Re: [msysGit] [PATCH] git grep: be careful to use mutices only when they are initialized

From: Pat Thoyts <patthoyts@gmail.com>
Date: Oct 26, 2011, 09:19 UTC
Message-ID: <CABNJ2GL7khag3uD=kX+Ui9aqn5A-bkM5wfK=of0-=3fRrjmJ4w@mail.gmail.com>
In-Reply-To: <alpine.DEB.1.00.1110251223500.32316@s15462909.onlinehome-server.info>

On 25 October 2011 18:25, Johannes Schindelin <Johannes.Schindelin@gmx.de> wrote:

Show 10 quoted lines

>
> Rather nasty things happen when a mutex is not initialized but locked
> nevertheless. Now, when we're not running in a threaded manner, the mutex
> is not initialized, which is correct. But then we went and used the mutex
> anyway, which -- at least on Windows -- leads to a hard crash (ordinarily
> it would be called a segmentation fault, but in Windows speak it is an
> access violation).
>
> This problem was identified by our faithful tests when run in the msysGit
> environment.

I did not see this failure when running the tests on my machine. But then threaded issues are often intermittent depending on load, number of cores, phase of the moon, etc. You never said _which_ test either although there are only 3 to try - most likey t7810-grep.sh

I was going to point out that it should be "mutexes" but I see it is committed already :)

> To avoid having to wrap the line due to the 80 column limit, we use

So last century!

Show 34 quoted lines

> the name "WHEN_THREADED" instead of "IF_USE_THREADS" because it is one
> character shorter. Which is all we need in this case.
>
> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
> ---
>
>        I looked around a bit but ran out of time to identify the reason why
>        this was not caught earlier.
>
>  builtin/grep.c |    9 +++++----
>  1 files changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/builtin/grep.c b/builtin/grep.c
> index 92eeada..e94c5fe 100644
> --- a/builtin/grep.c
> +++ b/builtin/grep.c
> @@ -78,10 +78,11 @@ static pthread_mutex_t grep_mutex;
>  /* Used to serialize calls to read_sha1_file. */
>  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 WHEN_THREADED(x) do { if (use_threads) (x); } while (0)
> +#define grep_lock() WHEN_THREADED(pthread_mutex_lock(&grep_mutex))
> +#define grep_unlock() WHEN_THREADED(pthread_mutex_unlock(&grep_mutex))
> +#define read_sha1_lock() WHEN_THREADED(pthread_mutex_lock(&read_sha1_mutex))
> +#define read_sha1_unlock() WHEN_THREADED(pthread_mutex_unlock(&read_sha1_mutex))
>
>  /* Signalled when a new work_item is added to todo. */
>  static pthread_cond_t cond_add;
> --
> 1.7.5.3.4540.g15f89

Works for me.

Pat.