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Diffstat (limited to 'include/mbgl/util/work_task_impl.hpp')
-rw-r--r-- | include/mbgl/util/work_task_impl.hpp | 92 |
1 files changed, 92 insertions, 0 deletions
diff --git a/include/mbgl/util/work_task_impl.hpp b/include/mbgl/util/work_task_impl.hpp new file mode 100644 index 0000000000..2c016601bb --- /dev/null +++ b/include/mbgl/util/work_task_impl.hpp @@ -0,0 +1,92 @@ +#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); +} + +template <class Fn, class Cb, class... Args> +std::shared_ptr<WorkTask> WorkTask::makeWithCallback(Fn&& fn, Cb&& callback, Args&&... args) { + auto flag = std::make_shared<std::atomic<bool>>(); + *flag = false; + + // 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)...); + } + }; + + auto tuple = std::make_tuple(std::move(args)..., after); + return std::make_shared<WorkTaskImpl<Fn, decltype(tuple)>>( + std::move(fn), + std::move(tuple), + flag); +} + +} // namespace mbgl |