c - 如何正确释放哈希表上的元素

Question

我正在编写一个程序，其中有一个哈希表，其中元素具有这种类型的结构

typedef struct _msg_list{
    message_t *msg;
    struct _msg_list *next;
}msg_list;

typedef struct _hash_elem{
    char *nickname;
    int nmsg;
    msg_list *msg_head;
    msg_list *msg_corr;
}hash_elem;

其中 msg_list 是指向已接收消息列表的指针。消息具有这种结构。

typedef struct {
    int     op;   
    char sender[33];
} message_hdr_t;

typedef struct {
    char receiver[33];
    unsigned int   len;  
} message_data_hdr_t;

typedef struct {
    message_data_hdr_t  hdr;
    char               *buf;
} message_data_t;

typedef struct {
    message_hdr_t  hdr;
    message_data_t data;
} message_t;

当我调用 freeHashData 函数来清理内存时，valgrind 给出了这个输出

==4709== Memcheck, a memory error detector
==4709== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==4709== Using Valgrind-3.13.0 and LibVEX; rerun with -h for copyright info
==4709== Command: ./chatty
==4709== 
==4709== 
==4709== HEAP SUMMARY:
==4709==     in use at exit: 98 bytes in 4 blocks
==4709==   total heap usage: 14 allocs, 10 frees, 8,622 bytes allocated
==4709== 
==4709== 16 bytes in 1 blocks are indirectly lost in loss record 1 of 4
==4709==    at 0x4C2FB0F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==4709==    by 0x108F0A: insertMsg (in /home/giacomo/Scrivania/chatty)
==4709==    by 0x1092DB: main (in /home/giacomo/Scrivania/chatty)
==4709== 
==4709== 32 (16 direct, 16 indirect) bytes in 1 blocks are definitely lost in loss record 2 of 4
==4709==    at 0x4C2FB0F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==4709==    by 0x108F0A: insertMsg (in /home/giacomo/Scrivania/chatty)
==4709==    by 0x1092C8: main (in /home/giacomo/Scrivania/chatty)
==4709== 
==4709== 33 bytes in 1 blocks are definitely lost in loss record 3 of 4
==4709==    at 0x4C2FB0F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==4709==    by 0x1090F4: main (in /home/giacomo/Scrivania/chatty)
==4709== 
==4709== 33 bytes in 1 blocks are definitely lost in loss record 4 of 4
==4709==    at 0x4C2FB0F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==4709==    by 0x109166: main (in /home/giacomo/Scrivania/chatty)
==4709== 
==4709== LEAK SUMMARY:
==4709==    definitely lost: 82 bytes in 3 blocks
==4709==    indirectly lost: 16 bytes in 1 blocks
==4709==      possibly lost: 0 bytes in 0 blocks
==4709==    still reachable: 0 bytes in 0 blocks
==4709==         suppressed: 0 bytes in 0 blocks

该程序只是在哈希表中注册了 2 个用户，然后我向一个用户发送消息并将它们存储在消息列表中。

这是主要功能和其他功能

typedef struct icl_entry_s {
    void* key;
    void *data;
    struct icl_entry_s* next;
} icl_entry_t;

typedef struct icl_hash_s {
    int nbuckets;
    int nentries;
    icl_entry_t **buckets;
    unsigned int (*hash_function)(void*);
    int (*hash_key_compare)(void*, void*);
} icl_hash_t;

icl_hash_t *hash; 

static inline void setHeader(message_hdr_t *hdr, int op, char *sender) {
#if defined(MAKE_VALGRIND_HAPPY)
    memset((char*)hdr, 0, sizeof(message_hdr_t));
#endif
    hdr->op  = op;
    strncpy(hdr->sender, sender, strlen(sender)+1);
}

static inline void setData(message_data_t *data, char *rcv, const char *buf, unsigned int len) {
#if defined(MAKE_VALGRIND_HAPPY)
    memset((char*)&(data->hdr), 0, sizeof(message_data_hdr_t));
#endif

    strncpy(data->hdr.receiver, rcv, strlen(rcv)+1);
    data->hdr.len  = len;
    data->buf      = (char *)buf;
}

/**
 * A simple string hash.
 *
 * An adaptation of Peter Weinberger's (PJW) generic hashing
 * algorithm based on Allen Holub's version. Accepts a pointer
 * to a datum to be hashed and returns an unsigned integer.
 * From: Keith Seymour's proxy library code
 *
 * @param[in] key -- the string to be hashed
 *
 * @returns the hash index
 */
unsigned int
hash_pjw(void* key)
{
    char *datum = (char *)key;
    unsigned int hash_value, i;

    if(!datum) return 0;

    for (hash_value = 0; *datum; ++datum) {
        hash_value = (hash_value << ONE_EIGHTH) + *datum;
        if ((i = hash_value & HIGH_BITS) != 0)
            hash_value = (hash_value ^ (i >> THREE_QUARTERS)) & ~HIGH_BITS;
    }
    return (hash_value);
}

static int string_compare(void* a, void* b) 
{
    return (strcmp( (char*)a, (char*)b ) == 0);
}


/**
 * Create a new hash table.
 *
 * @param[in] nbuckets -- number of buckets to create
 * @param[in] hash_function -- pointer to the hashing function to be used
 * @param[in] hash_key_compare -- pointer to the hash key comparison function to be used
 *
 * @returns pointer to new hash table.
 */

icl_hash_t *
icl_hash_create( int nbuckets, unsigned int (*hash_function)(void*), int (*hash_key_compare)(void*, void*) )
{
    icl_hash_t *ht;
    int i;

    ht = (icl_hash_t*) malloc(sizeof(icl_hash_t));
    if(!ht) return NULL;

    ht->nentries = 0;
    ht->buckets = (icl_entry_t**)malloc(nbuckets * sizeof(icl_entry_t*));
    if(!ht->buckets) return NULL;

    ht->nbuckets = nbuckets;
    for(i=0;i<ht->nbuckets;i++)
        ht->buckets[i] = NULL;

    ht->hash_function = hash_function ? hash_function : hash_pjw;
    ht->hash_key_compare = hash_key_compare ? hash_key_compare : string_compare;

    return ht;
}

/**
 * Search for an entry in a hash table.
 *
 * @param ht -- the hash table to be searched
 * @param key -- the key of the item to search for
 *
 * @returns pointer to the data corresponding to the key.
 *   If the key was not found, returns NULL.
 */

void *
icl_hash_find(icl_hash_t *ht, void* key)
{
    icl_entry_t* curr;
    unsigned int hash_val;

    if(!ht || !key) return NULL;

    hash_val = (* ht->hash_function)(key) % ht->nbuckets;

    for (curr=ht->buckets[hash_val]; curr != NULL; curr=curr->next)
        if ( ht->hash_key_compare(curr->key, key))
            return(curr->data);

    return NULL;
}

/**
 * Insert an item into the hash table.
 *
 * @param ht -- the hash table
 * @param key -- the key of the new item
 * @param data -- pointer to the new item's data
 *
 * @returns pointer to the new item.  Returns NULL on error.
 */

icl_entry_t *
icl_hash_insert(icl_hash_t *ht, void* key, void *data)
{
    icl_entry_t *curr;
    unsigned int hash_val;

    if(!ht || !key) return NULL;

    hash_val = (* ht->hash_function)(key) % ht->nbuckets;

    for (curr=ht->buckets[hash_val]; curr != NULL; curr=curr->next)
        if ( ht->hash_key_compare(curr->key, key))
            return(NULL); /* key already exists */

    /* if key was not found */
    curr = (icl_entry_t*)malloc(sizeof(icl_entry_t));
    if(!curr) return NULL;

    curr->key = key;
    curr->data = data;
    curr->next = ht->buckets[hash_val]; /* add at start */

    ht->buckets[hash_val] = curr;
    ht->nentries++;

    return curr;

/**
 * Free hash table structures (key and data are freed using functions).
 *
 * @param ht -- the hash table to be freed
 * @param free_key -- pointer to function that frees the key
 * @param free_data -- pointer to function that frees the data
 *
 * @returns 0 on success, -1 on failure.
 */
int
icl_hash_destroy(icl_hash_t *ht, void (*free_key)(void*), void (*free_data)(void*))
{
    icl_entry_t *bucket, *curr, *next;
    int i;

    if(!ht) return -1;

    for (i=0; i<ht->nbuckets; i++) {
        bucket = ht->buckets[i];
        for (curr=bucket; curr!=NULL; ) {
            next=curr->next;
            if (*free_key && curr->key) (*free_key)(curr->key);
            if (*free_data && curr->data) (*free_data)(curr->data);
            free(curr);
            curr=next;
        }
    }

    if(ht->buckets) free(ht->buckets);
    if(ht) free(ht);

    return 0;
}








int insertMsg(char* client_nickname,message_t *msg){
    char* buf=malloc(msg->data.hdr.len);
    strncpy(buf,msg->data.buf,msg->data.hdr.len);

    hash_elem *user = icl_hash_find(hash, client_nickname);
    if(user->nmsg == 32){
        return -1; 
    }

    msg_list *mex=malloc(sizeof(msg_list));
    if(mex==NULL){
        return -1;
    }

    mex->msg=malloc(sizeof(message_t));

    if(mex->msg==NULL){
        return -1;
    }

    mex->msg->data.buf=NULL;

    setHeader(&mex->msg->hdr,2,msg->hdr.sender);
    setData(&mex->msg->data,msg->data.hdr.receiver,buf,msg->data.hdr.len);

    mex->next=NULL;

    if(user->msg_head==NULL){
        user->msg_head=mex;
        user->msg_corr=user->msg_head;
    }else{
        user->msg_corr->next=mex;
        user->msg_corr=user->msg_corr->next;
    }
    user->nmsg++;       

    return 0;
}

void freeHashData(void* data){
    hash_elem* data2=(hash_elem*) data;
    msg_list* tmp=data2->msg_head;
    while(tmp!=NULL){
        free(tmp->msg->data.buf);
        free(tmp->msg);
        data2->msg_head=data2->msg_head->next;
        tmp=data2->msg_head;
    }
    //free(data2);
    free(data);
    free(tmp);
}


int main(int argc, char *argv[]) {

    //tabelle hash
    hash = icl_hash_create(1024, &hash_pjw, NULL); //rivedere 1024 forse troppo

    //fai insert per registrazioni

    hash_elem *user1 = malloc(sizeof(hash_elem));
    user1->nickname=malloc(33);
    strncpy(user1->nickname,"user1",33);
    user1->nmsg=0;
    user1->msg_head=NULL;
    user1->msg_corr=NULL;

    hash_elem *user2 = malloc(sizeof(hash_elem));
    user2->nickname=malloc(33);
    strncpy(user2->nickname,"user2",33);
    user2->nmsg=0;
    user2->msg_head=NULL;
    user2->msg_corr=NULL;

    icl_hash_insert(hash, "user1", (void*)user1);
    icl_hash_insert(hash, "user2", (void*)user2);

    message_t msg;
    memset(&msg,0,sizeof(message_t));
    msg.data.buf=NULL;

    message_t msg2;
    memset(&msg2,0,sizeof(message_t));
    msg2.data.buf=NULL;

    setHeader(&msg.hdr,1,"SERVER");
    setHeader(&msg2.hdr,1,"SERVER");

    setData(&msg.data,"user2","hello",strlen("hello")+1);
    setData(&msg2.data,"user2","hello",strlen("hello")+1);

    insertMsg("user2",&msg);
    insertMsg("user2",&msg2);


    icl_hash_destroy(hash, NULL, freeHashData);

    return 0;
}

Answer 1

您在freeHashData中没有足够的空闲，可能是:

void freeHashData(void* data){
    hash_elem* data2=(hash_elem*) data;
    msg_list* tmp=data2->msg_head;
    while (tmp !=  NULL) {
      msg_list* next = tmp->next;

      free(tmp->msg->data.buf);
      free(tmp->msg);
      free(tmp); /* you missed that */
      tmp = next;
    }
    free(data2->nickname); /* you missed that */
    free(data2);
}