Test for OutOfMemory exception

OOM error handling.cr

Kilobyte = 1024u32
Megabyte = 1024u32 * Kilobyte
Gigabyte = 1024u32 * Megabyte

def write_debug(str)
  LibC.write 1, str, str.size
end

class FatalOOMError < Exception
  def initialize
    super "pre-allocated OOM"
  end
end

class OOMError < Exception
  @@oom_pending = false
  @@fatal_oom = FatalOOMError.new # pre-allocated error

  def self.try_new
    if @@oom_pending
      write_debug "oom raise failed\n"
      return @@fatal_oom
    end

    @@oom_pending = true
    oom = new
    @@oom_pending = false

    write_debug "oom error..\n"
    oom
  end

  def initialize
    super "dynamically-allocated OOM"
    Pointer(Void).malloc(Megabyte) # simulate an alloc to crash on very low memory
  end
end

fun __crystal_malloc(size : UInt32) : Void*
  ptr = LibGC.malloc size
  if ptr.null?
    write_debug "null!\n"
    raise OOMError.try_new
  end
  ptr
end

module Test
  class_getter gb_alloced = 0
  class_getter mb_alloced = 0

  def self.giga
    __crystal_malloc(Gigabyte)
    @@gb_alloced += 1
    write_debug "giga "
  end

  def self.mega
    __crystal_malloc(Megabyte)
    @@mb_alloced += 1
    write_debug "mega "
  end
end


#------------------------------
GC.disable

loop do
  begin
    Test.giga
  rescue ex : OOMError
    puts "---------------------------------------"
    puts "Got an OOMError!!"
    puts "---------------------------------------"
    break
  end
end

loop do
  begin
    Test.mega
  rescue ex : FatalOOMError
    puts "---------------------------------------------"
    puts "Got a FatalOOMError!! Almost no memory left!"
    puts "---------------------------------------------"
    break
  end
end

puts
puts "alloc'ed: #{Test.gb_alloced}G #{Test.mb_alloced}M"