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bounded buffer implementation

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# 1  
Old 11-06-2011
bounded buffer implementation
Hi Experts,

I have a programming assignment that asks us to implement a pipegrep function. it basically has 5 stages and each stage has a thread and buffers are used between stages.

am currently implementing stage 1 . In stage 1 am suppose to read directory and store the filenames in buffer1 shared with stage2 which applies filter like filesize etc,eg: it puts the files having filesize > 4096 into buffer2.I have implemented but am facing problems , am getting desired out put sometime but most of the times it doesnt work as required.

Code:
#include<stdio.h>
#include<unistd.h>
#include<stdlib.h>
#include<sys/types.h>
#include<string.h>
#include<sys/wait.h>
#include<sys/stat.h>
#include<dirent.h>
#include<semaphore.h>
#include<pthread.h>

char *buffer1[10];
char *buffer2[10];

pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;

sem_t empty,full;
void *stage1();
void *stage2();

int main(){
	pthread_t thrd1,thrd2;
	
	sem_init(&empty, 0, 10);
	sem_init(&full,0,0);
	int tid1 = pthread_create(&thrd1,NULL,&stage1,(void *)0);
	if(tid1 == -1)
	perror("cant create thread \n");
	int tid2 = pthread_create(&thrd2,NULL,&stage2,(void *)0);
    if(tid2 == -1)
    perror("cant create thread \n");
    
     pthread_join(thrd1, NULL);
     pthread_join(thrd2, NULL);
//getchar();
pthread_exit(NULL);

}

void *stage1(){
	//printf("Inside thread 1 \n");
DIR *directory;
struct dirent *dir;
int in;

directory = opendir(".");

in=0;

while((dir=readdir(directory))!=NULL){
	if (strcmp(dir->d_name, ".") == 0|| strcmp(dir->d_name, "..")==0)
               continue;  
   sem_wait(&empty);
   //printf("buffer is not empty \n");
   pthread_mutex_lock(&mutex);
   //printf("thread 1 got access \n");
    /* if got access enter filename into buffer */ 
   buffer1[in]=dir->d_name;
   //printf(" ^%s^ \n",buffer1[in]);
   in=(in+1)%10;
   sem_post(&full);//indicate consumer filename is available
   pthread_mutex_unlock(&mutex);
   }
   
   closedir(directory);

pthread_exit(NULL);;
}


void *stage2(){
	//printf("Inside thread2 also \n");
int out =0 ;
int in = 0;
struct stat sb;
int fsize = 4096;
int s=0;	
	while(s != -1){
	//printf("File = %s ,File size = %d \n",buffer[i],(int)sb.st_size);
			sem_wait(&full);
			//printf("buffer is full goin ahead\n");
			pthread_mutex_lock(&mutex);
			//printf("thread2 got access \n");
	        s=stat(buffer1[out],&sb);
	        	
    if(sb.st_size > fsize){
				
    buffer2[in] = buffer1[out];
    printf(" file = %s and size = %d \n",buffer2[in],(int)sb.st_size);
    out = (out+1)%10;
    in = (in+1)%10;
   
    sem_post(&empty);
    pthread_mutex_unlock(&mutex);     
}
else {
	out = (out+1)%10;
	pthread_mutex_unlock(&mutex);
}
}


pthread_exit(NULL);
}

O/p:
Code:
ameya@ameya-Dell-System-Inspiron-N4110:~/os_concepts/Advanced_shell$ ./listfiles
 file = advanced_shell.c~ and size = 11141 
 file = advanced_shell and size = 16693 
 file = listfiles and size = 7919 
 file = advanced_shell.c and size = 10840 

program stuck here, i have closed the directory as well

Please check and provide u r feedback.

Regards,
Ameya
# 2  
Old 11-06-2011
Issue might be with the mutex and semaphores I guess. Why don't you try conditional var in mutex? You can signal when a directory is read into the buffer which can then be processed by the stage2.

--ahamed
# 3  
Old 11-06-2011
If you answer the following question for me, I am pretty sure you will find at least the semaphore issue yourself:

What happens to the "full" semaphore when you find a file, and the file size is greater than 4096?
Last edited by jjinno; 11-06-2011 at 05:10 AM..
# 4  
Old 11-07-2011
Also, you need to check what the pointers you're putting into your buffers actually point to....
# 5  
Old 11-08-2011
Quote:
Originally Posted by jjinno
If you answer the following question for me, I am pretty sure you will find at least the semaphore issue yourself:

What happens to the "full" semaphore when you find a file, and the file size is greater than 4096?

The full semaphore increments (sem_post) when a file is found after which the stage 2 tries to lock the mutex and stats the file for checking the size.
# 6  
Old 11-08-2011
Hi amejoish,
the main issue in your code is
Code:
while(s != -1)

Here you are waiting for the next file accd to the previous stat output. Its not a correct way as after the last file stage1 thread will stop and the stage2 thread will be in wait state forever. Change the condition, then your code will work fine.
# 7  
Old 11-11-2011
Code:
#include<stdio.h>
#include<unistd.h>
#include<stdlib.h>
#include<sys/types.h>
#include<string.h>
#include<sys/wait.h>
#include<sys/stat.h>
#include<dirent.h>
#include<semaphore.h>
#include<pthread.h>

char *buffer1[10];
char *buffer2[10];

int in =0;
int out =0 ;

pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;

sem_t empty,full;
void *stage1();
void *stage2();

int main(){
	pthread_t thrd1,thrd2;
	
	sem_init(&empty, 0, 10);
	sem_init(&full,0,0);
	int tid1 = pthread_create(&thrd1,NULL,&stage1,(void *)0);
	if(tid1 == -1)
	perror("cant create thread \n");
	int tid2 = pthread_create(&thrd2,NULL,&stage2,(void *)0);
    if(tid2 == -1)
    perror("cant create thread \n");
    
     pthread_join(thrd1, NULL);
     pthread_join(thrd2, NULL);
//getchar();
pthread_exit(NULL);

}

void *stage1(){
	//printf("Inside thread 1 \n");
DIR *directory;
struct dirent *dir;
int in = 0;

directory = opendir(".");



while((dir=readdir(directory))!=NULL){
	if (strcmp(dir->d_name, ".") == 0|| strcmp(dir->d_name, "..")==0)
               continue;  
   sem_wait(&empty);
   printf("buffer is not empty \n");
   pthread_mutex_lock(&mutex);
   //printf("thread 1 got access \n");
    /* if got access enter filename into buffer */ 
   buffer1[in]=dir->d_name;
   printf(" %s in buffer 1 now \n",buffer1[in]);
   in=(in+1)%10;
   pthread_mutex_unlock(&mutex);
   sem_post(&full);//indicate consumer filename is available
      }
   
   closedir(directory);

pthread_exit(NULL);
}


void *stage2(){
	//printf("Inside thread2 also \n");
int in2 = 0;

struct stat sb;
int fsize = 4096;
	
	while(1){
	//printf("File = %s ,File size = %d \n",buffer[i],(int)sb.st_size);
			sem_wait(&full);
			printf("buffer is full goin ahead\n");
			pthread_mutex_lock(&mutex);
			//printf("thread2 got access \n");
	        if(stat(buffer1[out],&sb)==-1){
				pthread_mutex_unlock(&mutex);
			    break;
		   }	
    else if((int)sb.st_size > fsize){
				
    buffer2[in2] = buffer1[out];
    buffer1[out] = NULL;
    printf(" file = %s and size = %d \n",buffer2[in2],(int)sb.st_size);
    in = (in+1)%10;
    out = (out+1)%10;
    
   pthread_mutex_unlock(&mutex);
   printf("thread 2 unlocked mutex \n");
   sem_post(&empty);
     
}else{
	out = (out+1)%10;
	pthread_mutex_unlock(&mutex);

}
}


pthread_exit(NULL);
}

i changed the condition but i think i am missing something.

Regards,
Ameya
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