the share memory of Apache
Some knowledge about apr_share_memoryFirst, I will give a small example to show what is apr_share_memory :
/ *pseudo code about the whole progress* /
#include
#include
#include
#include
#include
#include
#include
#include
Read();
Write();
int main()
{
apr_shm_t *shm = NULL;
apr_pool_t *pool = NULL;
const char *filename = "ab.txt";
apr_status_t rv;
char *buf = NULL;
apr_initialize();
apr_pool_create(&pool,NULL);
if(rv = apr_shm_create(&shm,1024,filename,pool) != APR_SUCCESS)
{
printf("%d!\n",rv);
return rv;
}
if(rv = apr_shm_attach(&shm,NULL,pool) != APR_SUCCESS)
{
printf("attach faild\n");
return rv;
}
//Read();
Write();
if(rv = apr_shm_detach(shm) != APR_SUCCESS)
{
printf("detach failed\n");
return rv;
}
printf("the whole progress success!\n");
apr_terminate();
return 0;
}
Now,to present the major function in the example:
1) apr_initialize()
This is called skeleton code, we call apr_initialize() at the initialization.
2) apr_pool_create()
the prototype:
/**
* Create a new pool.
* @param newpool The pool we have just created.
* @param parent The parent pool.If this is NULL, the new pool is a root
* pool.If it is non-NULL, the new pool will inherit all
* of its parent pool's attributes, except the apr_pool_t will
* be a sub-pool.
*/
APR_DECLARE(apr_status_t) apr_pool_create(apr_pool_t **newpool, apr_pool_t *parent);
3) apr_shm_create();
the prototype:
/**
* Create and make accessable a shared memory segment.
* @param m The shared memory structure to create.
* @param reqsize The desired size of the segment.
* @param filename The file to use for shared memory on platforms that
* require it.
* @param pool the pool from which to allocate the shared memory
* structure.
* @remark A note about Anonymous vs. Named shared memory segments:
* Not all plaforms support anonymous shared memory segments, but in
* some cases it is prefered over other types of shared memory
* implementations. Passing a NULL 'file' parameter to this function
* will cause the subsystem to use anonymous shared memory segments.
* If such a system is not available, APR_ENOTIMPL is returned.
* @remark A note about allocation sizes:
* On some platforms it is necessary to store some metainformation
* about the segment within the actual segment. In order to supply
* the caller with the requested size it may be necessary for the
* implementation to request a slightly greater segment length
* from the subsystem. In all cases, the apr_shm_baseaddr_get()
* function will return the first usable byte of memory.
*
*/
APR_DECLARE(apr_status_t) apr_shm_create(apr_shm_t **m,
apr_size_t reqsize,
const char *filename,
apr_pool_t *pool);
4) apr_shm_attach();
the prototype:
/**
* Attach to a shared memory segment that was created
* by another process.
* @param m The shared memory structure to create.
* @param filename The file used to create the original segment.
* (This MUST match the original filename.)
* @param pool the pool from which to allocate the shared memory
* structure for this process.
*/
APR_DECLARE(apr_status_t) apr_shm_attach(apr_shm_t **m,
const char *filename,
apr_pool_t *pool);
5) apr_shm_detach();
the prototype:
/**
* Detach from a shared memory segment without destroying it.
* @param m The shared memory structure representing the segment
* to detach from.
*/
APR_DECLARE(apr_status_t) apr_shm_detach(apr_shm_t *m);
6) apr_terminate();
As the apr_initialization ,we call apr_terminate() at the finalization
In addition:
This is another function which is apr_shm_destory()
/**
* Destroy a shared memory segment and associated memory.
* @param m The shared memory segment structure to destroy.
*/
APR_DECLARE(apr_status_t) apr_shm_destroy(apr_shm_t *m);
As we know, maybe it’s simple for us to use the function, but how the function work and why it works like this, we have to read and think the code. It’s a long way to master the apr_share_momory.
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