking Chain() [this=%p, chainedPromise=%p, isPending=%d]",
aCallSite, this, chainedPromise.get(), (int) IsPending());
if (!IsPending()) {
ForwardTo(chainedPromise);
} else {
mChainedPromises.AppendElement(chainedPromise);
}
}
// Note we expose the function AssertIsDead() instead of IsDead() since
// checking IsDead() is a data race in the situation where the request is not
// dead. Therefore we enforce the form |Assert(IsDead())| by exposing
// AssertIsDead() only.
void AssertIsDead() override
{
PROMISE_ASSERT(mMagic1 == sMagic && mMagic2 == sMagic && mMagic3 == sMagic && mMagic4 == &mMutex);
MutexAutoLock lock(mMutex);
for (auto&& then : mThenValues) {
then->AssertIsDead();
}
for (auto&& chained : mChainedPromises) {
chained->AssertIsDead();
}
}
protected:
bool IsPending() const { return mValue.IsNothing(); }
ResolveOrRejectValue& Value()
{
// This method should only be called once the value has stabilized. As
// such, we don't need to acquire the lock here.
MOZ_DIAGNOSTIC_ASSERT(!IsPending());
return mValue;
}
void DispatchAll()
{
mMutex.AssertCurrentThreadOwns();
for (auto&& thenValue : mThenValues) {
thenValue->Dispatch(this);
}
mThenValues.Clear();
for (auto&& chainedPromise : mChainedPromises) {
ForwardTo(chainedPromise);
}
mChainedPromises.Clear();
}
void ForwardTo(Private* aOther)
{
MOZ_ASSERT(!IsPending());
if (mValue.IsResolve()) {
aOther->Resolve(MaybeMove(mValue.ResolveValue()), "<chained promise>");
} else {
aOther->Reject(MaybeMove(mValue.RejectValue()), "<chained promise>");
}
}
virtual ~MozPromise()
{
PROMISE_LOG("MozPromise::~MozPromise [this=%p]", this);
AssertIsDead();
// We can't guarantee a completion promise will always be revolved or
// rejected since ResolveOrRejectRunnable might not run when dispatch fails.
if (!mIsCompletionPromise) {
MOZ_ASSERT(!IsPending());
MOZ_ASSERT(mThenValues.IsEmpty());
MOZ_ASSERT(mChainedPromises.IsEmpty());
}
#ifdef PROMISE_DEBUG
mMagic1 = 0;
mMagic2 = 0;
mMagic3 = 0;
mMagic4 = nullptr;
#endif
};
const char* mCreationSite; // For logging
Mutex mMutex;
ResolveOrRejectValue mValue;
#ifdef PROMISE_DEBUG
uint32_t mMagic1 = sMagic;
#endif
// Try shows we never have more than 3 elements when IsExclusive is false.
// So '3' is a good value to avoid heap allocation in most cases.
AutoTArray<RefPtr<ThenValueBase>, IsExclusive ? 1 : 3> mThenValues;
#ifdef PROMISE_DEBUG
uint32_t mMagic2 = sMagic;
#endif
nsTArray<RefPtr<Private>> mChainedPromises;
#ifdef PROMISE_DEBUG
uint32_t mMagic3 = sMagic;
#endif
bool mHaveRequest;
const bool mIsCompletionPromise;
#ifdef PROMISE_DEBUG
void* mMagic4;
#endif
};
template<typename ResolveValueT, typename RejectValueT, bool IsExclusive>
class MozPromise<ResolveValueT, RejectValueT, IsExclusive>::Private
: public MozPromise<ResolveValueT, RejectValueT, IsExclusive>
{
public:
explicit Private(const char* aCreationSite, bool aIsCompletionPromise = false)
: MozPromise(aCreationSite, aIsCompletionPromise) {}
template<typename ResolveValueT_>
void Resolve(ResolveValueT_&& aResolveValue, const char* aResolveSite)
{
PROMISE_ASSERT(mMagic1 == sMagic && mMagic2 == sMagic && mMagic3 == sMagic && mMagic4 == &mMutex);
MutexAutoLock lock(mMutex);
PROMISE_LOG("%s resolving MozPromise (%p created at %s)", aResolveSite, this, mCreationSite);
if (!IsPending()) {
PROMISE_LOG("%s ignored already resolved or rejected MozPromise (%p created at %s)", aResolveSite, this, mCreationSite);
return;
}
mValue.SetResolve(std::forward<ResolveValueT_>(aResolveValue));
DispatchAll();
}
template<typename RejectValueT_>
void Reject(RejectValueT_&& aRejectValue, const char* aRejectSite)
{
PROMISE_ASSERT(mMagic1 == sMagic && mMagic2 == sMagic && mMagic3 == sMagic && mMagic4 == &mMutex);
MutexAutoLock lock(mMutex);
PROMISE_LOG("%s rejecting MozPromise (%p created at %s)", aRejectSite, this, mCreationSite);
if (!IsPending()) {
PROMISE_LOG("%s ignored already resolved or rejected MozPromise (%p created at %s)", aRejectSite, this, mCreationSite);
return;
}
mValue.SetReject(std::forward<RejectValueT_>(aRejectValue));
DispatchAll();
}
template<typename ResolveOrRejectValue_>
void ResolveOrReject(ResolveOrRejectValue_&& aValue, const char* aSite)
{
PROMISE_ASSERT(mMagic1 == sMagic && mMagic2 == sMagic && mMagic3 == sMagic && mMagic4 == &mMutex);
MutexAutoLock lock(mMutex);
PROMISE_LOG("%s resolveOrRejecting MozPromise (%p created at %s)", aSite, this, mCreationSite);
if (!IsPending()) {
PROMISE_LOG("%s ignored already resolved or rejected MozPromise (%p created at %s)", aSite, this, mCreationSite);
return;
}
mValue = std::forward<ResolveOrRejectValue_>(aValue);
DispatchAll();
}
};
// A generic promise type that does the trick for simple use cases.
typedef MozPromise<bool, nsresult, /* IsExclusive = */ false> GenericPromise;
/*
* Class to encapsulate a promise for a particular role. Use this as the member
* variable for a class whose method returns a promise.
*/
template<typename PromiseType>
class MozPromiseHolder
{
public:
MozPromiseHolder()
: mMonitor(nullptr) {}
MozPromiseHolder(MozPromiseHolder&& aOther)
: mMonitor(nullptr), mPromise(aOther.mPromise.forget()) {}
// Move semantics.
MozPromiseHolder& operator=(MozPromiseHolder&& aOther)
{
MOZ_ASSERT(!mMonitor && !aOther.mMonitor);
MOZ_DIAGNOSTIC_ASSERT(!mPromise);
mPromise = aOther.mPromise;
aOther.mPromise = nullptr;
return *this;
}
~MozPromiseHolder() { MOZ_ASSERT(!mPromise); }
already_AddRefed<PromiseType> Ensure(const char* aMethodName) {
if (mMonitor) {
mMonitor->AssertCurrentThreadOwns();
}
if (!mPromise) {
mPromise = new (typename PromiseType::Private)(aMethodName);
}
RefPtr<PromiseType> p = mPromise.get();
return p.forget();
}
// Provide a Monitor that should always be held when accessing this instance.
void SetMonitor(Monitor* aMonitor) { mMonitor = aMonitor; }
bool IsEmpty() const
{
if (mMonitor) {
mMonitor->AssertCurrentThreadOwns();
}
return !mPromise;
}
already_AddRefed<typename PromiseType::Private> Steal()
{
if (mMonitor) {
mMonitor->AssertCurrentThreadOwns();
}
return mPromise.forget();
}
void Resolve(const typename PromiseType::ResolveValueType& aResolveValue,
const char* aMethodName)
{
if (mMonitor) {
mMonitor->AssertCurrentThreadOwns();
}
MOZ_ASSERT(mPromise);
mPromise->Resolve(aResolveValue, aMethodName);
mPromise = nullptr;
}
void Resolve(typename PromiseType::ResolveValueType&& aResolveValue,
const char* aMethodName)
{
if (mMonitor) {
mMonitor->AssertCurrentThreadOwns();
}
MOZ_ASSERT(mPromise);
mPromise->Resolve(std::move(aResolveValue), aMethodName);
mPromise = nullptr;
}
void ResolveIfExists(const typename PromiseType::ResolveValueType& aResolveValue,
const char* aMethodName)
{
if (!IsEmpty()) {
Resolve(aResolveValue, aMethodName);
}
}
void ResolveIfExists(typename PromiseType::ResolveValueType&& aResolveValue,
const char* aMethodName)
{
if (!IsEmpty()) {
Resolve(std::move(aResolveValue), aMethodName);
}
}
void Reject(const typename PromiseType::RejectValueType& aRejectValue,
const char* aMethodName)
{
if (mMonitor) {
mMonitor->AssertCurrentThreadOwns();
}
MOZ_ASSERT(mPromise);
mPromise->Reject(aRejectValue, aMethodName);
mPromise = nullptr;
}
void Reject(typename PromiseType::RejectValueType&& aRejectValue,
const char* aMethodName)
{
if (mMonitor) {
mMonitor->AssertCurrentThreadOwns();
}
MOZ_ASSERT(mPromise);
mPromise->Reject(std::move(aRejectValue), aMethodName);
mPromise = nullptr;
}
void RejectIfExists(const typename PromiseType::RejectValueType& aRejectValue,
const char* aMethodName)
{
if (!IsEmpty()) {
Reject(aRejectValue, aMethodName);
}
}
void RejectIfExists(typename PromiseType::RejectValueType&& aRejectValue,
const char* aMethodName)
{
if (!IsEmpty()) {
Reject(std::move(aRejectValue), aMethodName);
}
}
private:
Monitor* mMonitor;
RefPtr<typename PromiseType::Private> mPromise;
};
/*
* Class to encapsulate a MozPromise::Request reference. Use this as the member
* variable for a class waiting on a MozPromise.
*/
template<typename PromiseType>
class MozPromiseRequestHolder
{
public:
MozPromiseRequestHolder() {}
~MozPromiseRequestHolder() { MOZ_ASSERT(!mRequest); }
void Track(already_AddRefed<typename PromiseType::Request> aRequest)
{
MOZ_DIAGNOSTIC_ASSERT(!Exists());
mRequest = aRequest;
}
void Complete()
{
MOZ_DIAGNOSTIC_ASSERT(Exists());
mRequest = nullptr;
}
// Disconnects and forgets an outstanding promise. The resolve/reject methods
// will never be called.
void Disconnect() {
MOZ_ASSERT(Exists());
mRequest->Disconnect();
mRequest = nullptr;
}
void DisconnectIfExists() {
if (Exists()) {
Disconnect();
}
}
bool Exists() const { return !!mRequest; }
private:
RefPtr<typename PromiseType::Request> mRequest;
};
// Asynchronous Potentially-Cross-Thread Method Calls.
//
// This machinery allows callers to schedule a promise-returning function
// (a method and object, or a function object like a lambda) to be invoked
// asynchronously on a given thread, while at the same time receiving a
// promise upon which to invoke Then() immediately. InvokeAsync dispatches a
// task to invoke the function on the proper thread and also chain the
// resulting promise to the one that the caller received, so that resolve/
// reject values are forwarded through.
namespace detail {
// Non-templated base class to allow us to use MOZ_COUNT_{C,D}TOR, which cause
// assertions when used on templated types.
class MethodCallBase
{
public:
MethodCallBase() { MOZ_COUNT_CTOR(MethodCallBase); }
virtual ~MethodCallBase() { MOZ_COUNT_DTOR(MethodCallBase); }
};
template<typename PromiseType, typename MethodType, typename ThisType,
typename... Storages>
class MethodCall : public MethodCallBase
{
public:
template<typename... Args>
MethodCall(MethodType aMethod, ThisType* aThisVal, Args&&... aArgs)
: mMethod(aMethod)
, mThisVal(aThisVal)
, mArgs(std::forward<Args>(aArgs)...)
{
static_assert(sizeof...(Storages) == sizeof...(Args), "Storages and Args should have equal sizes");
}
RefPtr<PromiseType> Invoke()
{
return mArgs.apply(mThisVal.get(), mMethod);
}
private:
MethodType mMethod;
RefPtr<ThisType> mThisVal;
RunnableMethodArguments<Storages...> mArgs;
};
template<typename PromiseType, typename MethodType, typename ThisType,
typename... Storages>
class ProxyRunnable : public CancelableRunnable
{
public:
ProxyRunnable(
typename PromiseType::Private* aProxyPromise,
MethodCall<PromiseType, MethodType, ThisType, Storages...>* aMethodCall)
: CancelableRunnable("detail::ProxyRunnable")
, mProxyPromise(aProxyPromise)
, mMethodCall(aMethodCall)
{
}
NS_IMETHOD Run() override
{
RefPtr<PromiseType> p = mMethodCall->Invoke();
mMethodCall = nullptr;
p->ChainTo(mProxyPromise.forget(), "<Proxy Promise>");
return NS_OK;
}
nsresult Cancel() override
{
return Run();
}
private:
RefPtr<typename PromiseType::Private> mProxyPromise;
nsAutoPtr<MethodCall<PromiseType, MethodType, ThisType, Storages...>> mMethodCall;
};
template<typename... Storages,
typename PromiseType, typename ThisType, typename... ArgTypes,
typename... ActualArgTypes>
static RefPtr<PromiseType>
InvokeAsyncImpl(nsISerialEventTarget* aTarget, ThisType* aThisVal,
const char* aCallerName,
RefPtr<PromiseType>(ThisType::*aMethod)(ArgTypes...),
ActualArgTypes&&... aArgs)
{
MOZ_ASSERT(aTarget);
typedef RefPtr<PromiseType>(ThisType::*MethodType)(ArgTypes...);
typedef detail::MethodCall<PromiseType, MethodType, ThisType, Storages...> MethodCallType;
typedef detail::ProxyRunnable<PromiseType, MethodType, ThisType, Storages...> ProxyRunnableType;
MethodCallType* methodCall =
new MethodCallType(aMethod, aThisVal, std::forward<ActualArgTypes>(aArgs)...);
RefPtr<typename PromiseType::Private> p = new (typename PromiseType::Private)(aCallerName);
RefPtr<ProxyRunnableType> r = new ProxyRunnableType(p, methodCall);
aTarget->Dispatch(r.forget());
return p.forget();
}
constexpr bool Any()
{
return false;
}
template <typename T1>
constexpr bool Any(T1 a)
{
return static_cast<bool>(a);
}
template <typename T1, typename... Ts>
constexpr bool Any(T1 a, Ts... aOthers)
{
return a || Any(aOthers...);
}
} // namespace detail
// InvokeAsync with explicitly-specified storages.
// See ParameterStorage in nsThreadUtils.h for help.
template<typename... Storages,
typename PromiseType, typename ThisType, typename... ArgTypes,
typename... ActualArgTypes,
typename EnableIf<sizeof...(Storages) != 0, int>::Type = 0>
static RefPtr<PromiseType>
InvokeAsync(nsISerialEventTarget* aTarget, ThisType* aThisVal, const char* aCallerName,
RefPtr<PromiseType>(ThisType::*aMethod)(ArgTypes...),
ActualArgTypes&&... aArgs)
{
static_assert(sizeof...(Storages) == sizeof...(ArgTypes),
"Provided Storages and method's ArgTypes should have equal sizes");
static_assert(sizeof...(Storages) == sizeof...(ActualArgTypes),
"Provided Storages and ActualArgTypes should have equal sizes");
return detail::InvokeAsyncImpl<Storages...>(
aTarget, aThisVal, aCallerName, aMethod,
std::forward<ActualArgTypes>(aArgs)...);
}
// InvokeAsync with no explicitly-specified storages, will copy arguments and
// then move them out of the runnable into the target method parameters.
template<typename... Storages,
typename PromiseType, typename ThisType, typename... ArgTypes,
typename... ActualArgTypes,
typename EnableIf<sizeof...(Storages) == 0, int>::Type = 0>
static RefPtr<PromiseType>
InvokeAsync(nsISerialEventTarget* aTarget, ThisType* aThisVal, const char* aCallerName,
RefPtr<PromiseType>(ThisType::*aMethod)(ArgTypes...),
ActualArgTypes&&... aArgs)
{
static_assert(!detail::Any(IsPointer<typename RemoveReference<ActualArgTypes>::Type>::value...),
"Cannot pass pointer types through InvokeAsync, Storages must be provided");
static_assert(sizeof...(ArgTypes) == sizeof...(ActualArgTypes),
"Method's ArgTypes and ActualArgTypes should have equal sizes");
return detail::InvokeAsyncImpl<StoreCopyPassByRRef<typename Decay<ActualArgTypes>::Type>...>(
aTarget, aThisVal, aCallerName, aMethod,
std::forward<ActualArgTypes>(aArgs)...);
}
namespace detail {
template<typename Function, typename PromiseType>
class ProxyFunctionRunnable : public CancelableRunnable
{
typedef typename Decay<Function>::Type FunctionStorage;
public:
template<typename F>
ProxyFunctionRunnable(typename PromiseType::Private* aProxyPromise,
F&& aFunction)
: CancelableRunnable("detail::ProxyFunctionRunnable")
, mProxyPromise(aProxyPromise)
, mFunction(new FunctionStorage(std::forward<F>(aFunction)))
{
}
NS_IMETHOD Run() override
{
RefPtr<PromiseType> p = (*mFunction)();
mFunction = nullptr;
p->ChainTo(mProxyPromise.forget(), "<Proxy Promise>");
return NS_OK;
}
nsresult Cancel() override
{
return Run();
}
private:
RefPtr<typename PromiseType::Private> mProxyPromise;
UniquePtr<FunctionStorage> mFunction;
};
// Note: The following struct and function are not for public consumption (yet?)
// as we would prefer all calls to pass on-the-spot lambdas (or at least moved
// function objects). They could be moved outside of detail if really needed.
// We prefer getting function objects by non-lvalue-ref (to avoid copying them
// and their captures). This struct is a tag that allows the use of objects
// through lvalue-refs where necessary.
struct AllowInvokeAsyncFunctionLVRef {};
// Invoke a function object (e.g., lambda or std/mozilla::function)
// asynchronously; note that the object will be copied if provided by lvalue-ref.
// Return a promise that the function should eventually resolve or reject.
template<typename Function>
static auto
InvokeAsync(nsISerialEventTarget* aTarget, const char* aCallerName,
AllowInvokeAsyncFunctionLVRef, Function&& aFunction)
-> decltype(aFunction())
{
static_assert(IsRefcountedSmartPointer<decltype(aFunction())>::value
&& IsMozPromise<typename RemoveSmartPointer<
decltype(aFunction())>::Type>::value,
"Function object must return RefPtr<MozPromise>");
MOZ_ASSERT(aTarget);
typedef typename RemoveSmartPointer<decltype(aFunction())>::Type PromiseType;
typedef detail::ProxyFunctionRunnable<Function, PromiseType> ProxyRunnableType;
auto p = MakeRefPtr<typename PromiseType::Private>(aCallerName);
auto r = MakeRefPtr<ProxyRunnableType>(p, std::forward<Function>(aFunction));
aTarget->Dispatch(r.forget());
return p.forget();
}
} // namespace detail
// Invoke a function object (e.g., lambda) asynchronously.
// Return a promise that the function should eventually resolve or reject.
template<typename Function>
static auto
InvokeAsync(nsISerialEventTarget* aTarget, const char* aCallerName,
Function&& aFunction)
-> decltype(aFunction())
{
static_assert(!IsLvalueReference<Function>::value,
"Function object must not be passed by lvalue-ref (to avoid "
"unplanned copies); Consider move()ing the object.");
return detail::InvokeAsync(aTarget, aCallerName,
detail::AllowInvokeAsyncFunctionLVRef(),
std::forward<Function>(aFunction));
}
#undef PROMISE_LOG
#undef PROMISE_ASSERT
#undef PROMISE_DEBUG
} // namespace mozilla
#endif
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