Apache Portable Runtime
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 #include "apr_perms_set.h"
29 
30 #ifdef __cplusplus
31 extern "C" {
32 #endif /* __cplusplus */
33 
34 /**
35  * @defgroup apr_shm Shared Memory Routines
36  * @ingroup APR
37  * @{
38  */
39 
40 /**
41  * Private, platform-specific data struture representing a shared memory
42  * segment.
43  */
44 typedef struct apr_shm_t apr_shm_t;
45 
46 /**
47  * Create and make accessible a shared memory segment with default
48  * properties.
49  * @param m The shared memory structure to create.
50  * @param reqsize The desired size of the segment.
51  * @param filename The file to use for shared memory on platforms that
52  * require it.
53  * @param pool the pool from which to allocate the shared memory
54  * structure.
55  * @remark A note about Anonymous vs. Named shared memory segments:
56  * Not all plaforms support anonymous shared memory segments, but in
57  * some cases it is prefered over other types of shared memory
58  * implementations. Passing a NULL 'file' parameter to this function
59  * will cause the subsystem to use anonymous shared memory segments.
60  * If such a system is not available, APR_ENOTIMPL is returned.
61  * @remark A note about allocation sizes:
62  * On some platforms it is necessary to store some metainformation
63  * about the segment within the actual segment. In order to supply
64  * the caller with the requested size it may be necessary for the
65  * implementation to request a slightly greater segment length
66  * from the subsystem. In all cases, the apr_shm_baseaddr_get()
67  * function will return the first usable byte of memory.
68  *
69  */
71  apr_size_t reqsize,
72  const char *filename,
73  apr_pool_t *pool);
74 
75 /**
76  * Special processing flags for apr_shm_create_ex() and apr_shm_attach_ex().
77  */
78 #define APR_SHM_NS_LOCAL 1 /* Create or attach to named shared memory
79  * segment in the "Local" namespace on
80  * Windows. (Ignored on other platforms.)
81  * By default, the "Global" namespace is
82  * used for privileged processes and the
83  * "Local" namespace is used otherwise.
84  */
85 #define APR_SHM_NS_GLOBAL 2 /* Create or attach to named shared memory
86  * segment in the "Global" namespace on
87  * Windows. (Ignored on other platforms.)
88  */
89 
90 /**
91  * Create and make accessible a shared memory segment with platform-
92  * specific processing.
93  * @param m The shared memory structure to create.
94  * @param reqsize The desired size of the segment.
95  * @param filename The file to use for shared memory on platforms that
96  * require it.
97  * @param pool the pool from which to allocate the shared memory
98  * structure.
99  * @param flags mask of APR_SHM_* (defined above)
100  * @remark A note about Anonymous vs. Named shared memory segments:
101  * Not all plaforms support anonymous shared memory segments, but in
102  * some cases it is prefered over other types of shared memory
103  * implementations. Passing a NULL 'file' parameter to this function
104  * will cause the subsystem to use anonymous shared memory segments.
105  * If such a system is not available, APR_ENOTIMPL is returned.
106  * @remark A note about allocation sizes:
107  * On some platforms it is necessary to store some metainformation
108  * about the segment within the actual segment. In order to supply
109  * the caller with the requested size it may be necessary for the
110  * implementation to request a slightly greater segment length
111  * from the subsystem. In all cases, the apr_shm_baseaddr_get()
112  * function will return the first usable byte of memory.
113  *
114  */
116  apr_size_t reqsize,
117  const char *filename,
118  apr_pool_t *pool,
119  apr_int32_t flags);
120 
121 /**
122  * Remove named resource associated with a shared memory segment,
123  * preventing attachments to the resource, but not destroying it.
124  * @param filename The filename associated with shared-memory segment which
125  * needs to be removed
126  * @param pool The pool used for file operations
127  * @remark This function is only supported on platforms which support
128  * name-based shared memory segments, and will return APR_ENOTIMPL on
129  * platforms without such support. Removing the file while the shm
130  * is in use is not entirely portable, caller may use this to enhance
131  * obscurity of the resource, but be prepared for the call to fail,
132  * and for concurrent attempts to create a resource of the same name
133  * to also fail. The pool cleanup of apr_shm_create (apr_shm_destroy)
134  * also removes the named resource.
135  */
136 APR_DECLARE(apr_status_t) apr_shm_remove(const char *filename,
137  apr_pool_t *pool);
138 
139 /**
140  * Delete named resource associated with a shared memory segment,
141  * preventing attachments to the resource.
142  * @param m The shared memory segment structure to delete.
143  * @remark This function is only supported on platforms which support
144  * name-based shared memory segments, and will return APR_ENOTIMPL on
145  * platforms without such support. Removing the file while the shm
146  * is in use is not entirely portable, caller may use this to enhance
147  * obscurity of the resource, but be prepared for the call to fail,
148  * and for concurrent attempts to create a resource of the same name
149  * to also fail. The pool cleanup of apr_shm_create (apr_shm_destroy)
150  * also removes the named resource.
151  */
153 
154 /**
155  * Destroy a shared memory segment and associated memory.
156  * @param m The shared memory segment structure to destroy.
157  */
159 
160 /**
161  * Attach to a shared memory segment that was created
162  * by another process.
163  * @param m The shared memory structure to create.
164  * @param filename The file used to create the original segment.
165  * (This MUST match the original filename.)
166  * @param pool the pool from which to allocate the shared memory
167  * structure for this process.
168  */
170  const char *filename,
171  apr_pool_t *pool);
172 
173 /**
174  * Attach to a shared memory segment that was created
175  * by another process, with platform-specific processing.
176  * @param m The shared memory structure to create.
177  * @param filename The file used to create the original segment.
178  * (This MUST match the original filename.)
179  * @param pool the pool from which to allocate the shared memory
180  * structure for this process.
181  * @param flags mask of APR_SHM_* (defined above)
182  */
184  const char *filename,
185  apr_pool_t *pool,
186  apr_int32_t flags);
187 
188 /**
189  * Detach from a shared memory segment without destroying it.
190  * @param m The shared memory structure representing the segment
191  * to detach from.
192  */
194 
195 /**
196  * Retrieve the base address of the shared memory segment.
197  * NOTE: This address is only usable within the callers address
198  * space, since this API does not guarantee that other attaching
199  * processes will maintain the same address mapping.
200  * @param m The shared memory segment from which to retrieve
201  * the base address.
202  * @return address, aligned by APR_ALIGN_DEFAULT.
203  */
204 APR_DECLARE(void *) apr_shm_baseaddr_get(const apr_shm_t *m);
205 
206 /**
207  * Retrieve the length of a shared memory segment in bytes.
208  * @param m The shared memory segment from which to retrieve
209  * the segment length.
210  */
211 APR_DECLARE(apr_size_t) apr_shm_size_get(const apr_shm_t *m);
212 
213 /**
214  * Set shared memory permissions.
215  */
217 
218 /**
219  * Get the pool used by this shared memory segment.
220  */
222 
223 /** @} */
224 
225 #ifdef __cplusplus
226 }
227 #endif
228 
229 #endif /* APR_SHM_T */
apr_status_t apr_shm_create(apr_shm_t **m, apr_size_t reqsize, const char *filename, apr_pool_t *pool)
apr_size_t apr_shm_size_get(const apr_shm_t *m)
APR Process Locking Routines.
apr_status_t apr_shm_remove(const char *filename, apr_pool_t *pool)
apr_status_t apr_shm_attach(apr_shm_t **m, const char *filename, apr_pool_t *pool)
void * apr_shm_baseaddr_get(const apr_shm_t *m)
apr_status_t apr_shm_create_ex(apr_shm_t **m, apr_size_t reqsize, const char *filename, apr_pool_t *pool, apr_int32_t flags)
APR memory allocation.
struct apr_shm_t apr_shm_t
Definition: apr_shm.h:44
APR Error Codes.
#define APR_DECLARE(type)
Definition: apr.h:500
APR Platform Definitions.
apr_status_t apr_shm_destroy(apr_shm_t *m)
apr_status_t apr_shm_attach_ex(apr_shm_t **m, const char *filename, apr_pool_t *pool, apr_int32_t flags)
APR_PERMS_SET_IMPLEMENT(shm)
struct apr_pool_t apr_pool_t
Definition: apr_pools.h:60
int apr_status_t
Definition: apr_errno.h:44
#define APR_POOL_DECLARE_ACCESSOR(type)
Definition: apr_pools.h:81
apr_status_t apr_shm_delete(apr_shm_t *m)
apr_status_t apr_shm_detach(apr_shm_t *m)