[FFmpeg-devel] [PATCH 1/3] libavutil: prefix log messages with thread name

[Michael Niedermayer]

On Wed, Jul 18, 2012 at 11:22:19AM -0400, Martin Carroll wrote:
> To make it easier to see which thread is doing what, the logger can
> now be configured to prefix all log messages with the name of the
> calling thread.  The name is printed if the thread was previously
> registered with av_log_set_threadname().  To enable this feature,
> the variable print_threadname in libavutil/log.c must be set to 1.
> 
> Signed-off-by: Martin Carroll <martin.carroll at alcatel-lucent.com>
> ---
>  libavutil/log.c |  104 +++++++++++++++++++++++++++++++++++++++++++++++++------
>  libavutil/log.h |   11 ++++++
>  2 files changed, 104 insertions(+), 11 deletions(-)
> 
> diff --git a/libavutil/log.c b/libavutil/log.c
> index 53c756b..bee612f 100644
> --- a/libavutil/log.c
> +++ b/libavutil/log.c
> @@ -30,11 +30,34 @@
>  #include <unistd.h>
>  #endif
>  #include <stdlib.h>
> +#include <pthread.h>
>  #include "avutil.h"
>  #include "log.h"
>  
>  #define LINE_SZ 1024
>  
> +#define MAX_THREAD_INFOS 10

a single normal transcoding on a modern desktop might use
30+ threads through a single multithreaded encoder & decoder
considering the possibility of multiple encoders and decoders
a few hundread can surely end up existing at the same time ...


> +#define MAX_THREAD_NAMELEN 128
> +
> +/*
> + * we do *not* use thread-specific data to implement this

non doxygen compatible comment


> + * data structure, because we want the creat*ing* thread to
> + * be able to set the creat*ed* thread's name, and implementing

maybe iam missing something but why do we want the creating thread
to set it ?


> + * that functionality is easier with a globally accessed (and
> + * properly locked) table.
> + */
> +typedef struct {
> +    pthread_t pid;
> +    char name[MAX_THREAD_NAMELEN];
> +    void *fcn;
> +    int instance_num_of_fcn;
> +    int sole_instance_of_fcn;
> +} Thread_info;
> +
> +static pthread_rwlock_t thread_info_rwlock = PTHREAD_RWLOCK_INITIALIZER;
> +static Thread_info thread_info[MAX_THREAD_INFOS];
> +static int num_thread_infos = 0;
> +static int print_threadname = 0; /* set to 1 to prefix all log messages with name of thread */
>  static int av_log_level = AV_LOG_INFO;
>  static int flags;
>  
> @@ -163,11 +186,53 @@ static int get_category(void *ptr){
>      return avc->category + 16;
>  }
>  
> +void av_log_set_threadname(pthread_t pid, const char *name, void *fcn)
> +{
    
> +	pthread_rwlock_wrlock(&thread_info_rwlock);

tabs are forbidden in ffmpeg git


> +    if (num_thread_infos < MAX_THREAD_INFOS) {
> +        Thread_info *info;
> +        int instance_num_of_fcn = 0;
> +        int sole_instance_of_fcn = 1;
> +        int i;
> +
> +        for (i = 0; i < num_thread_infos; ++i) {
> +            info = &thread_info[i];
> +            if (info->fcn == fcn) {
> +                info->sole_instance_of_fcn = 0;
> +                sole_instance_of_fcn = 0;
> +                ++instance_num_of_fcn;
> +            }
> +        }
> +        info = &thread_info[num_thread_infos];
> +        info->pid = pid;
> +        info->fcn = fcn;
> +        info->instance_num_of_fcn = instance_num_of_fcn;
> +        info->sole_instance_of_fcn = sole_instance_of_fcn;
> +        snprintf(info->name, MAX_THREAD_NAMELEN, "%s", name);
> +        info->name[MAX_THREAD_NAMELEN-1] = 0;
> +        ++num_thread_infos;
> +    }
> +	pthread_rwlock_unlock(&thread_info_rwlock);
> +}

Thats just a function to add a thread, threads can be removed as
well, in a a multi thrededed converter that uses libavcodec there
could be millions of threads created and destroyed over its lifetime
just by converting a large directory of mp3 files ...


> +
> +static Thread_info* lookup_thread_info(void)
> +{
> +    int i;
> +
> +    pthread_t pid = pthread_self();
> +    for (i = 0; i < num_thread_infos; ++i) {
> +        Thread_info* info = &thread_info[i];
> +        if (pthread_equal(info->pid, pid))
> +            return info;
> +    }

this is O(n) where TLS could be O(1), or in other words this doesnt
scale well if the number of threads would be large

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

Good people do not need laws to tell them to act responsibly, while bad
people will find a way around the laws. -- Plato
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