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apr_shm.h
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16 
17 #ifndef APR_SHM_H
18 #define APR_SHM_H
19 
20 /**
21  * @file apr_shm.h
22  * @brief APR Shared Memory Routines
23  */
24 
25 #include "apr.h"
26 #include "apr_pools.h"
27 #include "apr_errno.h"
28 
29 #ifdef __cplusplus
30 extern "C" {
31 #endif /* __cplusplus */
32 
33 /**
34  * @defgroup apr_shm Shared Memory Routines
35  * @ingroup APR
36  * @{
37  */
38 
39 /**
40  * Private, platform-specific data struture representing a shared memory
41  * segment.
42  */
43 typedef struct apr_shm_t apr_shm_t;
44 
45 /**
46  * Create and make accessable a shared memory segment.
47  * @param m The shared memory structure to create.
48  * @param reqsize The desired size of the segment.
49  * @param filename The file to use for shared memory on platforms that
50  * require it.
51  * @param pool the pool from which to allocate the shared memory
52  * structure.
53  * @remark A note about Anonymous vs. Named shared memory segments:
54  * Not all plaforms support anonymous shared memory segments, but in
55  * some cases it is prefered over other types of shared memory
56  * implementations. Passing a NULL 'file' parameter to this function
57  * will cause the subsystem to use anonymous shared memory segments.
58  * If such a system is not available, APR_ENOTIMPL is returned.
59  * @remark A note about allocation sizes:
60  * On some platforms it is necessary to store some metainformation
61  * about the segment within the actual segment. In order to supply
62  * the caller with the requested size it may be necessary for the
63  * implementation to request a slightly greater segment length
64  * from the subsystem. In all cases, the apr_shm_baseaddr_get()
65  * function will return the first usable byte of memory.
66  *
67  */
69  apr_size_t reqsize,
70  const char *filename,
71  apr_pool_t *pool);
72 
73 /**
74  * Remove named resource associated with a shared memory segment,
75  * preventing attachments to the resource, but not destroying it.
76  * @param filename The filename associated with shared-memory segment which
77  * needs to be removed
78  * @param pool The pool used for file operations
79  * @remark This function is only supported on platforms which support
80  * name-based shared memory segments, and will return APR_ENOTIMPL on
81  * platforms without such support. Removing the file while the shm
82  * is in use is not entirely portable, caller may use this to enhance
83  * obscurity of the resource, but be prepared for the the call to fail,
84  * and for concurrent attempts to create a resource of the same name
85  * to also fail. The pool cleanup of apr_shm_create (apr_shm_destroy)
86  * also removes the named resource.
87  */
88 APR_DECLARE(apr_status_t) apr_shm_remove(const char *filename,
89  apr_pool_t *pool);
90 
91 /**
92  * Destroy a shared memory segment and associated memory.
93  * @param m The shared memory segment structure to destroy.
94  */
96 
97 /**
98  * Attach to a shared memory segment that was created
99  * by another process.
100  * @param m The shared memory structure to create.
101  * @param filename The file used to create the original segment.
102  * (This MUST match the original filename.)
103  * @param pool the pool from which to allocate the shared memory
104  * structure for this process.
105  */
107  const char *filename,
108  apr_pool_t *pool);
109 
110 /**
111  * Detach from a shared memory segment without destroying it.
112  * @param m The shared memory structure representing the segment
113  * to detach from.
114  */
116 
117 /**
118  * Retrieve the base address of the shared memory segment.
119  * NOTE: This address is only usable within the callers address
120  * space, since this API does not guarantee that other attaching
121  * processes will maintain the same address mapping.
122  * @param m The shared memory segment from which to retrieve
123  * the base address.
124  * @return address, aligned by APR_ALIGN_DEFAULT.
125  */
126 APR_DECLARE(void *) apr_shm_baseaddr_get(const apr_shm_t *m);
127 
128 /**
129  * Retrieve the length of a shared memory segment in bytes.
130  * @param m The shared memory segment from which to retrieve
131  * the segment length.
132  */
133 APR_DECLARE(apr_size_t) apr_shm_size_get(const apr_shm_t *m);
134 
135 /**
136  * Get the pool used by this shared memory segment.
137  */
139 
140 /** @} */
141 
142 #ifdef __cplusplus
143 }
144 #endif
145 
146 #endif /* APR_SHM_T */