**********************************************************************
* Author  : Brian Maher <maherb at brimworks dot com>
* Library : lua-ev - Lua 5.1 interface to libev
*
* The MIT License
*
* Copyright (c) 2009-1010 Brian Maher
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
**********************************************************************

To use this library, you need libev, get it here:
     http://dist.schmorp.de/libev/
     http://software.schmorp.de/pkg/libev.html

To build this library, you need CMake, get it here:
    http://www.cmake.org/cmake/resources/software.html

Loading the library:

    If you built the library as a loadable package
        [local] ev = require 'ev'

    If you compiled the package statically into your application, call
    the function "luaopen_ev(L)". It will create a table with the ev
    functions and leave it on the stack.

Choosing a backend:

    Set the LIBEV_FLAGS= environment variable to choose a backend:

    1 - select()
    2 - poll()
    4 - epoll()
    8 - kqueue
    16 - /dev/poll [not implemented]
    32 - Solaris port

    Please see the documentation for libev for more details.

WARNING:

  If your program fork()s, then you will need to re-initialize
  your event loop(s) in the child process.  You can do this
  re-initialization using the loop:fork() function.

NOTE:

  If you are new to event loop programming, take a look at example.lua

-- ev functions --

major, minor = ev.version()

    returns numeric ev version for the major and minor
    levels of the version dynamically linked in.

loop = ev.Loop.new()

    Create a new non-default event loop.  See ev.Loop object methods
    below.

loop = ev.Loop.default

    The "default" event loop.  See ev.Loop object methods below.
    Note that the default loop is "lazy loaded".

timer = ev.Timer.new(on_timeout, after_seconds [, repeat_seconds])

    Create a new timer that will call the on_timeout function when the
    timer expires.  The timer initially expires in after_seconds
    (floating point), then it will expire in repeat_seconds (floating
    point) over and over again (unless repeat_seconds is zero or is
    omitted in which case, this timer will only fire once).

    The returned timer is an ev.Timer object.  See below for the
    methods on this object.

    NOTE: You must explicitly register the timer with an event loop in
    order for it to take effect.

    The on_timeout function will be called with these arguments
    (return values are ignored):

    on_timeout(loop, timer, revents)

        The loop is the event loop for which the timer is registered,
        the timer is the ev.Timer object, and revents is ev.TIMEOUT.

    See also ev_timer_init() C function.

sig = ev.Signal.new(on_signal, signal_number)

    Create a new signal watcher that will call the on_signal function
    when the specified signal_number is delivered.

    The returned sig is an ev.Signal object.  See below for the methods on
    this object.

    NOTE: You must explicitly register the sig with an event loop in
    order for it to take effect.

    The on_signal function will be called with these arguments (return
    values are ignored):

    on_signal(loop, sig, revents)

        The loop is the event loop for which the io object is
        registered, the sig parameter is the ev.Signal object, and
        revents is ev.SIGNAL.

    See also ev_signal_init() C function.

io = ev.IO.new(on_io, file_descriptor, revents)

    Create a new io watcher that will call the on_io function when the
    specified file_descriptor is available for read and/or write
    depending on the revents.  The revents parameter must be either
    ev.READ, ev.WRITE, or the bitwise or of ev.READ and ev.WRITE (use
    bitlib to do bitwise or).

    The returned io is an ev.IO object.  See below for the methods on
    this object.

    NOTE: You must explicitly register the io with an event loop in
    order for it to take effect.

    The on_io function will be called with these arguments (return
    values are ignored):

    on_io(loop, io, revents)

        The loop is the event loop for which the io object is
        registered, the io parameter is the ev.IO object, and revents
        is a bit set consisting of ev.READ and/or ev.WRITE and/or
        ev.TIMEOUT depending on which event triggered this callback.
        Of course ev.TIMEOUT won't be in that set since this is the io
        watcher.

    See also ev_io_init() C function.

idle = ev.Idle.new(on_idle)

    Create a new io watcher that will call the on_idle function
    whenever there is nothing else to do.  This means that the loop
    will never block while an idle watcher is started.

    The returned io is an ev.Idle object.  See below for the methods on
    this object.

    NOTE: You must explicitly register the idle with an event loop in
    order for it to take effect.

    The on_idle function will be called with these arguments (return
    values are ignored):

    on_idle(loop, idle, revents)

        The loop is the event loop for which the idle object is
        registered, the idle parameter is the ev.Idle object, and
        revents is ev.IDLE.

    See also ev_idle_init() C function.

child = ev.Child.new(on_child, pid, trace)

    Create a new child watcher that will call the on_child function
    whenever SIGCHLD for registered pid is delivered.

    When pid is set to 0 the watcher will fire for any pid.

    When trace is false the watcher will be activated when the process
    terminates. If it's true - it will additionally be activated when
    the process is stopped or continued.

    The returned child is an ev.Child object.  See below for the methods on
    this object.

    NOTE: You must explicitly register the idle with an event loop in
    order for it to take effect.

    The on_child function will be called with these arguments (return
    values are ignored):

    on_child(loop, child, revents)

        The loop is the event loop for which the idle object is
        registered, the child parameter is the ev.Child object, and
        revents is ev.CHILD.

    See also ev_child_init() C function.

stat = ev.Stat.new(on_stat, path [, interval])

    Configures the watcher to wait for status changes of the given "path".
    The "interval" is a hint on how quickly a change is expected to be
    detected and may normally be left out to let libev choose a suitable
    value.

    The returned stat is an ev.Stat object.  See below for the methods on
    this object.

    NOTE: You must explicitly register the stat with an event loop in
    order for it to take effect.

    The on_stat function will be called with these arguments (return
    values are ignored):

    on_stat(loop, stat, revents)

        The loop is the event loop for which the idle object is
        registered, the stat parameter is the ev.Stat object, and
        revents is ev.STAT.

    See also ev_stat_init() C function.

ev.READ (constant)

    If this bit is set, the io watcher is ready to read.  See also
    EV_READ C definition.

ev.WRITE (constant)

    If this bit is set, the io watcher is ready to write.  See also
    EV_WRITE C definition.

ev.TIMEOUT (constant)

    If this bit is set, the watcher was triggered by a timeout. See
    also EV_TIMEOUT C definition.

ev.SIGNAL (constant)

   If this bit is set, the watcher was triggered by a signal.  See
   also EV_SIGNAL C definition.

ev.CHILD (constant)

   If this bit is set, the watcher was triggered by a child signal.
   See also EV_CHILD C definition.

ev.STAT (constant)

   If this bit is set, the watcher was triggered by a change in
   attributes of the file system path. See also EV_STAT C definition.

-- ev.Loop object methods --

loop:fork()

   You *must* call this function in the child process after fork(2)
   system call and before the next iteration of the event loop.

loop:loop()

    Run the event loop!  Returns when there are no more watchers
    registered with the event loop.  See special note below about
    calling ev_loop() C API.

    See also ev_loop() C function.

bool = loop:is_default()

    Returns true if the referenced loop object is the default event
    loop.

    See also ev_is_default_loop() C function.

num = loop:iteration()

    Returns the number of loop iterations.  Note that this function
    used to be called loop:count().

    See also ev_iterations() C function.

num = loop:depth() [libev >= 3.7]

    Returns the number of times loop:loop() was entered minus the
    number of times loop:loop() was exited, in other words, the
    recursion depth.
    
    This method is available only if lua-ev was linked 
    with libev 3.7 and higher.

    See also ev_depth() C function.

epochs = loop:now()

    Returns the non-integer epoch seconds time at which the current
    iteration of the event loop woke up.

    See also ev_now() C function.

epochs = loop:update_now()

    Updates the current time returned by loop.now(), and returns that
    timestamp.

    See also ev_now_update() C function.

loop:unloop()

    Process all outstanding events in the event loop, but do not make
    another iteration of the event loop.

    See also ev_unloop() C function.

backend_id = loop:backend()

    Returns the identifier of the current backend which is being used
    by this event loop.  See the libev documentation for what each
    number means:

    http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod#FUNCTIONS_CONTROLLING_THE_EVENT_LOOP

-- object methods common to all watcher types --

bool = watcher:is_active()

    Returns true if the watcher is active (has been start()ed, but not
    stop()ed).

    See also ev_is_active() C function.

bool = watcher:is_pending()

    Returns true if the watcher is pending (it has outstanding events
    but its callback has not yet been invoked).

    See also ev_is_pending() C function.

revents = watcher:clear_pending()

    If the watcher is pending, return the revents of the pending
    event, otherwise returns zero.  If the event was pending, the
    pending flag is cleared (and therefore this watcher event will not
    trigger the events callback).

    See also ev_clear_pending() C function.

old_priority = watcher:priority([new_priority])

    Get access to the priority of this watcher, optionally setting a
    new priority.  The priority should be a small integer between
    ev.MINPRI and ev.MAXPRI.  The default is 0.

    See also the ev_priority() and ev_set_priority() C functions.

old_callback = watcher:callback([new_callback])

    Get access to the callback function associated with this watcher,
    optionally setting a new callback function.

-- ev.Timer object methods --

timer:start(loop [, is_daemon])

    Start the timer in the specified event loop.  Optionally make this
    watcher a "daemon" watcher which means that the event loop will
    terminate even if this watcher has not triggered.

    See also ev_timer_start() C function (document as ev_TYPE_start()).

timer:stop(loop)

    Unregister this timer from the specified event loop.  Ensures that
    the watcher is neither active nor pending.

    See also ev_timer_stop() C function (document as ev_TYPE_stop()).

timer:again(loop [, seconds])

    Reset the timer so that it doesn't trigger again in the specified
    loop until the specified number of seconds from now have elapsed.
    If seconds is not specified, uses the repeat_seconds specified
    when the timer was created.

    See also ev_timer_again() C function.

-- ev.IO object methods --

io:start(loop [, is_daemon])

    Start the io in the specified event loop.  Optionally make this
    watcher a "daemon" watcher which means that the event loop will
    terminate even if this watcher has not triggered.

    See also ev_io_start() C function (document as ev_TYPE_start()).

io:stop(loop)

    Unregister this io from the specified event loop.  Ensures that
    the watcher is neither active nor pending.

    See also ev_io_stop() C function (document as ev_TYPE_stop()).

fd = io:getfd()

    Returns the file descriptor associated with the IO object.

-- ev.Idle object methods --

idle:start(loop [, is_daemon])

    Start the idle watcher in the specified event loop.  Optionally
    make this watcher a "daemon" watcher which means that the event
    loop will terminate even if this watcher has not triggered.

    See also ev_idle_start() C function (document as ev_TYPE_start()).

idle:stop(loop)

    Unregister this idle watcher from the specified event loop.
    Ensures that the watcher is neither active nor pending.

    See also ev_io_stop() C function (document as ev_TYPE_stop()).

-- ev.Child object methods --

child:start(loop [, is_daemon])

    Start the child watcher in the specified event loop.  Optionally
    make this watcher a "daemon" watcher which means that the event
    loop will terminate even if this watcher has not triggered.

    See also ev_child_start() C function (document as ev_TYPE_start()).

child:stop(loop)

    Unregister this child watcher from the specified event loop.
    Ensures that the watcher is neither active nor pending.

    See also ev_child_stop() C function (document as ev_TYPE_stop()).

child:getpid()

    Return the process id this watcher watches out for, or 0, meaning
    any process id.

child:getrpid()

    Return the process id that detected a status change.

child:getstatus()

    Returns the process exit/trace status caused by "rpid" (see your systems
    "waitpid" and "sys/wait.h" for details).

    It returns the table with the following fields:
    - exited: true if status was returned for a child process that terminated
      normally;
    - stopped: true if status was returned for a child process that is
      currently stopped;
    - signaled: true if status was returned for a child process that terminated
      due to receipt of a signal that was not caught;
    - exit_status: (only if exited == true) the low-order 8 bits of the status
      argument that the child process passed to _exit() or exit(), or the value
      the child process returned from main();
    - stop_signal: (only if stopped == true) the number of the signal that
      caused the child process to stop;
    - term_signal: (only if signaled == true) the number of the signal that
      caused the termination of the child process.

-- ev.Stat object methods --

stat:start(loop [, is_daemon])

    Start the stat watcher in the specified event loop.  Optionally
    make this watcher a "daemon" watcher which means that the event
    loop will terminate even if this watcher has not triggered.

    See also ev_stat_start() C function (document as ev_TYPE_start()).

stat:stop(loop)

    Unregister this stat watcher from the specified event loop.
    Ensures that the watcher is neither active nor pending.

    See also ev_stat_stop() C function (document as ev_TYPE_stop()).

stat:getdata()

    Returns a table with the following fields:
    * - path: the file system path that is being watched;
    * - interval: the specified interval;
    * - attr: the most-recently detected attributes of the file in a form
    *   of table with the following fields: dev, ino, mode, nlink, uid, gid,
    *   rdev, size, atime, mtime, ctime corresponding to struct stat members
    *   (st_dev, st_ino, etc.);
    * - prev: the previous attributes of the file with the same fields as
    *   attr fields.

EXCEPTION HANDLING NOTE:

   If there is an exception when calling a watcher callback, the error
   will be printed to stderr.  In the future, it would be cool if
   there was a linked list of error handlers, and that if a callback
   registers another callback, this linked list of error handlers
   would be inherited so that exception handling can be done more
   easily.  To do this, we just need to add a method for adding an
   error handler for the current callback context, and keep calling
   the error handlers in the linked list until an error handler
   actually handles the exception.  If the error handling stack
   unwinds, we will probably just resort to printing to stderr.

CALLING ev_loop() C API DIRECTLY:

   If you want to call the ev_loop() C API directly, then you *must*
   set the loop userdata field to the lua_State in which you want all
   callbacks to be ran in.  In the past, the lua_State was stored as
   a thread local which was set when loop:loop() lua function is
   called, but this made lua-ev dependent upon pthreads and forced
   ev_loop() to only be called from lua.  Next, I removed the pthreads
   dependency and stored the lua_State in which the callback was
   registered.  This doesn't bode well when working with coroutines as
   it means that loop:loop() may call back into a coroutine that is
   long gone.

   The current implementation relies on libev 3.7's ability to set a
   userdata field associated with an event loop, and the loop:loop()
   implementation simply sets the userdata field for the duration of
   loop:loop().  This does mean that if you want to call ev_loop()
   from C then you either need to be sure that no lua watchers are
   registered with that loop, or you need to set the userdata field to
   the lua_State* in which the callbacks should be ran.

TODO:

  * Add support for other watcher types (periodic, embed, async, etc).