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

[Marton Balint]

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);
+
+/**
+ * Free an allocated AVExprState struct and set its pointer to NULL
+ */
+void av_expr_state_free(AVExprState **ps);
+
 #endif /* AVUTIL_EVAL_H */
diff --git a/libavutil/version.h b/libavutil/version.h
index af8f614aff..2bc1b98615 100644
--- a/libavutil/version.h
+++ b/libavutil/version.h
@@ -79,7 +79,7 @@
  */
 
 #define LIBAVUTIL_VERSION_MAJOR  56
-#define LIBAVUTIL_VERSION_MINOR  38
+#define LIBAVUTIL_VERSION_MINOR  39
 #define LIBAVUTIL_VERSION_MICRO 100
 
 #define LIBAVUTIL_VERSION_INT   AV_VERSION_INT(LIBAVUTIL_VERSION_MAJOR, \
-- 
2.16.4