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From Taketo Kabe <k...@sra-tohoku.co.jp>
Subject mod_cgi/7273: [cgid] CGI response delayed if CGI forks off longrunning process
Date Mon, 19 Feb 2001 07:42:42 GMT

>Number:         7273
>Category:       mod_cgi
>Synopsis:       [cgid] CGI response delayed if CGI forks off longrunning process
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    apache
>State:          open
>Class:          sw-bug
>Submitter-Id:   apache
>Arrival-Date:   Sun Feb 18 23:50:00 PST 2001
>Originator:     kabe@sra-tohoku.co.jp
>Release:        httpd-2_0_11-alpha
SunOS 5.8 Generic_108528-05 sun4u sparc SUNW,Ultra-60
gcc version 2.95.2 19991024 (release)

CC=gcc CFLAGS='-mcpu=v8 -O -g' ./configure --localstatedir=/var/apache --disable-cgi --enable-cgid
When using mod_cgid (not mod_cgi), and the CGI forks off a 
longrunning backgroud process, such as
	sleep 600 &
the whole CGI response is delayed until all background jobs complete --
even if the main CGI process has exited long ago.

This was because the cgid waits for cgid-CGI channel (which is a dup() of
the accept()ed filedesc ) to be fully closed from the CGI side. 
Usually it is closed on CGI exit, but if CGI forks, 
the channel is inherited by the new process and not fully
closed even if the CGI exits.
This causes block in read() waiting for EOF from CGI's stdout.
configure --disable-cgi --enable-cgid ,
then invoke a CGI which backgrounds a long-running process, like

echo "Content-Type: text/plain"
echo ""
echo "<PLAINTEXT>dummy"
sleep 60 >/dev/null 2>&1 &
exit 0

Apache 1.3 will return the result to the client immediately 
(leaving "sleep" behind for 60secs), but httpd2.0 /w cgid will 
block for 60secs and then return the result.
Just closing the accept()ed filedes BEFORE forking cured it.
As the filedes is already dup()ed to other filedescs you can safetly 
close this on UNIX, but I'm not sure whether this is portable to non-UNIX.

--- modules/generators/mod_cgid.c.debug	Wed Feb 14 05:16:15 2001
+++ modules/generators/mod_cgid.c	Mon Feb 19 16:14:08 2001
@@ -549,11 +549,19 @@
         else {
             argv = (const char * const *)create_argv(r->pool, NULL, NULL, NULL, argv0,
+	    /* TODO: We want sd2 closed for new CGI process too.
+	     * If it's remained open it'll make ap_pass_brigade() block
+	     * waiting for EOF if CGI forked something running long.
+	     * close(sd2) here should be okay, as CGI channel
+	     * is already dup()ed by apr_procattr_child_{in,out}_set()
+	     * above -- but XXX is this portable?
+	     */
+            close(sd2);
             rc = ap_os_create_privileged_process(r, procnew, argv0, argv, 
                                                  (const char * const *)env, 
                                                  procattr, p);
-            close(sd2);
             if (rc != APR_SUCCESS) {
                 /* Bad things happened. Everyone should have cleaned up. */
                 ap_log_rerror(APLOG_MARK, APLOG_ERR, rc, r,
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