Thread Prog in C language (seg fault)

[Codeplug]

If an error occurs, you're allowing execution to continue. Use this construct instead:

if (error) 
{
   perror("error"); 
   exit(1);
}

>> Shared Memory Attach Error : Too many open files
That's EMFILE. When shmat() returns EMFILE "The number of shared memory segments attached to the calling process would exceed the system-imposed limit."

Having an entire shared memory segment for just one int is a bit wasteful. You may want to consider allocating one segment large enough to accommodate all the shared data.

gg

[kumars]

Actually I have sent you a piece of code. Here is the complete program to have a look at it.

I am able to run it successfully

./main -r 300 -w 3 -s 100
./main -r 100 -w 2 -s 100
./main -r 30 -w 3 -s 100


But I am not able to run the program as follows(It gives me the segmentation fault) and the reason is not known to me.

./main -r 1 -w 4 -s 100

I don't know why it fails, if I give "-w option" (4 or more). It works if "-w option" is less than or equal to 3.
It'll be of great help if you can look at the whole program and let me know where I am doing wrong. If possible do also provide me the solution as I gave up and have no clue to solve it.

/****************************************************/
/********************** header.h ********************/
/****************************************************/

#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <pthread.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/sem.h>
#include <sys/wait.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/signal.h>


/********************* User Defined Data ***************/

#define MAX_THREAD_NUMBER       5000
#define MAX_WRITER_NUMBER       100
#define MAX_READER_NUMBER       400
#define DEFAULT_NUM_READERS     2
#define DEFAULT_NUM_WRITERS     2
#define SHMEM_MODE              (SHM_R | SHM_W)
#define DEFAULT_SHMEM_SIZE      20000
#define MB                      (1024*1024)
#define MAX_SHMEM_NUMBER        11



#define USAGE   "\nUsage: %s [-r num_readers] [-w num_writers] [-s shmem_size]\n
\n" \
                "\t-r num_readers  number of reader thread to create\n" \
                "\t-w num_writers  number of writer thread to create\n" \
                "\t-s buffer_size  size of shmem segments in bytes\n"   \
                "\t                must be less than 256MB\n\n"



/************ Global Functions ****************/

int  parse_args(int , char **);
int *reader(void *);
int *writer(void *);
int  error(const char *, int);
int  release();
/*int sys_error(const char *, int);*/


/************ Global Variables ****************/

pthread_t *writer_th;
pthread_t *reader_th;


int              thread_hold[MAX_WRITER_NUMBER];
pthread_mutex_t  cond_mutex[MAX_WRITER_NUMBER];
pthread_mutex_t  mutex_r[MAX_WRITER_NUMBER];
pthread_cond_t   cond_var[MAX_WRITER_NUMBER];


int           *read_count[MAX_WRITER_NUMBER];
char          *shmptr[MAX_WRITER_NUMBER];
unsigned long *checksum[MAX_WRITER_NUMBER];
unsigned long cksum[MAX_WRITER_NUMBER];


int      shmem_size = DEFAULT_SHMEM_SIZE;
pid_t    parent_pid;


int      num_readers = DEFAULT_NUM_READERS;
int      buffer_size = DEFAULT_SHMEM_SIZE;
int      num_writers = DEFAULT_NUM_WRITERS;
int      shmid[MAX_THREAD_NUMBER + MAX_WRITER_NUMBER];



/****************************************************/
/********************** main.c **********************/
/****************************************************/

#include "header.h"


int main(int argc, char **argv)
{
        pthread_attr_t  newattr;

        int    i, j, k;
        size_t Size;

        unsigned long *ulptr;


        parse_args(argc, argv);


        printf("%s: Shared Memory Test Program\n\n", *argv);

        printf("\tNumber of  writers thread   = %d\n", num_writers);
        printf("\tNumber of  readers thread   = %d\n", num_readers);
        printf("\tShared Memory Size in Bytes = %d\n", buffer_size);
        printf("\n");



        for(i = 0; i < num_writers; i++) {
        j = i * 3;

        Size = sizeof(int);

        if((shmid[j] = shmget(IPC_PRIVATE, Size, SHMEM_MODE)) < 0)
                perror("Shmget Error");


        if((long)(read_count[i] = (int *) shmat(shmid[j], 0, 0)) == -1)
                perror("Shmat Error");


        *(read_count[i]) = 0;
        j++;
        Size = sizeof(unsigned long) * num_readers;

        if((shmid[j] = shmget(IPC_PRIVATE, Size, SHMEM_MODE)) < 0)
                perror("Checksum Shmget Failed");


        if((long)(checksum[i] = (unsigned long *) \
                                         shmat(shmid[j], 0, 0)) == -1)
                perror("Shmat Failed : Shared Memory Attach Error ");


        ulptr = checksum[i];

        for(k = 0; k < num_readers; k++)
        {
                *ulptr = 0;
                ulptr++;
        }

        Size = buffer_size;
        j++;

        if((shmid[j] = shmget(IPC_PRIVATE, Size, SHMEM_MODE)) < 0)
                perror("Shmptr Shmget Failed");


        if((long)(shmptr[i] = shmat(shmid[j], 0, 0)) == -1)
                perror("Shmat Failed Here *** : Shared Memory Attach Error ");

        }


        writer_th = (pthread_t *) malloc((size_t) (num_writers \
                                                   * sizeof(pthread_t)));
        reader_th = (pthread_t *) malloc((size_t) (num_writers \
                                     * num_readers * sizeof(pthread_t)));

        for(i = 0; i < num_writers; i++) {

        if(pthread_mutex_init(&mutex_r[i] , (pthread_mutexattr_t *)NULL) != 0)
                perror("Can't Initialise Mutex");


        if(pthread_mutex_init (&cond_mutex[i], (pthread_mutexattr_t *)NULL)!=0)
                perror("Can't Initialize Cond_Mutex");


        if(pthread_cond_init (&cond_var[i], (pthread_condattr_t *)NULL)!=0)
                perror("Cond_Var Failed");


        thread_hold[i] = 1;
        }
        if(pthread_attr_init(&newattr))
               perror("Attr_Init Failed");


        if(pthread_attr_setdetachstate(&newattr, PTHREAD_CREATE_UNDETACHED))
                perror("Attr_Setdetachstate Failed");



        for(i = 0; i < num_writers; i++)
        {


                if(pthread_create(&writer_th[i], &newattr, writer, \
                                                        (void *) (long)i))
                        perror("Writer Failed");

                k = i * num_readers;


                for(j = k; j < (k + num_readers) ; j++)
                {
                        if(pthread_create(&reader_th[j], &newattr, reader,\
                                                        (void *) (long)j))

                        perror("Reader Failed");
                }
        }


        for(i = 0; i < num_writers; i++)
        {
               if(pthread_join(writer_th[i], NULL)) {
                        printf("writer_th: pthread_join return: %d\n",i);

                        perror("Pthread_join Bad Status");
                }

                k = i * num_readers;


                for(j = k; j < (k + num_readers) ; j++)
                {
                        if(pthread_join(reader_th[j], NULL)) {
                        perror("Pthread_join Bad Status");
                        }
                }
        }

        for(i = 0; i < num_writers; i++)
        {
                ulptr = checksum[i];
                for(j = 0; j < num_readers; j++) {

                        if(cksum[i] != *ulptr )
                                error("checksums do not match", __LINE__);

                }
        }


        printf("\n\tMain: Readers calculated segment successfully\n");

        release();
        printf("\nsuccessful!\n");

        return(0);
}


/****************************************************/
/******************** reader.c **********************/
/****************************************************/

#include "header.h"



void *reader(void *parm)
{
        int num_p = (int) (long)parm;
        unsigned long cksum_r = 0;
        int     i, num_r, num_w;
        char    *ptr;
        unsigned long *ulptr_r;


        num_r = num_p % num_readers;
        num_w = num_p - num_r;
        num_w = num_w / num_readers;
        ptr = shmptr[num_w];
        ulptr_r = checksum[num_w];

        if(pthread_mutex_lock (&cond_mutex[num_w]))
                perror("Can't Take Cond Lock");

        while(thread_hold[num_w])
        {
                if(pthread_cond_wait(&cond_var[num_w], &cond_mutex[num_w]))
                        perror("cond_wait failed");
        }
        if(pthread_mutex_unlock(&cond_mutex[num_w]))
                perror("Release cond Lock Failed");

        if(pthread_mutex_lock(&mutex_r[num_w]))
                perror("Can't take read Lock");

        (*(read_count [num_w]))++;

        if(pthread_mutex_unlock(&mutex_r[num_w]))
                perror("Can't Release Read Lock");

        for(i = 0; i < buffer_size; i++)
                cksum_r += *ptr++;

        if(pthread_mutex_lock(&mutex_r[num_w]))
                perror("Can't Take Read Lock");

        (*(read_count[num_w]))--;

        if(pthread_mutex_unlock(&mutex_r[num_w]))
                perror("Can't Release 1 Read Lock");


        *ulptr_r = cksum_r;

        printf("\tReader (%d) of Writer (%d): checksum %04ld\n",\
                                                num_r,num_w,cksum_r);

        return NULL;
}


/****************************************************/
/******************** writer.c **********************/
/****************************************************/


#include "header.h"



void *writer(void *parm)
{
        int num_w = (int) (long)parm;
        unsigned long cksum_w = 0;
        char  data = 0;
        char  *ptr;
        int count = 0;


        data = num_w;

        for(ptr = shmptr[num_w]; ptr < (shmptr[num_w]+buffer_size); ptr++) {
                *ptr = data++;
                cksum_w += *ptr;

        }

        /*perror("Writer: Writer failed here 0: ");*/

        if(pthread_mutex_lock(&cond_mutex[num_w]))
                perror("Mutex_lock Failed");


        thread_hold[num_w] = 0;


        if(pthread_cond_broadcast(&cond_var[num_w]))
                perror("cond_signal Failed");


        if(pthread_mutex_unlock(&cond_mutex[num_w]))
                perror("Mutex_unlock Failed");



        cksum[num_w] = cksum_w;
        printf("\n\tWriter (%d): shared memory checksum %04ld\n", \
                                                         num_w, cksum_w);


        return NULL;
}


/****************************************************/
/******************** parseargs.c *******************/
/****************************************************/

#include "header.h"


int parse_args(int argc, char **argv)
{
        int         i;
        int         errflag = 0;
        char        *program_name = *argv;
        extern char *optarg;


        while((i = getopt(argc, argv, "r:s:w:?")) != EOF) {
                switch (i) {
                        case 'r':
                                num_readers = atoi(optarg);
                                break;
                        case 's':
                                buffer_size = atoi(optarg);
                                break;
                        case 'w':
                                num_writers = atoi(optarg);
                                break;
                        case '?':
                                errflag++;
                                break;
                }
        }
        if(num_writers >= MAX_WRITER_NUMBER) {
                errflag++;
                fprintf(stderr, "ERROR: num_writers must be less\
                                       than %d\n", MAX_WRITER_NUMBER);
        }
        if(num_readers >= MAX_READER_NUMBER) {
                errflag++;
                fprintf(stderr, "ERROR: num_readers must be less\
                                        than %d\n", MAX_READER_NUMBER);
        }
        i = num_readers * num_writers;

        if(i >= MAX_THREAD_NUMBER) {
                errflag++;
                fprintf(stderr, "ERROR: maximun threads number\
                         must be less than %d\n", MAX_THREAD_NUMBER);
        }

        if(errflag) {
                fprintf(stderr, USAGE, program_name);
                exit (2);
        }
}


int release()
{
        int i, j;

        for(i = 0; i < num_writers; i++) {
        if(pthread_mutex_destroy(&cond_mutex[i]) != 0)
                perror("Can't destroy cond_mutex");

        if(pthread_mutex_destroy(&mutex_r[i]) != 0)
                perror("Can't destroy mutex_r");
        }


        for(i = 0; i < num_writers; i++) {

        j = i * 3;
        if(shmctl(shmid[j], IPC_RMID, 0) < 0)
                perror("Read_count shmctl Failed");
        j++;
        if(shmctl(shmid[j], IPC_RMID, 0) < 0)
                perror("checksum shmctl failed");
        j++;
        if(shmctl(shmid[j], IPC_RMID, 0) < 0)
                perror("shmptr shmctl failed");

        }
}



int sys_error(const char *msg, int line)
{
        char syserr_msg [256];

        sprintf(syserr_msg, "%s: %s\n", msg, strerror (errno));
        error(syserr_msg, line);
}

int error(const char *msg, int line)
{
        fprintf(stderr, "ERROR [line: %d] %s\n", line, msg);
        if(line>= 260)
        release();
        exit(-1);
}

[Codeplug]

If an error occurs, you're allowing execution to continue. Use this construct instead:

if (error) 
{
   perror("error"); 
   exit(1);
}

>> Shared Memory Attach Error : Too many open files
That's EMFILE. When shmat() returns EMFILE "The number of shared memory segments attached to the calling process would exceed the system-imposed limit."

Having an entire shared memory segment for just one int is a bit wasteful. You may want to consider allocating one segment large enough to accommodate all the shared data.

gg

Assuming the error is still the same, my answer is still the same.

gg