Safely handle AMI connections/reload requests that occur during startup.

Safely handle AMI connections/reload requests that occur during startup.

During asterisk startup, a lock on the list of modules is obtained by the
primary thread while each module is initialized.  Issue 13778 pointed out a
problem with this approach, however.  Because the AMI is loaded before other
modules, it is possible for a module reload to be issued by a connected client
(via Action: Command), causing a deadlock.

The resolution for 13778 was to move initialization of the manager to happen
after the other modules had already been lodaded.  While this fixed this
particular issue, it caused a problem for users (like FreePBX) who call AMI
scripts via an #exec in a configuration file (See issue 15189).

The solution I have come up with is to defer any reload requests that come in
until after the server is fully booted.  When a call comes in to
ast_module_reload (from wherever) before we are fully booted, the request is
added to a queue of pending requests.  Once we are done booting up, we then
execute these deferred requests in turn.

Note that I have tried to make this a bit more intelligent in that it will not
queue up more than 1 request for the same module to be reloaded, and if a
general reload request comes in ('module reload') the queue is flushed and we
only issue a single deferred reload for the entire system.

As for how this will impact existing installations - Before 13778, a reload
issued before module initialization was completed would result in a deadlock.
After 13778, you simply couldn't connect to the manager during startup (which
causes problems with #exec-that-calls-AMI configuration files).  I believe this
is a good general purpose solution that won't negatively impact existing
installations.

(closes issue #15189)
(closes issue #13778)
Reported by: p_lindheimer
Patches:
      06032009_15189_deferred_reloads.diff uploaded by seanbright (license 71)
Tested by: p_lindheimer, seanbright

Review: https://reviewboard.asterisk.org/r/272/

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@199022 65c4cc65-6c06-0410-ace0-fbb531ad65f3