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/* env.h : managing the BDB environment
 *
 * ====================================================================
 *    Licensed to the Apache Software Foundation (ASF) under one
 *    or more contributor license agreements.  See the NOTICE file
 *    distributed with this work for additional information
 *    regarding copyright ownership.  The ASF licenses this file
 *    to you under the Apache License, Version 2.0 (the
 *    "License"); you may not use this file except in compliance
 *    with the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing,
 *    software distributed under the License is distributed on an
 *    "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 *    KIND, either express or implied.  See the License for the
 *    specific language governing permissions and limitations
 *    under the License.
 * ====================================================================
 */

#include <assert.h>

#include <apr.h>
#if APR_HAS_THREADS
#include <apr_thread_proc.h>
#include <apr_time.h>
#endif

#include <apr_strings.h>
#include <apr_hash.h>

#include "svn_hash.h"
#include "svn_path.h"
#include "svn_pools.h"
#include "svn_utf.h"
#include "private/svn_atomic.h"
#include "private/svn_mutex.h"

#include "bdb-err.h"
#include "bdb_compat.h"

#include "env.h"

/* A note about the BDB environment descriptor cache.

   With the advent of DB_REGISTER in BDB-4.4, a process may only open
   an environment handle once.  This means that we must maintain a
   cache of open environment handles, with reference counts.  We
   allocate each environment descriptor (a bdb_env_t) from its own
   pool.  The cache itself (and the cache pool) are shared between
   threads, so all direct or indirect access to the pool is serialized
   with a global mutex.

   Because several threads can now use the same DB_ENV handle, we must
   use the DB_THREAD flag when opening the environments, otherwise the
   env handles (and all of libsvn_fs_base) won't be thread-safe.

   If we use DB_THREAD, however, all of the code that reads data from
   the database without a cursor must use either DB_DBT_MALLOC,
   DB_DBT_REALLOC, or DB_DBT_USERMEM, as described in the BDB
   documentation.

   (Oh, yes -- using DB_THREAD might not work on some systems. But
   then, it's quite probable that threading is seriously broken on
   those systems anyway, so we'll rely on APR_HAS_THREADS.)
*/


/* The cache key for a Berkeley DB environment descriptor.  This is a
   combination of the device ID and INODE number of the Berkeley DB
   config file.

   XXX FIXME: Although the dev+inode combination is supposed do be
   unique, apparently that's not always the case with some remote
   filesystems.  We /should/ be safe using this as a unique hash key,
   because the database must be on a local filesystem.  We can hope,
   anyway. */
typedef struct bdb_env_key_t
{
  apr_dev_t device;
  apr_ino_t inode;
} bdb_env_key_t;

/* The cached Berkeley DB environment descriptor. */
struct bdb_env_t
{
  /**************************************************************************/
  /* Error Reporting */

  /* A (char *) casted pointer to this structure is passed to BDB's
     set_errpfx(), which treats it as a NUL-terminated character
     string to prefix all BDB error messages.  However, svn also
     registers bdb_error_gatherer() as an error handler with
     set_errcall() which turns off BDB's default printing of errors to
     stderr and anytime thereafter when BDB reports an error and
     before the BDB function returns, it calls bdb_error_gatherer()
     and passes the same error prefix (char *) pointer given to
     set_errpfx().  The bdb_error_gatherer() callback casts the
     (char *) it back to a (bdb_env_t *).

     To avoid problems should BDB ever try to interpret our baton as a
     string, the first field in the structure is a char
     errpfx_string[].  Initializers of this structure must strcpy the
     value of BDB_ERRPFX_STRING into this array.  */
  char errpfx_string[sizeof(BDB_ERRPFX_STRING)];

  /* Extended error information. */
#if APR_HAS_THREADS
  apr_threadkey_t *error_info;   /* Points to a bdb_error_info_t. */
#else
  bdb_error_info_t error_info;
#endif

  /**************************************************************************/
  /* BDB Environment Cache */

  /* The Berkeley DB environment. */
  DB_ENV *env;