This patch adds the ability to create a serializer from a thread pool. A
serializer is a ast_taskprocessor with the same contract as a default
taskprocessor (tasks execute serially) except instead of executing out
of a dedicated thread, execution occurs in a thread from a
ast_threadpool. Think of it as a lightweight thread.

While it guarantees that each task will complete before executing the
next, there is no guarantee as to which thread from the pool individual
tasks will execute. This normally only matters if your code relys on
thread specific information, such as thread locals.

This patch also fixes a bug in how the 'was_empty' parameter is computed
for the push callback, and gets rid of the unused 'shutting_down' field.

Review: https://reviewboard.asterisk.org/r/2323/


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@381326 65c4cc65-6c06-0410-ace0-fbb531ad65f3

* Add a max_size option for threadpools. Also added a test for this option.
* Fixed comments to be more accurate and have fewer typos.
* Updated copyright dates on new files.



git-svn-id: https://origsvn.digium.com/svn/asterisk/team/mmichelson/threadpool@379375 65c4cc65-6c06-0410-ace0-fbb531ad65f3

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git-svn-id: https://origsvn.digium.com/svn/asterisk/team/mmichelson/threadpool@379123 65c4cc65-6c06-0410-ace0-fbb531ad65f3

This replaces the destroy callback with a shutdown callback
instead.



git-svn-id: https://origsvn.digium.com/svn/asterisk/team/mmichelson/threadpool@379122 65c4cc65-6c06-0410-ace0-fbb531ad65f3

* Remove extraneous whitespace
* Bump up debug levels of messages and add identifying info to messages.
* Account for potential failures of ao2_link()
* Add additional test and some more test data
* Add some comments in places where they could be useful
* Make threadpool listeners and their callbacks optional



git-svn-id: https://origsvn.digium.com/svn/asterisk/team/mmichelson/threadpool@378652 65c4cc65-6c06-0410-ace0-fbb531ad65f3

This allows for the threadpool to automatically grow if tasks
are pushed to it and no idle threads are currently available.



git-svn-id: https://origsvn.digium.com/svn/asterisk/team/mmichelson/threadpool@377803 65c4cc65-6c06-0410-ace0-fbb531ad65f3

Unfortunately, this required a taskprocessor listener change that makes listener allocation
utterly silly. I'm going to change the scheme so that allocation of taskprocessor listeners
is done internally within taskprocessor code. This will make it parallel with threadpool
code, which is a good thing.



git-svn-id: https://origsvn.digium.com/svn/asterisk/team/mmichelson/threadpool@377687 65c4cc65-6c06-0410-ace0-fbb531ad65f3

git-svn-id: https://origsvn.digium.com/svn/asterisk/team/mmichelson/threadpool@377686 65c4cc65-6c06-0410-ace0-fbb531ad65f3

git-svn-id: https://origsvn.digium.com/svn/asterisk/team/mmichelson/threadpool@377654 65c4cc65-6c06-0410-ace0-fbb531ad65f3

The only test added so far is an idle thread timeout
option. This will greatly aid threadpool users who wish
to maintain a threadpool by allowing for idle threads to
die out as necessary.

Test passes.



git-svn-id: https://origsvn.digium.com/svn/asterisk/team/mmichelson/threadpool@377580 65c4cc65-6c06-0410-ace0-fbb531ad65f3

This helps tests to pass more often than before.
They are far less likely to queue extra processes
into the control taskprocessor since they are prevented
once the threadpool begins to shut down.



git-svn-id: https://origsvn.digium.com/svn/asterisk/team/mmichelson/threadpool@377578 65c4cc65-6c06-0410-ace0-fbb531ad65f3

git-svn-id: https://origsvn.digium.com/svn/asterisk/team/mmichelson/threadpool@377475 65c4cc65-6c06-0410-ace0-fbb531ad65f3

This one involves shrinking the threadpool in such
a way that both idle and active threads are affected.

This test made me re-realize why the zombie state exists,
so I re-added it. We don't want to clog up the control
taskprocessor by waiting on active threads to complete
what they are doing. Instead, we mark them as zombies so
that when they are done, they can clean themselves up
properly.

Without the zombie state available, the new test actually
will deadlock.



git-svn-id: https://origsvn.digium.com/svn/asterisk/team/mmichelson/threadpool@377474 65c4cc65-6c06-0410-ace0-fbb531ad65f3

git-svn-id: https://origsvn.digium.com/svn/asterisk/team/mmichelson/threadpool@377418 65c4cc65-6c06-0410-ace0-fbb531ad65f3

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git-svn-id: https://origsvn.digium.com/svn/asterisk/team/mmichelson/threadpool@377397 65c4cc65-6c06-0410-ace0-fbb531ad65f3

Passes!



git-svn-id: https://origsvn.digium.com/svn/asterisk/team/mmichelson/threadpool@377380 65c4cc65-6c06-0410-ace0-fbb531ad65f3

It passes.



git-svn-id: https://origsvn.digium.com/svn/asterisk/team/mmichelson/threadpool@377379 65c4cc65-6c06-0410-ace0-fbb531ad65f3

It worked on the first try. Fun time.



git-svn-id: https://origsvn.digium.com/svn/asterisk/team/mmichelson/threadpool@377378 65c4cc65-6c06-0410-ace0-fbb531ad65f3

git-svn-id: https://origsvn.digium.com/svn/asterisk/team/mmichelson/threadpool@377369 65c4cc65-6c06-0410-ace0-fbb531ad65f3

The new thread creation test fails because Asterisk locks up
while trying to lock a taskprocessor.

While trying to debug that, I found a race condition during taskprocessor
creation where a default taskprocessor listener could try to operate on
a partially started taskprocessor. This was fixed by adding a new callback
to taskprocessor listeners.

Then while testing that change, I found some bugs in the taskprocessor
tests where I was not properly unlocking when done with a lock. Scoped
locks have spoiled me a bit.

I still have not figured out why the threadpool thread creation test
is locking up.



git-svn-id: https://origsvn.digium.com/svn/asterisk/team/mmichelson/threadpool@377368 65c4cc65-6c06-0410-ace0-fbb531ad65f3

This one simply pushes a task into the threadpool and ensures
that the listener gets the callbacks expected.

It currently crashes, so I need to figure out what's wrong.



git-svn-id: https://origsvn.digium.com/svn/asterisk/team/mmichelson/threadpool@377351 65c4cc65-6c06-0410-ace0-fbb531ad65f3