Stat errors in pthread (S_ISDIR not working)

Question

I am currently attempting to write a program that finds the size of a directory tree as well as the size of all subdirectories within it by creating a thread for each new subdirectory and using that thread to find the size of the subdirectory. It's a pretty simple program, but it's really hard to debug. I am having a TON of issues with S_ISDIR not working as intended (regular files are passing the if statement and my program is trying to change dir into regular files). Below is the code that I have for the problem. I would like to have each parent directory wait for the subdirectories to finish, but don't want each subdirectory to wait for the next one.

#define NAMESIZE 256
#define NUM_THREADS 100
#define MAX_PATH_LENGTH 500

int totalSum = 0;
pthread_mutex_t sum_mutex ;
pthread_mutex_t thread_mutex ;

void *findSize(void *p)
{
    int levelSum = 0, numberThreads = 0, i = 0;
    DIR *dir ;
    struct dirent *entry ;
    struct stat entry_stat ;
    char cwd[2049] ;
    char threads[NUM_THREADS] ;
    char paths[NUM_THREADS][MAX_PATH_LENGTH];

    char *path = (char*)p ;

    // change into the directory that was passed in
    if(chdir (p) == -1)
    {
        perror("chdir");
        exit(1);
    }

    // get current working directory
    if(!getcwd (cwd, 2049))
    {
        perror("getcwd") ;
        return;
    }

    // open the directory to get entries within it
    dir = opendir(".") ;
    if(!dir)
    {
        perror("Cannot read directory");
        return;
    }

    while((entry = readdir(dir)))
    {
        // call stat on the current entry in the directory
        if(stat (entry->d_name, &entry_stat) == -1)
        {
            perror("stat error");
        }

        // skip the . and .. directories
        if(strcmp (entry->d_name, ".") == 0)
            continue;
        if(strcmp (entry->d_name, "..") == 0)
            continue;

        // check if current entry is a directory
        if(S_ISDIR (entry_stat.st_mode))
        {
            pthread_mutex_lock(&thread_mutex) ;
            strcpy(paths[numberThreads], cwd) ;
            strcat(paths[numberThreads], "/") ;
            strcat(paths[numberThreads], entry->d_name) ;

            pthread_t temp ;

            // create new thread in threads array
            if (pthread_create(&temp, NULL, findSize, (void *)paths[numberThreads]))
            {
                fprintf("failed to create thread for directory %s\n ", paths[numberThreads]) ;
                exit(1) ;
            }

            threads[numberThreads] = temp;

            // increment the number of threads created on this level of the directory tree

            numberThreads++ ;
            pthread_mutex_unlock(&thread_mutex) ;

        }


        if(S_ISREG(entry_stat.st_mode))
        {
            pthread_mutex_lock(&sum_mutex) ;
            int fileSize = entry_stat.st_size ;
            levelSum += fileSize ;
            totalSum += fileSize ;
            pthread_mutex_unlock(&sum_mutex) ;
        }
    }

    void *status ;

    for(i = 0; i < numberThreads; i++)
    {
        pthread_join(threads[i], NULL) ;
    }

}

In the main, I simply do pthread_create with my function findSize and the path that the user passes in. I get lots of stat errors, but I can't figure how to fix them..

I have removed all print statements, but my print statements in my code show attempts to change directory into a file within a subdirectory (which shouldn't be possible because I check S_ISDIR) — arc, Apr 19 '13 at 23:43
You don't need your own `MAX_PATH_LENGTH`, the system header files already provides `PATH_MAX` for you. — Some programmer dude, Apr 19 '13 at 23:50

score 4 · Answer 1 · answered Apr 19 '13 at 23:50

4

The current directory is not thread-local; it's a property of the process. Thus you're going to end up doing nonsense if each thread tries to chdir. You either need to construct full pathnames based on the results from readdir without using chdir, or use the "*at" interfaces (openat, fstatat, etc.) to open a file relative to a directory file descriptor.

answered Apr 19 '13 at 23:50

R.. GitHub STOP HELPING ICE

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okay, I'm trying to rewrite my code without chdir now, I'll update when I get something running. – arc Apr 20 '13 at 00:42
I still run into the issue of opendir trying to open regular files. opendir should only be called on new threads, which are only created for new directories – arc Apr 20 '13 at 01:03
Perhaps update your question with a description of the directory tree you're running it on (if that contains private information, try it on a simpler sample tree and see if you can reproduce the problem). – R.. GitHub STOP HELPING ICE Apr 20 '13 at 01:10

Stat errors in pthread (S_ISDIR not working)

1 Answers1