Re: r10788 (translation handle caching)

[kf...@collab.net]

Sorry, I don't have the original commit email for r10788 anymore, so
I'm using the output of tools/client-side/showchange.pl below:

> ------------------------------------------------------------------------
> r10788 | lundblad | 2004-08-31 14:20:47 -0500 (Tue, 31 Aug 2004) | 19 lines
> Changed paths:
>    M /trunk/subversion/include/svn_utf.h
>    M /trunk/subversion/libsvn_subr/cmdline.c
>    M /trunk/subversion/libsvn_subr/utf.c
> 
> Fix issue #2016.  Cache UTF8 translation handles in a global hash table
> instead of in the current pool, which improves performance, especially on
> Windows.
> 
> * include/svn_utf.h (svn_utf_initialize): New function.
> * libsvn_subr/utf.c (xlate_handle_mutex, xlate_handle_hash): New variables.
>   (xlate_handle_node_t): New struct.
>   (xlate_cleanup, svn_utf_initialize, put_xlate_handle_node): New functions.
>   (get_xlate_handle_node): Renamed from get_xlate_handle and rewritten using
>   a global hash table and locking in MT environments.
>   (get_ntou_xlate_handle_node, get_uton_xlate_handle_node,
>   svn_utf_stringbuf_to_utf8, svn_utf_string_to_utf8, svn_utf_cstring_to_utf8,
>   svn_utf_cstring_to_utf8_ex, svn_utf_stringbuf_from_utf8,
>   svn_utf_string_from_utf8, svn_utf_cstring_from_utf8,
>   svn_utf_cstring_from_utf8_ex, svn_utf_cstring_from_utf8_string): Use
>   {get,put}_xlate_handle_node for the
>   xlate handle.
> * libsvn_subr/cmdline.c (svn_cmdline_initialize): Initialize UTF-8 routines.

Okay, got that...

> --- subversion/libsvn_subr/utf.c        (revision 10787)
> +++ subversion/libsvn_subr/utf.c        (revision 10788)
>
> [...]
>
> @@ -44,27 +106,79 @@
>     return SVN_NO_ERROR; if fail for some other reason, return
>     error. */
>  static svn_error_t *
> -get_xlate_handle (apr_xlate_t **ret,
> -                  const char *topage, const char *frompage,
> -                  const char *userdata_key, apr_pool_t *pool)
> +get_xlate_handle_node (xlate_handle_node_t **ret,
> +                       const char *topage, const char *frompage,
> +                       const char *userdata_key, apr_pool_t *pool)
>  {
> -  void *old_handle = NULL;
> +  xlate_handle_node_t *old_handle = NULL;
>    apr_status_t apr_err;
>  
>    /* If we already have a handle, just return it. */
>    if (userdata_key)
>      {
> -      apr_pool_userdata_get (&old_handle, userdata_key, pool);
> -      if (old_handle != NULL)
> +#if APR_HAS_THREADS
> +      if (xlate_handle_mutex)
>          {
> -          *ret = old_handle;
> -          return SVN_NO_ERROR;
> +          apr_err = apr_thread_mutex_lock (xlate_handle_mutex);
> +          if (apr_err != APR_SUCCESS)
> +            return svn_error_create (apr_err, NULL,
> +                                     "Can't lock charset translation "
> +                                     "mutex");
> +          old_handle = apr_hash_get (xlate_handle_hash, userdata_key,
> +                                     APR_HASH_KEY_STRING);
> +          if (old_handle)
> +            {
> +              /* Remove from the hash table. */
> +              apr_hash_set (xlate_handle_hash, userdata_key,
> +                            APR_HASH_KEY_STRING, old_handle->next);
> +              old_handle->next = NULL;
> +              apr_err = apr_thread_mutex_unlock (xlate_handle_mutex);
> +              if (apr_err != APR_SUCCESS)
> +                return svn_error_create (apr_err, NULL,
> +                                         "Can't unlock charset "
> +                                         "translation mutex");
> +              *ret = old_handle;
> +              return SVN_NO_ERROR;
> +            }

That comment "Remove from the hash table" confuses me a bit.  To
remove something from a hash table, we set the value to NULL.  But if
'old_handle->next' was already NULL (which we have no reason to
believe it is, right?) then assignment line right afterwards

   old_handle->next = NULL;

would be pointless...

Am I misunderstanding something?

Haven't finished reviewing the commit, so I may have more questions
later.  I wanted to ask this now, though.

-Karl

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