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#
# How to use:
#
# db = PStore.new("/tmp/foo")
# db.transaction do
# p db.roots
# ary = db["root"] = [1,2,3,4]
# ary[0] = [1,1.5]
# end
# db.transaction do
# p db["root"]
# end
require "ftools"
require "digest/md5"
class PStore
class Error < StandardError
end
def initialize(file)
dir = File::dirname(file)
unless File::directory? dir
raise PStore::Error, format("directory %s does not exist", dir)
end
unless File::writable? dir
raise PStore::Error, format("directory %s not writable", dir)
end
if File::exist? file and not File::readable? file
raise PStore::Error, format("file %s not readable", file)
end
@transaction = false
@filename = file
@abort = false
end
def in_transaction
raise PStore::Error, "not in transaction" unless @transaction
end
private :in_transaction
def [](name)
in_transaction
@table[name]
end
def fetch(name, default=PStore::Error)
unless @table.key? name
if default==PStore::Error
raise PStore::Error, format("undefined root name `%s'", name)
else
default
end
end
self[name]
end
def []=(name, value)
in_transaction
@table[name] = value
end
def delete(name)
in_transaction
@table.delete name
end
def roots
in_transaction
@table.keys
end
def root?(name)
in_transaction
@table.key? name
end
def path
@filename
end
def commit
in_transaction
@abort = false
throw :pstore_abort_transaction
end
def abort
in_transaction
@abort = true
throw :pstore_abort_transaction
end
def transaction(read_only=false)
raise PStore::Error, "nested transaction" if @transaction
begin
@transaction = true
value = nil
backup = @filename+"~"
begin
file = File::open(@filename, "rb+")
orig = true
rescue Errno::ENOENT
raise if read_only
file = File::open(@filename, "wb+")
end
file.flock(read_only ? File::LOCK_SH : File::LOCK_EX)
if read_only
@table = Marshal::load(file)
elsif orig and (content = file.read) != ""
@table = Marshal::load(content)
size = content.size
md5 = Digest::MD5.digest(content)
content = nil # unreference huge data
else
@table = {}
end
begin
catch(:pstore_abort_transaction) do
value = yield(self)
end
rescue Exception
@abort = true
raise
ensure
if !read_only and !@abort
file.rewind
content = Marshal::dump(@table)
if !md5 || size != content.size || md5 != Digest::MD5.digest(content)
File::copy @filename, backup
begin
file.write(content)
file.truncate(file.pos)
content = nil # unreference huge data
rescue
File::rename backup, @filename if File::exist?(backup)
raise
end
end
end
if @abort and !orig
File.unlink(@filename)
end
@abort = false
end
ensure
@table = nil
@transaction = false
file.close if file
end
value
end
end
if __FILE__ == $0
db = PStore.new("/tmp/foo")
db.transaction do
p db.roots
ary = db["root"] = [1,2,3,4]
ary[1] = [1,1.5]
end
1000.times do
db.transaction do
db["root"][0] += 1
p db["root"][0]
end
end
db.transaction(true) do
p db["root"]
end
end
|
