apr_shm.h revision 251875 
1/* Licensed to the Apache Software Foundation (ASF) under one or more
2 * contributor license agreements.  See the NOTICE file distributed with
3 * this work for additional information regarding copyright ownership.
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
6 * the License.  You may obtain a copy of the License at
7 *
8 *     http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
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
29#ifdef __cplusplus
30extern "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 */
43typedef 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 */
68APR_DECLARE(apr_status_t) apr_shm_create(apr_shm_t **m,
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 */
88APR_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 */
95APR_DECLARE(apr_status_t) apr_shm_destroy(apr_shm_t *m);
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 */
106APR_DECLARE(apr_status_t) apr_shm_attach(apr_shm_t **m,
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 */
115APR_DECLARE(apr_status_t) apr_shm_detach(apr_shm_t *m);
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 */
126APR_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 */
133APR_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 */
138APR_POOL_DECLARE_ACCESSOR(shm);
139
140/** @} */
141
142#ifdef __cplusplus
143}
144#endif
145
146#endif  /* APR_SHM_T */
147