93 lines
3.0 KiB
C++
93 lines
3.0 KiB
C++
#pragma once
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#include <mbgl/util/work_task.hpp>
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#include <mbgl/util/run_loop.hpp>
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#include <mutex>
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namespace mbgl {
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template <class F, class P>
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class WorkTaskImpl : public WorkTask {
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public:
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WorkTaskImpl(F&& f, P&& p, std::shared_ptr<std::atomic<bool>> canceled_)
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: canceled(std::move(canceled_)),
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func(std::move(f)),
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params(std::move(p)) {
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}
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void operator()() override {
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// Lock the mutex while processing so that cancel() will block.
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std::lock_guard<std::recursive_mutex> lock(mutex);
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if (!*canceled) {
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invoke(std::make_index_sequence<std::tuple_size<P>::value>{});
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}
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}
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// If the task has not yet begun, this will cancel it.
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// If the task is in progress, this will block until it completed. (Currently
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// necessary because of shared state, but should be removed.) It will also
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// cancel the after callback.
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// If the task has completed, but the after callback has not executed, this
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// will cancel the after callback.
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// If the task has completed and the after callback has executed, this will
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// do nothing.
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void cancel() override {
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std::lock_guard<std::recursive_mutex> lock(mutex);
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*canceled = true;
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}
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private:
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template <std::size_t... I>
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void invoke(std::index_sequence<I...>) {
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func(std::move(std::get<I>(std::forward<P>(params)))...);
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}
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std::recursive_mutex mutex;
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std::shared_ptr<std::atomic<bool>> canceled;
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F func;
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P params;
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};
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template <class Fn, class... Args>
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std::shared_ptr<WorkTask> WorkTask::make(Fn&& fn, Args&&... args) {
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auto flag = std::make_shared<std::atomic<bool>>();
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*flag = false;
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auto tuple = std::make_tuple(std::move(args)...);
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return std::make_shared<WorkTaskImpl<Fn, decltype(tuple)>>(
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std::move(fn),
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std::move(tuple),
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flag);
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}
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template <class Fn, class Cb, class... Args>
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std::shared_ptr<WorkTask> WorkTask::makeWithCallback(Fn&& fn, Cb&& callback, Args&&... args) {
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auto flag = std::make_shared<std::atomic<bool>>();
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*flag = false;
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// Create a lambda L1 that invokes another lambda L2 on the current RunLoop R, that calls
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// the callback C. Both lambdas check the flag before proceeding. L1 needs to check the flag
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// because if the request was cancelled, then R might have been destroyed. L2 needs to check
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// the flag because the request may have been cancelled after L2 was invoked but before it
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// began executing.
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auto after = [flag, current = util::RunLoop::Get(), callback1 = std::move(callback)] (auto&&... results1) {
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if (!*flag) {
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current->invoke([flag, callback2 = std::move(callback1)] (auto&&... results2) {
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if (!*flag) {
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callback2(std::move(results2)...);
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}
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}, std::move(results1)...);
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}
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};
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auto tuple = std::make_tuple(std::move(args)..., after);
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return std::make_shared<WorkTaskImpl<Fn, decltype(tuple)>>(
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std::move(fn),
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std::move(tuple),
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flag);
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}
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} // namespace mbgl
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