Problems with Implementing Mutex in C - c

Question

I am implementing a program to read filenames with room names, connections, and room types. Ex:
ROOM NAME: chicago
CONNECTION 1: sarasota
CONNECTION 2: columbus
CONNECTION 3: miami
CONNECTION 4: boston
ROOM TYPE: END_ROOM
The program is designed to show the user the room they are starting in, ask for input from the user, check to see if the input is the end room or another connection. If it is another connection, the prompt will display again. If the user reaches the end room, the game ends. However, I am required to implement a mutex that, if the user enters "time", a file is created, the time is written to it, and it is displayed on the screen. After that, prompt is displayed again for the user. My code works fine when the mutex implementation is stripped out. Here is what I am seeing when the mutex is in the code. I appear to reach the time function and the program seems to recognize incorrect rooms but when a "correct" room is entered the cursor just returns and does nothing. Any clue on why I am getting this behavior only on mutex implementation?
The program is below, do you see anything that would cause this issue?
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <sys/types.h>
#include <dirent.h>
#include <string.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <pthread.h>
#include <fcntl.h>
//Read in the room data
//Perform the stat() function on the rooms directory in the same directory
//and open the file with the most recent st_mtime component of the returned stat struct
#define NUM_USED_ROOMS 7
char usedRooms[NUM_USED_ROOMS][256];
char roomFilePath[75];
char timeFilePath[75];
char* connections[NUM_USED_ROOMS];
int end = 0;
char input[20];
int numberOfSteps = -1;
char *steps[75];
int file_descriptor;
char timeText[100];
pthread_mutex_t myMutex = PTHREAD_MUTEX_INITIALIZER;
void * getTime() {
pthread_mutex_lock(&myMutex);
printf("You asked for the time!\n");
pthread_mutex_unlock(&myMutex);
return NULL;
}
//Check if the room number passed is the end
void isEnd(int roomNumber, char *dirName){
//Counting the number of steps for the end of the program
numberOfSteps++;
steps[numberOfSteps - 1] = usedRooms[roomNumber];
//Getting the name of the proper file
sprintf(roomFilePath, "%s/%s", dirName, usedRooms[roomNumber]);
char substring[20];
int numLine = 1;
FILE * filePointer;
filePointer = fopen(roomFilePath, "r");
int lines = 0;
char buffer[256];
while(fgets(buffer, sizeof(buffer), filePointer) != NULL){
lines = lines + 1;
}
fclose(filePointer);
//Opening the file to read to see if it is the end. If it is, assign end = 1.
filePointer = fopen(roomFilePath, "r");
while(fgets(buffer, sizeof(buffer), filePointer) != NULL) {
if (numLine == lines)
{
strcpy(substring, buffer+11);
}
numLine = numLine + 1;
}
if(strstr(substring, "END" ) != NULL) {
end = 1;
}
}
//Get the user input
void getInput() {
fflush(stdin);
scanf("%s", input);
fflush(stdin);
fflush(stdout);
}
void readFile(char *dirName){
DIR *dir;
struct dirent *ent;
int i = 0;
if ((dir = opendir (dirName)) != NULL) {
/* print all the files and directories within directory */
while ((ent = readdir (dir)) != NULL) {
if (strncmp(ent->d_name,".",sizeof(ent->d_name)) == 0 ||
strncmp(ent->d_name,"..",sizeof(ent->d_name)) == 0 )
{
} else {
strcpy(usedRooms[i],ent->d_name);
i++;
}
}
closedir (dir);
} else {
/* could not open directory */
perror ("");
}
}
void playGame(int roomNumber, char * dirName){
int i;
printf("usedRooms is %s", usedRooms[roomNumber]);
pthread_mutex_lock(&myMutex);
pthread_t secondThread;
pthread_create(&secondThread, NULL, getTime,NULL);
//Check if the user guessed the end room
if(end == 1) {
fflush(stdout);
return;
}
else{
isEnd(roomNumber, dirName);
if (end == 1)
{
fflush(stdout);
return;
}
}
int move = 1;
while(move == 1) {
//Open the file of the path of the room passed in
sprintf(roomFilePath, "%s/%s", dirName, usedRooms[roomNumber]);
FILE * filePointer;
filePointer = fopen(roomFilePath, "r");
int fileLines = 0;
char line[256];
//Count the lines in the file so I know how to traverse it
while(fgets(line, sizeof line, filePointer) != NULL) {
fileLines = fileLines + 1;
}
fclose(filePointer);
filePointer = fopen(roomFilePath, "r");
int currentLine = 0;
//Create the array for the rooms that can be navigated to
char gameRooms[6][30];
while(fgets(line, sizeof line, filePointer) != NULL) {
char *pos;
if((pos = strchr(line, '\n')) != NULL)
{
*pos = '\0';
}
//Print out the current room
if (currentLine == 0)
{
char substring[20];
strcpy(substring, line+11);
printf("CURRENT LOCATION: %s\n", substring);
}
//Print the first connection from this room
else if (currentLine == 1){
printf("POSSIBLE CONNECTIONS: ");
fflush(stdout);
char substring[20];
strcpy(substring, line+14);
printf("%s", substring);
fflush(stdout);
strcpy(gameRooms[currentLine - 1], substring);
}
//Print the rest of the connections, comma separated
else if (currentLine > 1 && currentLine < fileLines - 1) {
printf(",");
fflush(stdout);
char substring[20];
strcpy(substring, line+14);
printf("%s", substring);
fflush(stdout);
strcpy(gameRooms[currentLine - 1], substring);
//gameRooms[currentLine - 1] = substring;
}
else {
printf(".");
fflush(stdout);
}
currentLine = currentLine + 1;
}
fclose(filePointer);
printf("\nWHERE TO?>");
//Get the user input
getInput();
if(strcmp("time", input) == 0){
pthread_mutex_unlock(&myMutex);
pthread_join(secondThread, NULL);
pthread_mutex_lock(&myMutex);
pthread_create(&secondThread, NULL, getTime, NULL);
}
//Loop through the file to see if the input matches a room name in the array
for(i = 0; i < fileLines - 2; i++) {
if (strcmp(gameRooms[i], input) == 0)
{
int j;
for(j = 0; j < NUM_USED_ROOMS; j++) {
//If there is a match, play the game starting at the room entered
if(strcmp(usedRooms[j], input) == 0) {
printf("THE STRINGS MATCH usedRooms is %s "
"and input is %s\n",usedRooms[j],input);
playGame(j,dirName);
}
}
move = 0;
}
}
//If the user's input didn't match the list of rooms
if (move == 1) {
printf("\nHUH? I DON'T UNDERSTAND THAT ROOM. TRY AGAIN. \n\n");
fflush(stdout);
fflush(stdin);
}
}
}
int main() {
int newestDirTime = -1; // Modified timestamp of newest subdir examined
char targetDirPrefix[32] = "walterer.rooms."; // Prefix we're looking for
char newestDirName[256]; // Holds the name of the newest dir that contains prefix
memset(newestDirName, '\0', sizeof(newestDirName));
DIR* dirToCheck; // Holds the directory we're starting in
struct dirent *fileInDir; // Holds the current subdir of the starting dir
struct stat dirAttributes; // Holds information we've gained about subdir
dirToCheck = opendir("."); // Open up the directory this program was run in
if (dirToCheck > 0) // Make sure the current directory could be opened
{
while ((fileInDir = readdir(dirToCheck)) != NULL) // Check each entry in dir
{
if (strstr(fileInDir->d_name, targetDirPrefix) != NULL) // If entry has prefix
{
//printf("Found the prefex: %s\n", fileInDir->d_name);
stat(fileInDir->d_name, &dirAttributes); // Get attributes of the entry
if ((int)dirAttributes.st_mtime > newestDirTime) // If this time is bigger
{
newestDirTime = (int)dirAttributes.st_mtime;
memset(newestDirName, '\0', sizeof(newestDirName));
strcpy(newestDirName, fileInDir->d_name);
}
}
}
}
closedir(dirToCheck);
//Read the file at the specified directory
readFile(newestDirName);
int start;
int i;
for (i = 0; i < NUM_USED_ROOMS; i++)
{
memset(roomFilePath, '\0', sizeof(roomFilePath));
sprintf(roomFilePath,"%s/%s", newestDirName, usedRooms[i]);
char output[256];
memset(output, '\0', sizeof(output));
char* token;
char* connectRoom;
FILE *filePointer;
filePointer = fopen(roomFilePath,"r");
//Find the starting room and pass that into the playGame function
if (filePointer == NULL)
{
printf("Unable to open file!\n");
} else {
while(!feof(filePointer)) {
fgets(output, 256, filePointer);
token = strtok(output, "\n");
if(strstr(token, "START") != NULL){
start = i;
}
}
fclose(filePointer);
}
}
//Play the game with the starting room at the directory name
playGame(start, newestDirName);
printf("YOU HAVE FOUND THE END ROOM. CONGRATULATIONS!\n");
printf("YOU TOOK %d STEPS. YOUR PATH TO VICTORY WAS: \n", numberOfSteps);
for(i = 0; i < numberOfSteps; i++){
printf("%s\n", steps[i]);
}
return 0;
}

Answer 1

As a rule, you should lock a mutex for the shortest time possible. Violation of this rule is a severe anti-pattern called "asking for trouble" which is usually punished with deadlocks. Remove that anti-pattern from your code.