GTSchoolShit/CS4210/Project 2/common/shared_memory/shared_memory.c

#include "shared_memory.h"

#include <stdio.h>
#include <stdlib.h>

#include <sys/types.h>
#include <sys/shm.h>
#include <sys/sem.h>
#include <semaphore.h>

#include <pthread.h>

#include <errno.h>


static shmemNode *head;
static shmemNode *tail;

int shmid[NBUFF];     /* Shared Memory Segment Array    */
char* buffptr[NBUFF]; /* Used for each process to attach to */
int semprox;                 /* Proxy Shared Memory Semaphore  */
int semserv;                 /* Server Shared Memory Semaphore */

static pthread_mutex_t shmem_mutex;
static pthread_cond_t shmem_cond;

void fast_exit(char* error) {
    fprintf(stderr, "%s", error);
    destroy_shared_memory();
    exit(1);
}

/*
 * Retrieve a shared memory segment for use
 *
 * This is where it locks/waits
 */
shmemNode *getSharedMemorySegment() {
    shmemNode *toRet;
    
    //printf("Locking...");
    pthread_mutex_lock(&shmem_mutex);
    //printf("Done\n");    

    while (!head) {
        //printf("Head is Null\n");
        pthread_cond_wait(&shmem_cond, &shmem_mutex);   
    }
    
    toRet = head;
    head = head->next;

    toRet->next = NULL;
    
    pthread_mutex_unlock(&shmem_mutex);
    pthread_cond_signal(&shmem_cond);
    
    //printf("Returning..\n");
    return toRet;
}

/*
 * Release a shared memory segment into the pool
 *
 */
void releaseSharedMemorySegment(shmemNode* node) {
    pthread_mutex_lock(&shmem_mutex);
    
    if (!head) {
        head = tail = node;
        head->next = NULL;
    } else {
        tail->next = node;
        tail = node;
        tail->next = NULL;
    }
    
    pthread_mutex_unlock(&shmem_mutex);
    pthread_cond_signal(&shmem_cond);
}

/*
 * NO locking done here, must be initialized before shared memory and threads
 *  can be used.
 * Otherwise, there would be a deadlock.  non-runtime Race > deadlock.
 * 
 * This data structure is used by the proxy
 */
void init_queue() {
    int i;

    printf("** Initializing Queue\n");
    
    /* Initialize Mutexes */
    pthread_mutex_init(&shmem_mutex, NULL);
    pthread_cond_init(&shmem_cond,NULL);
    
    /* Initialize Queue */
    head = tail = NULL;
    
    for (i=0; i < NBUFF; i++) {
        shmemNode *temp;
        
        temp = malloc(sizeof(shmemNode));
        
        if (!temp) {
            printf("Malloc failed (init_queue), that stinks.\n");
            exit(1);
        }
        
        temp->shmid = shmid[i];
        temp->buff = buffptr[i];
        temp->semIndex = i;
        temp->next = NULL;
        
        if (!head) {
            head = tail = temp;
        } else {
            tail->next = temp;
            tail = temp;
        }
    }
}

/*
 * Initialize shared memory and semaphores
 */
int init_shared_memory() {
    int i;

    /* Initialize and attach Shared Memory Segments */
    for (i = 0; i < NBUFF; ++i) {
        shmid[i] = shmget(SHMKEY+i, BUFFSIZE, PERMS | IPC_CREAT);
        buffptr[i] = shmat(shmid[i], (char*)0, 0);
        
        if (shmid[i] < 0) {
            fprintf(stderr, "Couldn't allocate Shared Memory Segment %d\n", i);
            for (; i >= 0; --i) {
                shmctl(shmid[i], IPC_RMID, NULL);            
            }
            exit(1);
        }
    }

    semserv = semget(SEMSERV, NBUFF, PERMS | IPC_CREAT);
    
    if (semserv == -1) {
        semserv_err:
        printf("Error %d\n", errno);
        fast_exit("Failed to initialize semserv.\n");
    }
    
    for (i=0; i < NBUFF; i++) {
        if (semctl(semserv, i, SETVAL, 1) == -1) {
            goto semserv_err;
        }
    }
  
    
    semprox = semget(SEMPROX, NBUFF, PERMS | IPC_CREAT);
    if (semprox == -1) {
        semprox_err:
        printf("Error %d\n", errno);
        fast_exit("Failed to initialize semprox.\n");
    }
    for (i=0; i < NBUFF; i++) {
        if (semctl(semprox, i, SETVAL, 0) == -1) {
            goto semprox_err;
        }
    }
    
    return 0;
}

/*
 * Attach the process to the shared memory segments
 * 
 *  The queue is used by the client, so it is initialized here
 *
 */
int attach_shared_memory() {
    int i;

    for (i = 0; i < NBUFF; ++i) {
        shmid[i] = shmget(SHMKEY+i, BUFFSIZE, 0);
        buffptr[i] = shmat(shmid[i], (char*)0, 0);

        if (shmid[i] < 0) {
            fprintf(stderr, "Couldn't attach Shared Memory Segment %d\n", i);
            for (; i >= 0; --i) {
                shmctl(SHMKEY+i, IPC_RMID, NULL);            
            }
            return shmid[i];
        }
    }

    semserv = semget(SEMSERV, 0, PERMS);
    
    if (semserv == -1) {
        printf("Error %d\n", errno);
        fast_exit("Failed to initialize semserv.\n");
    }  
    
    semprox = semget(SEMPROX, 0, PERMS);
    if (semprox == -1) {
        printf("Error %d\n", errno);
        fast_exit("Failed to initialize semprox.\n");
    }
    
    init_queue();

    return 0;   
}

/*
 * Destroy the shared memory segments
 */
void destroy_shared_memory() {
    int i;

    for (i = 0; i < NBUFF; ++i) {
        if (shmdt(buffptr[i]) < 0) {
            fprintf(stderr, "Failed to detach Shared Memory segment %d\n", i);
        }
        if (shmctl(shmid[i], IPC_RMID, NULL) < 0) {
            fprintf(stderr, "Failed to free Shared Memory segment %d\n", i);
        }
    }
    
    if (semctl(semprox, 0, IPC_RMID) == -1) {
        fprintf(stderr, "Failed to cleanup semprox.\n");
    }
    if (semctl(semserv, 0, IPC_RMID) == -1) {
        fprintf(stderr, "Failed to cleanup semserv.\n");
    }
}

/*
 * Detach self from shared memory
 */
void detach_shared_memory() {
    int i;
    
    for (i = 0; i < NBUFF; ++i) {
        if (shmdt(buffptr[i]) < 0) {
            fprintf(stderr, "Failed to free Shared Memory segment %d\n", i);
        }
    }
}


void *attach_shmem(int index) {
    return shmat(SHMKEY+index, (void*)0, 0);
}

int detach_shmem(void *ptr) {
    return shmdt(ptr);
}