Apache Portable Runtime

apr_shm.h

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00001 /* Licensed to the Apache Software Foundation (ASF) under one or more
00002  * contributor license agreements.  See the NOTICE file distributed with
00003  * this work for additional information regarding copyright ownership.
00004  * The ASF licenses this file to You under the Apache License, Version 2.0
00005  * (the "License"); you may not use this file except in compliance with
00006  * the License.  You may obtain a copy of the License at
00007  *
00008  *     http://www.apache.org/licenses/LICENSE-2.0
00009  *
00010  * Unless required by applicable law or agreed to in writing, software
00011  * distributed under the License is distributed on an "AS IS" BASIS,
00012  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
00013  * See the License for the specific language governing permissions and
00014  * limitations under the License.
00015  */
00016 
00017 #ifndef APR_SHM_H
00018 #define APR_SHM_H
00019 
00020 /**
00021  * @file apr_shm.h
00022  * @brief APR Shared Memory Routines
00023  */
00024 
00025 #include "apr.h"
00026 #include "apr_pools.h"
00027 #include "apr_errno.h"
00028 #include "apr_perms_set.h"
00029 
00030 #ifdef __cplusplus
00031 extern "C" {
00032 #endif /* __cplusplus */
00033 
00034 /**
00035  * @defgroup apr_shm Shared Memory Routines
00036  * @ingroup APR 
00037  * @{
00038  */
00039 
00040 /**
00041  * Private, platform-specific data struture representing a shared memory
00042  * segment.
00043  */
00044 typedef struct apr_shm_t apr_shm_t;
00045 
00046 /**
00047  * Create and make accessible a shared memory segment with default
00048  * properties.
00049  * @param m The shared memory structure to create.
00050  * @param reqsize The desired size of the segment.
00051  * @param filename The file to use for shared memory on platforms that
00052  *        require it.
00053  * @param pool the pool from which to allocate the shared memory
00054  *        structure.
00055  * @remark A note about Anonymous vs. Named shared memory segments:
00056  *         Not all plaforms support anonymous shared memory segments, but in
00057  *         some cases it is prefered over other types of shared memory
00058  *         implementations. Passing a NULL 'file' parameter to this function
00059  *         will cause the subsystem to use anonymous shared memory segments.
00060  *         If such a system is not available, APR_ENOTIMPL is returned.
00061  * @remark A note about allocation sizes:
00062  *         On some platforms it is necessary to store some metainformation
00063  *         about the segment within the actual segment. In order to supply
00064  *         the caller with the requested size it may be necessary for the
00065  *         implementation to request a slightly greater segment length
00066  *         from the subsystem. In all cases, the apr_shm_baseaddr_get()
00067  *         function will return the first usable byte of memory.
00068  * 
00069  */
00070 APR_DECLARE(apr_status_t) apr_shm_create(apr_shm_t **m,
00071                                          apr_size_t reqsize,
00072                                          const char *filename,
00073                                          apr_pool_t *pool);
00074 
00075 /**
00076  * Special processing flags for apr_shm_create_ex() and apr_shm_attach_ex().
00077  */
00078 #define APR_SHM_NS_LOCAL    1 /* Create or attach to named shared memory
00079                                * segment in the "Local" namespace on
00080                                * Windows.  (Ignored on other platforms.)
00081                                * By default, the "Global" namespace is
00082                                * used for privileged processes and the
00083                                * "Local" namespace is used otherwise.
00084                                */
00085 #define APR_SHM_NS_GLOBAL   2 /* Create or attach to named shared memory
00086                                * segment in the "Global" namespace on
00087                                * Windows.  (Ignored on other platforms.)
00088                                */
00089 
00090 /**
00091  * Create and make accessible a shared memory segment with platform-
00092  * specific processing.
00093  * @param m The shared memory structure to create.
00094  * @param reqsize The desired size of the segment.
00095  * @param filename The file to use for shared memory on platforms that
00096  *        require it.
00097  * @param pool the pool from which to allocate the shared memory
00098  *        structure.
00099  * @param flags mask of APR_SHM_* (defined above)
00100  * @remark A note about Anonymous vs. Named shared memory segments:
00101  *         Not all plaforms support anonymous shared memory segments, but in
00102  *         some cases it is prefered over other types of shared memory
00103  *         implementations. Passing a NULL 'file' parameter to this function
00104  *         will cause the subsystem to use anonymous shared memory segments.
00105  *         If such a system is not available, APR_ENOTIMPL is returned.
00106  * @remark A note about allocation sizes:
00107  *         On some platforms it is necessary to store some metainformation
00108  *         about the segment within the actual segment. In order to supply
00109  *         the caller with the requested size it may be necessary for the
00110  *         implementation to request a slightly greater segment length
00111  *         from the subsystem. In all cases, the apr_shm_baseaddr_get()
00112  *         function will return the first usable byte of memory.
00113  * 
00114  */
00115 APR_DECLARE(apr_status_t) apr_shm_create_ex(apr_shm_t **m,
00116                                             apr_size_t reqsize,
00117                                             const char *filename,
00118                                             apr_pool_t *pool,
00119                                             apr_int32_t flags);
00120 
00121 /**
00122  * Remove named resource associated with a shared memory segment,
00123  * preventing attachments to the resource, but not destroying it.
00124  * @param filename The filename associated with shared-memory segment which
00125  *        needs to be removed
00126  * @param pool The pool used for file operations
00127  * @remark This function is only supported on platforms which support
00128  * name-based shared memory segments, and will return APR_ENOTIMPL on
00129  * platforms without such support.  Removing the file while the shm
00130  * is in use is not entirely portable, caller may use this to enhance
00131  * obscurity of the resource, but be prepared for the call to fail,
00132  * and for concurrent attempts to create a resource of the same name
00133  * to also fail.  The pool cleanup of apr_shm_create (apr_shm_destroy)
00134  * also removes the named resource.
00135  */
00136 APR_DECLARE(apr_status_t) apr_shm_remove(const char *filename,
00137                                          apr_pool_t *pool);
00138 
00139 /**
00140  * Delete named resource associated with a shared memory segment,
00141  * preventing attachments to the resource.
00142  * @param m The shared memory segment structure to delete.
00143  * @remark This function is only supported on platforms which support
00144  * name-based shared memory segments, and will return APR_ENOTIMPL on
00145  * platforms without such support.  Removing the file while the shm
00146  * is in use is not entirely portable, caller may use this to enhance
00147  * obscurity of the resource, but be prepared for the call to fail,
00148  * and for concurrent attempts to create a resource of the same name
00149  * to also fail.  The pool cleanup of apr_shm_create (apr_shm_destroy)
00150  * also removes the named resource.
00151  */
00152 APR_DECLARE(apr_status_t) apr_shm_delete(apr_shm_t *m);
00153 
00154 /**
00155  * Destroy a shared memory segment and associated memory.
00156  * @param m The shared memory segment structure to destroy.
00157  */
00158 APR_DECLARE(apr_status_t) apr_shm_destroy(apr_shm_t *m);
00159 
00160 /**
00161  * Attach to a shared memory segment that was created
00162  * by another process.
00163  * @param m The shared memory structure to create.
00164  * @param filename The file used to create the original segment.
00165  *        (This MUST match the original filename.)
00166  * @param pool the pool from which to allocate the shared memory
00167  *        structure for this process.
00168  */
00169 APR_DECLARE(apr_status_t) apr_shm_attach(apr_shm_t **m,
00170                                          const char *filename,
00171                                          apr_pool_t *pool);
00172 
00173 /**
00174  * Attach to a shared memory segment that was created
00175  * by another process, with platform-specific processing.
00176  * @param m The shared memory structure to create.
00177  * @param filename The file used to create the original segment.
00178  *        (This MUST match the original filename.)
00179  * @param pool the pool from which to allocate the shared memory
00180  *        structure for this process.
00181  * @param flags mask of APR_SHM_* (defined above)
00182  */
00183 APR_DECLARE(apr_status_t) apr_shm_attach_ex(apr_shm_t **m,
00184                                             const char *filename,
00185                                             apr_pool_t *pool,
00186                                             apr_int32_t flags);
00187 
00188 /**
00189  * Detach from a shared memory segment without destroying it.
00190  * @param m The shared memory structure representing the segment
00191  *        to detach from.
00192  */
00193 APR_DECLARE(apr_status_t) apr_shm_detach(apr_shm_t *m);
00194 
00195 /**
00196  * Retrieve the base address of the shared memory segment.
00197  * NOTE: This address is only usable within the callers address
00198  * space, since this API does not guarantee that other attaching
00199  * processes will maintain the same address mapping.
00200  * @param m The shared memory segment from which to retrieve
00201  *        the base address.
00202  * @return address, aligned by APR_ALIGN_DEFAULT.
00203  */
00204 APR_DECLARE(void *) apr_shm_baseaddr_get(const apr_shm_t *m);
00205 
00206 /**
00207  * Retrieve the length of a shared memory segment in bytes.
00208  * @param m The shared memory segment from which to retrieve
00209  *        the segment length.
00210  */
00211 APR_DECLARE(apr_size_t) apr_shm_size_get(const apr_shm_t *m);
00212 
00213 /**
00214  * Set shared memory permissions.
00215  */
00216 APR_PERMS_SET_IMPLEMENT(shm);
00217 
00218 /**
00219  * Get the pool used by this shared memory segment.
00220  */
00221 APR_POOL_DECLARE_ACCESSOR(shm);
00222 
00223 /** @} */ 
00224 
00225 #ifdef __cplusplus
00226 }
00227 #endif
00228 
00229 #endif  /* APR_SHM_T */
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