Topic: incremental page rendering not working

[Bob3Rocks]

I have created a number of CGI tools which print output from a Perl script to a web page. Sometimes the output from a script can be very slow to complete, and in these cases it is nice to see the output which has completed in real time. That way the end user is not waiting several minutes for a response from the server. I think this is called "incremental page rendering" on the web browser side.

This has worked great on many servers where I have installed scripts; most recently, Fedora 20 (more specifically, NST-20) --

root@NST_20:~# httpd -V
Server version: Apache/2.4.10 (Fedora)
Server built: Dec 17 2014 10:28:55
Server's Module Magic Number: 20120211:36
Server loaded: APR 1.5.1, APR-UTIL 1.5.3
Compiled using: APR 1.5.1, APR-UTIL 1.5.3
Architecture: 32-bit
Server MPM: prefork
threaded: no
forked: yes (variable process count)
Server compiled with....
-D APR_HAS_SENDFILE
-D APR_HAS_MMAP
-D APR_HAVE_IPV6 (IPv4-mapped addresses enabled)
-D APR_USE_SYSVSEM_SERIALIZE
-D APR_USE_PTHREAD_SERIALIZE
-D SINGLE_LISTEN_UNSERIALIZED_ACCEPT
-D APR_HAS_OTHER_CHILD
-D AP_HAVE_RELIABLE_PIPED_LOGS
-D DYNAMIC_MODULE_LIMIT=256
-D HTTPD_ROOT="/etc/httpd"
-D SUEXEC_BIN="/usr/sbin/suexec"
-D DEFAULT_PIDLOG="/run/httpd/httpd.pid"
-D DEFAULT_SCOREBOARD="logs/apache_runtime_status"
-D DEFAULT_ERRORLOG="logs/error_log"
-D AP_TYPES_CONFIG_FILE="conf/mime.types"
-D SERVER_CONFIG_FILE="conf/httpd.conf"

On a new server, Fedora 24 (NST-24), the incremental page rendering does not work --

root@NST24:~# httpd -V
Server version: Apache/2.4.23 (Fedora)
Server built: Jul 18 2016 15:38:14
Server's Module Magic Number: 20120211:61
Server loaded: APR 1.5.2, APR-UTIL 1.5.4
Compiled using: APR 1.5.2, APR-UTIL 1.5.4
Architecture: 64-bit
Server MPM: prefork
threaded: no
forked: yes (variable process count)
Server compiled with....
-D APR_HAS_SENDFILE
-D APR_HAS_MMAP
-D APR_HAVE_IPV6 (IPv4-mapped addresses enabled)
-D APR_USE_SYSVSEM_SERIALIZE
-D APR_USE_PTHREAD_SERIALIZE
-D SINGLE_LISTEN_UNSERIALIZED_ACCEPT
-D APR_HAS_OTHER_CHILD
-D AP_HAVE_RELIABLE_PIPED_LOGS
-D DYNAMIC_MODULE_LIMIT=256
-D HTTPD_ROOT="/etc/httpd"
-D SUEXEC_BIN="/usr/sbin/suexec"
-D DEFAULT_PIDLOG="/run/httpd/httpd.pid"
-D DEFAULT_SCOREBOARD="logs/apache_runtime_status"
-D DEFAULT_ERRORLOG="logs/error_log"
-D AP_TYPES_CONFIG_FILE="conf/mime.types"
-D SERVER_CONFIG_FILE="conf/httpd.conf"


I am sure there is a simple answer to this question, and I am still scratching my head trying to find it after much trial and error & Google searching.

Any insight would be appreciated.

[James Blond]

With other languages it is possible to use a flush() function to print a current output. I don't know if such a thing exists in perl.

[Bob3Rocks]

Thanks for the reply James Bond. I will look into that, although I've never used a function like that before to update the page. I think this must have to do with a security setting.

[glsmith]

Isn't this called "Server Push," at least that's what I thought it was but in perl server push doesn't work on all browsers. Not with my test years ago.

[James Blond]

Googling a bit I found for perl autoflush from IO::

I'm not sure if that does the same as http://php.net/manual/en/function.flush.php

A different strategie could be running a few smaller script and get the content with ajax requests to the front end.