Apache Portable Runtime
apr_shm.h
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1/* Licensed to the Apache Software Foundation (ASF) under one or more
2 * contributor license agreements. See the NOTICE file distributed with
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4 * The ASF licenses this file to You under the Apache License, Version 2.0
5 * (the "License"); you may not use this file except in compliance with
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7 *
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10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
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13 * See the License for the specific language governing permissions and
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15 */
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
31extern "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 */
44typedef 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 */
136APR_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 */
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 */
211APR_DECLARE(apr_size_t) apr_shm_size_get(const apr_shm_t *m);
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 Platform Definitions.
APR Error Codes.
APR Process Locking Routines.
APR memory allocation.
int apr_status_t
Definition: apr_errno.h:44
#define APR_DECLARE(type)
Definition: apr.h:498
#define APR_POOL_DECLARE_ACCESSOR(type)
Definition: apr_pools.h:81
struct apr_pool_t apr_pool_t
Definition: apr_pools.h:60
apr_status_t apr_shm_attach_ex(apr_shm_t **m, const char *filename, apr_pool_t *pool, apr_int32_t flags)
apr_status_t apr_shm_attach(apr_shm_t **m, const char *filename, apr_pool_t *pool)
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_size_t apr_shm_size_get(const apr_shm_t *m)
struct apr_shm_t apr_shm_t
Definition: apr_shm.h:44
apr_status_t apr_shm_destroy(apr_shm_t *m)
apr_status_t apr_shm_detach(apr_shm_t *m)
void * apr_shm_baseaddr_get(const apr_shm_t *m)
apr_status_t apr_shm_delete(apr_shm_t *m)
apr_status_t apr_shm_create(apr_shm_t **m, apr_size_t reqsize, const char *filename, apr_pool_t *pool)
apr_status_t apr_shm_remove(const char *filename, apr_pool_t *pool)
APR_PERMS_SET_IMPLEMENT(shm)