using threading and mutex locks to search directories - c

Question

I am new to threading and I believe I understand the concept. As locks are a necessary tool to use threading but are (or at least to me) confusing on how to use I need to use them but cannot seem to get them correct. The idea here is to search through directories to find CSV files. (more work will be done on CSVs but that is not relevant here) I have an algorithm to search through directories that works fine without the use of threading. (keep in mind that searching through directories is the kind of task that is perfect for recursion because you need to search through a directory to find another directory and when you find the new directory you want to search that directory) Since I need to use threading on each instance of finding new directory I have the same algorithm set up twice. Once in main where it finds directories and the calls a function (through threading) to search the found directories. Again, if I use this method without threading I have zero problems but with threading the arguments I send in to the function are overwritten. This happens even if I lock the entire function. Clearly I am not using locks and threading correctly but where I'm going wrong eludes me. I have test directories to verify that it is (or is not) working. I have 3 directories in the "." directory and then sub directories beyond that. It finds the first three directories (in main) fine then when it passes those into the threaded function it will search three different times but usually with searching the same directory more than once. In other words the path name seems to be overwritten. I'll post code so you can see what I'm doing. I thank you in advance. Links to complete code:sorter.h https://pastebin.com/0vQZbrmh sorter.c https://pastebin.com/9wd8aa74 dirWorker.c https://pastebin.com/Jd4i1ecr
In sorter.h
#define MAXTHREAD 255
extern pthread_mutex_t lock;
typedef
struct _dir_proc
{
char* path; //the path to the new found directory
char* colName; //related to the other work that must be done
} dir_proc;
In sorter.c
#include <pthread.h>
#include <assert.h>
#include <dirent.h>
#include "sorter.h"
pthread_mutex_t lock;
int main(int argc, char* argv[])
{
int err = 0;
pthread_t threads[MAXTHREAD];
DIR *dirPointer;
char* searchedDirectory = ".";
struct dirent *directEntry;
dir_proc *dir_proc_args = malloc(sizeof(struct _dir_proc));
assert(dir_proc_args != NULL);
dir_proc_args->path = (char*) malloc(256 * (sizeof(char));
assert(dir_proc_args->path != NULL);
dir_proc_args->colName = (char*) malloc(256 * sizeof(char));
assert(dir_proc_args->colName != NULL);
pthread_mutex_init(&lock, NULL)
//dir_proc_args->colName is saved here
if(!(dirPointer = opendir(searchedDirectory)))
{
fprintf(stderr, "opening of directory has failed");
exit(1);
}
while((directEntry = readdir(dirPointer)) != NULL)
{
//do stuff here to ensure it is a directory
//ensure that the dir we are looking at is not current or parent dir
//copy path of found directory to dir_proc_args->path
err = pthread_create(&threads[count++], NULL, &CSVFinder, (void*)dir_proc_args);
if(err != 0)
printf("can't create thread);
}
int i;
for(i=0; i < count; ++i)
{
pthread_join(threads[i], NULL);
}
pthread_mutex_destroy(&lock);
}
in CSVFinder function
#include <assert.h>
#include <pthread.h>
#include "sorter.h"
#include <dirent.h>
void *CSVFinder(void *args)
{
pthread_mutex_lock(&lock); //I have locked the entire function to see I can get it to work. this makes no sense to actually do
DIR *dirPointer;
struct dirent *directEntry;
dir_proc *funcArgs = (struct _dir_proc*)args;
char path[255];
strncpy(path, funcArgs->path, sizeof(path));
if(!(dirPointer = opendir(funcArgs->path)))
{
fprintf(stderr, "opening of directory has failed");
exit(1);
}
while((directEntry = readdir(dirPointer)) != NULL)
{
if(directEntry->d_type == DT_DIR) //if we are looking at a directory
{
//make sure the dir we are looking at is not current or parent dir
snprintf(funcArgs->path, (sizeof(path) + sizeof(directEntry->d_name)), "%s/%s", path, directEntry->d_name);
//I would like to be able to do a recursive call here
//to search for more directories but one thing at a time
}
}
closedir(dirPointer);
pthread_mutex_unlock(&lock);
return(NULL);
}
I hope I have not left out any relevant code. I tried to keep the code to a minimum while not leaving anything necessary out.

Answer 1

It's not clear to me why you want to create a thread to simply traverse a directory structure. However, I will point out a few issues I see.
One minor issue is you in the CSVFinder function, you call readder, not readdir.
But one glaring issue to me is that you do not initialize dirPointer in main or in the CSVFinder() function. I would expect to see a call like
dirPointer = opendir("/");
in the main() function before the while loop.
Then I would expect to see CSVFinder() initialize its dirPointer with a call to opendir(path) where path is a name to a subdirectory found in the main loop.
For a good reference to how to traverse a directory structure go here...
https://www.lemoda.net/c/recursive-directory/