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src/subversion/subversion/libsvn_subr/cache-membuffer.c  view on Meta::CPAN

    {
      apr_status_t status;
      if (cache->allow_blocking_writes)
        {
          status = apr_thread_rwlock_wrlock(cache->lock);
        }
      else
        {
          status = apr_thread_rwlock_trywrlock(cache->lock);
          if (SVN_LOCK_IS_BUSY(status))
            {
              *success = FALSE;
              status = APR_SUCCESS;
            }
        }

      if (status)
        return svn_error_wrap_apr(status,
                                  _("Can't write-lock cache mutex"));
    }
#endif
  return SVN_NO_ERROR;
}

/* If locking is supported for CACHE, acquire an unconditional write lock
 * for it.
 */
static svn_error_t *
force_write_lock_cache(svn_membuffer_t *cache)
{
#if APR_HAS_THREADS
  apr_status_t status = apr_thread_rwlock_wrlock(cache->lock);
  if (status)
    return svn_error_wrap_apr(status,
                              _("Can't write-lock cache mutex"));
#endif
  return SVN_NO_ERROR;
}

/* If locking is supported for CACHE, release the current lock
 * (read or write).
 */
static svn_error_t *
unlock_cache(svn_membuffer_t *cache, svn_error_t *err)
{
#if APR_HAS_THREADS
  if (cache->lock)
  {
    apr_status_t status = apr_thread_rwlock_unlock(cache->lock);
    if (err)
      return err;

    if (status)
      return svn_error_wrap_apr(status, _("Can't unlock cache mutex"));
  }
#endif
  return err;
}

/* If supported, guard the execution of EXPR with a read lock to cache.
 * Macro has been modeled after SVN_MUTEX__WITH_LOCK.
 */
#define WITH_READ_LOCK(cache, expr)         \
do {                                        \
  SVN_ERR(read_lock_cache(cache));          \
  SVN_ERR(unlock_cache(cache, (expr)));     \
} while (0)

/* If supported, guard the execution of EXPR with a write lock to cache.
 * Macro has been modeled after SVN_MUTEX__WITH_LOCK.
 *
 * The write lock process is complicated if we don't allow to wait for
 * the lock: If we didn't get the lock, we may still need to remove an
 * existing entry for the given key because that content is now stale.
 * Once we discovered such an entry, we unconditionally do a blocking
 * wait for the write lock.  In case no old content could be found, a
 * failing lock attempt is simply a no-op and we exit the macro.
 */
#define WITH_WRITE_LOCK(cache, expr)                            \
do {                                                            \
  svn_boolean_t got_lock = TRUE;                                \
  SVN_ERR(write_lock_cache(cache, &got_lock));                  \
  if (!got_lock)                                                \
    {                                                           \
      svn_boolean_t exists;                                     \
      SVN_ERR(entry_exists(cache, group_index, key, &exists));  \
      if (exists)                                               \
        SVN_ERR(force_write_lock_cache(cache));                 \
      else                                                      \
        break;                                                  \
    }                                                           \
  SVN_ERR(unlock_cache(cache, (expr)));                         \
} while (0)

/* Resolve a dictionary entry reference, i.e. return the entry
 * for the given IDX.
 */
static APR_INLINE entry_t *
get_entry(svn_membuffer_t *cache, apr_uint32_t idx)
{
  return &cache->directory[idx / GROUP_SIZE].entries[idx % GROUP_SIZE];
}

/* Get the entry references for the given ENTRY.
 */
static APR_INLINE apr_uint32_t
get_index(svn_membuffer_t *cache, entry_t *entry)
{
  apr_size_t group_index
    = ((char *)entry - (char *)cache->directory) / sizeof(entry_group_t);

  return (apr_uint32_t)group_index * GROUP_SIZE
       + (apr_uint32_t)(entry - cache->directory[group_index].entries);
}

/* Remove the used ENTRY from the CACHE, i.e. make it "unused".
 * In contrast to insertion, removal is possible for any entry.
 */
static void
drop_entry(svn_membuffer_t *cache, entry_t *entry)
{
  /* the group that ENTRY belongs to plus a number of useful index values
   */
  apr_uint32_t idx = get_index(cache, entry);
  apr_uint32_t group_index = idx / GROUP_SIZE;
  entry_group_t *group = &cache->directory[group_index];
  apr_uint32_t last_in_group = group_index * GROUP_SIZE + group->used - 1;

  /* Only valid to be called for used entries.
   */