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// Copyright 2023 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "third_party/blink/renderer/core/dom/subscriber.h"
#include "base/containers/adapters.h"
#include "base/containers/contains.h"
#include "third_party/blink/public/mojom/use_counter/metrics/web_feature.mojom-blink.h"
#include "third_party/blink/renderer/bindings/core/v8/v8_observer.h"
#include "third_party/blink/renderer/bindings/core/v8/v8_observer_callback.h"
#include "third_party/blink/renderer/bindings/core/v8/v8_observer_complete_callback.h"
#include "third_party/blink/renderer/bindings/core/v8/v8_script_runner.h"
#include "third_party/blink/renderer/bindings/core/v8/v8_subscribe_options.h"
#include "third_party/blink/renderer/bindings/core/v8/v8_void_function.h"
#include "third_party/blink/renderer/core/dom/abort_controller.h"
#include "third_party/blink/renderer/core/dom/abort_signal.h"
#include "third_party/blink/renderer/core/dom/observable.h"
#include "third_party/blink/renderer/core/dom/observable_internal_observer.h"
#include "third_party/blink/renderer/core/execution_context/execution_context.h"
#include "third_party/blink/renderer/platform/instrumentation/use_counter.h"
namespace blink {
using PassKey = base::PassKey<Subscriber>;
class Subscriber::ConsumerAbortSubscriptionAlgorithm final
: public AbortSignal::Algorithm {
public:
explicit ConsumerAbortSubscriptionAlgorithm(
Subscriber& subscriber,
ObservableInternalObserver& associated_observer,
AbortSignal& signal,
ScriptState& script_state)
: subscriber_(subscriber),
associated_observer_(associated_observer),
signal_(signal),
script_state_(script_state) {
CHECK(script_state_->ContextIsValid());
}
~ConsumerAbortSubscriptionAlgorithm() override = default;
void Run() override {
subscriber_->ConsumerUnsubscribe(script_state_, associated_observer_,
signal_->reason(script_state_));
}
void Trace(Visitor* visitor) const override {
visitor->Trace(subscriber_);
visitor->Trace(associated_observer_);
visitor->Trace(signal_);
visitor->Trace(script_state_);
Algorithm::Trace(visitor);
}
private:
Member<Subscriber> subscriber_;
// This is the observer associated with the `signal_` that it subscribed to
// `subscriber_` with. `this` keeps both around so when the `signal_` gets
// aborted (i.e., `Run()` is called above) we can alert `subscriber_` as to
// which observer needs to be unregistered so that it doesn't receive values
// from the producer.
Member<ObservableInternalObserver> associated_observer_;
Member<AbortSignal> signal_;
Member<ScriptState> script_state_;
};
Subscriber::Subscriber(base::PassKey<Observable>,
ScriptState* script_state,
ObservableInternalObserver* internal_observer,
SubscribeOptions* options)
: ExecutionContextClient(ExecutionContext::From(script_state)),
subscription_controller_(AbortController::Create(script_state)) {
internal_observers_.push_back(internal_observer);
// If a downstream `AbortSignal` is provided, setup an instance of
// `ConsumerAbortSubscriptionAlgorithm` as one of its internal abort
// algorithms. It enables `this` to close the subscription that `this`
// represents in response to downstream aborts.
if (options->hasSignal()) {
AbortSignal* downstream_signal = options->signal();
if (downstream_signal->aborted()) {
internal_observers_.pop_back();
CloseSubscription(
script_state,
/*abort_reason=*/downstream_signal->reason(script_state));
} else {
// Add an abort algorithm to the consumer's signal. Keep the algorithm
// alive by associating it with the `internal_observer`.
consumer_abort_algorithms_.insert(
internal_observer,
downstream_signal->AddAlgorithm(
MakeGarbageCollected<ConsumerAbortSubscriptionAlgorithm>(
*this, *internal_observer, *downstream_signal,
*script_state)));
}
}
}
void Subscriber::next(ScriptValue value) {
if (!active_) {
return;
}
// Call `Next()` on all observers. Do this by iterating over a *copy* of the
// list of observers, because `Next()` can actually complete one of the
// observers' subscriptions, thus removing `observer` from
// `internal_observers_`. That means `internal_observers_` can be mutated
// throughout this process, and we cannot iterate over it while it is
// mutating.
HeapVector<Member<ObservableInternalObserver>> internal_observers =
internal_observers_;
for (auto& observer : internal_observers) {
observer->Next(value);
}
}
void Subscriber::complete(ScriptState* script_state) {
if (!active_) {
return;
}
// `CloseSubscription()` makes it impossible to invoke user-provided callbacks
// via `internal_observers_` anymore/re-entrantly, which is why we pull the
// `internal_observer` out before calling this.
CloseSubscription(script_state, /*abort_reason=*/std::nullopt);
// See the documentation in `Subscriber::next()`.
HeapVector<Member<ObservableInternalObserver>> internal_observers =
internal_observers_;
for (auto& observer : internal_observers) {
observer->Complete();
}
}
void Subscriber::error(ScriptState* script_state, ScriptValue error_value) {
if (!active_) {
// If `active_` is false, the subscription has already been closed by
// `CloseSubscription()`. In this case, if the observable is still producing
// errors, we must surface them to the global via "report the exception":
// https://html.spec.whatwg.org/C#report-the-exception.
//
// Reporting the exception requires a valid `ScriptState`, which we don't
// have if we're in a detached context. See observable-constructor.window.js
// for tests.
if (!script_state->ContextIsValid()) {
CHECK(!GetExecutionContext());
return;
}
ScriptState::Scope scope(script_state);
V8ScriptRunner::ReportException(script_state->GetIsolate(),
error_value.V8Value());
return;
}
// `CloseSubscription()` makes it impossible to invoke user-provided callbacks
// via `internal_observers_` anymore/re-entrantly, which is why we pull the
// `internal_observer` out before calling this.
CloseSubscription(script_state, error_value);
// See the documentation in `Subscriber::next()`.
HeapVector<Member<ObservableInternalObserver>> internal_observers =
internal_observers_;
for (auto& observer : internal_observers) {
observer->Error(script_state, error_value);
}
}
void Subscriber::addTeardown(V8VoidFunction* teardown) {
if (active_) {
teardown_callbacks_.push_back(teardown);
} else {
// If the subscription is inactive, invoke the teardown immediately, because
// if we just queue it to `teardown_callbacks_` it will never run!
teardown->InvokeAndReportException(nullptr);
}
}
AbortSignal* Subscriber::signal() const {
return subscription_controller_->signal();
}
void Subscriber::ConsumerUnsubscribe(
ScriptState* script_state,
ObservableInternalObserver* associated_observer,
std::optional<ScriptValue> abort_reason) {
// If the producer closes the subscription before any consumer abort signal
// algorithms attempt, the consumer abort signal algorithms can still fire,
// attempting to close the subscription. Do nothing if it's already closed.
if (!active_) {
return;
}
// Now that the abort algorithm has run, clear the
// `AbortSignal::AlgorithmHandle` associated with `associated_observer` that's
// keeping it alive.
DCHECK(base::Contains(consumer_abort_algorithms_, associated_observer));
consumer_abort_algorithms_.erase(associated_observer);
// Also remove `associated_observer` from `internal_observers_`, since it no
// longer cares about values `this` produces.
DCHECK(base::Contains(internal_observers_, associated_observer));
internal_observers_.erase(
std::ranges::find(internal_observers_, associated_observer));
if (internal_observers_.empty()) {
CloseSubscription(script_state, abort_reason);
}
}
void Subscriber::CloseSubscription(ScriptState* script_state,
std::optional<ScriptValue> abort_reason) {
// Guard against re-entrant invocation, which can happen during
// producer-initiated unsubscription. For example: `complete()` ->
// `CloseSubscription()` -> Run script (either by aborting an `AbortSignal` or
// running a teardown) -> Script aborts the downstream `AbortSignal` (the one
// passed in via `SubscribeOptions` in the constructor) -> the downstream
// signal's internal abort algorithm runs ->
// `Subscriber::ConsumerAbortSubscriptionAlgorithm::Run()` ->
// `CloseSubscription()`.
if (!active_) {
return;
}
// We no longer need to hold onto the consumer abort algorithms.
consumer_abort_algorithms_.clear();
// There are three things to do when the signal associated with a subscription
// gets aborted.
// 1. Mark the subscription as inactive. This only makes the web-exposed
// `Subscriber#active` false, and makes it impossible for `this` to emit
// any more values to downstream `Observer`-provided callbacks.
active_ = false;
// 2. Abort `subscription_controller_`. This actually does two things:
// (a) Immediately aborts any "upstream" subscriptions, i.e., any
// observables that the observable associated with `this` had
// subscribed to, if any exist.
// (2) Fires the abort event at `this`'s signal.
CHECK(!subscription_controller_->signal()->aborted());
if (abort_reason) {
subscription_controller_->abort(script_state, *abort_reason);
} else {
subscription_controller_->abort(script_state);
}
// 3. Run all teardown callbacks that were registered with
// `Subscriber#addTeardown()` in LIFO order, and then remove all of them.
//
// Note that since the subscription is now inactive, `teardown_callbacks_`
// cannot be modified anymore. If any of these callbacks below invoke
// `addTeardown()` with a *new* callback, it will be invoked synchronously
// instead of added to this vector.
for (Member<V8VoidFunction> teardown : base::Reversed(teardown_callbacks_)) {
teardown->InvokeAndReportException(nullptr);
}
teardown_callbacks_.clear();
}
void Subscriber::RegisterNewObserver(ScriptState* script_state,
ObservableInternalObserver* observer,
SubscribeOptions* options) {
// We can only hit this path if there is already at least one subscriber that
// forced the creation of `this` and subscribed via `this`'s constructor.
CHECK_GE(internal_observers_.size(), 1u);
internal_observers_.push_back(observer);
if (options->hasSignal()) {
AbortSignal* downstream_signal = options->signal();
if (downstream_signal->aborted()) {
internal_observers_.pop_back();
return;
}
ConsumerAbortSubscriptionAlgorithm* abort_algorithm =
MakeGarbageCollected<ConsumerAbortSubscriptionAlgorithm>(
*this, *observer, *downstream_signal, *script_state);
AbortSignal::AlgorithmHandle* maybe_close_algorithm_handle =
downstream_signal->AddAlgorithm(abort_algorithm);
consumer_abort_algorithms_.insert(observer, maybe_close_algorithm_handle);
}
}
void Subscriber::Trace(Visitor* visitor) const {
visitor->Trace(subscription_controller_);
visitor->Trace(consumer_abort_algorithms_);
visitor->Trace(teardown_callbacks_);
visitor->Trace(internal_observers_);
ScriptWrappable::Trace(visitor);
ExecutionContextClient::Trace(visitor);
}
} // namespace blink
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