Could anyone please help me in finding out the reason behind segmentation fault. This program is working fine as long as the command line input is as follows: ./test -r 300 -w 3 -s 100 (gives desired o/p) ./test -r 100 -w 3 -s 200 (gives desired o/p) ./test -r 10 -w 3 -s 10 (gives desired o/p) But at the same time this program fails the moment I am trying to give following command line input ./test -r 3 -w 4 -s 100 (seg fault) ./test -r 1 -w 4 -s 10 (seg fault) I have tried my level best to resolve this and to find out the reason behind failing. But could not able to find the solution. While using dbx I came to know the point where it's failing but unfortunately I don't know how to resolve it. I have mentioned the dbx output below to have a look at it and it may save your time to help me in solving this problem. midibm14:subh:/home/users/subh/demo #dbx test Type 'help' for help. reading symbolic information ... (dbx) stop in main [1] stop in main (dbx) r -r 300 -w 3 -s 100 [1] stopped in main at line 14 ($t1) 14 parse_args(argc, argv); (dbx) c test: Shared Memory Test Program Number of writers thread = 3 Number of readers thread = 300 Shared Memory Size in Bytes = 100 execution completed (dbx) q midibm14:subh:/home/users/subh/demo #dbx test Type 'help' for help. reading symbolic information ... (dbx) stop in main [1] stop in main (dbx) r -r 1 -w 4 -s 100 [1] stopped in main at line 14 ($t1) 14 parse_args(argc, argv); (dbx) cont test: Shared Memory Test Program Number of writers thread = 4 Number of readers thread = 1 Shared Memory Size in Bytes = 100 Shmat Failed Here *** : Shared Memory Attach Error : Too many open files execution completed (dbx) It's failing when I tried to increase the "-w option" in the 2nd execution. Let me summarise the problem once again. I can run this program with the writer thread ("-w option") less than or equal to 3. But I can't run this program with the writer thread ("-w option") 4 or more. May I request you to look into the problem and please provide me the solution. Code: /*********************************************/ /****************** head.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/limits.h> #include <sys/signal.h> /********************* User Defined Data ***************/ #define MAX_THREAD_NUMBER 30000 #define MAX_WRITER_NUMBER 100 #define MAX_READER_NUMBER 999 #define DEFAULT_NUM_READERS 2 #define DEFAULT_NUM_WRITERS 2 #define SHMEM_MODE (SHM_R | SHM_W) /*#define DEFAULT_SHMEM_SIZE 2000000000*/ #define DEFAULT_SHMEM_SIZE 200 #define MB (1024*1024) #define MAX_SHMEM_NUMBER 100 #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 ****************/ void parse_args(int , char **); void *reader(void *); void *writer(void *); void error(const char *, int); void 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_READER_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]; Code: /*********************************************/ /****************** test.c *********************/ /*********************************************/ #include "head.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 : 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 "); } } void 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); } }
