在C中使用a_list结构（共享内存中的链表）实现共享内存段

我需要创建一个共享内存段，使用我创建的结构来保存节点

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; }; 

我尝试在堆栈上查找答案，但他们实现了一个Node而不是我的struct，这是一个包含节点的列表

我也有这个缓冲区和追加方法，我曾经附加到这个列表（使用malloc），但我知道对于共享内存我不能这样做

 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; } 

在我的主要内容中，我尝试初始化所有内容

 if ((shmid = shmget(key, (BUFFER_SIZE+2)*sizeof(int), IPC_CREAT | 0666)) < 0) { perror("shmget"); exit(1); } if ((shm = shmat(shmid, NULL, 0)) in = 0; buffer_p->out = 0; 

我不喜欢它是如何工作的，因为我指的是一些指向malloc的东西（它不能用于共享内存）所以我想改变它以便它实际上可以使用共享内存。 我在共享内存上使用了Beej的指南作为指南以及几个堆栈溢出问题，但似乎没有给我这个特定的情况（或者至少我不明白答案）。 任何帮助将不胜感激，即使它只是一个可能缺少的概念。 a_list结构（fileQueue）中的list_head结构是引用内核链表实现的头文件中的结构。

编辑：这是在这个程序中使用的list_head结构，它基本上是使用列表的内核实现

 /** * * 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 * * - [e-mail] */ #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 

Answer 1

这是我的解决方法：

 #include  #include  #include  #include  #include  #include  #include  #include  #include  #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 ; } 

Answer 2

您的第一步应该是为malloc()和free() （也可能是realloc() ）创建代理，这些代理管理来自共享内存而不是普通堆内存的内存分配。 您可以从大多数其余代码中单独调试它们。 他们需要知道共享内存块的总体大小，并且需要记录分配的内容或者空闲内容（或两者）。 如果内存在进程之间共享，则控制信息也需要在共享内存中（否则只有一个进程可以修改内存分配），并且需要适当的并发控制（互斥等）来保护它。 如果进程之间没有共享内存，则首先不应使用共享内存。

有了这些原语，您就可以修改代码，以便在需要分配空间时将它们用于代码中的内存分配。

请注意，您的代码分配了一个unsigned long ，由struct a_list的val成员指向。 这是毫无意义的。 您只是使用指针浪费空间而不是直接存储在结构中的unsigned long 。 如果它是一个unsigned long数组，那将是另一回事，但这不是你所展示的。

您的问题还显示了对struct a_list的index成员的访问权限，该成员未在结构定义中显示。 并且您不显示struct list_head类型。 这意味着人们无法编译您的代码以观察是否存在其他问题。 制作可编译的代码是个好主意。 值得花时间创建一个MCVE（ 如何创建一个最小的，完整的，可validation的示例？ ）或SSCCE（ 简短的，自包含的，正确的示例 ） – 两个名称和链接用于相同的基本思想。