C multi-thread wordcount program segmentation fault issue - c

Question

I've been racking my brain against this program for a couple months now. This was an assignment of a class I took last semester and while I passed, I could never make this one assignment work correctly (Seg Fault). I welcome any help or tips but I greatly appreciate explanations with answers to follow along.
This program is supposed to receive a filename that contains a list of filenames (240 for my example). Those files are located in a folder within the same directory as the list and the program. This program is supposed to take this list and parse it for 4 threads, splitting the filenames evenly for each thread (60 per thread for my example). Each thread then takes this list of 60 file names and opens each file one by one performing a WordCount function on each file. Once the threads complete their tasks, they are supposed to print the results for each file in order with each thread in its own block(i.e. Thread1 Results | Thread2 Results | Thread 3 Results, etc...).
I've debugged quite a bit and know that up until the threads are created everything works as it is supposed to. My problem seems to be during thread launch/execution. I've tried adding mutex to the mix but sadly it hasn't helped. I seem to be missing something or over thinking something as some of my class mates have shown me their much more compact code. Please assist. Thanks!
Here is the Main:
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#define MaxLine 200
#define NUMTHREADS 4
char Line[MaxLine];
pthread_mutex_t Lock = PTHREAD_MUTEX_INITIALIZER;
typedef struct thread {
int id;
char file;
}ThreadData;
/* ThreadFunction will give each thread its processes to execute */
void *threadFunc (void *td) {
ThreadData *data = (ThreadData*)td;
int thread_num=data->id;
char filename=data->file;
printf("thread debug tid: %d and file: %c",thread_num, filename);
pthread_mutex_trylock(&Lock);
FILE *fn = fopen(filename, "r");
if (fn == NULL) {
error("ERROR: Opening file");
return 1;
}
while (fgets(Line, sizeof(Line), fn) != NULL) {
CountWord(thread_num, Line);
}
fclose(fn);
free(data);
pthread_mutex_unlock(&Lock);
pthread_exit(NULL);
}
int main(int argc, char *argv[]){
char buf[20];
int c, i, t, tnum, QUEUETOTAL;
pthread_t thread[NUMTHREADS];
ThreadData td[NUMTHREADS];
if (argc != 2){
fprintf(stderr,"ERROR: Usage must be Countfile filename\n", argv[0]);
exit(0);
}
char const* const filename = argv[1];
FILE* file = fopen(filename, "r");
if ( file == 0 ){
printf( "Could not open file!\n" );
exit(0);
}
/* Count iterations of while loop to divide files among threads. */
while (fgets(Line, sizeof(Line), file)){
QUEUETOTAL++;
}
/* Divide work for threads. */
int thread2taskstart=(QUEUETOTAL/NUMTHREADS); //60
int thread3taskstart=(QUEUETOTAL/NUMTHREADS)*2; //120
int thread4taskstart=(QUEUETOTAL/NUMTHREADS)*3; //180
// QUEUETOTAL = 240
rewind(file);
FILE *tempfile1 = fopen("temp1.txt","w");
for (i=0; i<thread2taskstart; i++) {
// populate tempfile1 with entries 1-60
if(fgets(Line,sizeof(Line),file)!=NULL) {
fputs(Line,tempfile1);
//printf("Debug temp1: %s",Line);
}
}
fclose(tempfile1);
FILE *tempfile2 = fopen("temp2.txt","w");
for (i=thread2taskstart; i<thread3taskstart; i++) {
// populate tempfile2 with entries 60-120
if(fgets(Line,sizeof(Line),file)!=NULL) {
fputs(Line,tempfile2);
//printf("Debug temp2: %s",Line);
}
}
fclose(tempfile2);
FILE *tempfile3 = fopen("temp3.txt","w");
for (i=thread3taskstart; i<thread4taskstart; i++) {
// populate tempfile3 with entries 120-180
if(fgets(Line,sizeof(Line),file)!=NULL) {
fputs(Line,tempfile3);
//printf("Debug temp3: %s",Line);
}
}
fclose(tempfile3);
FILE *tempfile4 = fopen("temp4.txt","w");
for (i=thread4taskstart; i<=QUEUETOTAL; i++) {
// populate tempfile3 with entries 180-240
if(fgets(Line,sizeof(Line),file)!=NULL) {
fputs(Line,tempfile4);
//printf("Debug temp4: %s",Line);
}
}
fclose(tempfile4);
fclose(file);
/* Prepare parameters & launch (4) threads. Wait for threads
to finish & print out results as specified in assignment. */
printf("Counting files …\n");
for(t=0;t<NUMTHREADS;t++){
tnum=t+1;
snprintf(buf, "temp%d.txt", tnum);
printf("debug tnum and array: %d and %s\n",tnum, buf);
td[t].id = tnum;
td[t].file = buf;
// Creates a new thread for each temp file.
pthread_create(&thread[t], NULL, threadFunc, td);
}
// Joins threads.
printf("debug: printing threads \n");
for(t=0;t<NUMTHREADS;t++){
pthread_join(thread[t], NULL);
printf("------------------------- Processes finished for Thread %d ----------------------- \n",t+1);
}
return 0;
}
Here is the Count Function:
#include <stdio.h>
int CountWord(int tinfo, char cfile){
int i;
int ccount = 0;
int wcount = 0;
int lcount = 0;
FILE *fname;
char fn[strlen(cfile) + 18];
sprintf(fn, "./CountingFolder/%s", cfile);
printf("Debug: %s\n", fn);
fname = fopen(fn, "r");
if (fname == NULL) {
error("ERROR: Opening file");
}
while ((i = fgetc(fname)) != EOF){
if (i == '\n') {
lcount++;
}
if (i == '\t' || i == ' '){
wcount++;
}
ccount++;
}
printf("Threadid %d processes %s which has %d characters, %d words and %d lines\n", tinfo, cfile, ccount, wcount, lcount);
fclose(fname);
return 0;
}

Answer 1

1) Probably a typo. But
int CountWord(int tinfo, char cfile){ .. }
should be
int CountWord(int tinfo, char *cfile){ .. }
2) You are passing the same buf to all threads from main(). Data race and undefined behaviour.
3) None of the snprintf() calls take the size argument. Undefined behaviour.
4) Since all threads work on different data, you don't need a lock at all.
5) You didn't allocate td array. So you can't call free(data); in the thread function. Undefined behaviour.
There may be more issues with the code but the segfault is likely because of (3) or (5).

Answer 2

In your code here
snprintf(buf, "temp%d.txt", tnum);
printf("debug tnum and array: %d and %s\n",tnum, buf);
td[t].id = tnum;
td[t].file = buf;
the last line assigns a pointer into the file field of this struct
typedef struct thread {
int id;
char file;
}ThreadData;
Shouldn't it be char *file; ? I don't have thread.h in MSVC so I can't compile it. Surely you have all warnings enabled??