Re: [PATCH] traceeval: Add way to extract the number of elements

[Ross Zwisler <zwisler@google.com>]

On Thu, Sep 28, 2023 at 10:24:34AM -0400, Steven Rostedt wrote:
> From: "Steven Rostedt (Google)" <rostedt@goodmis.org>
> 
> Add traceeval_count() that will return the number of elements in the
> traceeval. This can be useful for allocating an array to store the
> elements. By getting the count, the allocation can be done first and
> then iterated to load the elements into the array.
> 
> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
> ---
>  include/traceeval-hist.h |  2 ++
>  src/histograms.c         | 11 +++++++++++
>  2 files changed, 13 insertions(+)
> 
> diff --git a/include/traceeval-hist.h b/include/traceeval-hist.h
> index eefa48d..44d071f 100644
> --- a/include/traceeval-hist.h
> +++ b/include/traceeval-hist.h
> @@ -204,6 +204,8 @@ int traceeval_query_size(struct traceeval *teval, const struct traceeval_data *k
>  void traceeval_results_release(struct traceeval *teval,
>  			       const struct traceeval_data *results);
>  
> +size_t traceeval_count(struct traceeval *teval);
> +
>  #define traceeval_stat(teval, keys, type)				\
>  	traceeval_stat_size(teval, keys, TRACEEVAL_ARRAY_SIZE(keys), type)
>  
> diff --git a/src/histograms.c b/src/histograms.c
> index 2456342..ac3f7f7 100644
> --- a/src/histograms.c
> +++ b/src/histograms.c
> @@ -1006,6 +1006,17 @@ int traceeval_remove_size(struct traceeval *teval,
>  	return 1;
>  }
>  
> +/**
> + * traceeval_count - Return the number of elements in the traceeval
> + * @teval: The traceeval handle to get the count from
> + *
> + * Returns the number of elements stored by unique keys in the @teval.
> + */
> +size_t traceeval_count(struct traceeval *teval)
> +{
> +	return teval->update_counter;

I don't think this is going to do what you want.  'teval->update_counter'
is a generation number, is monotonically increasing, and is incremented any
time an element is added or removed from the hash.

I think we either need to actually keep an element count (increment in
create_entry(), decrement in traceeval_remove_size() and
traceeval_iterator_remove()), or else we're going to have to count the
elements by walking the 'struct hash_table' buckets.  Probably easier to just
keep an explicit element count.

> +}
> +
>  /**
>   * traceeval_iterator_put - release a given iterator
>   * @iter: The iterartor to release
> -- 
> 2.40.1
>