Class: PStore
- Inherits:
-
Object
- Object
- PStore
- Defined in:
- lib/pstore.rb
Overview
PStore implements a file based persistence mechanism based on a Hash. User code can store hierarchies of Ruby objects (values) into the data store file by name (keys). An object hierarchy may be just a single object. User code may later read values back from the data store or even update data, as needed.
The transactional behavior ensures that any changes succeed or fail together. This can be used to ensure that the data store is not left in a transitory state, where some values were updated but others were not.
Behind the scenes, Ruby objects are stored to the data store file with Marshal. That carries the usual limitations. Proc objects cannot be marshalled, for example.
Usage example:
require "pstore"
# a mock wiki object...
class WikiPage
def initialize( page_name, , contents )
@page_name = page_name
@revisions = Array.new
add_revision(, contents)
end
attr_reader :page_name
def add_revision( , contents )
@revisions << { :created => Time.now,
:author => ,
:contents => contents }
end
def wiki_page_references
[@page_name] + @revisions.last[:contents].scan(/\b(?:[A-Z]+[a-z]+){2,}/)
end
# ...
end
# create a new page...
home_page = WikiPage.new( "HomePage", "James Edward Gray II",
"A page about the JoysOfDocumentation..." )
# then we want to update page data and the index together, or not at all...
wiki = PStore.new("wiki_pages.pstore")
wiki.transaction do # begin transaction; do all of this or none of it
# store page...
wiki[home_page.page_name] = home_page
# ensure that an index has been created...
wiki[:wiki_index] ||= Array.new
# update wiki index...
wiki[:wiki_index].push(*home_page.wiki_page_references)
end # commit changes to wiki data store file
### Some time later... ###
# read wiki data...
wiki.transaction(true) do # begin read-only transaction, no changes allowed
wiki.roots.each do |data_root_name|
p data_root_name
p wiki[data_root_name]
end
end
Transaction modes
By default, file integrity is only ensured as long as the operating system (and the underlying hardware) doesn’t raise any unexpected I/O errors. If an I/O error occurs while PStore is writing to its file, then the file will become corrupted.
You can prevent this by setting pstore.ultra_safe = true. However, this results in a minor performance loss, and only works on platforms that support atomic file renames. Please consult the documentation for ultra_safe
for details.
Needless to say, if you’re storing valuable data with PStore, then you should backup the PStore files from time to time.
Defined Under Namespace
Classes: Error
Constant Summary collapse
- VERSION =
"0.1.1"
- RDWR_ACCESS =
{mode: IO::RDWR | IO::CREAT | IO::BINARY, encoding: Encoding::ASCII_8BIT}.freeze
- RD_ACCESS =
{mode: IO::RDONLY | IO::BINARY, encoding: Encoding::ASCII_8BIT}.freeze
- WR_ACCESS =
{mode: IO::WRONLY | IO::CREAT | IO::TRUNC | IO::BINARY, encoding: Encoding::ASCII_8BIT}.freeze
Instance Attribute Summary collapse
-
#ultra_safe ⇒ Object
Whether PStore should do its best to prevent file corruptions, even when under unlikely-to-occur error conditions such as out-of-space conditions and other unusual OS filesystem errors.
Instance Method Summary collapse
-
#[](name) ⇒ Object
Retrieves a value from the PStore file data, by name.
-
#[]=(name, value) ⇒ Object
Stores an individual Ruby object or a hierarchy of Ruby objects in the data store file under the root name.
-
#abort ⇒ Object
Ends the current PStore#transaction, discarding any changes to the data store.
-
#commit ⇒ Object
Ends the current PStore#transaction, committing any changes to the data store immediately.
-
#delete(name) ⇒ Object
Removes an object hierarchy from the data store, by name.
-
#fetch(name, default = PStore::Error) ⇒ Object
This method is just like PStore#[], save that you may also provide a default value for the object.
-
#initialize(file, thread_safe = false) ⇒ PStore
constructor
To construct a PStore object, pass in the file path where you would like the data to be stored.
-
#path ⇒ Object
Returns the path to the data store file.
-
#root?(name) ⇒ Boolean
Returns true if the supplied name is currently in the data store.
-
#roots ⇒ Object
Returns the names of all object hierarchies currently in the store.
-
#transaction(read_only = false) ⇒ Object
Opens a new transaction for the data store.
Constructor Details
#initialize(file, thread_safe = false) ⇒ PStore
To construct a PStore object, pass in the file path where you would like the data to be stored.
PStore objects are always reentrant. But if thread_safe is set to true, then it will become thread-safe at the cost of a minor performance hit.
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# File 'lib/pstore.rb', line 121 def initialize(file, thread_safe = false) dir = File::dirname(file) unless File::directory? dir raise PStore::Error, format("directory %s does not exist", dir) end if File::exist? file and not File::readable? file raise PStore::Error, format("file %s not readable", file) end @filename = file @abort = false @ultra_safe = false @thread_safe = thread_safe @lock = Thread::Mutex.new end |
Instance Attribute Details
#ultra_safe ⇒ Object
Whether PStore should do its best to prevent file corruptions, even when under unlikely-to-occur error conditions such as out-of-space conditions and other unusual OS filesystem errors. Setting this flag comes at the price in the form of a performance loss.
This flag only has effect on platforms on which file renames are atomic (e.g. all POSIX platforms: Linux, MacOS X, FreeBSD, etc). The default value is false.
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# File 'lib/pstore.rb', line 112 def ultra_safe @ultra_safe end |
Instance Method Details
#[](name) ⇒ Object
Retrieves a value from the PStore file data, by name. The hierarchy of Ruby objects stored under that root name will be returned.
WARNING: This method is only valid in a PStore#transaction. It will raise PStore::Error if called at any other time.
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# File 'lib/pstore.rb', line 157 def [](name) in_transaction @table[name] end |
#[]=(name, value) ⇒ Object
Stores an individual Ruby object or a hierarchy of Ruby objects in the data store file under the root name. Assigning to a name already in the data store clobbers the old data.
Example:
require "pstore"
store = PStore.new("data_file.pstore")
store.transaction do # begin transaction
# load some data into the store...
store[:single_object] = "My data..."
store[:obj_hierarchy] = { "Kev Jackson" => ["rational.rb", "pstore.rb"],
"James Gray" => ["erb.rb", "pstore.rb"] }
end # commit changes to data store file
WARNING: This method is only valid in a PStore#transaction and it cannot be read-only. It will raise PStore::Error if called at any other time.
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# File 'lib/pstore.rb', line 202 def []=(name, value) in_transaction_wr @table[name] = value end |
#abort ⇒ Object
Ends the current PStore#transaction, discarding any changes to the data store.
Example:
require "pstore"
store = PStore.new("data_file.pstore")
store.transaction do # begin transaction
store[:one] = 1 # this change is not applied, see below...
store[:two] = 2 # this change is not applied, see below...
store.abort # end transaction here, discard all changes
store[:three] = 3 # this change is never reached
end
WARNING: This method is only valid in a PStore#transaction. It will raise PStore::Error if called at any other time.
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# File 'lib/pstore.rb', line 290 def abort in_transaction @abort = true throw :pstore_abort_transaction end |
#commit ⇒ Object
Ends the current PStore#transaction, committing any changes to the data store immediately.
Example:
require "pstore"
store = PStore.new("data_file.pstore")
store.transaction do # begin transaction
# load some data into the store...
store[:one] = 1
store[:two] = 2
store.commit # end transaction here, committing changes
store[:three] = 3 # this change is never reached
end
WARNING: This method is only valid in a PStore#transaction. It will raise PStore::Error if called at any other time.
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# File 'lib/pstore.rb', line 264 def commit in_transaction @abort = false throw :pstore_abort_transaction end |
#delete(name) ⇒ Object
Removes an object hierarchy from the data store, by name.
WARNING: This method is only valid in a PStore#transaction and it cannot be read-only. It will raise PStore::Error if called at any other time.
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# File 'lib/pstore.rb', line 212 def delete(name) in_transaction_wr @table.delete name end |
#fetch(name, default = PStore::Error) ⇒ Object
This method is just like PStore#[], save that you may also provide a default value for the object. In the event the specified name is not found in the data store, your default will be returned instead. If you do not specify a default, PStore::Error will be raised if the object is not found.
WARNING: This method is only valid in a PStore#transaction. It will raise PStore::Error if called at any other time.
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# File 'lib/pstore.rb', line 171 def fetch(name, default=PStore::Error) in_transaction unless @table.key? name if default == PStore::Error raise PStore::Error, format("undefined root name `%s'", name) else return default end end @table[name] end |
#path ⇒ Object
Returns the path to the data store file.
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# File 'lib/pstore.rb', line 238 def path @filename end |
#root?(name) ⇒ Boolean
Returns true if the supplied name is currently in the data store.
WARNING: This method is only valid in a PStore#transaction. It will raise PStore::Error if called at any other time.
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# File 'lib/pstore.rb', line 233 def root?(name) in_transaction @table.key? name end |
#roots ⇒ Object
Returns the names of all object hierarchies currently in the store.
WARNING: This method is only valid in a PStore#transaction. It will raise PStore::Error if called at any other time.
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# File 'lib/pstore.rb', line 223 def roots in_transaction @table.keys end |
#transaction(read_only = false) ⇒ Object
Opens a new transaction for the data store. Code executed inside a block passed to this method may read and write data to and from the data store file.
At the end of the block, changes are committed to the data store automatically. You may exit the transaction early with a call to either PStore#commit or PStore#abort. See those methods for details about how changes are handled. Raising an uncaught Exception in the block is equivalent to calling PStore#abort.
If read_only is set to true
, you will only be allowed to read from the data store during the transaction and any attempts to change the data will raise a PStore::Error.
Note that PStore does not support nested transactions.
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# File 'lib/pstore.rb', line 313 def transaction(read_only = false) # :yields: pstore value = nil if !@thread_safe raise PStore::Error, "nested transaction" unless @lock.try_lock else begin @lock.lock rescue ThreadError raise PStore::Error, "nested transaction" end end begin @rdonly = read_only @abort = false file = open_and_lock_file(@filename, read_only) if file begin @table, checksum, original_data_size = load_data(file, read_only) catch(:pstore_abort_transaction) do value = yield(self) end if !@abort && !read_only save_data(checksum, original_data_size, file) end ensure file.close end else # This can only occur if read_only == true. @table = {} catch(:pstore_abort_transaction) do value = yield(self) end end ensure @lock.unlock end value end |