/*
 * ====================================================================
 * Copyright (c) 2006 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/.
 * ====================================================================
 */

#include <apr_thread_mutex.h>
#include <apr_hash.h>

#include "svn_dso.h"
#include "svn_pools.h"
#include "svn_private_config.h"

/* A mutex to protect our global pool and cache. */
#if APR_HAS_THREADS
static apr_thread_mutex_t *dso_mutex;
#endif

/* Global pool to allocate DSOs in. */
static apr_pool_t *dso_pool;

/* Global cache for storing DSO objects. */
static apr_hash_t *dso_cache;

/* Just an arbitrary location in memory... */
static int not_there_sentinel;

/* A specific value we store in the dso_cache to indicate that the
   library wasn't found.  This keeps us from allocating extra memory
   from dso_pool when trying to find libraries we already know aren't
   there.  */
#define NOT_THERE ((void *) &not_there_sentinel)

void
svn_dso_initialize()
{
  if (dso_pool)
    return;

  dso_pool = svn_pool_create(NULL);

#if APR_HAS_THREADS
  apr_thread_mutex_create(&dso_mutex, APR_THREAD_MUTEX_DEFAULT, dso_pool);
#endif

  dso_cache = apr_hash_make(dso_pool);
}

#if APR_HAS_DSO
svn_error_t *
svn_dso_load(apr_dso_handle_t **dso, const char *fname)
{
  apr_status_t status;

  if (! dso_pool)
    svn_dso_initialize();

#if APR_HAS_THREADS
  status = apr_thread_mutex_lock(dso_mutex);
  if (status)
    return svn_error_wrap_apr(status, _("Can't grab DSO mutex"));
#endif

  *dso = apr_hash_get(dso_cache, fname, APR_HASH_KEY_STRING);

  /* First check to see if we've been through this before...  We do this
     to avoid calling apr_dso_load multiple times for a given library,
     which would result in wasting small amounts of memory each time. */
  if (*dso == NOT_THERE)
    {
      *dso = NULL;
#if APR_HAS_THREADS
      status = apr_thread_mutex_unlock(dso_mutex);
      if (status)
        return svn_error_wrap_apr(status, _("Can't ungrab DSO mutex"));
#endif
      return SVN_NO_ERROR;
    }

  /* If we got nothing back from the cache, try and load the library. */
  if (! *dso)
    {
      status = apr_dso_load(dso, fname, dso_pool);
      if (status)
        {
          *dso = NULL;

          /* It wasn't found, so set the special "we didn't find it" value. */
          apr_hash_set(dso_cache,
                       apr_pstrdup(dso_pool, fname),
                       APR_HASH_KEY_STRING,
                       NOT_THERE);

#if APR_HAS_THREADS
          status = apr_thread_mutex_unlock(dso_mutex);
          if (status)
            return svn_error_wrap_apr(status, _("Can't ungrab DSO mutex"));
#endif
          return SVN_NO_ERROR;
        }

      /* Stash the dso so we can use it next time. */
      apr_hash_set(dso_cache,
                   apr_pstrdup(dso_pool, fname),
                   APR_HASH_KEY_STRING,
                   *dso);
    }

#if APR_HAS_THREADS
  status = apr_thread_mutex_unlock(dso_mutex);
  if (status)
    return svn_error_wrap_apr(status, _("Can't ungrab DSO mutex"));
#endif

  return SVN_NO_ERROR;
}
#endif /* APR_HAS_DSO */