sets up a child process serving any object
as a DRb server running locally on unix domain sockets. the child process
has a LifeLine established between it and
the parent, making it impossible for the child to outlive the parent
(become a zombie). the object to serve is
specfied either directly using the ‘object’/:object keyword
Slave.new :object => MyServer.new
or, preferably, using the block form
Slave.new{ MyServer.new }
when the block form is used the object is
contructed in the child process itself. this is quite advantageous if the
child object consumes resources or opens
file handles (db connections, etc). by contructing the object in the child any resources are
consumed from the child‘s address space and things like open file
handles will not be carried into subsequent child processes (via standard
unix fork semantics). in the event that a
block is specified but the object cannot
be constructed and, instead, throws and Exception, that exception will be
propogated to the parent process.
opts may contain the following keys, as either strings or symbols
object : specify the slave object. otherwise block value is used.
socket_creation_attempts : specify how many attempts to create a unix domain socket will be made
debug : turn on some logging to STDERR
psname : specify the name that will appear in 'top' ($0)
at_exit : specify a lambda to be called in the *parent* when the child dies
dumped : specify that the slave object should *not* be DRbUndumped (default is DRbUndumped)
threadsafe : wrap the slave object with ThreadSafe to implement gross thread safety
[Source]
319: def initialize opts = {}, &block
320:
321: getopt = getopts opts
322:
323: @obj = getopt['object']
324: @socket_creation_attempts = getopt['socket_creation_attempts'] || default('socket_creation_attempts')
325: @debug = getopt['debug'] || default('debug')
326: @psname = getopt['psname']
327: @at_exit = getopt['at_exit']
328: @dumped = getopt['dumped']
329: @threadsafe = getopt['threadsafe'] || default('threadsafe')
330:
331: raise ArgumentError, 'no slave object or slave object block provided!' if
332: @obj.nil? and block.nil?
333:
334: @shutdown = false
335: @waiter = @status = nil
336: @lifeline = LifeLine.new
337:
338:
339: init_failure = lambda do |e|
340: trace{ %Q[#{ e.message } (#{ e.class })\n#{ e.backtrace.join "\n" }] }
341: o = Object.new
342: class << o
343: attr_accessor '__slave_object_failure__'
344: end
345: o.__slave_object_failure__ = Marshal.dump [e.class, e.message, e.backtrace]
346: @object = o
347: end
348:
349:
350:
351:
352: unless((@pid = Slave::fork))
353: e = nil
354: begin
355: Kernel.at_exit{ Kernel.exit! }
356: @lifeline.catch
357:
358: if @obj
359: @object = @obj
360: else
361: begin
362: @object = block.call
363: rescue Exception => e
364: init_failure[e]
365: end
366: end
367:
368: if block and @obj
369: begin
370: block[@obj]
371: rescue Exception => e
372: init_failure[e]
373: end
374: end
375:
376: $0 = (@psname ||= gen_psname(@object))
377:
378: unless @dumped or @object.respond_to?('__slave_object_failure__')
379: @object.extend DRbUndumped
380: end
381:
382: if @threadsafe
383: @object = ThreadSafe.new @object
384: end
385:
386: @ppid, @pid = Process::ppid, Process::pid
387: @socket = nil
388: @uri = nil
389:
390: tmpdir, basename = Dir::tmpdir, File::basename(@psname)
391:
392: @socket_creation_attempts.times do |attempt|
393: se = nil
394: begin
395: s = File::join(tmpdir, "#{ basename }_#{ attempt }_#{ rand }")
396: u = "drbunix://#{ s }"
397: DRb::start_service u, @object
398: @socket = s
399: @uri = u
400: trace{ "child - socket <#{ @socket }>" }
401: trace{ "child - uri <#{ @uri }>" }
402: break
403: rescue Errno::EADDRINUSE => se
404: nil
405: end
406: end
407:
408: if @socket and @uri
409: trap('SIGUSR2') do
410: DBb::thread.kill rescue nil
411: FileUtils::rm_f @socket rescue nil
412: exit
413: end
414:
415: @lifeline.puts @socket
416: @lifeline.cling
417: else
418: @lifeline.release
419: warn "slave(#{ $$ }) could not create socket!"
420: exit
421: end
422: rescue Exception => e
423: trace{ %Q[#{ e.message } (#{ e.class })\n#{ e.backtrace.join "\n" }] }
424: ensure
425: status = e.respond_to?('status') ? e.status : 1
426: exit(status)
427: end
428:
429:
430:
431: else
432: detach
433: @lifeline.throw
434:
435: buf = @lifeline.gets
436: raise "failed to find slave socket" if buf.nil? or buf.strip.empty?
437: @socket = buf.strip
438: trace{ "parent - socket <#{ @socket }>" }
439:
440: if @at_exit
441: @at_exit_thread = @lifeline.on_cut{
442: @at_exit.respond_to?('call') ? @at_exit.call(self) : send(@at_exit.to_s, self)
443: }
444: end
445:
446: if @socket and File::exist? @socket
447: Kernel.at_exit{ FileUtils::rm_f @socket }
448: @uri = "drbunix://#{ socket }"
449: trace{ "parent - uri <#{ @uri }>" }
450:
451:
452:
453: DRb::start_service('druby://localhost:0', nil) unless DRb::thread
454: @object = DRbObject::new nil, @uri
455: if @object.respond_to? '__slave_object_failure__'
456: c, m, bt = Marshal.load @object.__slave_object_failure__
457: (e = c.new(m)).set_backtrace bt
458: trace{ %Q[#{ e.message } (#{ e.class })\n#{ e.backtrace.join "\n" }] }
459: raise e
460: end
461: @psname ||= gen_psname(@object)
462: else
463: raise "failed to find slave socket <#{ @socket }>"
464: end
465: end
466:
467: end
