复杂类型的 mmap 问题
我在尝试使用复杂类型的 mmap 访问共享内存时遇到问题。
因此，我在父进程中分配内存：
/* Create mmap file */
fid = open(TMP_FILE_NAME, O_RDWR | O_CREAT | O_EXCL, (mode_t) 0755);
if (fid < 0)
{
printf("Bad Open of mmap file <%s>\n", TMP_FILE_NAME);
die(-1);
}
/* Make mmap file Buffer Size */
status = ftruncate(fid, INPUT_BUFFER_SIZE);
if (status)
{
printf("Failed to ftruncate the file <%s>, status = %d\n", TMP_FILE_NAME, status);
die(-1);
}
/* Initialize Shared Memory */
mmap_ptr = mmap((caddr_t) 0,
INPUT_BUFFER_SIZE, // Default Buffer Size
PROT_WRITE | PROT_READ, // R/W Permissions
MAP_SHARED, // No file backing
fid,
(off_t) 0);
if (mmap_ptr == MAP_FAILED)
{
printf("Failed to perform mmap, Exiting\n");
die(-1);
}
现在，我在内存中传递给子进程的结构如下：
/* Data structue for IPC */
typedef struct {
int current_active_id;
int consume_remaining;
Queue buffer;
} input_buffer;
其中 Queue 是来自以下内容的数据结构类： http://www.idevelopment.info/data/Programming/data_structs /c/Queue/Queue.shtml
在我的子进程中，当我这样做时，它会返回正确的值：
printf("Got here... Shared Mem: %d\n", input_queue->consume_remaining);
但是当我执行以下操作时：
IsEmpty(input_queue->buffer)
它会崩溃，并且在队列的代码中它只执行以下操作：
return Q->Size == 0;
任何帮助都会不胜感激，谢谢！！
I have an issue attempting to access shared memory using mmap for complex types.
So I allocate my memory as so in my parent process:
/* Create mmap file */
fid = open(TMP_FILE_NAME, O_RDWR | O_CREAT | O_EXCL, (mode_t) 0755);
if (fid < 0)
{
printf("Bad Open of mmap file <%s>\n", TMP_FILE_NAME);
die(-1);
}
/* Make mmap file Buffer Size */
status = ftruncate(fid, INPUT_BUFFER_SIZE);
if (status)
{
printf("Failed to ftruncate the file <%s>, status = %d\n", TMP_FILE_NAME, status);
die(-1);
}
/* Initialize Shared Memory */
mmap_ptr = mmap((caddr_t) 0,
INPUT_BUFFER_SIZE, // Default Buffer Size
PROT_WRITE | PROT_READ, // R/W Permissions
MAP_SHARED, // No file backing
fid,
(off_t) 0);
if (mmap_ptr == MAP_FAILED)
{
printf("Failed to perform mmap, Exiting\n");
die(-1);
}
Now the Struct that I'm passing in memory to my child process is as follows:
/* Data structue for IPC */
typedef struct {
int current_active_id;
int consume_remaining;
Queue buffer;
} input_buffer;
where Queue is a data structure class from the following:
http://www.idevelopment.info/data/Programming/data_structures/c/Queue/Queue.shtml
In my child process it's okay when I do this, it returns the correct value:
printf("Got here... Shared Mem: %d\n", input_queue->consume_remaining);
but when I do something like:
IsEmpty(input_queue->buffer)
it crashes and in the code of the Queue it's only doing this:
return Q->Size == 0;
Any help would be appreciated, thanks!!
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Queue是一个指向struct QueueRecord的指针，应该这样分配，大概使用相同的共享内存段。请注意，这也应该映射到父级和子级中的同一地址，否则您将无法取消引用它。Queueis a pointer tostruct QueueRecord, and should be allocated as such, presumably using the same shared memory segment. note that this should also be mapped at the same address in both parent and child, or you will not be able to dereference it.您放入映射中的结构包含指针。这些指针都与创建它们的进程的地址空间相关。
如果其他进程没有映射到同一地址，或者映射了，但队列的分配不是从该缓冲区内部获取的，则指针在其他进程中将无效。
The structure you are putting in the map contains pointers. The pointers are all relative to the address space of the process that created them.
If the other process doesn't mmap at the same address, or if it does but the allocations made for the queue aren't taken from inside that buffer, the pointers will be invalid in the other process.