[英]Implement shared memory segment with a_list struct (linked list in shared memory) in C
我需要使用我制作的此結構制作一個共享內存段來保存節點
struct a_list
{
//The head of the list that acts as a node, this list has a next* and a prev*
struct list_head list;
unsigned long* val;
char* str;
char state;
};
我嘗試在堆棧上查找答案,但是它們實現了一個Node而不是我的struct,它是一個列表,其中包含節點
我也有這個緩沖區和append方法,我曾經將其追加到此列表(使用malloc),但是我知道對於共享內存,我無法做到這一點
struct buffer
{
struct a_list* buffer[BUFFER_SIZE];
int in;
int out;
};
//Method to append a file to the end of the queue (Most recently used files are at the tail)
static void append(struct a_list* ptr,const char* str, unsigned long val)
{
struct a_list* tmp;
tmp = (struct a_list*)malloc(sizeof(struct a_list));
// tmp->str = str;
tmp->str = (char *)malloc(strlen(str)+1);
strcpy(tmp->str, str);
tmp->val = (unsigned long*)malloc(sizeof(unsigned long));
memcpy(tmp->val, &val, sizeof(unsigned long));
tmp->index = (int *)malloc(sizeof(int));
memcpy(tmp->index, &buffer_p->in, sizeof(int));
tmp->address = (struct a_list*)malloc(sizeof(struct a_list*));
memcpy(tmp->address, &fileQueue, sizeof(struct a_list*));
if(list_empty(&fileQueue.list)){ //If this is the first element to be inserted into the fileQueue, initialize the head
list_add_tail( &(tmp->list), &(ptr->list) );
head = list_entry(fileQueue.list.next,struct a_list, list);
}
else{ //Else just add it to the tail of the list
list_add_tail( &(tmp->list), &(ptr->list) );
}
// while(((buffer_p->in+1)%BUFFER_SIZE) == buffer_p->out)
// ;
buffer_p->buffer[buffer_p->in] = tmp->address;
//printf("Placed: %d\n", counter);
buffer_p->in = (buffer_p->in+1) % BUFFER_SIZE;
}
在我的主要工作中,我嘗試使用
if ((shmid = shmget(key, (BUFFER_SIZE+2)*sizeof(int), IPC_CREAT | 0666)) < 0) {
perror("shmget");
exit(1);
}
if ((shm = shmat(shmid, NULL, 0)) < 0) {
perror("shmat");
exit(1);
}
buffer_p = (struct buffer*) shm;
buffer_p->in = 0;
buffer_p->out = 0;
我不喜歡它的工作方式,因為我正在指向已分配的對象(不適用於共享內存)的指針,所以我想對其進行更改,以使其實際上可與共享內存一起使用。 我已經將Beej's Guide用作共享內存以及一些堆棧溢出問題的指南,但似乎沒有一個給我這個特定的案例(或者至少我不明白答案)。 任何幫助將不勝感激,即使只是一個概念可能會丟失。 a_list結構(fileQueue)中的list_head結構是來自頭文件的結構,該結構引用內核鏈接列表實現。
編輯:這是此程序中使用的list_head結構,它基本上是使用列表的內核實現
/**
*
* I grub it from linux kernel source code and fix it for user space
* program. Of course, this is a GPL licensed header file.
*
* Here is a recipe to cook list.h for user space program
*
* 1. copy list.h from linux/include/list.h
* 2. remove
* - #ifdef __KERNE__ and its #endif
* - all #include line
* - prefetch() and rcu related functions
* 3. add macro offsetof() and container_of
*
* - kazutomo@mcs.anl.gov
*/
#ifndef _LINUX_LIST_H
#define _LINUX_LIST_H
/**
* @name from other kernel headers
*/
/*@{*/
/**
* Get offset of a member
*/
#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)
/**
* Casts a member of a structure out to the containing structure
* @param ptr the pointer to the member.
* @param type the type of the container struct this is embedded in.
* @param member the name of the member within the struct.
*
*/
#define container_of(ptr, type, member) ({ \
const typeof( ((type *)0)->member ) *__mptr = (ptr); \
(type *)( (char *)__mptr - offsetof(type,member) );})
/*@}*/
/*
* These are non-NULL pointers that will result in page faults
* under normal circumstances, used to verify that nobody uses
* non-initialized list entries.
*/
#define LIST_POISON1 ((void *) 0x00100100)
#define LIST_POISON2 ((void *) 0x00200200)
/**
* Simple doubly linked list implementation.
*
* Some of the internal functions ("__xxx") are useful when
* manipulating whole lists rather than single entries, as
* sometimes we already know the next/prev entries and we can
* generate better code by using them directly rather than
* using the generic single-entry routines.
*/
struct list_head {
struct list_head *next, *prev;
};
#define LIST_HEAD_INIT(name) { &(name), &(name) }
#define LIST_HEAD(name) \
struct list_head name = LIST_HEAD_INIT(name)
#define INIT_LIST_HEAD(ptr) do { \
(ptr)->next = (ptr); (ptr)->prev = (ptr); \
} while (0)
/*
* Insert a new entry between two known consecutive entries.
*
* This is only for internal list manipulation where we know
* the prev/next entries already!
*/
static inline void __list_add(struct list_head *new,
struct list_head *prev,
struct list_head *next)
{
next->prev = new;
new->next = next;
new->prev = prev;
prev->next = new;
}
/**
* list_add - add a new entry
* @new: new entry to be added
* @head: list head to add it after
*
* Insert a new entry after the specified head.
* This is good for implementing stacks.
*/
static inline void list_add(struct list_head *new, struct list_head *head)
{
__list_add(new, head, head->next);
}
/**
* list_add_tail - add a new entry
* @new: new entry to be added
* @head: list head to add it before
*
* Insert a new entry before the specified head.
* This is useful for implementing queues.
*/
static inline void list_add_tail(struct list_head *new, struct list_head *head)
{
__list_add(new, head->prev, head);
}
/*
* Delete a list entry by making the prev/next entries
* point to each other.
*
* This is only for internal list manipulation where we know
* the prev/next entries already!
*/
static inline void __list_del(struct list_head * prev, struct list_head * next)
{
next->prev = prev;
prev->next = next;
}
/**
* list_del - deletes entry from list.
* @entry: the element to delete from the list.
* Note: list_empty on entry does not return true after this, the entry is
* in an undefined state.
*/
static inline void list_del(struct list_head *entry)
{
__list_del(entry->prev, entry->next);
entry->next = LIST_POISON1;
entry->prev = LIST_POISON2;
}
/**
* list_del_init - deletes entry from list and reinitialize it.
* @entry: the element to delete from the list.
*/
static inline void list_del_init(struct list_head *entry)
{
__list_del(entry->prev, entry->next);
INIT_LIST_HEAD(entry);
}
/**
* list_move - delete from one list and add as another's head
* @list: the entry to move
* @head: the head that will precede our entry
*/
static inline void list_move(struct list_head *list, struct list_head *head)
{
__list_del(list->prev, list->next);
list_add(list, head);
}
/**
* list_move_tail - delete from one list and add as another's tail
* @list: the entry to move
* @head: the head that will follow our entry
*/
static inline void list_move_tail(struct list_head *list,
struct list_head *head)
{
__list_del(list->prev, list->next);
list_add_tail(list, head);
}
/**
* list_empty - tests whether a list is empty
* @head: the list to test.
*/
static inline int list_empty(const struct list_head *head)
{
return head->next == head;
}
static inline void __list_splice(struct list_head *list,
struct list_head *head)
{
struct list_head *first = list->next;
struct list_head *last = list->prev;
struct list_head *at = head->next;
first->prev = head;
head->next = first;
last->next = at;
at->prev = last;
}
/**
* list_splice - join two lists
* @list: the new list to add.
* @head: the place to add it in the first list.
*/
static inline void list_splice(struct list_head *list, struct list_head *head)
{
if (!list_empty(list))
__list_splice(list, head);
}
/**
* list_splice_init - join two lists and reinitialise the emptied list.
* @list: the new list to add.
* @head: the place to add it in the first list.
*
* The list at @list is reinitialised
*/
static inline void list_splice_init(struct list_head *list,
struct list_head *head)
{
if (!list_empty(list)) {
__list_splice(list, head);
INIT_LIST_HEAD(list);
}
}
/**
* list_entry - get the struct for this entry
* @ptr: the &struct list_head pointer.
* @type: the type of the struct this is embedded in.
* @member: the name of the list_struct within the struct.
*/
#define list_entry(ptr, type, member) \
container_of(ptr, type, member)
/**
* list_for_each - iterate over a list
* @pos: the &struct list_head to use as a loop counter.
* @head: the head for your list.
*/
#define list_for_each(pos, head) \
for (pos = (head)->next; pos != (head); \
pos = pos->next)
/**
* __list_for_each - iterate over a list
* @pos: the &struct list_head to use as a loop counter.
* @head: the head for your list.
*
* This variant differs from list_for_each() in that it's the
* simplest possible list iteration code, no prefetching is done.
* Use this for code that knows the list to be very short (empty
* or 1 entry) most of the time.
*/
#define __list_for_each(pos, head) \
for (pos = (head)->next; pos != (head); pos = pos->next)
/**
* list_for_each_prev - iterate over a list backwards
* @pos: the &struct list_head to use as a loop counter.
* @head: the head for your list.
*/
#define list_for_each_prev(pos, head) \
for (pos = (head)->prev; prefetch(pos->prev), pos != (head); \
pos = pos->prev)
/**
* list_for_each_safe - iterate over a list safe against removal of list entry
* @pos: the &struct list_head to use as a loop counter.
* @n: another &struct list_head to use as temporary storage
* @head: the head for your list.
*/
#define list_for_each_safe(pos, n, head) \
for (pos = (head)->next, n = pos->next; pos != (head); \
pos = n, n = pos->next)
/**
* list_for_each_entry - iterate over list of given type
* @pos: the type * to use as a loop counter.
* @head: the head for your list.
* @member: the name of the list_struct within the struct.
*/
#define list_for_each_entry(pos, head, member) \
for (pos = list_entry((head)->next, typeof(*pos), member); \
pos->member != (head); \
pos = list_entry(pos->member->next, typeof(*pos), member))
/**
* list_for_each_entry_reverse - iterate backwards over list of given type.
* @pos: the type * to use as a loop counter.
* @head: the head for your list.
* @member: the name of the list_struct within the struct.
*/
#define list_for_each_entry_reverse(pos, head, member) \
for (pos = list_entry((head)->prev, typeof(*pos), member); \
&pos->member != (head); \
pos = list_entry(pos->member.prev, typeof(*pos), member))
/**
* list_prepare_entry - prepare a pos entry for use as a start point in
* list_for_each_entry_continue
* @pos: the type * to use as a start point
* @head: the head of the list
* @member: the name of the list_struct within the struct.
*/
#define list_prepare_entry(pos, head, member) \
((pos) ? : list_entry(head, typeof(*pos), member))
/**
* list_for_each_entry_continue - iterate over list of given type
* continuing after existing point
* @pos: the type * to use as a loop counter.
* @head: the head for your list.
* @member: the name of the list_struct within the struct.
*/
#define list_for_each_entry_continue(pos, head, member) \
for (pos = list_entry(pos->member.next, typeof(*pos), member); \
&pos->member != (head); \
pos = list_entry(pos->member.next, typeof(*pos), member))
/**
* list_for_each_entry_safe - iterate over list of given type safe against removal of list entry
* @pos: the type * to use as a loop counter.
* @n: another type * to use as temporary storage
* @head: the head for your list.
* @member: the name of the list_struct within the struct.
*/
#define list_for_each_entry_safe(pos, n, head, member) \
for (pos = list_entry((head)->next, typeof(*pos), member), \
n = list_entry(pos->member.next, typeof(*pos), member); \
&pos->member != (head); \
pos = n, n = list_entry(n->member.next, typeof(*n), member))
/**
* list_for_each_entry_safe_continue - iterate over list of given type
* continuing after existing point safe against removal of list entry
* @pos: the type * to use as a loop counter.
* @n: another type * to use as temporary storage
* @head: the head for your list.
* @member: the name of the list_struct within the struct.
*/
#define list_for_each_entry_safe_continue(pos, n, head, member) \
for (pos = list_entry(pos->member.next, typeof(*pos), member), \
n = list_entry(pos->member.next, typeof(*pos), member); \
&pos->member != (head); \
pos = n, n = list_entry(n->member.next, typeof(*n), member))
/**
* list_for_each_entry_safe_reverse - iterate backwards over list of given type safe against
* removal of list entry
* @pos: the type * to use as a loop counter.
* @n: another type * to use as temporary storage
* @head: the head for your list.
* @member: the name of the list_struct within the struct.
*/
#define list_for_each_entry_safe_reverse(pos, n, head, member) \
for (pos = list_entry((head)->prev, typeof(*pos), member), \
n = list_entry(pos->member.prev, typeof(*pos), member); \
&pos->member != (head); \
pos = n, n = list_entry(n->member.prev, typeof(*n), member))
/*
* Double linked lists with a single pointer list head.
* Mostly useful for hash tables where the two pointer list head is
* too wasteful.
* You lose the ability to access the tail in O(1).
*/
struct hlist_head {
struct hlist_node *first;
};
struct hlist_node {
struct hlist_node *next, **pprev;
};
#define HLIST_HEAD_INIT { .first = NULL }
#define HLIST_HEAD(name) struct hlist_head name = { .first = NULL }
#define INIT_HLIST_HEAD(ptr) ((ptr)->first = NULL)
#define INIT_HLIST_NODE(ptr) ((ptr)->next = NULL, (ptr)->pprev = NULL)
static inline int hlist_unhashed(const struct hlist_node *h)
{
return !h->pprev;
}
static inline int hlist_empty(const struct hlist_head *h)
{
return !h->first;
}
static inline void __hlist_del(struct hlist_node *n)
{
struct hlist_node *next = n->next;
struct hlist_node **pprev = n->pprev;
*pprev = next;
if (next)
next->pprev = pprev;
}
static inline void hlist_del(struct hlist_node *n)
{
__hlist_del(n);
n->next = LIST_POISON1;
n->pprev = LIST_POISON2;
}
static inline void hlist_del_init(struct hlist_node *n)
{
if (n->pprev) {
__hlist_del(n);
INIT_HLIST_NODE(n);
}
}
static inline void hlist_add_head(struct hlist_node *n, struct hlist_head *h)
{
struct hlist_node *first = h->first;
n->next = first;
if (first)
first->pprev = &n->next;
h->first = n;
n->pprev = &h->first;
}
/* next must be != NULL */
static inline void hlist_add_before(struct hlist_node *n,
struct hlist_node *next)
{
n->pprev = next->pprev;
n->next = next;
next->pprev = &n->next;
*(n->pprev) = n;
}
static inline void hlist_add_after(struct hlist_node *n,
struct hlist_node *next)
{
next->next = n->next;
n->next = next;
next->pprev = &n->next;
if(next->next)
next->next->pprev = &next->next;
}
#define hlist_entry(ptr, type, member) container_of(ptr,type,member)
#define hlist_for_each(pos, head) \
for (pos = (head)->first; pos && ({ prefetch(pos->next); 1; }); \
pos = pos->next)
#define hlist_for_each_safe(pos, n, head) \
for (pos = (head)->first; pos && ({ n = pos->next; 1; }); \
pos = n)
/**
* hlist_for_each_entry - iterate over list of given type
* @tpos: the type * to use as a loop counter.
* @pos: the &struct hlist_node to use as a loop counter.
* @head: the head for your list.
* @member: the name of the hlist_node within the struct.
*/
#define hlist_for_each_entry(tpos, pos, head, member) \
for (pos = (head)->first; \
pos && ({ prefetch(pos->next); 1;}) && \
({ tpos = hlist_entry(pos, typeof(*tpos), member); 1;}); \
pos = pos->next)
/**
* hlist_for_each_entry_continue - iterate over a hlist continuing after existing point
* @tpos: the type * to use as a loop counter.
* @pos: the &struct hlist_node to use as a loop counter.
* @member: the name of the hlist_node within the struct.
*/
#define hlist_for_each_entry_continue(tpos, pos, member) \
for (pos = (pos)->next; \
pos && ({ prefetch(pos->next); 1;}) && \
({ tpos = hlist_entry(pos, typeof(*tpos), member); 1;}); \
pos = pos->next)
/**
* hlist_for_each_entry_from - iterate over a hlist continuing from existing point
* @tpos: the type * to use as a loop counter.
* @pos: the &struct hlist_node to use as a loop counter.
* @member: the name of the hlist_node within the struct.
*/
#define hlist_for_each_entry_from(tpos, pos, member) \
for (; pos && ({ prefetch(pos->next); 1;}) && \
({ tpos = hlist_entry(pos, typeof(*tpos), member); 1;}); \
pos = pos->next)
/**
* hlist_for_each_entry_safe - iterate over list of given type safe against removal of list entry
* @tpos: the type * to use as a loop counter.
* @pos: the &struct hlist_node to use as a loop counter.
* @n: another &struct hlist_node to use as temporary storage
* @head: the head for your list.
* @member: the name of the hlist_node within the struct.
*/
#define hlist_for_each_entry_safe(tpos, pos, n, head, member) \
for (pos = (head)->first; \
pos && ({ n = pos->next; 1; }) && \
({ tpos = hlist_entry(pos, typeof(*tpos), member); 1;}); \
pos = n)
#endif
第一步可能應該為malloc()
和free()
(可能還有realloc()
)創建代理,以從共享內存而不是普通堆內存管理內存分配。 您可以將它們與大多數其余代碼分開調試。 他們將需要知道整個共享內存塊有多大,並且需要記錄分配的內存或空閑的內存(或兩者都記錄)。 如果在進程之間共享內存,則控制信息也必須位於共享內存中(否則只有一個進程可以修改內存分配),並且您需要適當的並發控制(互斥量等)來保護它。 如果未在進程之間共享內存,則不應首先使用共享內存。
有了這些原語之后,您就可以修改代碼,以在需要分配空間時將它們用於代碼中的內存分配。
請注意,您的代碼分配了一個unsigned long
struct a_list
,以供struct a_list
的val
成員指向。 那是毫無意義的。 您只是在使用指針而不是直接存儲在結構中的unsigned long
浪費空間。 如果它是一個unsigned long
數組,那將是另一回事,但這不是您所顯示的。
您的問題還顯示了對struct a_list
的index
成員的訪問,該成員未在結構的定義中顯示。 而且您不顯示struct list_head
類型。 這意味着人們無法編譯您的代碼來觀察是否還有其他問題。 制作可編譯代碼是一個好主意。 花費時間來創建MCVE( 如何創建最小,完整和可驗證的示例? )或SSCCE( 簡短,自包含,正確的示例 )是值得的-兩個名稱和相同基本思想的鏈接。
這是我的解決方法:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <fcntl.h>
#include <signal.h>
#include <sys/types.h>
#include <sys/shm.h>
#define MAX_SHM_ID_NUM 100
typedef struct node
{
int val;
struct node * next;
} node;
int shm_id_arr[MAX_SHM_ID_NUM];
int current_index = -1 ;
void insert_at_tail (int num);
node * my_head = NULL;
int * num_of_elements = NULL ;
key_t key_first = 5681;
key_t key_current;
void * my_malloc(int size)
{
void * ptr = NULL;
key_current = key_first ++;
int shm_id;
if ((shm_id = shmget(key_current, size , IPC_CREAT | 0666)) < 0) {
perror("shmget error.");printf("errno= %d EINVAL=%d \n ", errno , EINVAL);
return NULL;
}
if ((ptr = shmat(shm_id, NULL, 0)) == (void *) - 1) {
perror("shmat error");
//exit(1);
return NULL;
}
current_index ++ ;
shm_id_arr[current_index] = shm_id ;
return ptr;
}
void insert_at_tail (int num)
{
if(my_head == NULL)
{
my_head = my_malloc(sizeof(node));
my_head->val = num;
my_head->next = NULL;
}else
{
node * tmp = my_head;
while(tmp->next != NULL)
tmp = tmp->next;
tmp->next = my_malloc(sizeof(node));
tmp->next->val = num;
tmp->next->next = NULL;
}
(* num_of_elements) ++;
}
/* deAttach the shared memory without removing. */
void deattach_shared_mem()
{
if (shmdt(num_of_elements) < 0) { /* deAttach num_of_elements */
perror("shmdt error num_of_elements\n");
}
if (shmdt(my_head) < 0) {
perror("shmdt error my_head\n");
}
//how to deattach all pointers in list?
}
void remove_shared_mem()
{
int i;
for(i = 0 ; i < current_index ; i ++)
{
if (shmctl(shm_id_arr[i], IPC_RMID, NULL) < 0) { /* remove the shared memory segment. */
perror("shmctl error.\n");
}
}
}
void print_it()
{
node * tmp = my_head;
while(tmp != NULL)
{
printf("%d\n" , tmp->val);
tmp = tmp->next;
}
}
int main()
{
num_of_elements = (int *)my_malloc(sizeof(int));
(* num_of_elements) = 0 ;
insert_at_tail(10);
insert_at_tail(8);
insert_at_tail(6);
insert_at_tail(4);
insert_at_tail(2);
printf("we have %d elements.\n" , (*num_of_elements));
print_it();
deattach_shared_mem();
remove_shared_mem();
return 0 ;
}
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