[RFC] try* interfaces in posix_mq 0.8.0pre

[Eric Wong <normalperson@yhbt.net>]

I just pushed this out to RubyGems.org (and ruby_posix_mq.git).
Let us know what you think, thanks!

  posix_mq 0.8.0pre - kinder, gentler and less exceptional

  This adds trysend, tryreceive, and tryshift interfaces to avoid
  exceptions on common EAGAIN errors for non-blocking users.  EAGAIN
  during non-blocking messages is common when there are multiple
  readers/writer threads/processes working on the same queue.

  trysend is like send, except it returns true for success and false for
  EAGAIN.  send (still) returns nil, which I now consider a mistake but
  won't change until post-1.0...

  tryreceive and tryshift are like receive and shift respectively,
  but they return nil for EAGAIN and the same return values
  for their non-shift variants.

  None of these methods call mq_setattr() beforehand to set the
  non-blocking flag, it assumes the user set it once before they were ever
  called and never changes it.  Checking/setting the non-blocking flag
  every time is needless overhead and still subject to race conditions if
  multiple processes/queues keep flipping flag on the same queue
  descriptor.

  These interfaces are not yet final, feedback is appreciated
  at ruby.posix.mq@librelist.org.

-- 
Eric Wong