我没有什么好的解决办法。我有一段代码:
#include <iostream>
#include <future>
#include <memory>
#include <functional>
#include <cstddef>
#include <tuple>
#include <typeinfo>
#include <queue>
#include <type_traits>
#include "threadsafe_queue.hpp"
using namespace std;
template<int ...>
struct seq { };
template<int N, int ...S>
struct gens : gens<N-1, N-1, S...> { };
template<int ...S>
struct gens<0, S...> {
typedef seq<S...> type;
};
class JoinThreads {
vector<std::thread>& m_threads;
public:
explicit JoinThreads(vector<std::thread>& threads): m_threads(threads) {}
~JoinThreads() {
for (unsigned long a = 0; a < this-> m_threads.size(); a++) {
if (this->m_threads[a].joinable()) {
this->m_threads[a].join();
}
}
}
};
template<typename T>
class Callable {
T m_proc;
public:
Callable() {}
Callable(T proc): m_proc(proc) {
//
}
template<typename ... V>
typename std::result_of<T>::type Call(V ... args) {
return this-> m_proc(args ...);
}
};
template<typename ResultType>
class TaskResult {
ResultType m_result;
public:
TaskResult(ResultType result) {}
ResultType result() const {
return this-> m_result;
}
};
template<typename CallableType, typename ... ArgType>
class Task {
Callable<CallableType> m_callable;
std::tuple<ArgType...> m_args;
void (*m_callback)(TaskResult<CallableType>);
template<int ...S>
typename std::result_of<CallableType>::type invokeCallable(seq<S...>) {
return this-> m_callable.Call(std::get<S>(this-> m_args) ...);
}
protected:
typedef typename std::result_of<CallableType>::type callableType;
public:
Task() {}
Task(Callable<CallableType> callable, ArgType ... args, TaskResult<CallableType> callback): m_callable(callable), m_callback(callback) {
this-> m_args = std::make_tuple(args ...);
}
void Execute() {
typename std::result_of<CallableType>::type result = this-> invokeCallable(typename gens<sizeof...(ArgType)>::type());
void (*callback)(TaskResult<CallableType>) = reinterpret_cast<void (*)(TaskResult<CallableType>) >(this-> m_callback);
if (0 < (size_t)callback) {
this-> m_callback(TaskResult<CallableType>(result));
}
}
};
template<typename T>
class Dequeue {
threadsafe_queue<T> m_tasks;
std::vector<std::thread> m_threads;
std::atomic_bool m_done;
JoinThreads m_joiner;
void Process() {
typename threadsafe_queue<T>::m_size_type size = 0;
while (!m_done) {
T task;
if (this-> m_tasks.try_pop(task)) {
task.Execute();
} else {
std::this_thread::yield();
}
}
}
public:
Dequeue(unsigned threads = 0): m_done(false), m_joiner(m_threads) {
unsigned const threadCount = threads > 0 ? threads : std::thread::hardware_concurrency();
cout << "Threads count: " << threadCount << endl;
try {
for (unsigned i = 0; i < threadCount; ++i) {
this-> m_threads.push_back(std::thread(&Dequeue::Process, this));
}
} catch (...) {
this-> m_done = true;
throw;
}
}
~Dequeue() {
this-> m_done = true;
}
template<typename CallableType, typename CallbackType, typename ... ArgType>
void Subscribe(CallableType callable, CallbackType callback, ArgType ... args) {
this-> m_tasks.push(Task<CallableType, CallbackType, ArgType...> (callable, args ..., callback));
}
void Subscribe(T task) {
this-> m_tasks.push(task);
}
};
template<typename CallableType, typename CallbackType, typename ... ArgType>
Task<CallableType, CallbackType, ArgType ...> SubscribeTask(CallableType callable, CallbackType callback, ArgType ... args) {
return Task<CallableType, CallbackType, ArgType...> (callable, args ..., callback);
}
int foo(int a, int b) {
int N = 1024, tab[N], z = 0;
//Some long task
return tab[0];
}
void callback(TaskResult<int (*)(int, int)> res) {
cout << "Callback" << endl;
}
/*
* Callback jednak warto zrobić z parametrem jako obiekt jakiegoś zdarzenia i
* nie wymuszać konieczności podania parametru szablonu.
*/
int main() {
cout << "Hello world!" << endl;
Dequeue<Task<int (*)(int, int), int, int> > dequeue(4);
cout << "Pushing tasks..." << endl;
dequeue.Subscribe(foo, callback, 2156, 55);
for (int a = 0; a < 1024; a++) {
for (int b = 0; b < 1024; b++) {
dequeue.Subscribe(foo, callback, a, b);
}
}
cout << "Processing..." << endl;
int a;
cin >> a;
return 0;
}
编辑:这里是标题
#include <mutex>
#include <condition_variable>
#include <queue>
#include <memory>
template<typename T>
class threadsafe_queue {
private:
mutable std::mutex mut;
std::queue<T> data_queue;
std::condition_variable data_cond;
public:
typedef
typename
std::queue<T>::size_type m_size_type;
threadsafe_queue() {
}
threadsafe_queue(threadsafe_queue const& other) {
std::lock_guard < std::mutex > lk(other.mut);
data_queue = other.data_queue;
}
void push(T new_value) {
std::lock_guard < std::mutex > lk(mut);
data_queue.push(new_value);
data_cond.notify_one();
}
void wait_and_pop(T& value) {
std::unique_lock < std::mutex > lk(mut);
data_cond.wait(lk, [this] {return !data_queue.empty();});
value = data_queue.front();
data_queue.pop();
}
std::shared_ptr<T> wait_and_pop() {
std::unique_lock < std::mutex > lk(mut);
data_cond.wait(lk, [this] {return !data_queue.empty();});
std::shared_ptr<T> res(std::make_shared < T > (data_queue.front()));
data_queue.pop();
return res;
}
bool try_pop(T& value) {
std::lock_guard < std::mutex > lk(mut);
if (data_queue.empty())
return false;
value = data_queue.front();
data_queue.pop();
return true;
}
std::shared_ptr<T> try_pop() {
std::lock_guard < std::mutex > lk(mut);
if (data_queue.empty())
return std::shared_ptr<T>();
std::shared_ptr<T> res(std::make_shared < T > (data_queue.front()));
data_queue.pop();
return res;
}
bool empty() const {
std::lock_guard < std::mutex > lk(mut);
return data_queue.empty();
}
m_size_type size() const {
std::lock_guard < std::mutex > lk(mut);
return data_queue.size();
}
};
我有错误:
main.cpp: In instantiation of ‘class Callable<int (*)(int, int)>’:
main.cpp:69:25: required from ‘class Task<int (*)(int, int), void (*)(TaskResult<int (*)(int, int)>), int, int>’
main.cpp:135:3: required from ‘void Dequeue<T>::Subscribe(CallableType, CallbackType, ArgType ...) [with CallableType = int (*)(int, int); CallbackType = void (*)(TaskResult<int (*)(int, int)>); ArgType = {int, int}; T = Task<int (*)(int, int), int, int>]’
main.cpp:175:43: required from here
main.cpp:51:35: error: invalid use of incomplete type ‘class std::result_of<int (*)(int, int)>’
typename std::result_of<T>::type Call(V ... args) {
^
In file included from /usr/include/c++/4.9/bits/move.h:57:0,
from /usr/include/c++/4.9/bits/stl_pair.h:59,
from /usr/include/c++/4.9/bits/stl_algobase.h:64,
from /usr/include/c++/4.9/bits/char_traits.h:39,
from /usr/include/c++/4.9/ios:40,
from /usr/include/c++/4.9/ostream:38,
from /usr/include/c++/4.9/iostream:39,
from main.cpp:1:
/usr/include/c++/4.9/type_traits:2060:11: error: declaration of ‘class std::result_of<int (*)(int, int)>’
class result_of;
^
main.cpp: In instantiation of ‘class Task<int (*)(int, int), void (*)(TaskResult<int (*)(int, int)>), int, int>’:
main.cpp:135:3: required from ‘void Dequeue<T>::Subscribe(CallableType, CallbackType, ArgType ...) [with CallableType = int (*)(int, int); CallbackType = void (*)(TaskResult<int (*)(int, int)>); ArgType = {int, int}; T = Task<int (*)(int, int), int, int>]’
main.cpp:175:43: required from here
main.cpp:74:46: error: invalid use of incomplete type ‘class std::result_of<int (*)(int, int)>’
typename std::result_of<CallableType>::type invokeCallable(seq<S...>) {
^
In file included from /usr/include/c++/4.9/bits/move.h:57:0,
from /usr/include/c++/4.9/bits/stl_pair.h:59,
from /usr/include/c++/4.9/bits/stl_algobase.h:64,
from /usr/include/c++/4.9/bits/char_traits.h:39,
from /usr/include/c++/4.9/ios:40,
from /usr/include/c++/4.9/ostream:38,
from /usr/include/c++/4.9/iostream:39,
from main.cpp:1:
/usr/include/c++/4.9/type_traits:2060:11: error: declaration of ‘class std::result_of<int (*)(int, int)>’
class result_of;
^
main.cpp:78:54: error: invalid use of incomplete type ‘class std::result_of<int (*)(int, int)>’
typedef typename std::result_of<CallableType>::type callableType;
^
In file included from /usr/include/c++/4.9/bits/move.h:57:0,
from /usr/include/c++/4.9/bits/stl_pair.h:59,
from /usr/include/c++/4.9/bits/stl_algobase.h:64,
from /usr/include/c++/4.9/bits/char_traits.h:39,
from /usr/include/c++/4.9/ios:40,
from /usr/include/c++/4.9/ostream:38,
from /usr/include/c++/4.9/iostream:39,
from main.cpp:1:
/usr/include/c++/4.9/type_traits:2060:11: error: declaration of ‘class std::result_of<int (*)(int, int)>’
class result_of;
^
main.cpp: In instantiation of ‘void Dequeue<T>::Subscribe(CallableType, CallbackType, ArgType ...) [with CallableType = int (*)(int, int); CallbackType = void (*)(TaskResult<int (*)(int, int)>); ArgType = {int, int}; T = Task<int (*)(int, int), int, int>]’:
main.cpp:175:43: required from here
main.cpp:135:3: error: no matching function for call to ‘Task<int (*)(int, int), void (*)(TaskResult<int (*)(int, int)>), int, int>::Task(int (*&)(int, int), int&, int&, void (*&)(TaskResult<int (*)(int, int)>))’
this-> m_tasks.push(Task<CallableType, CallbackType, ArgType...> (callable, args ..., callback));
^
main.cpp:135:3: note: candidates are:
main.cpp:82:2: note: Task<CallableType, ArgType>::Task(Callable<CallableType>, ArgType ..., TaskResult<CallableType>) [with CallableType = int (*)(int, int); ArgType = {void (*)(TaskResult<int (*)(int, int)>), int, int}]
Task(Callable<CallableType> callable, ArgType ... args, TaskResult<CallableType> callback): m_callable(callable), m_callback(callback) {
^
main.cpp:82:2: note: candidate expects 5 arguments, 4 provided
main.cpp:80:2: note: Task<CallableType, ArgType>::Task() [with CallableType = int (*)(int, int); ArgType = {void (*)(TaskResult<int (*)(int, int)>), int, int}]
Task() {}
^
main.cpp:80:2: note: candidate expects 0 arguments, 4 provided
main.cpp:68:7: note: constexpr Task<int (*)(int, int), void (*)(TaskResult<int (*)(int, int)>), int, int>::Task(const Task<int (*)(int, int), void (*)(TaskResult<int (*)(int, int)>), int, int>&)
class Task {
^
main.cpp:68:7: note: candidate expects 1 argument, 4 provided
main.cpp:68:7: note: constexpr Task<int (*)(int, int), void (*)(TaskResult<int (*)(int, int)>), int, int>::Task(Task<int (*)(int, int), void (*)(TaskResult<int (*)(int, int)>), int, int>&&)
main.cpp:68:7: note: candidate expects 1 argument, 4 provided
main.cpp: In instantiation of ‘class Task<int (*)(int, int), int, int>’:
main.cpp:105:6: required from ‘void Dequeue<T>::Process() [with T = Task<int (*)(int, int), int, int>]’
main.cpp:121:44: required from ‘Dequeue<T>::Dequeue(unsigned int) [with T = Task<int (*)(int, int), int, int>]’
main.cpp:173:55: required from here
main.cpp:74:46: error: invalid use of incomplete type ‘class std::result_of<int (*)(int, int)>’
typename std::result_of<CallableType>::type invokeCallable(seq<S...>) {
^
In file included from /usr/include/c++/4.9/bits/move.h:57:0,
from /usr/include/c++/4.9/bits/stl_pair.h:59,
from /usr/include/c++/4.9/bits/stl_algobase.h:64,
from /usr/include/c++/4.9/bits/char_traits.h:39,
from /usr/include/c++/4.9/ios:40,
from /usr/include/c++/4.9/ostream:38,
from /usr/include/c++/4.9/iostream:39,
from main.cpp:1:
/usr/include/c++/4.9/type_traits:2060:11: error: declaration of ‘class std::result_of<int (*)(int, int)>’
class result_of;
^
main.cpp:78:54: error: invalid use of incomplete type ‘class std::result_of<int (*)(int, int)>’
typedef typename std::result_of<CallableType>::type callableType;
^
In file included from /usr/include/c++/4.9/bits/move.h:57:0,
from /usr/include/c++/4.9/bits/stl_pair.h:59,
from /usr/include/c++/4.9/bits/stl_algobase.h:64,
from /usr/include/c++/4.9/bits/char_traits.h:39,
from /usr/include/c++/4.9/ios:40,
from /usr/include/c++/4.9/ostream:38,
from /usr/include/c++/4.9/iostream:39,
from main.cpp:1:
/usr/include/c++/4.9/type_traits:2060:11: error: declaration of ‘class std::result_of<int (*)(int, int)>’
class result_of;
我尝试在使用 result_of 之前添加类型名称，但它导致了其他错误:“不完整类型的有效使用...”。
我想要像您在 main 函数中看到的那样。我想将新任务添加到线程池之类的东西中。模板参数应尽可能少。完美的解决方案是完全推导 :-)。
最佳答案
在result_of<>您不仅必须传递函数的类型(在您的情况下为 T)，还必须传递参数的类型。
所以，如果我理解你的意图，你的 Callable类还应该接收可变参数列表(例如 ArgsT )并使用它们( std::result_of<T(ArgsT...)>::type )。
换句话说，我想你的 Callable类应该是
template<typename T, typename ... ArgsT>
class Callable {
T m_proc;
public:
Callable() {}
Callable(T proc): m_proc(proc) {
//
}
template<typename ... V>
typename std::result_of<T(ArgsT...)>::type Call(V ... args) {
return this-> m_proc(args ...);
}
};
并且，通过 Task 中的示例, 应称为
Callable<CallableType, ArgType...> m_callable;
与 result_of<> 的其他用途相同的解决方案: 将 arg 类型传递给类型函数
typename std::result_of<CallableType(ArgType...)>::type
关于c++ - 在 ‘typename’ 之前需要 ‘std::result_of<_Signature>::type’ 因为 ‘std::result_of<_Signature>’ 是一个依赖范围，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/40057013/