[FFmpeg-devel] [PATCH] avcodec/fft_template: use ff_thread_once on costable initialization

[wm4]

On Wed, 5 Jul 2017 16:12:07 +0100
Rostislav Pehlivanov <atomnuker at gmail.com> wrote:

> On 5 July 2017 at 07:15, Muhammad Faiz <mfcc64 at gmail.com> wrote:
> 
> > Make it thread-safe and avoid redundant initialization.
> >
> > Signed-off-by: Muhammad Faiz <mfcc64 at gmail.com>
> > ---
> >  libavcodec/fft_template.c | 81 ++++++++++++++++++++++++++++++
> > +++++++++++------
> >  1 file changed, 71 insertions(+), 10 deletions(-)
> >
> > diff --git a/libavcodec/fft_template.c b/libavcodec/fft_template.c
> > index 6477372..6c77854 100644
> > --- a/libavcodec/fft_template.c
> > +++ b/libavcodec/fft_template.c
> > @@ -29,11 +29,19 @@
> >  #include <stdlib.h>
> >  #include <string.h>
> >  #include "libavutil/mathematics.h"
> > +#include "libavutil/thread.h"
> >  #include "fft.h"
> >  #include "fft-internal.h"
> >
> >  #if FFT_FIXED_32
> >  #include "fft_table.h"
> > +
> > +static void av_cold fft_lut_init(void)
> > +{
> > +    int n = 0;
> > +    ff_fft_lut_init(ff_fft_offsets_lut, 0, 1 << 17, &n);
> > +}
> > +
> >  #else /* FFT_FIXED_32 */
> >
> >  /* cos(2*pi*x/n) for 0<=x<=n/4, followed by its reverse */
> > @@ -52,6 +60,66 @@ COSTABLE(16384);
> >  COSTABLE(32768);
> >  COSTABLE(65536);
> >  COSTABLE(131072);
> > +
> > +static av_cold void init_ff_cos_tabs(int index)
> > +{
> > +    int i;
> > +    int m = 1<<index;
> > +    double freq = 2*M_PI/m;
> > +    FFTSample *tab = FFT_NAME(ff_cos_tabs)[index];
> > +    for(i=0; i<=m/4; i++)
> > +        tab[i] = FIX15(cos(i*freq));
> > +    for(i=1; i<m/4; i++)
> > +        tab[m/2-i] = tab[i];
> > +}
> > +
> > +typedef struct CosTabsInitOnce {
> > +    void (*func)(void);
> > +    AVOnce control;
> > +} CosTabsInitOnce;
> > +
> > +#define INIT_FF_COS_TABS_FUNC(index, size)          \
> > +static av_cold void init_ff_cos_tabs_ ## size (void)\
> > +{                                                   \
> > +    init_ff_cos_tabs(index);                        \
> > +}
> > +
> > +INIT_FF_COS_TABS_FUNC(4, 16)
> > +INIT_FF_COS_TABS_FUNC(5, 32)
> > +INIT_FF_COS_TABS_FUNC(6, 64)
> > +INIT_FF_COS_TABS_FUNC(7, 128)
> > +INIT_FF_COS_TABS_FUNC(8, 256)
> > +INIT_FF_COS_TABS_FUNC(9, 512)
> > +INIT_FF_COS_TABS_FUNC(10, 1024)
> > +INIT_FF_COS_TABS_FUNC(11, 2048)
> > +INIT_FF_COS_TABS_FUNC(12, 4096)
> > +INIT_FF_COS_TABS_FUNC(13, 8192)
> > +INIT_FF_COS_TABS_FUNC(14, 16384)
> > +INIT_FF_COS_TABS_FUNC(15, 32768)
> > +INIT_FF_COS_TABS_FUNC(16, 65536)
> > +INIT_FF_COS_TABS_FUNC(17, 131072)
> > +
> > +static CosTabsInitOnce cos_tabs_init_once[] = {
> > +    { NULL },
> > +    { NULL },
> > +    { NULL },
> > +    { NULL },
> > +    { init_ff_cos_tabs_16, AV_ONCE_INIT },
> > +    { init_ff_cos_tabs_32, AV_ONCE_INIT },
> > +    { init_ff_cos_tabs_64, AV_ONCE_INIT },
> > +    { init_ff_cos_tabs_128, AV_ONCE_INIT },
> > +    { init_ff_cos_tabs_256, AV_ONCE_INIT },
> > +    { init_ff_cos_tabs_512, AV_ONCE_INIT },
> > +    { init_ff_cos_tabs_1024, AV_ONCE_INIT },
> > +    { init_ff_cos_tabs_2048, AV_ONCE_INIT },
> > +    { init_ff_cos_tabs_4096, AV_ONCE_INIT },
> > +    { init_ff_cos_tabs_8192, AV_ONCE_INIT },
> > +    { init_ff_cos_tabs_16384, AV_ONCE_INIT },
> > +    { init_ff_cos_tabs_32768, AV_ONCE_INIT },
> > +    { init_ff_cos_tabs_65536, AV_ONCE_INIT },
> > +    { init_ff_cos_tabs_131072, AV_ONCE_INIT },
> > +};
> > +
> >  #endif
> >  COSTABLE_CONST FFTSample * const FFT_NAME(ff_cos_tabs)[] = {
> >      NULL, NULL, NULL, NULL,
> > @@ -90,14 +158,7 @@ static int split_radix_permutation(int i, int n, int
> > inverse)
> >  av_cold void ff_init_ff_cos_tabs(int index)
> >  {
> >  #if (!CONFIG_HARDCODED_TABLES) && (!FFT_FIXED_32)
> > -    int i;
> > -    int m = 1<<index;
> > -    double freq = 2*M_PI/m;
> > -    FFTSample *tab = FFT_NAME(ff_cos_tabs)[index];
> > -    for(i=0; i<=m/4; i++)
> > -        tab[i] = FIX15(cos(i*freq));
> > -    for(i=1; i<m/4; i++)
> > -        tab[m/2-i] = tab[i];
> > +    ff_thread_once(&cos_tabs_init_once[index].control,
> > cos_tabs_init_once[index].func);
> >  #endif
> >  }
> >
> > @@ -176,8 +237,8 @@ av_cold int ff_fft_init(FFTContext *s, int nbits, int
> > inverse)
> >
> >  #if FFT_FIXED_32
> >      {
> > -        int n=0;
> > -        ff_fft_lut_init(ff_fft_offsets_lut, 0, 1 << 17, &n);
> > +        static AVOnce control = AV_ONCE_INIT;
> >  
> 
> This needs to be a global variable.

It's not global, but it's static, so good enough for the purpose?

I'm not sure how the file being a template factors into this, though.

(Patch LGTM btw.)