Re: Re: [PATCH] fix threaded grep for machines with only one cpu

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On Mon, Feb 15, 2010 at 06:39:48PM -0800, Junio C Hamano wrote:
> Junio C Hamano <gitster@xxxxxxxxx> writes:
> 
> > Is this the answer to my question?

Sorry I forgot to add a reference to the thread from which the patch
originated: http://groups.google.com/group/msysgit/msg/5da53cf1ccf417cf

> IOW, please try this patch.  I am planning to queue it to 'maint' as part
> of 1.7.0.1 if this is the right solution (which I obviously think it is).

Yes your patch does it correctly I just verified that the segfaults are
gone as well. I think your solution is even nicer than mine. Thanks.

> -- >8 --
> From: Junio C Hamano <gitster@xxxxxxxxx>
> Date: Mon, 15 Feb 2010 18:34:28 -0800
> Subject: [PATCH] Fix use of mutex in threaded grep
[...]
> diff --git a/builtin-grep.c b/builtin-grep.c
> index 26d4deb..5c1545e 100644
> --- a/builtin-grep.c
> +++ b/builtin-grep.c
> @@ -81,8 +81,8 @@ static pthread_mutex_t read_sha1_mutex;
>  
>  #define grep_lock() pthread_mutex_lock(&grep_mutex)
>  #define grep_unlock() pthread_mutex_unlock(&grep_mutex)
> -#define read_sha1_lock() pthread_mutex_lock(&read_sha1_mutex)
> -#define read_sha1_unlock() pthread_mutex_unlock(&read_sha1_mutex)
> +#define read_sha1_lock() do { if (use_threads) pthread_mutex_lock(&read_sha1_mutex); } while (0)
> +#define read_sha1_unlock() do { if (use_threads) pthread_mutex_unlock(&read_sha1_mutex); } while (0)

One minor thing: Would it not be even nicer having the while loop inside
the if clause? E.g like this

#define read_sha1_lock() if (use_threads) do { pthread_mutex_lock(&read_sha1_mutex); } while (0)
#define read_sha1_unlock() if (use_threads) do { pthread_mutex_unlock(&read_sha1_mutex); } while (0)

If the purpose was to force a thread switch it is not necessary when not
using threads.

cheers Heiko
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