wp_ob_end_flush_all() hangs the output buffering, during plugin update/install

[mamborambo]

Symptom: During plugin update process, the screen displays "Downloading {plugin}" then appears to hang.

System: Apache2 on LinuxMint-11

I traced the fault to the following function:
send_message() in /wp-admin/includes/misc.php

this function writes out the message, then tries to flush
the buffers by calling wp_ob_end_flush_all()

the mechanism of the ob_flush is to repeatedly call ob_end_flush until there is no more levels.

On the default configuration of LinuxMint / Debian, zlib.output_compression is ON, and this interferes with ob_end_flush

Based on notes from php.net, ob flushing is not necessary.

SOLUTION:

1) Either change php.ini to set zlib.output_compression to OFF, or

2) shortcircuit the wp_ob_end_flush_all() by adding an immediate return to the first line.

RECOMMENDATION:

In future versions of Wordpress, the interaction between ob and zlib should be studied carefully to derive the most universal solution.