path: root/js/src/builtin/Promise.h

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 * 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/. */

#ifndef builtin_Promise_h
#define builtin_Promise_h

#include "builtin/SelfHostingDefines.h"
#include "vm/NativeObject.h"

namespace js {

enum PromiseSlots {
    PromiseSlot_Flags = 0,
    PromiseSlot_ReactionsOrResult,
    PromiseSlot_RejectFunction,
    PromiseSlot_AwaitGenerator = PromiseSlot_RejectFunction,
    PromiseSlot_DebugInfo,
    PromiseSlots,
};

#define PROMISE_FLAG_RESOLVED  0x1
#define PROMISE_FLAG_FULFILLED 0x2
#define PROMISE_FLAG_HANDLED   0x4
#define PROMISE_FLAG_REPORTED  0x8
#define PROMISE_FLAG_DEFAULT_RESOLVING_FUNCTIONS 0x10
#define PROMISE_FLAG_ASYNC    0x20

class AutoSetNewObjectMetadata;

class PromiseObject : public NativeObject
{
  public:
    static const unsigned RESERVED_SLOTS = PromiseSlots;
    static const Class class_;
    static const Class protoClass_;
    static PromiseObject* create(JSContext* cx, HandleObject executor,
                                 HandleObject proto = nullptr, bool needsWrapping = false);

    static PromiseObject* createSkippingExecutor(JSContext* cx);

    static JSObject* unforgeableResolve(JSContext* cx, HandleValue value);
    static JSObject* unforgeableReject(JSContext* cx, HandleValue value);

    int32_t flags() {
        return getFixedSlot(PromiseSlot_Flags).toInt32();
    }
    JS::PromiseState state() {
        int32_t flags = this->flags();
        if (!(flags & PROMISE_FLAG_RESOLVED)) {
            MOZ_ASSERT(!(flags & PROMISE_FLAG_FULFILLED));
            return JS::PromiseState::Pending;
        }
        if (flags & PROMISE_FLAG_FULFILLED)
            return JS::PromiseState::Fulfilled;
        return JS::PromiseState::Rejected;
    }
    Value reactions() {
        MOZ_ASSERT(state() == JS::PromiseState::Pending);
        return getFixedSlot(PromiseSlot_ReactionsOrResult);
    }
    Value value()  {
        MOZ_ASSERT(state() == JS::PromiseState::Fulfilled);
        return getFixedSlot(PromiseSlot_ReactionsOrResult);
    }
    Value reason() {
        MOZ_ASSERT(state() == JS::PromiseState::Rejected);
        return getFixedSlot(PromiseSlot_ReactionsOrResult);
    }
    Value valueOrReason()  {
        MOZ_ASSERT(state() != JS::PromiseState::Pending);
        return getFixedSlot(PromiseSlot_ReactionsOrResult);
    }

    static MOZ_MUST_USE bool resolve(JSContext* cx, Handle<PromiseObject*> promise,
                                     HandleValue resolutionValue);
    static MOZ_MUST_USE bool reject(JSContext* cx, Handle<PromiseObject*> promise,
                                    HandleValue rejectionValue);

    static void onSettled(JSContext* cx, Handle<PromiseObject*> promise);

    double allocationTime();
    double resolutionTime();
    JSObject* allocationSite();
    JSObject* resolutionSite();
    double lifetime();
    double timeToResolution() {
        MOZ_ASSERT(state() != JS::PromiseState::Pending);
        return resolutionTime() - allocationTime();
    }
    MOZ_MUST_USE bool dependentPromises(JSContext* cx, MutableHandle<GCVector<Value>> values);
    uint64_t getID();
    bool isUnhandled() {
        MOZ_ASSERT(state() == JS::PromiseState::Rejected);
        return !(flags() & PROMISE_FLAG_HANDLED);
    }
    void markAsReported() {
        MOZ_ASSERT(isUnhandled());
        int32_t flags = getFixedSlot(PromiseSlot_Flags).toInt32();
        setFixedSlot(PromiseSlot_Flags, Int32Value(flags | PROMISE_FLAG_REPORTED));
    }
};

/**
 * Unforgeable version of the JS builtin Promise.all.
 *
 * Takes an AutoObjectVector of Promise objects and returns a promise that's
 * resolved with an array of resolution values when all those promises have
 * been resolved, or rejected with the rejection value of the first rejected
 * promise.
 *
 * Asserts that all objects in the `promises` vector are, maybe wrapped,
 * instances of `Promise` or a subclass of `Promise`.
 */
MOZ_MUST_USE JSObject*
GetWaitForAllPromise(JSContext* cx, const JS::AutoObjectVector& promises);

enum class CreateDependentPromise {
    Always,
    SkipIfCtorUnobservable,
    Never
};

/**
 * Enqueues resolve/reject reactions in the given Promise's reactions lists
 * as though calling the original value of Promise.prototype.then.
 *
 * If the `createDependent` flag is not set, no dependent Promise will be
 * created. This is used internally to implement DOM functionality.
 * Note: In this case, the reactions pushed using this function contain a
 * `promise` field that can contain null. That field is only ever used by
 * devtools, which have to treat these reactions specially.
 */
MOZ_MUST_USE bool
OriginalPromiseThen(JSContext* cx, Handle<PromiseObject*> promise,
                    HandleValue onFulfilled, HandleValue onRejected,
                    MutableHandleObject dependent, CreateDependentPromise createDependent);

/**
 * PromiseResolve ( C, x )
 *
 * The abstract operation PromiseResolve, given a constructor and a value,
 * returns a new promise resolved with that value.
 */
MOZ_MUST_USE JSObject*
PromiseResolve(JSContext* cx, HandleObject constructor, HandleValue value);

MOZ_MUST_USE bool
RejectPromiseWithPendingError(JSContext* cx, Handle<PromiseObject*> promise);

MOZ_MUST_USE PromiseObject*
CreatePromiseObjectForAsync(JSContext* cx, HandleValue generatorVal);

MOZ_MUST_USE bool
IsPromiseForAsync(JSObject* promise);

MOZ_MUST_USE bool
AsyncFunctionReturned(JSContext* cx, Handle<PromiseObject*> resultPromise, HandleValue value);

MOZ_MUST_USE bool
AsyncFunctionThrown(JSContext* cx, Handle<PromiseObject*> resultPromise);

MOZ_MUST_USE bool
AsyncFunctionAwait(JSContext* cx, Handle<PromiseObject*> resultPromise, HandleValue value);

class AsyncGeneratorObject;

MOZ_MUST_USE bool
AsyncGeneratorAwait(JSContext* cx, Handle<AsyncGeneratorObject*> asyncGenObj, HandleValue value);

MOZ_MUST_USE bool
AsyncGeneratorResolve(JSContext* cx, Handle<AsyncGeneratorObject*> asyncGenObj,
                      HandleValue value, bool done);

MOZ_MUST_USE bool
AsyncGeneratorReject(JSContext* cx, Handle<AsyncGeneratorObject*> asyncGenObj,
                     HandleValue exception);

MOZ_MUST_USE bool
AsyncGeneratorEnqueue(JSContext* cx, HandleValue asyncGenVal, CompletionKind completionKind,
                      HandleValue completionValue, MutableHandleValue result);

bool
AsyncFromSyncIteratorMethod(JSContext* cx, CallArgs& args, CompletionKind completionKind);

class MOZ_NON_TEMPORARY_CLASS PromiseLookup final
{
    /*
     * A PromiseLookup holds the following:
     *
     *  Promise's shape (promiseConstructorShape_)
     *       To ensure that Promise has not been modified.
     *
     *  Promise.prototype's shape (promiseProtoShape_)
     *      To ensure that Promise.prototype has not been modified.
     *
     *  Promise's shape for the @@species getter. (promiseSpeciesShape_)
     *      To quickly retrieve the @@species getter for Promise.
     *
     *  Promise's slot number for resolve (promiseResolveSlot_)
     *      To quickly retrieve the Promise.resolve function.
     *
     *  Promise.prototype's slot number for constructor (promiseProtoConstructorSlot_)
     *      To quickly retrieve the Promise.prototype.constructor property.
     *
     *  Promise.prototype's slot number for then (promiseProtoThenSlot_)
     *      To quickly retrieve the Promise.prototype.then function.
     *
     * MOZ_INIT_OUTSIDE_CTOR fields below are set in |initialize()|.  The
     * constructor only initializes a |state_| field, that defines whether the
     * other fields are accessible.
     */

    // Shape of matching Promise object.
    MOZ_INIT_OUTSIDE_CTOR Shape* promiseConstructorShape_;

#ifdef DEBUG
    // Accessor Shape containing the @@species property.
    // See isPromiseStateStillSane() for why this field is debug-only.
    MOZ_INIT_OUTSIDE_CTOR Shape* promiseSpeciesShape_;
#endif

    // Shape of matching Promise.prototype object.
    MOZ_INIT_OUTSIDE_CTOR Shape* promiseProtoShape_;

    // Slots Promise.resolve, Promise.prototype.constructor, and
    // Promise.prototype.then.
    MOZ_INIT_OUTSIDE_CTOR uint32_t promiseResolveSlot_;
    MOZ_INIT_OUTSIDE_CTOR uint32_t promiseProtoConstructorSlot_;
    MOZ_INIT_OUTSIDE_CTOR uint32_t promiseProtoThenSlot_;

    enum class State : uint8_t {
        // Flags marking the lazy initialization of the above fields.
        Uninitialized,
        Initialized,

        // The disabled flag is set when we don't want to try optimizing
        // anymore because core objects were changed.
        Disabled
    };

    State state_ = State::Uninitialized;

    // Initialize the internal fields.
    //
    // The cache is successfully initialized iff
    // 1. Promise and Promise.prototype classes are initialized.
    // 2. Promise.prototype.constructor is equal to Promise.
    // 3. Promise.prototype.then is the original `then` function.
    // 4. Promise[@@species] is the original @@species getter.
    // 5. Promise.resolve is the original `resolve` function.
    void initialize(JSContext* cx);

    // Reset the cache.
    void reset();

    // Check if the global promise-related objects have not been messed with
    // in a way that would disable this cache.
    bool isPromiseStateStillSane(JSContext* cx);

    // Flags to control whether or not ensureInitialized() is allowed to
    // reinitialize the cache when the Promise state is no longer sane.
    enum class Reinitialize : bool {
        Allowed,
        Disallowed
    };

    // Return true if the lookup cache is properly initialized for usage.
    bool ensureInitialized(JSContext* cx, Reinitialize reinitialize);

    // Return true if the prototype of the given Promise object is
    // Promise.prototype and the object doesn't shadow properties from
    // Promise.prototype.
    bool hasDefaultProtoAndNoShadowedProperties(JSContext* cx, PromiseObject* promise);

    // Return true if the given Promise object uses the default @@species,
    // "constructor", and "then" properties.
    bool isDefaultInstance(JSContext* cx, PromiseObject* promise, Reinitialize reinitialize);

    // Return the built-in Promise constructor or null if not yet initialized.
    static JSFunction* getPromiseConstructor(JSContext* cx);

    // Return the built-in Promise prototype or null if not yet initialized.
    static NativeObject* getPromisePrototype(JSContext* cx);

    // Return true if the slot contains the given native.
    static bool isDataPropertyNative(JSContext* cx, NativeObject* obj, uint32_t slot,
                                     JSNative native);

    // Return true if the accessor shape contains the given native.
    static bool isAccessorPropertyNative(JSContext* cx, Shape* shape, JSNative native);

  public:
    /** Construct a |PromiseSpeciesLookup| in the uninitialized state. */
    PromiseLookup() {
        reset();
    }

    // Return true if the Promise constructor and Promise.prototype still use
    // the default built-in functions.
    bool isDefaultPromiseState(JSContext* cx);

    // Return true if the given Promise object uses the default @@species,
    // "constructor", and "then" properties.
    bool isDefaultInstance(JSContext* cx, PromiseObject* promise) {
        return isDefaultInstance(cx, promise, Reinitialize::Allowed);
    }

    // Return true if the given Promise object uses the default @@species,
    // "constructor", and "then" properties.
    bool isDefaultInstanceWhenPromiseStateIsSane(JSContext* cx, PromiseObject* promise) {
        return isDefaultInstance(cx, promise, Reinitialize::Disallowed);
    }

    // Purge the cache and all info associated with it.
    void purge() {
        if (state_ == State::Initialized)
            reset();
    }
};

/**
 * A PromiseTask represents a task that can be dispatched to a helper thread
 * (via StartPromiseTask), executed (by implementing PromiseTask::execute()),
 * and then resolved back on the original JSContext owner thread.
 * Because it contains a PersistentRooted, a PromiseTask will only be destroyed
 * on the JSContext's owner thread.
 */
class PromiseTask : public JS::AsyncTask
{
    JSRuntime* runtime_;
    PersistentRooted<PromiseObject*> promise_;

    // PromiseTask implements JS::AsyncTask and prevents derived classes from
    // overriding; derived classes should implement the new pure virtual
    // functions introduced below. Both of these methods 'delete this'.
    void finish(JSContext* cx) override final;
    void cancel(JSContext* cx) override final;

  protected:
    // Called by PromiseTask on the JSContext's owner thread after execute()
    // completes on the helper thread, assuming JS::FinishAsyncTaskCallback
    // succeeds. After this method returns, the task will be deleted.
    virtual bool finishPromise(JSContext* cx, Handle<PromiseObject*> promise) = 0;

  public:
    PromiseTask(JSContext* cx, Handle<PromiseObject*> promise);
    ~PromiseTask();
    JSRuntime* runtime() const { return runtime_; }

    // Called on a helper thread after StartAsyncTask. After execute()
    // completes, the JS::FinishAsyncTaskCallback will be called. If this fails
    // the task will be enqueued for deletion at some future point without ever
    // calling finishPromise().
    virtual void execute() = 0;

    // May be called in the absence of helper threads to synchronously execute
    // and finish a PromiseTask.
    bool executeAndFinish(JSContext* cx);
};

} // namespace js

#endif /* builtin_Promise_h */