SegFault with Producer/Consumer File Copy

问题

back with another segfault. Not sure why, as this readdir line is the same one i've been using in other file copy assignments. Below is the code I crafted in lieu of the assignment shared here. I have commented where the segfault occurs in hopes of aiding better minds find my flaw!

This is copyDirs.cpp

//cmd: ./a.out [#ofConsumerThreads] [src directory] [dest directory]

#include "copyDirs.h"

int main(int ac,char* av[])
{
pthread_mutex_init(&buflock,NULL);
pthread_t prodT;

if(ac == 4)
{
    int consNum = atoi(av[1]);

    pthread_t thread[consNum];

    strcpy(f1,av[2]);
    strcpy(f2,av[3]);

    directory = opendir(f1);
    pthread_create(&prodT,NULL,producer,NULL); //segfault happens in producer function

        pthread_join(prodT, NULL);

    for(int i=0;i<consNum && buffer.size() > 0;i++)
    {
        pthread_create(&thread[i],NULL,consumer,NULL);
            pthread_join(thread[i],NULL);
    }

    closedir(directory);
}
else cout<<"Try that again ;)"<<endl;

pthread_mutex_destroy(&buflock);
pthread_exit(NULL);

return 0;
}

and the relevant header file;

#ifndef COPYDIRS_H
#define COPYDIRS_H 

#include <iostream>
#include <stdio.h>
#include <sys/stat.h>
#include <string.h>
#include <dirent.h>
#include <pthread.h>
#include <time.h>
#include <stack>

using namespace std;

struct FD
{
public:
char* i ;
char* o;

FD(){}

FD(char* input, char* output)
{
    i=input;
    o=output;
}
};

char f1[PATH_MAX];
char f2[PATH_MAX];

struct dirent *curDir;
DIR* directory = NULL;

pthread_mutex_t buflock;
stack <FD> buffer;

void* producer(void*)
{
cout<<"SegTest"<<endl;
    //shows

while (curDir = readdir(directory)) //segfault on this line
{
    cout<<"SegTest"<<endl;
        //doesn't show

    char* file = curDir -> d_name;
    char* i = new char[256];
    char* o = new char[256];

    strcpy(i,f1);
    strcpy(o,f2);
    strcat(i,file);
    strcat(o,file);
    FD prodFD(i,o);

    cout<<"Pushing "<<file<<" to buffer!"<<endl;
    pthread_mutex_lock(&buflock);
        buffer.push(prodFD);
    pthread_mutex_unlock(&buflock);

    i = NULL;
    o = NULL;
}

pthread_exit(NULL);
}

void* consumer(void*)
{
FD consFD;
char c;

consFD = buffer.top();
buffer.pop();
    //ERROR: "statement cannot resolve address of overloaded function

cout << "Copying file: "<<consFD.i<<endl;
pthread_mutex_lock(&buflock);
    FILE * consIF = fopen(consFD.i,"r");
    FILE * consOF = fopen(consFD.o,"w");
pthread_mutex_unlock(&buflock);

pthread_exit(NULL);
}
#endif

回答1:

Try checking that the value of directory is not NULL before calling readdir. You have this line

 directory = opendir(f1);

but are not checking if the return value is NULL which could be the cause of the segfault. At the very least this will prevent a segfault in the event that you pass in an invalid command line argument for the directories.

来源：https://stackoverflow.com/questions/13148673/segfault-with-producer-consumer-file-copy

标签

c++

segmentation-fault

variable-assignment

producer-consumer

file-copying