CODEWITHSUNDEEP
cmultithreading
optomus
optomus

Reputation: 66

pthread malloc SegFault

I am trying to create a buffer queue using a linked list. I am using pthreads for a generating thread and multiple reading threads. My program correctly uses a pthread to open a file and start reading lines of the file into char plain_text[120]; and adds a null character, which then passes that parameter into the following function.

void enqueue(char word[])
{
struct queue_node *new_node = malloc(sizeof(struct queue_node));
if(new_node == NULL)
{
    printf("Failed to allocate memory in enqueue\n");
    exit(-1);
}

new_node->word = malloc(sizeof(strlen(word)+1));
if(new_node->password == NULL)
{
    printf("Failed to allocate memory in enqueue for the password\n");
    exit(-1);
}

strcpy(new_node->word, word);

new_node->next_node = NULL;
enqueued++;

if(head==NULL)
{
    head = new_node;
    previous_node = head;
    current_node = head;                    
    deleting_node = head;
}
else
{
    previous_node->next_node = new_node;
    previous_node = previous_node->next_node;


}

}

The struct used is this:

struct queue_node
{
    char* password;
    struct queue_node *next_node;
};

My code runs for about 2000 words and then hits me with a SegFault.

GDB where, produces this:

0 0x00007ffff71a3118 in _int_malloc () from /usr/lib/libc.so.6

1 0x00007ffff71a43d4 in malloc () from /usr/lib/libc.so.6

2 0x00000000004017cd in enqueue (word=0x7ffff6d0deb0 "!!626Ru") at main.c:217

3 0x0000000000401779 in Dictionary_fill (arg=0x7fffffffeba5) at main.c:195

4 0x00007ffff74d44a4 in start_thread () from /usr/lib/libpthread.so.0

5 0x00007ffff721213d in clone () from /usr/lib/libc.so.6

I am guessing that I am improperly allocating with malloc, but I have searched and banged my head against the wall for a few days now and just can't seem to figure it out.

Upvotes: 0

Views: 475

Answers (2)

ameyCU
ameyCU

Reputation: 16607

 new_node->word = malloc(sizeof(strlen(word)+1));

Don't use sizeof here . Just write -

new_node->word = malloc(strlen(word)+1);

And in this you allocate memory to new_node->word so check it for NULL -

if(new_node->password == NULL)

Check this instead-

if(new_node->word== NULL)

Upvotes: 1

Paul R
Paul R

Reputation: 212979

This is wrong:

new_node->word = malloc(sizeof(strlen(word)+1));

You don't want sizeof in there, otherwise you are not allocating enough storage for your string.

It should of course be:

new_node->word = malloc(strlen(word)+1);

Upvotes: 2

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