PROMPT_COMMAND='history -a; history -n' causes shell hang in OX 10.10 Yosemite / bash 3.2.53

[Graham Jones]

Since upgrading to OS X 10.10 Yosemite and thus bash 3.2.53 use of the 
PROMPT_COMMAND='history -a; history -n'
workaround to get a single ksh-style history causes the shell to become less 
and less responsive until it permanently hangs.

The problem is somewhat intermitant in terms of how quickly it starts, but it's 
more pronounced after a su - to root (or probably any su). It can be readily 
reproduced by:
1) Putting the above command in your .bashrc file
2) Start a new terminal session
3) su -
4) Hit return around 20-40 times (optionally entering commands)
5) Watch as the prompt returns more and more slowly, then never at all, and PS 
reports ~98% CPU usage for bash.

For a complete description, please see this stack exchange post:
http://apple.stackexchange.com/questions/153361/prompt-command-history-a-history-n-changed-broken-in-yosemite-bash-3-2
 
<http://apple.stackexchange.com/questions/153361/prompt-command-history-a-history-n-changed-broken-in-yosemite-bash-3-2>