如何完成c ++中的多线程处理 [英] How Multithreading in c++ is done

问题描述

嗨！

我设计了一个c ++多线程应用程序（第一次），其中一个线程执行以下任务：它从文件&读取值插入动态队列。第二个线程从队列中读取值并写入输出文件;有时我的任务就像'Queue is write complete'（第一个线程的输出）和'Queue read completed'（第二个线程的输出）之后完成，但有时它表现异常意味着它显示第二个线程的输出&然后输出第一个线程;有时也输出第一个线程，而不是第二个和更明智的输出。

下面我复制了我的代码，请建议所需的任何更改。

另外我的疑问：该操作系统是否监控这些线程，因此显示不同的输出？

  #include   <   iostream  > ;  
  使用 命名空间标准; 
  #include   <   windows.h  >  
   const   int  MAX =  2  *  1048576  ; 
  int 大小; 
 HANDLE hThread1，hThread2; 
 DWORD dwID1，dwID2; 
 DWORD Thread1（LPVOID param）; 
 DWORD Thread2（LPVOID param）; 
 FILE * fp，* fpOut; 
  class  cqueue 
 {
 
  public ：
  static   int  front，rear; 
  static   int  * a;  //   = new int [1048576];  
 cqueue（）
 {
 front = rear =  -   1 ; 
 a =  new   int  [MAX]; 
} 
~cqueue（）
 {
  delete  [] a; 
} 
 
 静态  void  insertWithAck（炭）; 
  static   int  deletionWithAck（）; 
}; 
 
  int  cqueue :: front; 
  int  cqueue :: rear; 
  int  * cqueue :: a; 
 
  void  cqueue :: insertWithAck（ char  val）
 { 
  while （（后面== MAX-  1 ）||（后面+ 1 ==面前）） ; 
  if （后面== MAX-  1 ）
 rear =  0 ; 
  else  
 rear ++; 
 a [后方] = val; 
  if （前==  -   1 ）
 front =  0 ; 
} 
 
  int  cqueue :: deletionWithAck（）
 {
  char  k; 
  while （front ==  -   1 ）; 
 
 k = a [front]; 
  if （front == rear）
 front = rear =  -   1 ; 
  else  
 {
  if （front == MAX- < span class =code-digit> 1 ）
 front =  0 ; 
  else  
 front ++; 
} 
 
  return  k; 
} 
 DWORD Thread1（LPVOID参数）
 {
  int  i，val; 
 
 fp = fopen（  1MB_TEST_FILE.txt，  rb）; 
 fseek（fp， 0 ，SEEK_END）; 
尺寸= ftell（fp）; 
倒带（fp）; 
  for （i =  0 ; i< Size; i ++）{
 fread （& val， 1 ， 1 ，fp）; 
 cqueue :: insertWithAck（val）; 
} 
 fclose（fp）; 
 cout<<  队列写完成\ n; 
  return   0 ; 
} 
 DWORD Thread2（LPVOID参数）
 {
 fpOut = fopen（  OutFile.txt，  wb）; 
  char  retVal; 
 
  for （ int  i =  0 ; i< Size; i ++）{
 retVal = cqueue :: deletionWithAck（）; 
 fwrite（& retVal， 1 ， 1 ，fpOut）; 
} 
 fclose（fpOut）; 
 cout<<  队列读取已完成\ n; 
  return   0 ; 
} 
 
  void  main（）
 {
 cqueue c1; 
 hThread1 = CreateThread（NULL， 0 ，（LPTHREAD_START_ROUTINE）Thread1，NULL， 0 ，& ; dwID1）; 
 
 hThread2 = CreateThread（NULL， 0 ，（LPTHREAD_START_ROUTINE）Thread2，NULL， 0 ，&安培; dwID2）; 
 system（  pause）
} 

解决方案

您需要在 cqueue 函数上添加一个锁，以确保线程不会覆盖彼此指针或以其他方式不同步。请参阅 https://www.google.com/search?q=c%2B%2B+lock [ ^ ]

Hi!
I have design one c++ multithreading application (first time) in which one thread does following task: it read values from file & insert into dynamic queue. Second thread does read values from queue and write into output file; Sometimes task is done as i wish like 'Queue is write complete'(output of first thread) and after 'Queue read completed'(output of second thread),but sometimes it behaves abnormal means it shows output of second thread & then output of first thread;also sometimes output of first thread,not second and wiseversa.
Below i copied my code,please suggest any changes required for it.
Also my doubt:Is that operating system monitors these threads,so it shows different output?

#include <iostream>
using namespace std;
#include<windows.h>
const int MAX = 2*1048576;
int Size ;
HANDLE hThread1,hThread2;
DWORD dwID1,dwID2;
DWORD Thread1(LPVOID param);
DWORD Thread2(LPVOID param);
FILE *fp,*fpOut;
  class cqueue
  {
	 
	public :
		static int front,rear;
		static int *a;//=new int[1048576];
	   cqueue()
	   {
		 front=rear=-1;
		 a=new int[MAX];
	   }
	   ~cqueue()
	   {
		delete[] a;
	   }
	  
	  static void insertWithAck(char);
	  static int deletionWithAck();
  };

int cqueue::front;
int cqueue::rear;
int* cqueue::a;

void cqueue :: insertWithAck(char val)
{
 while((rear==MAX-1) || (rear+1==front)) ;
   if(rear==MAX-1)
	  rear=0;
   else	
	 rear++;
   a[rear]=val;
 if(front==-1)
   front=0;
}

int cqueue :: deletionWithAck()
{
 char k;
 while(front== -1);
	
	k=a[front];
	if(front==rear)
	   front=rear=-1;
	else
	{
	   if(front==MAX-1)
		  front=0;
	   else
		  front++;
	}
 
 return k;
}
DWORD Thread1(LPVOID param)
{
	int i,val;

	fp=fopen("1MB_TEST_FILE.txt","rb");
	fseek(fp,0,SEEK_END);
	Size=ftell(fp);
	rewind(fp);
	for(i=0;i<Size;i++){
			fread(&val,1,1,fp);
			cqueue::insertWithAck(val);
	}
	fclose(fp);
	cout<<"Queue write completed\n";   
   return 0;
}
DWORD Thread2(LPVOID param)
{	
	fpOut=fopen("OutFile.txt","wb");
	char retVal;
	
	for(int i=0;i<Size;i++){
		retVal=cqueue::deletionWithAck();
		fwrite(&retVal,1,1,fpOut);
	}
	fclose(fpOut);
	cout<<"Queue read completed\n";
	return 0;
}

void main()
{
	 cqueue c1;
	 hThread1= CreateThread(NULL,0,(LPTHREAD_START_ROUTINE)Thread1,NULL,0,&dwID1);
	
	 hThread2= CreateThread(NULL,0,(LPTHREAD_START_ROUTINE)Thread2,NULL,0,&dwID2);
system("pause")
}

解决方案

You need to add a lock on the cqueue functions to ensure that the threads do not overwrite each others pointers or otherwise get out of sync. See https://www.google.com/search?q=c%2B%2B+lock[^].

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