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module ActiveSupport #:nodoc:
module CoreExtensions #:nodoc:
module File #:nodoc:
module Atomic
# Write to a file atomically. Useful for situations where you don't
# want other processes or threads to see half-written files.
#
# File.atomic_write("important.file") do |file|
# file.write("hello")
# end
#
# If your temp directory is not on the same filesystem as the file you're
# trying to write, you can provide a different temporary directory.
#
# File.atomic_write("/data/something.important", "/data/tmp") do |f|
# file.write("hello")
# end
def atomic_write(file_name, temp_dir = Dir.tmpdir)
require 'tempfile' unless defined?(Tempfile)
temp_file = Tempfile.new(basename(file_name), temp_dir)
yield temp_file
temp_file.close
begin
# Get original file permissions
old_stat = stat(file_name)
rescue Errno::ENOENT
# No old permissions, write a temp file to determine the defaults
check_name = join(dirname(file_name), ".permissions_check.#{Thread.current.object_id}.#{Process.pid}.#{rand(1000000)}")
open(check_name, "w") { }
old_stat = stat(check_name)
unlink(check_name)
end
# Overwrite original file with temp file
rename(temp_file.path, file_name)
# Set correct permissions on new file
chown(old_stat.uid, old_stat.gid, file_name)
chmod(old_stat.mode, file_name)
end
end
end
end
end
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