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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 accessible a shared memory segment with default
47  * properties.
48  * @param m The shared memory structure to create.
49  * @param reqsize The desired size of the segment.
50  * @param filename The file to use for shared memory on platforms that
51  * require it.
52  * @param pool the pool from which to allocate the shared memory
53  * structure.
54  * @remark A note about Anonymous vs. Named shared memory segments:
55  * Not all plaforms support anonymous shared memory segments, but in
56  * some cases it is prefered over other types of shared memory
57  * implementations. Passing a NULL 'file' parameter to this function
58  * will cause the subsystem to use anonymous shared memory segments.
59  * If such a system is not available, APR_ENOTIMPL is returned.
60  * @remark A note about allocation sizes:
61  * On some platforms it is necessary to store some metainformation
62  * about the segment within the actual segment. In order to supply
63  * the caller with the requested size it may be necessary for the
64  * implementation to request a slightly greater segment length
65  * from the subsystem. In all cases, the apr_shm_baseaddr_get()
66  * function will return the first usable byte of memory.
67  *
68  */
70  apr_size_t reqsize,
71  const char *filename,
72  apr_pool_t *pool);
73 
74 /**
75  * Special processing flags for apr_shm_create_ex() and apr_shm_attach_ex().
76  */
77 #define APR_SHM_NS_LOCAL 1 /* Create or attach to named shared memory
78  * segment in the "Local" namespace on
79  * Windows. (Ignored on other platforms.)
80  * By default, the "Global" namespace is
81  * used for privileged processes and the
82  * "Local" namespace is used otherwise.
83  */
84 #define APR_SHM_NS_GLOBAL 2 /* Create or attach to named shared memory
85  * segment in the "Global" namespace on
86  * Windows. (Ignored on other platforms.)
87  */
88 
89 /**
90  * Create and make accessible a shared memory segment with platform-
91  * specific processing.
92  * @param m The shared memory structure to create.
93  * @param reqsize The desired size of the segment.
94  * @param filename The file to use for shared memory on platforms that
95  * require it.
96  * @param pool the pool from which to allocate the shared memory
97  * structure.
98  * @param flags mask of APR_SHM_* (defined above)
99  * @remark A note about Anonymous vs. Named shared memory segments:
100  * Not all plaforms support anonymous shared memory segments, but in
101  * some cases it is prefered over other types of shared memory
102  * implementations. Passing a NULL 'file' parameter to this function
103  * will cause the subsystem to use anonymous shared memory segments.
104  * If such a system is not available, APR_ENOTIMPL is returned.
105  * @remark A note about allocation sizes:
106  * On some platforms it is necessary to store some metainformation
107  * about the segment within the actual segment. In order to supply
108  * the caller with the requested size it may be necessary for the
109  * implementation to request a slightly greater segment length
110  * from the subsystem. In all cases, the apr_shm_baseaddr_get()
111  * function will return the first usable byte of memory.
112  *
113  */
115  apr_size_t reqsize,
116  const char *filename,
117  apr_pool_t *pool,
118  apr_int32_t flags);
119 
120 /**
121  * Remove named resource associated with a shared memory segment,
122  * preventing attachments to the resource, but not destroying it.
123  * @param filename The filename associated with shared-memory segment which
124  * needs to be removed
125  * @param pool The pool used for file operations
126  * @remark This function is only supported on platforms which support
127  * name-based shared memory segments, and will return APR_ENOTIMPL on
128  * platforms without such support. Removing the file while the shm
129  * is in use is not entirely portable, caller may use this to enhance
130  * obscurity of the resource, but be prepared for the call to fail,
131  * and for concurrent attempts to create a resource of the same name
132  * to also fail. The pool cleanup of apr_shm_create (apr_shm_destroy)
133  * also removes the named resource.
134  */
135 APR_DECLARE(apr_status_t) apr_shm_remove(const char *filename,
136  apr_pool_t *pool);
137 
138 /**
139  * Destroy a shared memory segment and associated memory.
140  * @param m The shared memory segment structure to destroy.
141  */
143 
144 /**
145  * Attach to a shared memory segment that was created
146  * by another process.
147  * @param m The shared memory structure to create.
148  * @param filename The file used to create the original segment.
149  * (This MUST match the original filename.)
150  * @param pool the pool from which to allocate the shared memory
151  * structure for this process.
152  */
154  const char *filename,
155  apr_pool_t *pool);
156 
157 /**
158  * Attach to a shared memory segment that was created
159  * by another process, with platform-specific processing.
160  * @param m The shared memory structure to create.
161  * @param filename The file used to create the original segment.
162  * (This MUST match the original filename.)
163  * @param pool the pool from which to allocate the shared memory
164  * structure for this process.
165  * @param flags mask of APR_SHM_* (defined above)
166  */
168  const char *filename,
169  apr_pool_t *pool,
170  apr_int32_t flags);
171 
172 /**
173  * Detach from a shared memory segment without destroying it.
174  * @param m The shared memory structure representing the segment
175  * to detach from.
176  */
178 
179 /**
180  * Retrieve the base address of the shared memory segment.
181  * NOTE: This address is only usable within the callers address
182  * space, since this API does not guarantee that other attaching
183  * processes will maintain the same address mapping.
184  * @param m The shared memory segment from which to retrieve
185  * the base address.
186  * @return address, aligned by APR_ALIGN_DEFAULT.
187  */
188 APR_DECLARE(void *) apr_shm_baseaddr_get(const apr_shm_t *m);
189 
190 /**
191  * Retrieve the length of a shared memory segment in bytes.
192  * @param m The shared memory segment from which to retrieve
193  * the segment length.
194  */
195 APR_DECLARE(apr_size_t) apr_shm_size_get(const apr_shm_t *m);
196 
197 /**
198  * Get the pool used by this shared memory segment.
199  */
201 
202 /** @} */
203 
204 #ifdef __cplusplus
205 }
206 #endif
207 
208 #endif /* APR_SHM_T */