c++ - 插入双映射的线程

Question

我想使用多个线程来插入一个bimap。我尝试了以下代码:

parallel_index.cpp

#include <iostream>
#include <string>
#include <algorithm>
#include <thread>
#include <mutex>
#include <boost/bimap.hpp>
#include <boost/bimap/unordered_set_of.hpp>
#include <boost/bimap/unordered_multiset_of.hpp>
#include "parallel_index.h"


namespace bimaps = boost::bimaps;
typedef boost::bimap<bimaps::unordered_set_of<uint64_t>,
        bimaps::unordered_multiset_of<std::string> > bimap_reference;
typedef bimap_reference::value_type position;
bimap_reference reference_index_vector;


size_t total_threads = std::thread::hardware_concurrency();

std::string sequence_content = "ABCDDBACDDDCBBAAACBDAADCBDAAADCBDADADACBDDCBBBCDCBCDAADCBBCDAAADCBDA";
uint64_t sequence_length = sequence_content.length();
int split = 5;
uint64_t erase_length = 0;
unsigned int seq_itr = 0;

std::mutex mtx;   // to protect against concurent access
int main(){
    thread_test::create_index index;
    std::thread threads[total_threads-1];

    for(unsigned int i = 0; i < total_threads; i++){
        threads[i] = std::thread(&thread_test::create_index::reference_index_hash, std::ref(index), sequence_length, split, sequence_content, erase_length);
    }

    for(unsigned int i = 0; i < total_threads; i++){
        threads[i].join();
    }
}



/*
 * Creating index
 */
void thread_test::create_index::reference_index_hash(uint64_t &sequence_length, int &split,
        std::string &sequence_content, uint64_t &erase_length  ){

    for (; seq_itr < sequence_length; ++seq_itr ){
        std::string splitstr = sequence_content.substr(erase_length, split);

        std::lock_guard<std::mutex> lck(mtx);
        reference_index_vector.insert(position(seq_itr, splitstr));
        seq_itr += split-1;
        erase_length += split;


// the length of test is very large so erase some text
        if(erase_length > 10000){ 
            sequence_content.erase(0,erase_length);
            erase_length = 0;
        }
    }


//  for( bimap_reference::const_iterator iter = reference_index_vector.begin(), iend = reference_index_vector.end();
//          iter != iend; ++iter ) {
//      std::cout << iter->left << " <--> "<< iter->right <<std::endl;
//  }

}

parallel_index.h

#ifndef PARALLEL_INDEX_H_
#define PARALLEL_INDEX_H_


#include<iostream>
#include <algorithm>
#include <utility>
#include <boost/bimap.hpp>
#include <boost/bimap/unordered_set_of.hpp>
#include <boost/bimap/unordered_multiset_of.hpp>




//typedef boost::unordered_map<int, std::pair<int, unsigned long int>& > reference_map;

namespace bimaps = boost::bimaps;

typedef boost::bimap<bimaps::unordered_set_of<uint64_t>,
        bimaps::unordered_multiset_of<std::string > > bimap_reference;
typedef bimap_reference::value_type position;
extern bimap_reference reference_index_vector;


namespace thread_test{

class create_index{
public:
    void reference_index_hash(uint64_t &sequence_length, int &split,
            std::string &sequence_content, uint64_t &erase_length);
};
}


#endif /* PARALLEL_INDEX_H_ */

我使用eclipse IDE编译代码，但出现错误

g++ -std=c++17 -I/home/ahussain/boost_1_65_1 -O3 -Wall -c -fmessage-length=0 -MMD -MP -MF"parallel_index.d" -MT"parallel_index.o" -o "parallel_index.o" "../parallel_index.cpp"
In file included from /usr/include/c++/5/thread:39:0,
                 from ../parallel_index.cpp:13:
/usr/include/c++/5/functional: In instantiation of ‘struct std::_Bind_simple<std::_Mem_fn<void (thread_test::create_index::*)(long unsigned int&, int&, std::__cxx11::basic_string<char>&, long unsigned int&)>(std::reference_wrapper<thread_test::create_index>, long unsigned int, int, std::__cxx11::basic_string<char>, long unsigned int)>’:
/usr/include/c++/5/thread:137:59:   required from ‘std::thread::thread(_Callable&&, _Args&& ...) [with _Callable = void (thread_test::create_index::*)(long unsigned int&, int&, std::__cxx11::basic_string<char>&, long unsigned int&); _Args = {std::reference_wrapper<thread_test::create_index>, long unsigned int&, int&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >&, long unsigned int&}]’
../parallel_index.cpp:42:149:   required from here
/usr/include/c++/5/functional:1505:61: error: no type named ‘type’ in ‘class std::result_of<std::_Mem_fn<void (thread_test::create_index::*)(long unsigned int&, int&, std::__cxx11::basic_string<char>&, long unsigned int&)>(std::reference_wrapper<thread_test::create_index>, long unsigned int, int, std::__cxx11::basic_string<char>, long unsigned int)>’
       typedef typename result_of<_Callable(_Args...)>::type result_type;
                                                             ^
/usr/include/c++/5/functional:1526:9: error: no type named ‘type’ in ‘class std::result_of<std::_Mem_fn<void (thread_test::create_index::*)(long unsigned int&, int&, std::__cxx11::basic_string<char>&, long unsigned int&)>(std::reference_wrapper<thread_test::create_index>, long unsigned int, int, std::__cxx11::basic_string<char>, long unsigned int)>’
         _M_invoke(_Index_tuple<_Indices...>)
         ^
subdir.mk:18: recipe for target 'parallel_index.o' failed
make: *** [parallel_index.o] Error 1

我看了here ，但无法摆脱错误。

Answer 1

index 可以作为简单指针而不是包装引用传递，但其余变量应该是引用，因此它们需要 std::ref 处理.

换句话说

threads[i] = std::thread(&thread_test::create_index::reference_index_hash,
                         &index,
                         std::ref(sequence_length),
                         std::ref(split),
                         std::ref(sequence_content),
                         std::ref(erase_length));

将编译。

但是……

不幸的是，这意味着您将有多个线程都使用相同的变量。这通常是行不通的，因为线程将同时访问变量存储的值并对其造成严重破坏。您将不得不重新考虑如何使用这些变量，或者按值传递它们，或者找到更好的方法来隔离或保护它们。

还有……

std::thread threads[total_threads-1];

结合

for(unsigned int i = 0; i < total_threads; i++)

将导致过多的线程进入数组。 0 到 total_threads 是 total_threads thread 的计数，而不是 total_threads-1。