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require 'singleton'

# Provides a handler for interrupt signals (SIGINT), allowing the application to

# finish what it's currently working on.

class InterruptHandler

include Singleton

attr_accessor :isolate_signals, :signal_received, :reenable_on_interrupt

# Initialize safe interrupt signal handling.

def initialize

self.isolate_signals = false

self.signal_received = false

self.reenable_on_interrupt = false

Signal.trap('INT') do

if isolate_signals

self.signal_received = true

else

if reenable_on_interrupt

self.reenable_on_interrupt = false

self.isolate_signals = true

end

raise Interrupt # Allow interrupt to propagate to code

end

class << self

# Provide a way to allow a single Ctrl-C interrupt to happen and atomically

# re-enable interrupt protections once that interrupt is propagated.

# This prevents a race condition where code like the following:

# begin

# InterruptHandler.disable!

# ... do stuff ...

# rescue Interrupt

# ... handle it ...

# ensure

# InterruptHandler.enable!

# end

# ...could have the `enable!` call to the interrupt handler not called in

# the event another interrupt was received in between the interrupt being

# handled and the `ensure` block being entered.

# Thus you should always write:

# begin

# InterruptHandler.disable_until_finished_or_interrupted do

# ... do stuff ...

# end

# rescue Interrupt

# ... handle it ...

# rescue

# ... handle any other exceptions ...

# end

def disable_until_finished_or_interrupted

instance.reenable_on_interrupt = true

instance.isolate_signals = false

yield

ensure

instance.isolate_signals = true

end

# Disable interrupt isolation.

def disable!

instance.isolate_signals = false

end

# Enable interrupt isolation.

def enable!

instance.isolate_signals = true

end

# Enable interrupt isolation while executing the provided block.

# @yield block to execute with interrupt isolation

def isolate_from_interrupts

instance.signal_received = false

instance.isolate_signals = true

result = yield

instance.isolate_signals = false

result

end

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