RFC : process ids are independent of nprocs() and others

[amitmurthy]

This patch is a starting point for cleanly removing workers :

• process ids are now independent of nprocs().
• rmprocs() removes specified list of processes.
• death of worker process results in it being cleanly removed
• list_allprocs() gives the list of valid processors
• list_workers() is the above minus the client process (pid 1), unless nprocs() is 1, then it is same as the client process.
• application code written using for pid in 1:nprocs() will break. It needs to be changed to for pid in list_allprocs() or for pid in list_workers()

To be done:

• RemoteRefs related to the exited worker are currently not being notified or cleaned up.
  I could not follow all the various data structures from where they have to be removed. Need some help here.
• NOT throwing an exception when the socket connection breaks due to an exiting worker results in a seg fault in the client (console) process.

[amitmurthy]

Need some help here. I could not follow the various data structures that need to be cleaned up.

[samtkaplan]

cool! Can 'list_allprocs()' be shortened to 'procs()', and 'list_allworkers()' be shortened to 'workers()'? Note that procs(d::DArray) is used to list all process id's used by a distributed array. I guess it would be nice to keep consistant with that.

[ViralBShah]

Being a huge fan of tab completion, I prefer all these functions to be procs*. It is just that procsadd does not have the same ring to it as addprocs.

In any case, the list suffixes should be dropped. We do need bikeshedding of the names here. It is not immediately obvious how procs and workers are related.

[ViralBShah]

That said - this is probably the first in a series of PRs, and the bikeshedding does not have to block this one.

[JeffBezanson]

This is great. I can do the RemoteRef part and I'll look into the segfault. I also prefer the names procs and workers. The latter could perhaps be procs(client=false).

[amitmurthy]

rebased and changed names to procs() and workers().

procs(client=false) will not work since the client process is also treated as a worker when nprocs() == 1