c++多线程读取文件

我有一个大文件，超过8900万行。我想读取一个文件，将其转换为哈希表，然后进行一些计算。

问题是使用istream读取文件并将其传递到哈希表的速度太慢。

是否有可能使用更多线程读取文件？使用线程库？

或者我应该把锉刀切成小块，然后每一块都用一根线？

散列函数的计算不需要花费太多时间。

对于冲突，我使用列表。表格的数字是100万。

// Adding_date_too_file.cpp : This file contains the 'main' function. Program execution begins and ends there.
//
#include "pch.h"
#include <iostream>
#include <string>
#include "hash.h"
#include <iostream>
#include <fstream>
using namespace std;
int main()
{
hasho Hashy;
string f1, f2, f3, f4, f5, f6, f7;
bool is_first_line = true;
fstream file_input;
fstream  file_2_Collums;
cout << "Please give the name of the file that you want to run: n(The file should end with the format type (txt,csv etc.)) and it has to have the first column sorted !! (file with only two columnn which is going to be used for searching based on that file)" << flush;
while (true)
{
string infilename;
getline(cin, infilename);
file_input.open(infilename.c_str());
if (file_input)break;
cout << "Invalid file. Please enter a valid input file name> " << flush;
}

cout << "Please give the name of the file that you want to run: n(The file should end with the format type (txt,csv etc.)) and it has to have the first column sorted !! (file with only one column )" << flush;
while (true)
{
string infilename;
getline(cin, infilename);
file_2_Collums.open(infilename.c_str());
if (file_2_Collums)break;
cout << "Invalid file. Please enter a valid input file name> " << flush;
}
//creating output file

int * table;
table = new int[2];
int count_file_lines = 0;
int line_counter_inventors = 0;
if (file_input.is_open())
{
while (!file_input.eof())
{
if (is_first_line == true) {
getline(file_input, f1, 'n');
is_first_line = false;
}

getline(file_input, f1, 't');// patent id
getline(file_input, f2, 't');// patent id
getline(file_input, f3, 't');// patent id
getline(file_input, f3, 't');// patent id
getline(file_input, f6, 't');// patent id
getline(file_input, f3, 'n');//date

//cout << "adding these items " << f1 << 't' << f6 << endl;
Hashy.AddItem(f2, f6);
cout << count_file_lines << endl;
count_file_lines++;
//  cout << f2 << 't' << f6 << endl;
}
}
int lines_2 = 0;
if (file_2_Collums.is_open())
{
Hashy.openOutputFile();
while (!file_2_Collums.eof())
{
getline(file_2_Collums, f1, 't');//patent_id
getline(file_2_Collums, f4, 'n');//assignee_id
//cout << f1 << endl;

Hashy.FindDateId(f1, f4);
lines_2++;
}
}


system("pause");
return 0;}

Hash.cpp

#include "pch.h"
#include <iostream>
#include <string>
#include "hash.h"
#include "hash.h"
#include <fstream>
using namespace std;
static ofstream output_file;
hasho::hasho()
{
for (int i = 0; i < tableSize; i++) {
//cout << i << endl;
HashTable[i] = new item;
HashTable[i]->pattent_id = "empty";
HashTable[i]->date = "empty";
HashTable[i]->next = NULL;
}
}
void hasho::openOutputFile() {
cout << "Please give the name of the output file: n(The file should end with the format type (txt,csv etc.)) " << flush;
while (true)
{
string infilename;
getline(cin, infilename);
output_file.open(infilename.c_str(), fstream::out);
break;
}
}
int hasho::NumberOfItemsInIndex(int index) {
int count = 0;
if (HashTable[index]->date == "empty") {
return count;
}
else {
count++;
item* ptr = HashTable[index];
while (ptr->next != NULL) {
count++;
ptr = ptr->next;
}
}
return count;
}
void hasho::PrintTable() {
int number;
for (int i = 0; i < tableSize; i++) {

number = NumberOfItemsInIndex(i);
cout << "---------------------------------------n";
cout << "index= " << i << endl;
cout << HashTable[i]->pattent_id << endl;
cout << HashTable[i]->date << endl;
cout << "# of items= " << number << endl;
cout << "---------------------------------------n";
}
}

void hasho::PrintItemsInIndex(int index) {

item* ptr = HashTable[index];
if (ptr->date == "empty") {
cout << "index  = " << index << " is empty." << endl;
}
else {
cout << "index = " << index << " contains the following itemsn";
while (ptr != NULL) {

cout << "-----------" << endl;
cout << ptr->date << endl;
cout << ptr->pattent_id << endl;
cout << "-----------" << endl;
ptr = ptr->next;
}
}
}

void hasho::AddItem(string pattend_id, string date)
{
int index = Hash(pattend_id);
if (HashTable[index]->pattent_id == "empty")
{
HashTable[index]->pattent_id = pattend_id;
HashTable[index]->date = date;
}
else {
item* ptr = HashTable[index];
item* n = new item;
n->date = date ;
n->pattent_id = pattend_id;
n->next = NULL;
while (ptr->next != NULL) {
ptr = ptr->next;
}
ptr->next = n;
}
}
void hasho::FindDateId(string pattend_id, string assignee_id1) {
int found = 0;
int nfound = 0;
int index = Hash(pattend_id);
bool foundDateId = false;
string date;
item* ptr = HashTable[index];
int count = 1;
//write to file
//cout << "WE are looking for the date of " <<pattend_id << " in Index:  " << index <<endl;
while (ptr != NULL) {
//cout << "NOw we are looking with : " << pattend_id << endl;
if (ptr->pattent_id == pattend_id) {
//cout << "NOw we are looking with : " << pattend_id <<endl;

foundDateId = true;
date = ptr->date;
//write to file 

output_file << pattend_id << "t";
output_file << assignee_id1 << endl;
output_file << date << "t";
//cout << " " << date << endl;
found = 1;
count++;
}
ptr = ptr->next;
}
if (foundDateId == false) {
nfound++;

}
cout << "found " << found << endl;
cout << "not found " << nfound << endl;
cout << endl;
}
int hasho::Hash(string key)
{
int unsigned hash = 0;
int  unsigned index;
//cout << key << endl;
for (int unsigned i = 0; i < key.length(); i++) {
hash = hash + (int)key[i] *(i+1);
}
index =hash % tableSize;
//cout << index << endl;
return index;

}

Hash.h

#pragma once
#include "pch.h"
#include <iostream>
#include <string>
//#include "hash.cpp"
using namespace std;
#pragma comment(linker, "/STACK:7000000")
#pragma comment(linker, "/HEAP:7000000")
#ifndef  HASH_H
#define HASH_H

class hasho {
private:
static const int tableSize = 300003;
struct item {
string pattent_id;
string date;
item* next;
};
item* HashTable[tableSize];

public:
hasho();
int Hash(string key);
void AddItem(string pattend_id, string date);
int NumberOfItemsInIndex(int index);
void PrintTable();
void PrintItemsInIndex(int index);
void FindDateId(string pattent_id, string assgnee_id);
void openOutputFile();
};

#endif // ! HASH_H