Apache Portable Runtime
apr_shm.h
Go to the documentation of this file.
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 
00029 #ifdef __cplusplus
00030 extern "C" {
00031 #endif /* __cplusplus */
00032 
00033 /**
00034  * @defgroup apr_shm Shared Memory Routines
00035  * @ingroup APR 
00036  * @{
00037  */
00038 
00039 /**
00040  * Private, platform-specific data struture representing a shared memory
00041  * segment.
00042  */
00043 typedef struct apr_shm_t apr_shm_t;
00044 
00045 /**
00046  * Create and make accessable a shared memory segment.
00047  * @param m The shared memory structure to create.
00048  * @param reqsize The desired size of the segment.
00049  * @param filename The file to use for shared memory on platforms that
00050  *        require it.
00051  * @param pool the pool from which to allocate the shared memory
00052  *        structure.
00053  * @remark A note about Anonymous vs. Named shared memory segments:
00054  *         Not all plaforms support anonymous shared memory segments, but in
00055  *         some cases it is prefered over other types of shared memory
00056  *         implementations. Passing a NULL 'file' parameter to this function
00057  *         will cause the subsystem to use anonymous shared memory segments.
00058  *         If such a system is not available, APR_ENOTIMPL is returned.
00059  * @remark A note about allocation sizes:
00060  *         On some platforms it is necessary to store some metainformation
00061  *         about the segment within the actual segment. In order to supply
00062  *         the caller with the requested size it may be necessary for the
00063  *         implementation to request a slightly greater segment length
00064  *         from the subsystem. In all cases, the apr_shm_baseaddr_get()
00065  *         function will return the first usable byte of memory.
00066  * 
00067  */
00068 APR_DECLARE(apr_status_t) apr_shm_create(apr_shm_t **m,
00069                                          apr_size_t reqsize,
00070                                          const char *filename,
00071                                          apr_pool_t *pool);
00072 
00073 /**
00074  * Remove named resource associated with a shared memory segment,
00075  * preventing attachments to the resource, but not destroying it.
00076  * @param filename The filename associated with shared-memory segment which
00077  *        needs to be removed
00078  * @param pool The pool used for file operations
00079  * @remark This function is only supported on platforms which support
00080  * name-based shared memory segments, and will return APR_ENOTIMPL on
00081  * platforms without such support.  Removing the file while the shm
00082  * is in use is not entirely portable, caller may use this to enhance
00083  * obscurity of the resource, but be prepared for the the call to fail,
00084  * and for concurrent attempts to create a resource of the same name
00085  * to also fail.  The pool cleanup of apr_shm_create (apr_shm_destroy)
00086  * also removes the named resource.
00087  */
00088 APR_DECLARE(apr_status_t) apr_shm_remove(const char *filename,
00089                                          apr_pool_t *pool);
00090 
00091 /**
00092  * Destroy a shared memory segment and associated memory.
00093  * @param m The shared memory segment structure to destroy.
00094  */
00095 APR_DECLARE(apr_status_t) apr_shm_destroy(apr_shm_t *m);
00096 
00097 /**
00098  * Attach to a shared memory segment that was created
00099  * by another process.
00100  * @param m The shared memory structure to create.
00101  * @param filename The file used to create the original segment.
00102  *        (This MUST match the original filename.)
00103  * @param pool the pool from which to allocate the shared memory
00104  *        structure for this process.
00105  */
00106 APR_DECLARE(apr_status_t) apr_shm_attach(apr_shm_t **m,
00107                                          const char *filename,
00108                                          apr_pool_t *pool);
00109 
00110 /**
00111  * Detach from a shared memory segment without destroying it.
00112  * @param m The shared memory structure representing the segment
00113  *        to detach from.
00114  */
00115 APR_DECLARE(apr_status_t) apr_shm_detach(apr_shm_t *m);
00116 
00117 /**
00118  * Retrieve the base address of the shared memory segment.
00119  * NOTE: This address is only usable within the callers address
00120  * space, since this API does not guarantee that other attaching
00121  * processes will maintain the same address mapping.
00122  * @param m The shared memory segment from which to retrieve
00123  *        the base address.
00124  * @return address, aligned by APR_ALIGN_DEFAULT.
00125  */
00126 APR_DECLARE(void *) apr_shm_baseaddr_get(const apr_shm_t *m);
00127 
00128 /**
00129  * Retrieve the length of a shared memory segment in bytes.
00130  * @param m The shared memory segment from which to retrieve
00131  *        the segment length.
00132  */
00133 APR_DECLARE(apr_size_t) apr_shm_size_get(const apr_shm_t *m);
00134 
00135 /**
00136  * Get the pool used by this shared memory segment.
00137  */
00138 APR_POOL_DECLARE_ACCESSOR(shm);
00139 
00140 /** @} */ 
00141 
00142 #ifdef __cplusplus
00143 }
00144 #endif
00145 
00146 #endif  /* APR_SHM_T */
 All Data Structures Files Functions Variables Typedefs Enumerations Enumerator Defines