[FFmpeg-devel] [PATCH 1/3] avutil/eval: separate AVExpr state to a new AVExprState struct

[Michael Niedermayer]

On Sat, Dec 28, 2019 at 03:46:23PM +0100, Marton Balint wrote:
> Also add helper functions to allocate and free such a struct, and make it
> usable by providing a new av_eval_expr2 function for which you can specify a
> custom AVExprState.
> 
> Signed-off-by: Marton Balint <cus at passwd.hu>
> ---
>  doc/APIchanges      |  3 +++
>  libavutil/eval.c    | 31 +++++++++++++++++++++++++------
>  libavutil/eval.h    | 27 +++++++++++++++++++++++++++
>  libavutil/version.h |  2 +-
>  4 files changed, 56 insertions(+), 7 deletions(-)
> 
> diff --git a/doc/APIchanges b/doc/APIchanges
> index 3c24dc6fbc..e4ad364ed9 100644
> --- a/doc/APIchanges
> +++ b/doc/APIchanges
> @@ -15,6 +15,9 @@ libavutil:     2017-10-21
>  
>  API changes, most recent first:
>  
> +2020-01-xx - xxxxxxxxxx - lavu 56.39.100 - eval.h
> +  Add av_expr_eval2, av_expr_state_alloc, av_expr_state_free
> +
>  2019-12-27 - xxxxxxxxxx - lavu 56.38.100 - eval.h
>    Add av_expr_count_func().
>  
> diff --git a/libavutil/eval.c b/libavutil/eval.c
> index d527f6a9d0..86fb634fd8 100644
> --- a/libavutil/eval.c
> +++ b/libavutil/eval.c
> @@ -173,7 +173,11 @@ struct AVExpr {
>          double (*func2)(void *, double, double);
>      } a;
>      struct AVExpr *param[3];
> -    double *var;
> +    AVExprState *state;
> +};
> +
> +struct AVExprState {
> +    double vars[VARS];
>  };
>  
>  static double etime(double v)
> @@ -333,13 +337,23 @@ static double eval_expr(Parser *p, AVExpr *e)
>  
>  static int parse_expr(AVExpr **e, Parser *p);
>  
> +AVExprState *av_expr_state_alloc(void)
> +{
> +    return av_mallocz(sizeof(AVExprState));
> +}
> +
> +void av_expr_state_free(AVExprState **ps)
> +{
> +    av_freep(ps);
> +}
> +
>  void av_expr_free(AVExpr *e)
>  {
>      if (!e) return;
>      av_expr_free(e->param[0]);
>      av_expr_free(e->param[1]);
>      av_expr_free(e->param[2]);
> -    av_freep(&e->var);
> +    av_expr_state_free(&e->state);
>      av_freep(&e);
>  }
>  
> @@ -724,8 +738,8 @@ int av_expr_parse(AVExpr **expr, const char *s,
>          ret = AVERROR(EINVAL);
>          goto end;
>      }
> -    e->var= av_mallocz(sizeof(double) *VARS);
> -    if (!e->var) {
> +    e->state = av_expr_state_alloc();
> +    if (!e->state) {
>          ret = AVERROR(ENOMEM);
>          goto end;
>      }
> @@ -763,16 +777,21 @@ int av_expr_count_func(AVExpr *e, unsigned *counter, int size, int arg)
>      return expr_count(e, counter, size, ((int[]){e_const, e_func1, e_func2})[arg]);
>  }
>  
> -double av_expr_eval(AVExpr *e, const double *const_values, void *opaque)
> +double av_expr_eval2(AVExpr *e, AVExprState *s, const double *const_values, void *opaque)
>  {
>      Parser p = { 0 };
> -    p.var= e->var;
> +    p.var = s ? s->vars : e->state->vars;
>  
>      p.const_values = const_values;
>      p.opaque     = opaque;
>      return eval_expr(&p, e);
>  }
>  
> +double av_expr_eval(AVExpr *e, const double *const_values, void *opaque)
> +{
> +    return av_expr_eval2(e, NULL, const_values, opaque);
> +}
> +
>  int av_expr_parse_and_eval(double *d, const char *s,
>                             const char * const *const_names, const double *const_values,
>                             const char * const *func1_names, double (* const *funcs1)(void *, double),
> diff --git a/libavutil/eval.h b/libavutil/eval.h
> index 068c62cdab..8bd1592f6c 100644
> --- a/libavutil/eval.h
> +++ b/libavutil/eval.h
> @@ -29,6 +29,7 @@
>  #include "avutil.h"
>  
>  typedef struct AVExpr AVExpr;
> +typedef struct AVExprState AVExprState;
>  
>  /**
>   * Parse and evaluate an expression.
> @@ -86,6 +87,22 @@ int av_expr_parse(AVExpr **expr, const char *s,
>   */
>  double av_expr_eval(AVExpr *e, const double *const_values, void *opaque);
>  
> +/**
> + * Evaluate a previously parsed expression using a custom state.
> + *
> + * Some expressions can use stateful functions, like random(), st() and ld().
> + * With this function you can provide your own state to the evaluator instead
> + * of using the internal state of the AVExpr. This makes it possible to use the
> + * same AVExpr in multiple threads each with their own AVExprState avoiding
> + * unprotected concurrent access of the internal AVExpr state.
> + *
> + * @param s the state of the expression, if NULL, the internal state of AVExpr will be used
> + * @param const_values a zero terminated array of values for the identifiers from av_expr_parse() const_names
> + * @param opaque a pointer which will be passed to all functions from funcs1 and funcs2
> + * @return the value of the expression
> + */
> +double av_expr_eval2(AVExpr *e, AVExprState *s, const double *const_values, void *opaque);
> +
>  /**
>   * Track the presence of variables and their number of occurrences in a parsed expression
>   *
> @@ -134,4 +151,14 @@ void av_expr_free(AVExpr *e);
>   */
>  double av_strtod(const char *numstr, char **tail);
>  
> +/**
> + * Allocate a new AVExprState struct
> + */
> +AVExprState *av_expr_state_alloc(void);

maybe this should have a double [] argument so the caller can set the
initial variables (or pass NULL if not)

thx

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Modern terrorism, a quick summary: Need oil, start war with country that
has oil, kill hundread thousand in war. Let country fall into chaos,
be surprised about raise of fundamantalists. Drop more bombs, kill more
people, be surprised about them taking revenge and drop even more bombs
and strip your own citizens of their rights and freedoms. to be continued
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