From Andy:

What needs to change for async caching support:

1)    XrdPosix package to add async POSIX style I/O

2)    XrdPss package to use async POSIX style I/O

3)    XrdOucCache package to provide async cache interface, this also impacts XrdPosix package because it is responsible for loading and using the caching interface.

The issue here is that all of these interfaces are public which means we need to implement this without breaking ABI compatibility (i.e. is must be backward compatible).

Time estimates:

a)    1 week to design and code up the new caching interface (4/5/16).

b)    2 weeks to retrofit XrdPosix package to use (a) (3/21/16).

c)    1 week to retrofit XrdPss package to use (b) (3/25/16).

The above will always be available as work proceeds in the pssasync branch in the xroot github repo so other parallel work can proceed. Please be aware I go on vacation 3/28/16 for 12 days with limited if any internet connectivity so it is likely that we will not have a production quality version until 4/15/16 to 4/20/16, depending on how it goes.