[Mesa-dev] [PATCH 3/3] mesa: glGet: fix parameter lookup for apps using multiple APIs

[Brian Paul]

On 08/23/2012 08:55 AM, Imre Deak wrote:
> The glGet hash was initialized only once for a single GL API, even if
> the application later created a context for a different API. This
> resulted in glGet failing for otherwise valid parameters in a context
> if that parameter was invalid in another context created earlier.
>
> Amend this by also adding to the hash the parameters of a new API if the
> application starts to use one.
>
> With the change the hash collision statistics reported by GET_DEBUG for
> the combined API lookup tables aren't significantly different from the
> single API case. The worst case is still 6 collisions for a single
> parameter.
>
> Signed-off-by: Imre Deak<imre.deak at intel.com>
> ---
>   src/mesa/main/context.c |    5 ++---
>   src/mesa/main/get.c     |   41 ++++++++++++++++++++++++++++++++---------
>   2 files changed, 34 insertions(+), 12 deletions(-)
>
> diff --git a/src/mesa/main/context.c b/src/mesa/main/context.c
> index b78bcee..9831a5f 100644
> --- a/src/mesa/main/context.c
> +++ b/src/mesa/main/context.c
> @@ -404,9 +404,6 @@ one_time_init( struct gl_context *ctx )
>
>         _mesa_get_cpu_features();
>
> -      /* context dependence is never a one-time thing... */
> -      _mesa_init_get_hash(ctx);
> -
>         for (i = 0; i<  256; i++) {
>            _mesa_ubyte_to_float_color_tab[i] = (float) i / 255.0F;
>         }
> @@ -425,6 +422,8 @@ one_time_init( struct gl_context *ctx )
>
>      /* per-API one-time init */
>      if (!(api_init_mask&  (1<<  ctx->API))) {
> +      _mesa_init_get_hash(ctx);
> +
>         /*
>          * This is fine as ES does not use the remap table, but it may not be
>          * future-proof.  We cannot always initialize the remap table because
> diff --git a/src/mesa/main/get.c b/src/mesa/main/get.c
> index 38d6cc3..e4818ba 100644
> --- a/src/mesa/main/get.c
> +++ b/src/mesa/main/get.c
> @@ -1380,7 +1380,14 @@ static const struct value_desc values[] = {
>    * collisions for any enum (typical numbers).  And the code is very
>    * simple, even though it feels a little magic. */
>
> -static unsigned short table[1024];
> +#define TABLE_IDX_BITS        10
> +
> +#define TABLE_IDX(v)          ((v)&  ((1<<  TABLE_IDX_BITS) - 1))
> +#define TABLE_API(v)          ((v)>>  TABLE_IDX_BITS)
> +
> +#define TABLE_VALUE(api, idx) (((api)<<  TABLE_IDX_BITS) | (idx))
> +
> +static unsigned short table[1<<  TABLE_IDX_BITS];
>   static const int prime_factor = 89, prime_step = 281;
>
>   #ifdef GET_DEBUG
> @@ -1398,14 +1405,14 @@ print_table_stats(void)
>         if (!table[i])
>   	 continue;
>         count++;
> -      d =&values[table[i]];
> +      d =&values[TABLE_IDX(table[i])];
>         hash = (d->pname * prime_factor);
>         j = 0;
>         while (1) {
> -	 if (values[table[hash&  mask]].pname == d->pname)
> -	    break;
> -	 hash += prime_step;
> -	 j++;
> +        if (values[TABLE_IDX(table[hash&  mask])].pname == d->pname)
> +           break;
> +        hash += prime_step;
> +        j++;
>         }
>
>         if (j<  10)
> @@ -1435,6 +1442,8 @@ void _mesa_init_get_hash(struct gl_context *ctx)
>      int i, hash, index, mask;
>      int api_mask = 0, api_bit;
>
> +   assert(Elements(values)<= 1<<  TABLE_IDX_BITS);
> +
>      mask = Elements(table) - 1;
>      api_bit = 1<<  ctx->API;
>
> @@ -1450,9 +1459,13 @@ void _mesa_init_get_hash(struct gl_context *ctx)
>         while (1) {
>            index = hash&  mask;
>            if (!table[index]) {
> -            table[index] = i;
> +            table[index] = TABLE_VALUE(api_mask, i);
>               break;
>            }
> +         /* Did some other API install the entry already? */
> +         if (TABLE_IDX(table[index]) == i&&
> +             TABLE_API(table[index]) == api_mask)
> +               break;
>            hash += prime_step;
>         }
>      }
> @@ -1981,11 +1994,16 @@ find_value(const char *func, GLenum pname, void **p, union value *v)
>      struct gl_texture_unit *unit;
>      int mask, hash;
>      const struct value_desc *d;
> +   int api_bit;
> +
> +   api_bit = 1<<  ctx->API;
>
>      mask = Elements(table) - 1;
>      hash = (pname * prime_factor);
>      while (1) {
> -      d =&values[table[hash&  mask]];
> +      unsigned table_val = table[hash&  mask];
> +
> +      d =&values[TABLE_IDX(table_val)];
>
>         /* If the enum isn't valid, the hash walk ends with index 0,
>          * which is the API mask entry at the beginning of values[]. */
> @@ -1995,7 +2013,12 @@ find_value(const char *func, GLenum pname, void **p, union value *v)
>            return&error_value;
>         }
>
> -      if (likely(d->pname == pname))
> +      if (likely(d->pname == pname&&  (TABLE_API(table_val)&  api_bit)))
> +         /*
> +          * Don't bail out here if the API doesn't match, since the same pname
> +          * can be present in the table for other APIs (with different
> +          * semantics).
> +          */
>            break;
>
>         hash += prime_step;

I don't fully grok the hashing changes but this looks OK to me 
assuming you've run piglit, etc.

Is this a candidate for the 8.0 branch too?

For the series:
Reviewed-by: Brian Paul <brianp at vmware.com>

-Brian