#include <cstddef>
#include <cstdlib>
+#include <cstring>
+#include <array>
#include <exception>
#include <functional>
#include <memory>
#include <string>
#include <tuple>
+#include <type_traits>
#include <utility>
#include <vector>
code_(std::move(code)),
args_(std::make_shared<const std::vector<std::string>>(std::move(args)))
{}
- int operator()() const
+ void operator()() const
{
+ char noarg[] = {'\0'};
const int argc = args_->size();
std::vector<std::string> args = *args_;
std::unique_ptr<char*[]> argv(new char*[argc + 1]);
for (int i = 0; i != argc; ++i)
- argv[i] = args[i].empty() ? const_cast<char*>(""): &args[i].front();
+ argv[i] = args[i].empty() ? noarg : &args[i].front();
argv[argc] = nullptr;
- return code_(argc, argv.get());
+ code_(argc, argv.get());
}
};
*
* auto args = std::make_tuple(1, false);
* int res = apply(foo, args);
- * @encode
+ * @endcode
**/
template <class F, class Tuple>
constexpr auto apply(F&& f, Tuple&& t)
template<class R, class... Args>
class Task<R(Args...)> {
private:
- // Type-erasure for the code:
- class Base {
- public:
- virtual ~Base() {}
- virtual R operator()(Args...) = 0;
+
+ // Placeholder for some class type:
+ struct whatever {};
+
+ // Union used for storage:
+#if 0
+ typedef typename std::aligned_union<0,
+ void*,
+ std::pair<void(*)(),void*>,
+ std::pair<void(whatever::*)(), whatever*>
+ >::type TaskUnion;
+#else
+ union TaskUnion {
+ void* ptr;
+ std::pair<void(*)(),void*> funcptr;
+ std::pair<void(whatever::*)(), whatever*> memberptr;
+ char any1[sizeof(std::pair<void(*)(),void*>)];
+ char any2[sizeof(std::pair<void(whatever::*)(), whatever*>)];
+ TaskUnion() {}
+ ~TaskUnion() {}
};
+#endif
+
+ // Is F suitable for small buffer optimization?
template<class F>
- class Impl : public Base {
- public:
- Impl(F&& code) : code_(std::move(code)) {}
- Impl(F const& code) : code_(code) {}
- ~Impl() override {}
- R operator()(Args... args) override
- {
- return code_(std::forward<Args>(args)...);
- }
- private:
- F code_;
+ static constexpr bool canSBO()
+ {
+ return sizeof(F) <= sizeof(TaskUnion) &&
+ alignof(F) <= alignof(TaskUnion);
+ }
+
+ static_assert(canSBO<std::reference_wrapper<whatever>>(),
+ "SBO not working for reference_wrapper");
+
+ // Call (and possibly destroy) the function:
+ typedef R (*call_function)(TaskUnion&, Args...);
+ // Destroy the function (of needed):
+ typedef void (*destroy_function)(TaskUnion&);
+ // Move the function (otherwise memcpy):
+ typedef void (*move_function)(TaskUnion& dest, TaskUnion& src);
+
+ // Vtable of functions for manipulating whatever is in the TaskUnion:
+ struct TaskVtable {
+ call_function call;
+ destroy_function destroy;
+ move_function move;
};
- std::unique_ptr<Base> code_;
+
+ TaskUnion buffer_;
+ const TaskVtable* vtable_ = nullptr;
+
+ void clear()
+ {
+ if (vtable_ && vtable_->destroy)
+ vtable_->destroy(buffer_);
+ }
+
public:
+
Task() {}
Task(std::nullptr_t) {}
+ ~Task()
+ {
+ this->clear();
+ }
+
+ Task(Task const&) = delete;
+
+ Task(Task&& that)
+ {
+ if (that.vtable_ && that.vtable_->move)
+ that.vtable_->move(buffer_, that.buffer_);
+ else
+ std::memcpy(&buffer_, &that.buffer_, sizeof(buffer_));
+ vtable_ = that.vtable_;
+ that.vtable_ = nullptr;
+ }
+ Task& operator=(Task that)
+ {
+ this->clear();
+ if (that.vtable_ && that.vtable_->move)
+ that.vtable_->move(buffer_, that.buffer_);
+ else
+ std::memcpy(&buffer_, &that.buffer_, sizeof(buffer_));
+ vtable_ = that.vtable_;
+ that.vtable_ = nullptr;
+ return *this;
+ }
+
+private:
+
+ template<class F>
+ typename std::enable_if<canSBO<F>()>::type
+ init(F code)
+ {
+ const static TaskVtable vtable {
+ // Call:
+ [](TaskUnion& buffer, Args... args) -> R {
+ F* src = reinterpret_cast<F*>(&buffer);
+ F code = std::move(*src);
+ src->~F();
+ code(std::forward<Args>(args)...);
+ },
+ // Destroy:
+ std::is_trivially_destructible<F>::value ?
+ static_cast<destroy_function>(nullptr) :
+ [](TaskUnion& buffer) {
+ F* code = reinterpret_cast<F*>(&buffer);
+ code->~F();
+ },
+ // Move:
+ [](TaskUnion& dst, TaskUnion& src) {
+ F* src_code = reinterpret_cast<F*>(&src);
+ F* dst_code = reinterpret_cast<F*>(&dst);
+ new(dst_code) F(std::move(*src_code));
+ src_code->~F();
+ }
+ };
+ new(&buffer_) F(std::move(code));
+ vtable_ = &vtable;
+ }
template<class F>
- Task(F&& code) :
- code_(new Impl<F>(std::forward<F>(code))) {}
+ typename std::enable_if<!canSBO<F>()>::type
+ init(F code)
+ {
+ const static TaskVtable vtable {
+ // Call:
+ [](TaskUnion& buffer, Args... args) -> R {
+ // Delete F when we go out of scope:
+ std::unique_ptr<F> code(*reinterpret_cast<F**>(&buffer));
+ return (*code)(std::forward<Args>(args)...);
+ },
+ // Destroy:
+ [](TaskUnion& buffer) {
+ F* code = *reinterpret_cast<F**>(&buffer);
+ delete code;
+ },
+ // Move:
+ nullptr
+ };
+ *reinterpret_cast<F**>(&buffer_) = new F(std::move(code));
+ vtable_ = &vtable;
+ }
+
+public:
+
+ template<class F>
+ Task(F code)
+ {
+ this->init(std::move(code));
+ }
- operator bool() const { return code_ != nullptr; }
- bool operator!() const { return code_ == nullptr; }
+ operator bool() const { return vtable_ != nullptr; }
+ bool operator!() const { return vtable_ == nullptr; }
- template<class... OtherArgs>
- R operator()(OtherArgs&&... args)
+ R operator()(Args... args)
{
- std::unique_ptr<Base> code = std::move(code_);
- return (*code)(std::forward<OtherArgs>(args)...);
+ if (vtable_ == nullptr)
+ throw std::bad_function_call();
+ const TaskVtable* vtable = vtable_;
+ vtable_ = nullptr;
+ return vtable->call(buffer_, std::forward<Args>(args)...);
}
};
