Add ASYNCerr support to give some meaningful error message in the event of
a failure.
Reviewed-by: NRich Salz <rsalz@openssl.org>

Tidied up the naming of functions and structures to be consistent
Reviewed-by: NRich Salz <rsalz@openssl.org>

Fix some warnings in the async code when compiling on windows.
Reviewed-by: NRich Salz <rsalz@openssl.org>

Don't recreate a new ASYNC_CTX every time we call ASYNC_start_job() - the
same one can be used for the life of the thread. Instead we only free it
up when we call ASYNC_free_pool().
Reviewed-by: NRich Salz <rsalz@openssl.org>

The ASYNC null implementation has not kept pace with the rest of the async
development and so was failing to compile.
Reviewed-by: NRich Salz <rsalz@openssl.org>

The ASYNC_in_job() function is redundant. The same effect can be achieved by
using ASYNC_get_current_job().
Reviewed-by: NRich Salz <rsalz@openssl.org>

Port the async pool and notify code to windows.
Reviewed-by: NRich Salz <rsalz@openssl.org>

Implement the ASYNC_JOB as a local thread pool. Remove the API support
for global pools.
Reviewed-by: NRich Salz <rsalz@openssl.org>

Initial API implemented for notifying applications that an ASYNC_JOB
has completed. Currently only s_server is using this. The Dummy Async
engine "cheats" in that it notifies that it has completed *before* it
pauses the job. A normal async engine would not do that.

Only the posix version of this has been implemented so far, so it will
probably fail to compile on Windows at the moment.
Reviewed-by: NRich Salz <rsalz@openssl.org>

It is expensive to create the ASYNC_JOB objects due to the "makecontext"
call. This change adds support for pools of ASYNC_JOB objects so that we
don't have to create a new ASYNC_JOB every time we want to use one.
Reviewed-by: NRich Salz <rsalz@openssl.org>

Where we can we should use longjmp and setjmp in preference to swapcontext/
setcontext as they seem to be more performant.
Reviewed-by: NRich Salz <rsalz@openssl.org>

Removed the function ASYNC_job_is_waiting() as it was redundant. The only
time user code has a handle on a job is when one is waiting, so all they
need to do is check whether the job is NULL. Also did some cleanups to
make sure the job really is NULL after it has been freed!
Reviewed-by: NRich Salz <rsalz@openssl.org>

Some assembler code puts a lot of stuff on the stack, so up the stack size.
Reviewed-by: NRich Salz <rsalz@openssl.org>

Create a "null" async implementation for platforms that lack support. This
just does nothing when called and therefore performs synchronously.
Reviewed-by: NRich Salz <rsalz@openssl.org>

Reviewed-by: NRich Salz <rsalz@openssl.org>

Provides support for running asynchronous jobs. Currently this is completely
stand alone. Future commits will integrate this into libssl and s_server/
s_client. An asynchronous capable engine will be required to see any benefit
from this capability.
Reviewed-by: NRich Salz <rsalz@openssl.org>