workaround reopen atomicity issues for stdio vs non-stdio

In multithreaded apps, we must use dup2/dup3 with a temporary
descriptor to reopen log files atomically.  This is the only way
to protect all concurrent userspace access to a file when reopening.

ref: http://bugs.ruby-lang.org/issues/9036
ref: yahns commit bcb10abe53cfb1d6a8ef7daef59eb10ced397c8a
attempt to rename PID file when possible

This will preserve mtime on successful renames for comparisions.
While we're at it, avoid writing the new PID until the listeners are
inherited successfully.  This can be useful to avoid accidentally
clobbering a good PID if binding the listener or building the app
(preload_app==true) fails
tests: limit oobgc check to accepted sockets

Otherwise these tests fail if we start using IO#autoclose=true
on Ruby 1.9 (and also if we use IPv6 sockets for tests).
support SO_REUSEPORT on new listeners (:reuseport)

This allows users to start an independent instance of unicorn on
a the same port as a running unicorn (as long as both instances
use :reuseport).

ref: https://lwn.net/Articles/542629/
avoid IO_PURGATORY on Ruby 1.9+

Ruby 1.9 and later includes IO#autoclose=, so we can use it
and prevent some dead IO objects from hanging around.
http_server: fixup comments for PID file renaming

Thanks to Hongli Lai for noticing my typo.  While we're at it, finish up
a halfway-written comment for the EXDEV case
license: allow all future versions of the GNU GPL

There is currently no GPLv4, so this change has no effect at the
moment.

In case the GPLv4 arrives and I am not alive to approve/review it,
the lesser of evils is have give blanket approval of all future GPL
versions (as published by the FSF).  The worse evil is to be stuck
with a license which cannot guarantee the Free-ness of this project
in the future.

This unfortunately means the FSF can theoretically come out with
license terms I do not agree with, but the GPLv2 and GPLv3 will
always be an option to all users.
configurator: validate :reuseport for boolean-ess

In case we (and Linux) supports other values in the future,
we can update it then.  Until now, ensure users only set
true or false for this option.
construct listener_fds Hash in 1.8.6 compatible way

This renables the ability for Ruby 1.8.6 environments to perform reexecs

[ew: clarified this is for 1.8.6,
 favor literal {} over Hash.new,
 tweaked LISTENERS.map => LISTENERS.each, thanks to Hleb Valoshka
]

Signed-off-by: Eric Wong <normalperson@yhbt.net>
bin/*: enforce -p/--port argument to be a valid integer

Users may confuse '-p' with the (to-be-deprecated) '-P/--pid'
option, leading to surprising behavior if a pathname is passed as a
port, because String#to_i would convert it to zero, causing:

    TCPServer.new(host, port = 0)

to bind to a random, unused port.
unicorn 4.7.0 - minor updates, license tweak

* support SO_REUSEPORT on new listeners (:reuseport)

  This allows users to start an independent instance of unicorn on
  a the same port as a running unicorn (as long as both instances
  use :reuseport).

  ref: https://lwn.net/Articles/542629/

* unicorn is now GPLv2-or-later and Ruby 1.8-licensed
  (instead of GPLv2-only, GPLv3-only, and Ruby 1.8-licensed)

  This changes nothing at the moment.  Once the FSF publishes the next
  version of the GPL, users may choose the newer GPL version without the
  unicorn BDFL approving it.  Two years ago when I got permission to add
  GPLv3 to the license options, I also got permission from all past
  contributors to approve future versions of the GPL.  So now I'm
  approving all future versions of the GPL for use with unicorn.

  Reasoning below:

  In case the GPLv4 arrives and I am not alive to approve/review it,
  the lesser of evils is have give blanket approval of all future GPL
  versions (as published by the FSF).  The worse evil is to be stuck
  with a license which cannot guarantee the Free-ness of this project
  in the future.

  This unfortunately means the FSF can theoretically come out with
  license terms I do not agree with, but the GPLv2 and GPLv3 will
  always be an option to all users.

  Note: we currently prefer GPLv3

Two improvements thanks to Ernest W. Durbin III:

* USR2 redirects fixed for Ruby 1.8.6 (broken since 4.1.0)
* unicorn(1) and unicorn_rails(1) enforces valid integer for -p/--port

A few more odd, minor tweaks and fixes:

* attempt to rename PID file when possible (on USR2)
* workaround reopen atomicity issues for stdio vs non-stdio
* improve handling of client-triggerable socket errors
tests: fix SO_REUSEPORT tests for old Linux and non-Linux

On BSD-derived platforms the getsockopt true value may be any
(>= 0) value, not just one as it is on Linux.

Additionally, SO_REUSEPORT is only supported since Linux 3.9, so
folks on older kernels may not have it available.  We still define it
for Linux since kernel upgrades are usually more common than glibc
upgrades.

Note: we will still raise an exception at runtime if a user
explicitly requests :reuseport in their config and runs an
older Linux kernel.

Reported-by: Andrew Hobson <ahobson@gmail.com>
stream_input: avoid IO#close on client disconnect

This can avoid IOError from being seen by the application, and also
reduces points where IO#close may be called.  This is a good thing
if we eventually port this code into a low-level server like
cmogstored where per-client memory space is defined by FD number of
a client.

Reported-by: Andrew Hobson <ahobson@gmail.com>
t0300: kill off stray processes in test

We shouldn't leave processes running after the test.
always write PID file early for compatibility

This reduces the window for a non-existent PID for folks who monitor
PIDs (not a great idea anyways).  Unfortunately, this change also brings
us back to the case where having a PID later (for other process monitors)
is beneficial but more unicorn releases exist where we write the PID
early.

Thanks to Jimmy Soho for reporting this issue.
ref: <CAHStS5gFYcPBDxkVizAHrOeDKAkjT69kruFdgaY0CbB+vLbK8Q@mail.gmail.com>

This partially reverts 7d6ac0c17eb29a00a5b74099dbb3d4d015999f27

Folks: please monitor your app with HTTP requests rather than checking
processes, a stuck/wedged Ruby VM is still a running one.
doc: clarify SIGNALS and reference init example

"interactive terminal" needed clarification.

While we're at it, link to the init.sh example since it may
be shared with nginx.

Reported-by: Rodrigo Rosenfeld Rosas
ref: <5294E9D4.5030608@gmail.com>
rework master-to-worker signaling to use a pipe

Signaling using normal kill(2) is preserved, but the master now
prefers to signal workers using a pipe rather than kill(2).
Non-graceful signals (:TERM/:KILL) are still sent using kill(2),
as they ask for immediate shutdown.

This change is necessary to avoid triggering the ubf (unblocking
function) for rb_thread_call_without_gvl (and similar) functions
extensions.  Most notably, this fixes compatibility with newer
versions of the 'pg' gem which will cancel a running DB query if
signaled[1].

This also has the nice side-effect of allowing a premature
master death (assuming preload_app didn't cause the master to
spawn off rogue child daemons).

Note: users should also refrain from using "killall" if using the
'pg' gem or something like it.

Unfortunately, this increases FD usage in the master as the writable
end of the pipe is preserved in the master.  This limit the number
of worker processes the master may run to the open file limit of the
master process.  Increasing the open file limit of the master
process may be needed.  However, the FD use on the workers is
reduced by one as the internal self-pipe is no longer used.  Thus,
overall pipe allocation for the kernel remains unchanged.

[1] - pg is correct to cancel a query, as it cannot know if
      the signal was for a) graceful unicorn shutdown or
      b) oh-noes-I-started-a-bad-query-ABORT-ABORT-ABORT!!
unicorn 4.8.0pre1

Eric Wong (6):
      tests: fix SO_REUSEPORT tests for old Linux and non-Linux
      stream_input: avoid IO#close on client disconnect
      t0300: kill off stray processes in test
      always write PID file early for compatibility
      doc: clarify SIGNALS and reference init example
      rework master-to-worker signaling to use a pipe
GNUmakefile: add "check" target for running all tests

"check" rolls off the fingers of users familiar with GNU Automake
more easily.  The "test-all" target is preserved for compatibility.
unicorn 4.8.0 - big internal changes, but compatible

This release contains fairly major internal workings of master-to-worker
notifications.  The master process no longer sends signals to workers
for most tasks.  This works around some compatibility issues with some
versions of the "pg" gem (and potentially any other code which may not
handle EINTR properly).  One extra benefit is it also helps stray
workers notice a rare, unexpected master death more easily.  Workers
continue to (and will always) accept existing signals for compatibility
with tools/scripts which may signal workers.

PID file are always written early (even on upgrade) again to avoid
breaking strange monitoring setups which use PID files.  Keep in mind we
have always discouraged monitoring based on PID files as they are
fragile.

We now avoid bubbling IOError to the Rack app on premature client
disconnects when streaming the input body.  This is usually not a
problem with nginx, but may be on some LAN setups without nginx).

Thanks to Sam Saffron, Jimmy Soho, Rodrigo Rosenfeld Rosas,
Michael Fischer, and Andrew Hobson for their help with this release.

Note: the unicorn mailing list will be moved/changed soon due to the
RubyForge shutdown.  unicorn will always rely only on Free Software.
There will never be any sign-up requirements nor terms-of-service to
agree to when communicating with us.