Mailing-List: contact modules-dev-help@httpd.apache.org; run by ezmlm
Precedence: bulk
Reply-To: modules-dev@httpd.apache.org
Received-SPF: pass (herse.apache.org: domain of gushaow@gmail.com designates
 64.233.182.184 as permitted sender)
DomainKey-Signature: a=rsa-sha1; c=nofws;
        d=gmail.com; s=beta;
        h=received:message-id:date:from:to:subject:mime-version:content-type;
        b=GuPGlgHrf+OjkRL0/fI56fXy9koh1kEpiuCLa2UJhYucKOc6KVBRs4WfisplRpBu08V7FfnvNM5bVdOrLa/+PjzwQcscn0O2DUU9usacJJhfFbiY1GVqT9iAxLiSgbqfXMGPQu5m3HsTXCvzllLdlzT47Wbd/Cz4dT3/7Ssqe1I=
Message-ID: <50df4dd70701310201o285c1e0eia9e15061a26356a8@mail.gmail.com>
Date: Wed, 31 Jan 2007 18:01:18 +0800
From: Weilt <gushaow@gmail.com>
To: modules-dev@httpd.apache.org
Subject: a strange problem of gcc -O2 optimization flag in a output filter
MIME-Version: 1.0
Content-Type: multipart/alternative;
	boundary="----=_Part_485_9092673.1170237678746"

------=_Part_485_9092673.1170237678746
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Content-Disposition: inline

Hi,

I have wrote a module, which has an output filter. The filter collects all
the buckets of a request and does some processing, then it produces a new
brigade containing the new output data and pass it to the next filter in the
filter chains.

The output filter code is like this:

static apr_status_t TestOutFilter(ap_filter_t *f,
                                        apr_bucket_brigade *pbbIn)
    {
    request_rec *r = f->r;
    conn_rec *c = r->connection;
    OutContext *pCtx;

    if(!(pCtx = f->ctx)){
      f->ctx = pCtx=apr_palloc(r->pool,sizeof *pCtx);
      pCtx->pbbTmp = apr_brigade_create(r->pool,c->bucket_alloc);
    }
    apr_bucket_brigade *pbbOut = pCtx->pbbTmp;
    while(!APR_BRIGADE_EMPTY(pbbIn)){
      apr_bucket *pbktIn,*tmpbucket;

      pbktIn=APR_BRIGADE_FIRST(pbbIn);
      APR_BUCKET_REMOVE(pbktIn);
      APR_BRIGADE_INSERT_TAIL(pbbOut, pbktIn);

      if(APR_BUCKET_IS_FLUSH(pbktIn))
        continue;

      if(APR_BUCKET_IS_EOS(pbktIn)) {
/*       we have all the buckets in pbbTmp;
         do  some processing and  create a new  bucket
         outputbuffer contains the new data to pass to next filter
*/
           tmpbucket=apr_bucket_heap_create(outputbuffer,
lenofbuffer,0,c->bucket_alloc);
           APR_BRIGADE_INSERT_TAIL(pbbOut, tmpbucket);
        }
        APR_BRIGADE_INSERT_TAIL(pbbOut, pbktIn);
        ap_remove_output_filter(f);
        return ap_pass_brigade(f->next,pbbOut);
      }

    }
    return APR_SUCCESS;
}

The strange thing is when I use "/usr/local/apache2/bin/apxs -i -a -c -Wc,O0
-Wc,-ggdb testmodule.c" to compile the module, it works well, but if I
"/usr/local/apache2/bin/apxs -i -a -c  -Wc,O2 -Wc,-ggdb testmodule.c", it
has death cycle in the function. Here '-Wc' means add gcc flag, '-Wc,O0'
means 'gcc -O0' ,which is no optimization. '-Wc,O2' is the default value if
it's not specified.

I use gdb to debug this, and find that in "-Wc,O2" case, the function  has
death loop in the while loop. The pbbIn and pbbOut values are not changed
after a loop, which means:
"pbktIn=APR_BRIGADE_FIRST(pbbIn);
      APR_BUCKET_REMOVE(pbktIn);
      APR_BRIGADE_INSERT_TAIL(pbbOut, pbktIn);"
aren't executed correctly or even optimized out.

By the way, even "-Wc,O1" flat works correctly.

I can't figure out the reason and how to solve it.
Any one knows something about this?

Thanks!

------=_Part_485_9092673.1170237678746--