subversion/include/svn_pools.h

/* svn_pools.h:  APR pool management for Subversion
 *
 * ====================================================================
 * Copyright (c) 2000-2002 CollabNet.  All rights reserved.
 *
 * This software is licensed as described in the file COPYING, which
 * you should have received as part of this distribution.  The terms
 * are also available at http://subversion.tigris.org/license-1.html.
 * If newer versions of this license are posted there, you may use a
 * newer version instead, at your option.
 *
 * This software consists of voluntary contributions made by many
 * individuals.  For exact contribution history, see the revision
 * history and logs, available at http://subversion.tigris.org/.
 * ====================================================================
 */




#ifndef SVN_POOLS_H
#define SVN_POOLS_H

#include <apr.h>
#include <apr_errno.h>     /* APR's error system */
#include <apr_pools.h>

#include <svn_types.h>

#ifdef __cplusplus
extern "C" {
#endif /* __cplusplus */



/*** Wrappers around APR pools, so we get error pools. ***/


/* THE ERROR POOL
 *
 * When SVN allocates an svn_error_t, it must do so from a pool. There is
 * almost always a pool available for a function to provide to the error
 * creation functions. However, that pool may have a shorter lifetime than
 * is required for the error (in many cases, the error needs to bubble all
 * the way to the top-most control function). Assuming that these shorter-
 * lifetime pools are cleared or even destroyed as the error propagates,
 * then we need a way to ensure that the error is allocated within the
 * proper pool, to get the proper lifetime.
 *
 * We create a pool specifically for errors. This pool is then "hung from"
 * the top-most pool that SVN will be using (whether this top-most pool is
 * provided by an embeddor such as Apache, or whether an SVN tool creates
 * the top-most pool itself). Since this error pool has a lifetime *at least*
 * as long as the top-most pool, then any errors allocated within it will
 * survive back to the top-most control function.
 *
 * We use a subpool rather than the top-most pool itself because we may want
 * to occasionally clear the error pool (say, if we get an error, recover,
 * and restart the operation).
 *
 * This subpool is called "the error pool". Using APR's "userdata" feature,
 * we associate the error pool with every subpool that SVN creates. When
 * the SVN error system allocates a new error, it first fetches the subpool
 * from the pool..
 */

/* You may be wondering why is this is in svn_error, instead of
   svn_pool or whatever.  The reason is the needs of the SVN error
   system are our only justification for wrapping APR's pool creation
   funcs -- because errors have to live as long as the top-most pool
   in a test program or a `request'.  If you're not using SVN errors,
   there's no reason not to use APR's native pool interface.  But you
   are using SVN errors, aren't you? */

/* Initalize the given pool as SVN's top-most pool. This is needed when SVN
 * is embedded in another application, and all of SVN's work will occur
 * within a given pool.
 *
 * This function will construct the error pool (for all errors to live
 * within), and hang it off of the given pool.  When subpools are created
 * with svn_pool_create(), they will inherit the error pool.
 *
 * Note: we return an apr_status_t since a catch-22 means we cannot allocate
 * an svn_error_t.
 *
 * WARNING: this is ONLY to be used for pools provided by an embeddor. Do not
 * use it for pools returned by svn_pool_create().  */
apr_status_t svn_error_init_pool (apr_pool_t *top_pool);


/* Return a new pool.  If PARENT_POOL is non-null, then the new
 * pool will be a subpool of it, and will inherit the containing
 * pool's dedicated error subpool.
 *
 * If PARENT_POOL is NULL, then the returned pool will be a new
 * "global" pool (with no parent), and an error pool will be created.
 *
 * If anything goes wrong with the pool creation, then an abort function
 * will be called, which will exit the program. If future allocations from
 * this pool cannot be fulfilled, then the abort function will be called,
 * terminating the program.  */
apr_pool_t *svn_pool_create (apr_pool_t *parent_pool);

apr_pool_t *svn_pool_create_debug (apr_pool_t *parent_pool,
                                   const char *file_line);

#if APR_POOL_DEBUG
#define svn_pool_create(p) svn_pool_create_debug(p, APR_POOL__FILE_LINE__)
#endif /* APR_POOL_DEBUG */


/* Clear the passed in pool.
 *
 * The reason we need this wrapper to apr_pool_clear, is because
 * apr_pool_clear removes the association with the appropriate error
 * pool. This wrapper calls apr_pool_clear, and then reattaches or
 * recreates the error pool.
 *
 * If anything goes wrong, an abort function will be called.  */
void svn_pool_clear (apr_pool_t *p);

void svn_pool_clear_debug (apr_pool_t *p,
                           const char *file_line);

#if APR_POOL_DEBUG
#define svn_pool_clear(p) svn_pool_clear_debug(p, APR_POOL__FILE_LINE__)
#endif /* APR_POOL_DEBUG */


/* Destroy a POOL and all of its children. 
 *
 * This define for svn_pool_destroy exists for symmatry (the
 * not-so-grand reason) and for the existence of a great memory usage
 * debugging hook (the grand reason).
 */
#define svn_pool_destroy apr_pool_destroy


#ifdef __cplusplus
}
#endif /* __cplusplus */

#endif /* SVN_ERROR_H */


/* ----------------------------------------------------------------
 * local variables:
 * eval: (load-file "../../tools/dev/svn-dev.el")
 * end:
 */