dispatcher.h

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//
// Copyright 2016 Pixar
//
// Licensed under the terms set forth in the LICENSE.txt file available at
// https://openusd.org/license.
//
#ifndef PXR_BASE_WORK_DISPATCHER_H
#define PXR_BASE_WORK_DISPATCHER_H
 
 
#include "pxr/pxr.h"
#include "pxr/base/work/api.h"
#include "pxr/base/work/impl.h"
#include "pxr/base/work/threadLimits.h"
 
#include "pxr/base/tf/errorMark.h"
#include "pxr/base/tf/errorTransport.h"
 
#include <functional>
#include <type_traits>
#include <utility>
 
PXR_NAMESPACE_OPEN_SCOPE
 
// The Work_Dispatcher interface, specialized with a dispatcher impl template
// argument.
// 
// Clients expected to use the WorkDispatcher type instead.
template <class Impl>
class Work_Dispatcher
{
protected:
    // Prevent construction of the work dispatcher base class.
    WORK_API Work_Dispatcher();
 
public:
    WORK_API ~Work_Dispatcher() noexcept;
 
    Work_Dispatcher(Work_Dispatcher const &) = delete;
    Work_Dispatcher &operator=(Work_Dispatcher const &) = delete;
 
#ifdef doxygen
 
    template <class Callable, class A1, class A2, ... class AN>
    void Run(Callable &&c, A1 &&a1, A2 &&a2, ... AN &&aN);
 
#else // doxygen
 
    template <class Callable>
    inline void Run(Callable &&c) {
        _dispatcher.Run(
            _InvokerTask<typename std::remove_reference<Callable>::type>(
                std::forward<Callable>(c), &_errors));
    }
 
    template <class Callable, class A0, class ... Args>
    inline void Run(Callable &&c, A0 &&a0, Args&&... args) {
        Run(std::bind(std::forward<Callable>(c),
                      std::forward<A0>(a0),
                      std::forward<Args>(args)...));
    }
    
#endif // doxygen
 
    WORK_API void Wait();
 
    WORK_API void Cancel();
 
    WORK_API bool IsCancelled() const;
 
private:
    typedef tbb::concurrent_vector<TfErrorTransport> _ErrorTransports;
 
    // Function invoker helper that wraps the invocation with an ErrorMark so we
    // can transmit errors that occur back to the thread that Wait() s for tasks
    // to complete.
    template <class Fn>
    struct _InvokerTask {
        explicit _InvokerTask(Fn &&fn, _ErrorTransports *err) 
            : _fn(std::move(fn)), _errors(err) {}
 
        explicit _InvokerTask(Fn const &fn, _ErrorTransports *err) 
            : _fn(fn), _errors(err) {}
 
        // Ensure only moves happen, no copies.
        _InvokerTask(_InvokerTask &&other) = default;
        _InvokerTask(const _InvokerTask &other) = delete;
        _InvokerTask &operator=(const _InvokerTask &other) = delete;
 
        void operator()() const {
            TfErrorMark m;
            _fn();
            if (!m.IsClean())
                Work_Dispatcher::_TransportErrors(m, _errors);
        }
    private:
        Fn _fn;
        _ErrorTransports *_errors;
    };
 
    // Helper function that removes errors from \p m and stores them in a new
    // entry in \p errors.
    WORK_API static void
    _TransportErrors(const TfErrorMark &m, _ErrorTransports *errors);
 
    // WorkDispatcher implementation
    Impl _dispatcher;
    std::atomic<bool> _isCancelled;
 
    // The error transports we use to transmit errors in other threads back to
    // this thread.
    _ErrorTransports _errors;
 
    // Concurrent calls to Wait() have to serialize certain cleanup operations.
    std::atomic_flag _waitCleanupFlag;
};
 
class WorkDispatcher 
    : public Work_Dispatcher<PXR_WORK_IMPL_NS::WorkImpl_Dispatcher>
{};
 
// Wrapper class for non-const tasks.
template <class Fn>
struct Work_DeprecatedMutableTask {
    explicit Work_DeprecatedMutableTask(Fn &&fn) 
        : _fn(std::move(fn)) {}
 
    explicit Work_DeprecatedMutableTask(Fn const &fn) 
        : _fn(fn) {}
 
    // Ensure only moves happen, no copies.
    Work_DeprecatedMutableTask
        (Work_DeprecatedMutableTask &&other) = default;
    Work_DeprecatedMutableTask
        (const Work_DeprecatedMutableTask &other) = delete;
    Work_DeprecatedMutableTask
        &operator= (const Work_DeprecatedMutableTask &other) = delete;
 
    void operator()() const {
        _fn();
    }
private:
    mutable Fn _fn;
};
 
// Wrapper function to convert non-const tasks to a Work_DeprecatedMutableTask. 
// When adding new tasks refrain from using this wrapper, instead ensure the 
// call operator of the task is const such that it is compatible with oneTBB.
template <typename Fn>
Work_DeprecatedMutableTask<typename std::remove_reference_t<Fn>> 
WorkMakeDeprecatedMutableTask(Fn &&fn) {
    return Work_DeprecatedMutableTask<typename std::remove_reference_t<Fn>>
            (std::forward<Fn>(fn));
}
 
 
PXR_NAMESPACE_CLOSE_SCOPE
 
#endif // PXR_BASE_WORK_DISPATCHER_H