gecko-dev/xpcom/threads/MozPromise.h

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C++

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim:set ts=2 sw=2 sts=2 et cindent: */
/* 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/AbstractThread.h"
#include "mozilla/IndexSequence.h"
#include "mozilla/Logging.h"
#include "mozilla/Maybe.h"
#include "mozilla/Mutex.h"
#include "mozilla/Monitor.h"
#include "mozilla/Tuple.h"
#include "nsTArray.h"
#include "nsThreadUtils.h"
namespace mozilla {
extern LazyLogModule gMozPromiseLog;
#define PROMISE_LOG(x, ...) \
MOZ_LOG(gMozPromiseLog, mozilla::LogLevel::Debug, (x, ##__VA_ARGS__))
namespace detail {
template<typename ThisType, typename Ret, typename ArgType>
static TrueType TakesArgumentHelper(Ret (ThisType::*)(ArgType));
template<typename ThisType, typename Ret, typename ArgType>
static TrueType TakesArgumentHelper(Ret (ThisType::*)(ArgType) const);
template<typename ThisType, typename Ret>
static FalseType TakesArgumentHelper(Ret (ThisType::*)());
template<typename ThisType, typename Ret>
static FalseType TakesArgumentHelper(Ret (ThisType::*)() const);
template<typename ThisType, typename Ret, typename ArgType>
static Ret ReturnTypeHelper(Ret (ThisType::*)(ArgType));
template<typename ThisType, typename Ret, typename ArgType>
static Ret ReturnTypeHelper(Ret (ThisType::*)(ArgType) const);
template<typename ThisType, typename Ret>
static Ret ReturnTypeHelper(Ret (ThisType::*)());
template<typename ThisType, typename Ret>
static Ret ReturnTypeHelper(Ret (ThisType::*)() const);
template<typename MethodType>
struct ReturnType {
typedef decltype(detail::ReturnTypeHelper(DeclVal<MethodType>())) Type;
};
} // namespace detail
template<typename MethodType>
struct TakesArgument {
static const bool value = decltype(detail::TakesArgumentHelper(DeclVal<MethodType>()))::value;
};
template<typename MethodType, typename TargetType>
struct ReturnTypeIs {
static const bool value = IsConvertible<typename detail::ReturnType<MethodType>::Type, TargetType>::value;
};
/*
* 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 MozPromise::Request.
* The Request object serves several purposes for the consumer.
*
* (1) 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) It provides access to a "Completion Promise", which is roughly analagous
* to the Promise returned directly by ->then() calls on JS promises. 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() {}
};
template<typename T> class MozPromiseHolder;
template<typename ResolveValueT, typename RejectValueT, bool IsExclusive>
class MozPromise : public MozPromiseRefcountable
{
public:
typedef ResolveValueT ResolveValueType;
typedef RejectValueT RejectValueType;
class ResolveOrRejectValue
{
public:
template<typename ResolveValueType_>
void SetResolve(ResolveValueType_&& aResolveValue)
{
MOZ_ASSERT(IsNothing());
mResolveValue.emplace(Forward<ResolveValueType_>(aResolveValue));
}
template<typename RejectValueType_>
void SetReject(RejectValueType_&& aRejectValue)
{
MOZ_ASSERT(IsNothing());
mRejectValue.emplace(Forward<RejectValueType_>(aRejectValue));
}
template<typename ResolveValueType_>
static ResolveOrRejectValue MakeResolve(ResolveValueType_&& aResolveValue)
{
ResolveOrRejectValue val;
val.SetResolve(Forward<ResolveValueType_>(aResolveValue));
return val;
}
template<typename RejectValueType_>
static ResolveOrRejectValue MakeReject(RejectValueType_&& aRejectValue)
{
ResolveOrRejectValue val;
val.SetReject(Forward<RejectValueType_>(aRejectValue));
return val;
}
bool IsResolve() const { return mResolveValue.isSome(); }
bool IsReject() const { return mRejectValue.isSome(); }
bool IsNothing() const { return mResolveValue.isNothing() && mRejectValue.isNothing(); }
const ResolveValueType& ResolveValue() const { return mResolveValue.ref(); }
const RejectValueType& RejectValue() const { return mRejectValue.ref(); }
private:
Maybe<ResolveValueType> mResolveValue;
Maybe<RejectValueType> mRejectValue;
};
protected:
// MozPromise is the public type, and never constructed directly. Construct
// a MozPromise::Private, defined below.
explicit MozPromise(const char* aCreationSite)
: mCreationSite(aCreationSite)
, mMutex("MozPromise Mutex")
, mHaveRequest(false)
{
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(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(Forward<RejectValueType_>(aRejectValue), aRejectSite);
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)
{
mResolveValues.SetLength(aDependentPromises);
}
void Resolve(size_t aIndex, const ResolveValueType& aResolveValue)
{
if (!mPromise) {
// Already rejected.
return;
}
mResolveValues[aIndex].emplace(aResolveValue);
if (--mOutstandingPromises == 0) {
nsTArray<ResolveValueType> resolveValues;
resolveValues.SetCapacity(mResolveValues.Length());
for (size_t i = 0; i < mResolveValues.Length(); ++i) {
resolveValues.AppendElement(mResolveValues[i].ref());
}
mPromise->Resolve(resolveValues, __func__);
mPromise = nullptr;
mResolveValues.Clear();
}
}
void Reject(const RejectValueType& aRejectValue)
{
if (!mPromise) {
// Already rejected.
return;
}
mPromise->Reject(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(AbstractThread* aProcessingThread, nsTArray<RefPtr<MozPromise>>& aPromises)
{
RefPtr<AllPromiseHolder> holder = new AllPromiseHolder(aPromises.Length());
for (size_t i = 0; i < aPromises.Length(); ++i) {
aPromises[i]->Then(aProcessingThread, __func__,
[holder, i] (ResolveValueType aResolveValue) -> void { holder->Resolve(i, aResolveValue); },
[holder] (RejectValueType aRejectValue) -> void { holder->Reject(aRejectValue); }
);
}
return holder->Promise();
}
class Request : public MozPromiseRefcountable
{
public:
virtual void Disconnect() = 0;
// MSVC complains when an inner class (ThenValueBase::{Resolve,Reject}Runnable)
// tries to access an inherited protected member.
bool IsDisconnected() const { return mDisconnected; }
virtual MozPromise* CompletionPromise() = 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
{
public:
class ResolveOrRejectRunnable : public nsRunnable
{
public:
ResolveOrRejectRunnable(ThenValueBase* aThenValue, MozPromise* aPromise)
: mThenValue(aThenValue)
, mPromise(aPromise)
{
MOZ_DIAGNOSTIC_ASSERT(!mPromise->IsPending());
}
~ResolveOrRejectRunnable()
{
MOZ_DIAGNOSTIC_ASSERT(!mThenValue || mThenValue->IsDisconnected());
}
NS_IMETHODIMP Run()
{
PROMISE_LOG("ResolveOrRejectRunnable::Run() [this=%p]", this);
mThenValue->DoResolveOrReject(mPromise->Value());
mThenValue = nullptr;
mPromise = nullptr;
return NS_OK;
}
private:
RefPtr<ThenValueBase> mThenValue;
RefPtr<MozPromise> mPromise;
};
explicit ThenValueBase(AbstractThread* aResponseTarget, const char* aCallSite)
: mResponseTarget(aResponseTarget), mCallSite(aCallSite) {}
MozPromise* CompletionPromise() override
{
MOZ_DIAGNOSTIC_ASSERT(mResponseTarget->IsCurrentThreadIn());
MOZ_DIAGNOSTIC_ASSERT(!Request::mComplete);
if (!mCompletionPromise) {
mCompletionPromise = new MozPromise::Private("<completion promise>");
}
return mCompletionPromise;
}
void Dispatch(MozPromise *aPromise)
{
aPromise->mMutex.AssertCurrentThreadOwns();
MOZ_ASSERT(!aPromise->IsPending());
RefPtr<nsRunnable> runnable =
static_cast<nsRunnable*>(new (typename ThenValueBase::ResolveOrRejectRunnable)(this, aPromise));
PROMISE_LOG("%s Then() call made from %s [Runnable=%p, Promise=%p, ThenValue=%p]",
aPromise->mValue.IsResolve() ? "Resolving" : "Rejecting", ThenValueBase::mCallSite,
runnable.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(runnable.forget(), AbstractThread::DontAssertDispatchSuccess);
}
virtual void Disconnect() override
{
MOZ_ASSERT(ThenValueBase::mResponseTarget->IsCurrentThreadIn());
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(!mCompletionPromise);
}
protected:
virtual already_AddRefed<MozPromise> DoResolveOrRejectInternal(const ResolveOrRejectValue& aValue) = 0;
void DoResolveOrReject(const ResolveOrRejectValue& aValue)
{
Request::mComplete = true;
if (Request::mDisconnected) {
PROMISE_LOG("ThenValue::DoResolveOrReject disconnected - bailing out [this=%p]", this);
return;
}
// Invoke the resolve or reject method.
RefPtr<MozPromise> p = DoResolveOrRejectInternal(aValue);
// If there's a completion promise, resolve it appropriately with the
// result of the method.
//
// We jump through some hoops to cast to MozPromise::Private here. This
// can go away when we can just declare mCompletionPromise as
// MozPromise::Private. See the declaration below.
RefPtr<MozPromise::Private> completionPromise =
dont_AddRef(static_cast<MozPromise::Private*>(mCompletionPromise.forget().take()));
if (completionPromise) {
if (p) {
p->ChainTo(completionPromise.forget(), "<chained completion promise>");
} else {
completionPromise->ResolveOrReject(aValue, "<completion of non-promise-returning method>");
}
}
}
RefPtr<AbstractThread> mResponseTarget; // May be released on any thread.
// Declaring RefPtr<MozPromise::Private> here causes build failures
// on MSVC because MozPromise::Private is only forward-declared at this
// point. This hack can go away when we inline-declare MozPromise::Private,
// which is blocked on the B2G ICS compiler being too old.
RefPtr<MozPromise> mCompletionPromise;
const char* mCallSite;
};
/*
* 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<ReturnTypeIs<MethodType, RefPtr<MozPromise>>::value &&
TakesArgument<MethodType>::value,
already_AddRefed<MozPromise>>::Type
InvokeCallbackMethod(ThisType* aThisVal, MethodType aMethod, ValueType&& aValue)
{
return ((*aThisVal).*aMethod)(Forward<ValueType>(aValue)).forget();
}
template<typename ThisType, typename MethodType, typename ValueType>
static typename EnableIf<ReturnTypeIs<MethodType, void>::value &&
TakesArgument<MethodType>::value,
already_AddRefed<MozPromise>>::Type
InvokeCallbackMethod(ThisType* aThisVal, MethodType aMethod, ValueType&& aValue)
{
((*aThisVal).*aMethod)(Forward<ValueType>(aValue));
return nullptr;
}
template<typename ThisType, typename MethodType, typename ValueType>
static typename EnableIf<ReturnTypeIs<MethodType, RefPtr<MozPromise>>::value &&
!TakesArgument<MethodType>::value,
already_AddRefed<MozPromise>>::Type
InvokeCallbackMethod(ThisType* aThisVal, MethodType aMethod, ValueType&& aValue)
{
return ((*aThisVal).*aMethod)().forget();
}
template<typename ThisType, typename MethodType, typename ValueType>
static typename EnableIf<ReturnTypeIs<MethodType, void>::value &&
!TakesArgument<MethodType>::value,
already_AddRefed<MozPromise>>::Type
InvokeCallbackMethod(ThisType* aThisVal, MethodType aMethod, ValueType&& aValue)
{
((*aThisVal).*aMethod)();
return nullptr;
}
template<typename ThisType, typename ResolveMethodType, typename RejectMethodType>
class MethodThenValue : public ThenValueBase
{
public:
MethodThenValue(AbstractThread* aResponseTarget, ThisType* aThisVal,
ResolveMethodType aResolveMethod, RejectMethodType aRejectMethod,
const char* aCallSite)
: ThenValueBase(aResponseTarget, aCallSite)
, mThisVal(aThisVal)
, mResolveMethod(aResolveMethod)
, mRejectMethod(aRejectMethod) {}
virtual 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:
virtual already_AddRefed<MozPromise> DoResolveOrRejectInternal(const ResolveOrRejectValue& aValue) override
{
RefPtr<MozPromise> completion;
if (aValue.IsResolve()) {
completion = InvokeCallbackMethod(mThisVal.get(), mResolveMethod, aValue.ResolveValue());
} else {
completion = InvokeCallbackMethod(mThisVal.get(), mRejectMethod, aValue.RejectValue());
}
// 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;
return completion.forget();
}
private:
RefPtr<ThisType> mThisVal; // Only accessed and refcounted on dispatch thread.
ResolveMethodType mResolveMethod;
RejectMethodType mRejectMethod;
};
// NB: We could use std::function here instead of a template if it were supported. :-(
template<typename ResolveFunction, typename RejectFunction>
class FunctionThenValue : public ThenValueBase
{
public:
FunctionThenValue(AbstractThread* aResponseTarget,
ResolveFunction&& aResolveFunction,
RejectFunction&& aRejectFunction,
const char* aCallSite)
: ThenValueBase(aResponseTarget, aCallSite)
{
mResolveFunction.emplace(Move(aResolveFunction));
mRejectFunction.emplace(Move(aRejectFunction));
}
virtual 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:
virtual already_AddRefed<MozPromise> DoResolveOrRejectInternal(const 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.
RefPtr<MozPromise> completion;
if (aValue.IsResolve()) {
completion = InvokeCallbackMethod(mResolveFunction.ptr(), &ResolveFunction::operator(), aValue.ResolveValue());
} else {
completion = InvokeCallbackMethod(mRejectFunction.ptr(), &RejectFunction::operator(), aValue.RejectValue());
}
// 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();
return completion.forget();
}
private:
Maybe<ResolveFunction> mResolveFunction; // Only accessed and deleted on dispatch thread.
Maybe<RejectFunction> mRejectFunction; // Only accessed and deleted on dispatch thread.
};
public:
void ThenInternal(AbstractThread* aResponseThread, ThenValueBase* aThenValue,
const char* aCallSite)
{
MutexAutoLock lock(mMutex);
MOZ_ASSERT(aResponseThread->IsDispatchReliable());
MOZ_DIAGNOSTIC_ASSERT(!IsExclusive || !mHaveRequest);
mHaveRequest = true;
PROMISE_LOG("%s invoking Then() [this=%p, aThenValue=%p, isPending=%d]",
aCallSite, this, aThenValue, (int) IsPending());
if (!IsPending()) {
aThenValue->Dispatch(this);
} else {
mThenValues.AppendElement(aThenValue);
}
}
public:
template<typename ThisType, typename ResolveMethodType, typename RejectMethodType>
RefPtr<Request> Then(AbstractThread* aResponseThread, const char* aCallSite, ThisType* aThisVal,
ResolveMethodType aResolveMethod, RejectMethodType aRejectMethod)
{
RefPtr<ThenValueBase> thenValue = new MethodThenValue<ThisType, ResolveMethodType, RejectMethodType>(
aResponseThread, aThisVal, aResolveMethod, aRejectMethod, aCallSite);
ThenInternal(aResponseThread, thenValue, aCallSite);
return thenValue.forget(); // Implicit conversion from already_AddRefed<ThenValueBase> to RefPtr<Request>.
}
template<typename ResolveFunction, typename RejectFunction>
RefPtr<Request> Then(AbstractThread* aResponseThread, const char* aCallSite,
ResolveFunction&& aResolveFunction, RejectFunction&& aRejectFunction)
{
RefPtr<ThenValueBase> thenValue = new FunctionThenValue<ResolveFunction, RejectFunction>(aResponseThread,
Move(aResolveFunction), Move(aRejectFunction), aCallSite);
ThenInternal(aResponseThread, thenValue, aCallSite);
return thenValue.forget(); // Implicit conversion from already_AddRefed<ThenValueBase> to RefPtr<Request>.
}
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);
}
}
protected:
bool IsPending() const { return mValue.IsNothing(); }
const ResolveOrRejectValue& Value() const
{
// 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 (size_t i = 0; i < mThenValues.Length(); ++i) {
mThenValues[i]->Dispatch(this);
}
mThenValues.Clear();
for (size_t i = 0; i < mChainedPromises.Length(); ++i) {
ForwardTo(mChainedPromises[i]);
}
mChainedPromises.Clear();
}
void ForwardTo(Private* aOther)
{
MOZ_ASSERT(!IsPending());
if (mValue.IsResolve()) {
aOther->Resolve(mValue.ResolveValue(), "<chained promise>");
} else {
aOther->Reject(mValue.RejectValue(), "<chained promise>");
}
}
virtual ~MozPromise()
{
PROMISE_LOG("MozPromise::~MozPromise [this=%p]", this);
MOZ_ASSERT(!IsPending());
MOZ_ASSERT(mThenValues.IsEmpty());
MOZ_ASSERT(mChainedPromises.IsEmpty());
};
const char* mCreationSite; // For logging
Mutex mMutex;
ResolveOrRejectValue mValue;
nsTArray<RefPtr<ThenValueBase>> mThenValues;
nsTArray<RefPtr<Private>> mChainedPromises;
bool mHaveRequest;
};
template<typename ResolveValueT, typename RejectValueT, bool IsExclusive>
class MozPromise<ResolveValueT, RejectValueT, IsExclusive>::Private
: public MozPromise<ResolveValueT, RejectValueT, IsExclusive>
{
public:
explicit Private(const char* aCreationSite) : MozPromise(aCreationSite) {}
template<typename ResolveValueT_>
void Resolve(ResolveValueT_&& aResolveValue, const char* aResolveSite)
{
MutexAutoLock lock(mMutex);
MOZ_ASSERT(IsPending());
PROMISE_LOG("%s resolving MozPromise (%p created at %s)", aResolveSite, this, mCreationSite);
mValue.SetResolve(Forward<ResolveValueT_>(aResolveValue));
DispatchAll();
}
template<typename RejectValueT_>
void Reject(RejectValueT_&& aRejectValue, const char* aRejectSite)
{
MutexAutoLock lock(mMutex);
MOZ_ASSERT(IsPending());
PROMISE_LOG("%s rejecting MozPromise (%p created at %s)", aRejectSite, this, mCreationSite);
mValue.SetReject(Forward<RejectValueT_>(aRejectValue));
DispatchAll();
}
template<typename ResolveOrRejectValue_>
void ResolveOrReject(ResolveOrRejectValue_&& aValue, const char* aSite)
{
MutexAutoLock lock(mMutex);
MOZ_ASSERT(IsPending());
PROMISE_LOG("%s resolveOrRejecting MozPromise (%p created at %s)", aSite, this, mCreationSite);
mValue = 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) {}
// 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()
{
if (mMonitor) {
mMonitor->AssertCurrentThreadOwns();
}
return !mPromise;
}
already_AddRefed<typename PromiseType::Private> Steal()
{
if (mMonitor) {
mMonitor->AssertCurrentThreadOwns();
}
RefPtr<typename PromiseType::Private> p = mPromise;
mPromise = nullptr;
return p.forget();
}
void Resolve(typename PromiseType::ResolveValueType aResolveValue,
const char* aMethodName)
{
if (mMonitor) {
mMonitor->AssertCurrentThreadOwns();
}
MOZ_ASSERT(mPromise);
mPromise->Resolve(aResolveValue, aMethodName);
mPromise = nullptr;
}
void ResolveIfExists(typename PromiseType::ResolveValueType aResolveValue,
const char* aMethodName)
{
if (!IsEmpty()) {
Resolve(aResolveValue, aMethodName);
}
}
void Reject(typename PromiseType::RejectValueType aRejectValue,
const char* aMethodName)
{
if (mMonitor) {
mMonitor->AssertCurrentThreadOwns();
}
MOZ_ASSERT(mPromise);
mPromise->Reject(aRejectValue, aMethodName);
mPromise = nullptr;
}
void RejectIfExists(typename PromiseType::RejectValueType aRejectValue,
const char* aMethodName)
{
if (!IsEmpty()) {
Reject(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 Begin(RefPtr<typename PromiseType::Request>&& aRequest)
{
MOZ_DIAGNOSTIC_ASSERT(!Exists());
mRequest = Move(aRequest);
}
void Begin(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() { return !!mRequest; }
private:
RefPtr<typename PromiseType::Request> mRequest;
};
// Asynchronous Potentially-Cross-Thread Method Calls.
//
// This machinery allows callers to schedule a promise-returning method 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 method 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 {
template<typename ReturnType, typename ThisType, typename... ArgTypes, size_t... Indices>
ReturnType
MethodCallInvokeHelper(ReturnType(ThisType::*aMethod)(ArgTypes...), ThisType* aThisVal,
Tuple<ArgTypes...>& aArgs, IndexSequence<Indices...>)
{
return ((*aThisVal).*aMethod)(Get<Indices>(aArgs)...);
}
// 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 ThisType, typename... ArgTypes>
class MethodCall : public MethodCallBase
{
public:
typedef RefPtr<PromiseType>(ThisType::*MethodType)(ArgTypes...);
MethodCall(MethodType aMethod, ThisType* aThisVal, ArgTypes... aArgs)
: mMethod(aMethod)
, mThisVal(aThisVal)
, mArgs(Forward<ArgTypes>(aArgs)...)
{}
RefPtr<PromiseType> Invoke()
{
return MethodCallInvokeHelper(mMethod, mThisVal.get(), mArgs, typename IndexSequenceFor<ArgTypes...>::Type());
}
private:
MethodType mMethod;
RefPtr<ThisType> mThisVal;
Tuple<ArgTypes...> mArgs;
};
template<typename PromiseType, typename ThisType, typename ...ArgTypes>
class ProxyRunnable : public nsRunnable
{
public:
ProxyRunnable(typename PromiseType::Private* aProxyPromise, MethodCall<PromiseType, ThisType, ArgTypes...>* aMethodCall)
: mProxyPromise(aProxyPromise), mMethodCall(aMethodCall) {}
NS_IMETHODIMP Run()
{
RefPtr<PromiseType> p = mMethodCall->Invoke();
mMethodCall = nullptr;
p->ChainTo(mProxyPromise.forget(), "<Proxy Promise>");
return NS_OK;
}
private:
RefPtr<typename PromiseType::Private> mProxyPromise;
nsAutoPtr<MethodCall<PromiseType, ThisType, ArgTypes...>> mMethodCall;
};
} // namespace detail
template<typename PromiseType, typename ThisType, typename ...ArgTypes, typename ...ActualArgTypes>
static RefPtr<PromiseType>
InvokeAsync(AbstractThread* aTarget, ThisType* aThisVal, const char* aCallerName,
RefPtr<PromiseType>(ThisType::*aMethod)(ArgTypes...), ActualArgTypes&&... aArgs)
{
typedef detail::MethodCall<PromiseType, ThisType, ArgTypes...> MethodCallType;
typedef detail::ProxyRunnable<PromiseType, ThisType, ArgTypes...> ProxyRunnableType;
MethodCallType* methodCall = new MethodCallType(aMethod, aThisVal, Forward<ActualArgTypes>(aArgs)...);
RefPtr<typename PromiseType::Private> p = new (typename PromiseType::Private)(aCallerName);
RefPtr<ProxyRunnableType> r = new ProxyRunnableType(p, methodCall);
MOZ_ASSERT(aTarget->IsDispatchReliable());
aTarget->Dispatch(r.forget());
return p.forget();
}
#undef PROMISE_LOG
} // namespace mozilla
#endif