1 /* Licensed to the Apache Software Foundation (ASF) under one or more
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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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8 * http://www.apache.org/licenses/LICENSE-2.0
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
14 * limitations under the License.
22 * @brief APR Shared Memory Routines
26 #include "apr_pools.h"
27 #include "apr_errno.h"
31 #endif /* __cplusplus */
34 * @defgroup apr_shm Shared Memory Routines
40 * Private, platform-specific data struture representing a shared memory
43 typedef struct apr_shm_t apr_shm_t;
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
51 * @param pool the pool from which to allocate the shared memory
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.
68 APR_DECLARE(apr_status_t) apr_shm_create(apr_shm_t **m,
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
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.
88 APR_DECLARE(apr_status_t) apr_shm_remove(const char *filename,
92 * Destroy a shared memory segment and associated memory.
93 * @param m The shared memory segment structure to destroy.
95 APR_DECLARE(apr_status_t) apr_shm_destroy(apr_shm_t *m);
98 * Attach to a shared memory segment that was created
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.
106 APR_DECLARE(apr_status_t) apr_shm_attach(apr_shm_t **m,
107 const char *filename,
111 * Detach from a shared memory segment without destroying it.
112 * @param m The shared memory structure representing the segment
115 APR_DECLARE(apr_status_t) apr_shm_detach(apr_shm_t *m);
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
124 * @return address, aligned by APR_ALIGN_DEFAULT.
126 APR_DECLARE(void *) apr_shm_baseaddr_get(const apr_shm_t *m);
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.
133 APR_DECLARE(apr_size_t) apr_shm_size_get(const apr_shm_t *m);
136 * Get the pool used by this shared memory segment.
138 APR_POOL_DECLARE_ACCESSOR(shm);
146 #endif /* APR_SHM_T */