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Merge pull request #334 from ged/reentrant_signal_handlers

Add deferred signal-handling (fixes #332).
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commit 9fe7ddb8bd818318722d687a915f3ad316020aee 2 parents f954a42 + 1691883
@ddollar authored
Showing with 118 additions and 9 deletions.
  1. +118 −9 lib/foreman/engine.rb
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127 lib/foreman/engine.rb
@@ -9,6 +9,10 @@
class Foreman::Engine
+ # The signals that the engine cares about.
+ #
+ HANDLED_SIGNALS = [ :TERM, :INT, :HUP ]
+
attr_reader :env
attr_reader :options
attr_reader :processes
@@ -33,6 +37,16 @@ def initialize(options={})
@processes = []
@running = {}
@readers = {}
+
+ # Self-pipe for deferred signal-handling (ala djb: http://cr.yp.to/docs/selfpipe.html)
+ reader, writer = create_pipe
+ reader.close_on_exec = true if reader.respond_to?(:close_on_exec)
+ writer.close_on_exec = true if writer.respond_to?(:close_on_exec)
+ @selfpipe = { :reader => reader, :writer => writer }
+
+ # Set up a global signal queue
+ # http://blog.rubybestpractices.com/posts/ewong/016-Implementing-Signal-Handlers.html
+ Thread.main[:signal_queue] = []
end
# Start the processes registered to this +Engine+
@@ -41,10 +55,7 @@ def start
# Make sure foreman is the process group leader.
Process.setpgrp unless Foreman.windows?
- trap("TERM") { puts "SIGTERM received"; terminate_gracefully }
- trap("INT") { puts "SIGINT received"; terminate_gracefully }
- trap("HUP") { puts "SIGHUP received"; terminate_gracefully } if ::Signal.list.keys.include? 'HUP'
-
+ register_signal_handlers
startup
spawn_processes
watch_for_output
@@ -53,6 +64,74 @@ def start
shutdown
end
+ # Set up deferred signal handlers
+ #
+ def register_signal_handlers
+ HANDLED_SIGNALS.each do |sig|
+ if ::Signal.list.include? sig.to_s
+ trap(sig) { Thread.main[:signal_queue] << sig ; notice_signal }
+ end
+ end
+ end
+
+ # Unregister deferred signal handlers
+ #
+ def restore_default_signal_handlers
+ HANDLED_SIGNALS.each do |sig|
+ trap(sig, :DEFAULT) if ::Signal.list.include? sig.to_s
+ end
+ end
+
+ # Wake the main thread up via the selfpipe when there's a signal
+ #
+ def notice_signal
+ @selfpipe[:writer].write_nonblock( '.' )
+ rescue Errno::EAGAIN
+ # Ignore writes that would block
+ rescue Errno::EINT
+ # Retry if another signal arrived while writing
+ retry
+ end
+
+ # Invoke the real handler for signal +sig+. This shouldn't be called directly
+ # by signal handlers, as it might invoke code which isn't re-entrant.
+ #
+ # @param [Symbol] sig the name of the signal to be handled
+ #
+ def handle_signal(sig)
+ case sig
+ when :TERM
+ handle_term_signal
+ when :INT
+ handle_interrupt
+ when :HUP
+ handle_hangup
+ else
+ system "unhandled signal #{sig}"
+ end
+ end
+
+ # Handle a TERM signal
+ #
+ def handle_term_signal
+ puts "SIGTERM received"
+ terminate_gracefully
+ end
+
+ # Handle an INT signal
+ #
+ def handle_interrupt
+ puts "SIGINT received"
+ terminate_gracefully
+ end
+
+ # Handle a HUP signal
+ #
+ def handle_hangup
+ puts "SIGHUP received"
+ terminate_gracefully
+ end
+
# Register a process to be run by this +Engine+
#
# @param [String] name A name for this process
@@ -98,11 +177,11 @@ def load_env(filename)
end
end
- # Send a signal to all processesstarted by this +Engine+
+ # Send a signal to all processes started by this +Engine+
#
# @param [String] signal The signal to send to each process
#
- def killall(signal="SIGTERM")
+ def kill_children(signal="SIGTERM")
if Foreman.windows?
@running.each do |pid, (process, index)|
system "sending #{signal} to #{name_for(pid)} at pid #{pid}"
@@ -113,6 +192,21 @@ def killall(signal="SIGTERM")
end
else
begin
+ Process.kill signal, *@running.keys unless @running.empty?
+ rescue Errno::ESRCH, Errno::EPERM
+ end
+ end
+ end
+
+ # Send a signal to the whole process group.
+ #
+ # @param [String] signal The signal to send
+ #
+ def killall(signal="SIGTERM")
+ if Foreman.windows?
+ kill_children(signal)
+ else
+ begin
Process.kill "-#{signal}", Process.getpgrp
rescue Errno::ESRCH, Errno::EPERM
end
@@ -277,8 +371,22 @@ def watch_for_output
Thread.new do
begin
loop do
- io = IO.select(@readers.values, nil, nil, 30)
+ io = IO.select([@selfpipe[:reader]] + @readers.values, nil, nil, 30)
+
+ begin
+ @selfpipe[:reader].read_nonblock(11)
+ rescue Errno::EAGAIN, Errno::EINTR => err
+ # ignore
+ end
+
+ # Look for any signals that arrived and handle them
+ while sig = Thread.main[:signal_queue].shift
+ self.handle_signal(sig)
+ end
+
(io.nil? ? [] : io.first).each do |reader|
+ next if reader == @selfpipe[:reader]
+
if reader.eof?
@readers.delete_if { |key, value| value == reader }
else
@@ -305,13 +413,14 @@ def watch_for_termination
def terminate_gracefully
return if @terminating
+ restore_default_signal_handlers
@terminating = true
if Foreman.windows?
system "sending SIGKILL to all processes"
- killall "SIGKILL"
+ kill_children "SIGKILL"
else
system "sending SIGTERM to all processes"
- killall "SIGTERM"
+ kill_children "SIGTERM"
end
Timeout.timeout(options[:timeout]) do
watch_for_termination while @running.length > 0
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