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#pragma once
#include <mbgl/util/work_task.hpp>
#include <mbgl/util/run_loop.hpp>
#include <mutex>
namespace mbgl {
template <class F, class P>
class WorkTaskImpl : public WorkTask {
public:
WorkTaskImpl(F&& f, P&& p, std::shared_ptr<std::atomic<bool>> canceled_)
: canceled(std::move(canceled_)),
func(std::move(f)),
params(std::move(p)) {
}
void operator()() override {
// Lock the mutex while processing so that cancel() will block.
std::lock_guard<std::recursive_mutex> lock(mutex);
if (!*canceled) {
invoke(std::make_index_sequence<std::tuple_size<P>::value>{});
}
}
// If the task has not yet begun, this will cancel it.
// If the task is in progress, this will block until it completed. (Currently
// necessary because of shared state, but should be removed.) It will also
// cancel the after callback.
// If the task has completed, but the after callback has not executed, this
// will cancel the after callback.
// If the task has completed and the after callback has executed, this will
// do nothing.
void cancel() override {
std::lock_guard<std::recursive_mutex> lock(mutex);
*canceled = true;
}
private:
template <std::size_t... I>
void invoke(std::index_sequence<I...>) {
func(std::move(std::get<I>(std::forward<P>(params)))...);
}
std::recursive_mutex mutex;
std::shared_ptr<std::atomic<bool>> canceled;
F func;
P params;
};
template <class Fn, class... Args>
std::shared_ptr<WorkTask> WorkTask::make(Fn&& fn, Args&&... args) {
auto flag = std::make_shared<std::atomic<bool>>();
*flag = false;
auto tuple = std::make_tuple(std::move(args)...);
return std::make_shared<WorkTaskImpl<Fn, decltype(tuple)>>(
std::move(fn),
std::move(tuple),
flag);
}
namespace detail {
template <class Tuple, size_t... Indexes>
auto packageArgumentsAndCallback(std::shared_ptr<std::atomic<bool>> flag,
Tuple&& args,
std::index_sequence<Indexes...>) {
auto callback = std::get<sizeof...(Indexes)>(args);
// Create a lambda L1 that invokes another lambda L2 on the current RunLoop R, that calls
// the callback C. Both lambdas check the flag before proceeding. L1 needs to check the flag
// because if the request was cancelled, then R might have been destroyed. L2 needs to check
// the flag because the request may have been cancelled after L2 was invoked but before it
// began executing.
auto after = [flag, current = util::RunLoop::Get(), callback1 = std::move(callback)] (auto&&... results1) {
if (!*flag) {
current->invoke([flag, callback2 = std::move(callback1)] (auto&&... results2) {
if (!*flag) {
callback2(std::move(results2)...);
}
}, std::move(results1)...);
}
};
return std::make_tuple(std::move(std::get<Indexes>(args))..., after);
}
} // namespace detail
template <class Fn, class... Args>
std::shared_ptr<WorkTask> WorkTask::makeWithCallback(Fn&& fn, Args&&... args) {
auto flag = std::make_shared<std::atomic<bool>>();
*flag = false;
auto tuple = detail::packageArgumentsAndCallback(flag,
std::forward_as_tuple(std::forward<Args>(args)...),
std::make_index_sequence<sizeof...(Args) - 1>());
return std::make_shared<WorkTaskImpl<Fn, decltype(tuple)>>(
std::move(fn),
std::move(tuple),
flag);
}
} // namespace mbgl
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