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/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* 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 mozilla_PrintBackgroundTask_h_
#define mozilla_PrintBackgroundTask_h_
#include "mozilla/dom/Promise.h"
#include "mozilla/ErrorResult.h"
#include "mozilla/Telemetry.h"
#include <tuple>
#include <utility>
// A helper to resolve a DOM Promise with the result of a const method, executed
// in another thread.
//
// Once in the main thread, the caller can turn the result of the method into a
// JSValue by specializing ResolveOrReject.
namespace mozilla {
template <typename T, typename Result>
void ResolveOrReject(dom::Promise& aPromise, T&, Result& aResult) {
aPromise.MaybeResolve(std::forward<Result>(aResult));
}
template <typename T, typename Result, typename... Args>
using PrintBackgroundTask = Result (T::*)(Args...) const;
template <typename T, typename Result, typename... Args>
void SpawnPrintBackgroundTask(
T& aReceiver, dom::Promise& aPromise, const nsCString& aTelemetryKey,
PrintBackgroundTask<T, Result, Args...> aBackgroundTask, Args... aArgs) {
auto promiseHolder = MakeRefPtr<nsMainThreadPtrHolder<dom::Promise>>(
"nsPrinterBase::SpawnBackgroundTaskPromise", &aPromise);
// We actually want to allow to access the printer data from the callback, so
// disable strict checking. They should of course only access immutable
// members.
auto holder = MakeRefPtr<nsMainThreadPtrHolder<T>>(
"nsPrinterBase::SpawnBackgroundTaskPrinter", &aReceiver,
/* strict = */ false);
// See
// https://stackoverflow.com/questions/47496358/c-lambdas-how-to-capture-variadic-parameter-pack-from-the-upper-scope
// about the tuple shenanigans. It could be improved with C++20
NS_DispatchBackgroundTask(
NS_NewRunnableFunction(
"SpawnPrintBackgroundTask",
[holder = std::move(holder), promiseHolder = std::move(promiseHolder),
aTelemetryKey, startRoundTrip = TimeStamp::Now(),
backgroundTask = aBackgroundTask,
aArgs = std::make_tuple(std::forward<Args>(aArgs)...)] {
auto start = TimeStamp::Now();
Result result = std::apply(
[&](auto&&... args) {
return (holder->get()->*backgroundTask)(args...);
},
std::move(aArgs));
Telemetry::AccumulateTimeDelta(
Telemetry::PRINT_BACKGROUND_TASK_TIME_MS, aTelemetryKey, start);
NS_DispatchToMainThread(NS_NewRunnableFunction(
"SpawnPrintBackgroundTaskResolution",
[holder = std::move(holder),
promiseHolder = std::move(promiseHolder),
telemetryKey = std::move(aTelemetryKey), startRoundTrip,
result = std::move(result)] {
Telemetry::AccumulateTimeDelta(
Telemetry::PRINT_BACKGROUND_TASK_ROUND_TRIP_TIME_MS,
telemetryKey, startRoundTrip);
ResolveOrReject(*promiseHolder->get(), *holder->get(),
result);
}));
}),
NS_DISPATCH_EVENT_MAY_BLOCK);
}
// Gets a fresh promise into aResultPromise, that resolves whenever the print
// background task finishes.
template <typename T, typename Result, typename... Args>
nsresult PrintBackgroundTaskPromise(
T& aReceiver, JSContext* aCx, dom::Promise** aResultPromise,
const nsCString& aTelemetryKey,
PrintBackgroundTask<T, Result, Args...> aTask, Args... aArgs) {
ErrorResult rv;
RefPtr<dom::Promise> promise =
dom::Promise::Create(xpc::CurrentNativeGlobal(aCx), rv);
if (MOZ_UNLIKELY(rv.Failed())) {
return rv.StealNSResult();
}
SpawnPrintBackgroundTask(aReceiver, *promise, aTelemetryKey, aTask,
std::forward<Args>(aArgs)...);
promise.forget(aResultPromise);
return NS_OK;
}
// Resolves an async attribute via a background task, creating and storing a
// promise as needed in aPromiseSlot.
template <typename T, typename Result, typename... Args>
nsresult AsyncPromiseAttributeGetter(
T& aReceiver, RefPtr<dom::Promise>& aPromiseSlot, JSContext* aCx,
dom::Promise** aResultPromise, const nsCString& aTelemetryKey,
PrintBackgroundTask<T, Result, Args...> aTask, Args... aArgs) {
if (RefPtr<dom::Promise> existing = aPromiseSlot) {
existing.forget(aResultPromise);
return NS_OK;
}
nsresult rv =
PrintBackgroundTaskPromise(aReceiver, aCx, aResultPromise, aTelemetryKey,
aTask, std::forward<Args>(aArgs)...);
NS_ENSURE_SUCCESS(rv, rv);
aPromiseSlot = *aResultPromise;
return NS_OK;
}
} // namespace mozilla
#endif
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