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README.txt
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README.txt
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= InstantCache - Variables in memcached
* http://instantcache.rubyforge.org/
* github: http://github.com/RoUS/rubygem-instantcache
* rubyforge: http://rubyforge.org/scm/?group_id=10054
== DESCRIPTION:
*rubygem-instantcache* provides the InstantCache module, a mixin
which has accessors that allow you to declare 'instance variables'
that are actually stored in a memcached cluster rather than
local memory.
== GLOSSARY:
- <b><i>blob</i></b>, <b><i>blob object</i></b>, or <b><i>blob instance</i></b>: An instrumented InstantCache::Blob or InstantCache::Counter object that has been instantiated and stored in an <i>instance variable</i>.
* <b><i>cached value</i></b>: The value actually stored in the memcached cluster.
* <b><i>cache</i></b> (or <b><i>cached</i></b>) <b><i>variable</i></b>: an instance variable declared with one of the <tt>memcached_<i>xxx</i></tt> declarators and holding a <i>blob instance</i>.
* <b><i>cell</i></b> or <b><i>cache cell</i></b>: The named location in the memcached cluster where a <i>cached value</i> is stored.
* <b><i>instance variable</i></b>: This has its canonical meaning: a named cell local to an object. <i>Blob objects</i> are stored in <i>instance variables</i> to form <i>cached variables</i>.
== FEATURES:
* Provides <tt>memcached_reader</tt>, <tt>memcached_accessor</tt>, and <tt>memcached_counter</tt> accessor declarations.
* Cached variables declared with <tt>memcached_counter</tt> are restricted to integer values, and are incrementable/decrementable atomically.
* Cached variables may be shared, using cells in memcache named by the user, or may be private, with opaque names unique to each instance.
* Cached variables may be locked and unlocked for atomic operations.
* If an instance variable is inadvertently overwritten, a new connexion to the cached value will be created (a new blob object will be instantiated) the next time one of InstantCache's methods is used to access it.
== CAVEATS AND WARNINGS
* InstantCache works by storing a specially-instrumented object in the actual instance variable. References from within the class to an instance variable declared as a cached variable should use the "<tt>self.</tt>" prefix (<i>e.g.</i>, <tt>self.ivar</tt>) or the blob object's methods directly (<i>e.g.</i>, <tt>@ivar.get</tt> or <tt>@ivar.set(17)</tt>).
* Direct assignment to an instance variable (<i>e.g.</i>, <tt>@ivar = 17</tt>) will lose the instrumented object and result in a new one being created.
== KNOWN PROBLEMS:
* If an cached variable is locked, and is then re-instantiated/reconnected, the variable will <b>remain</b> locked and cannot be unlocked.
* Multiple references to a cached variable can get out of sync, leading to confusion if they are updated independently. That is,
class Foo
include InstantCache
memcached_accessor(:ivar)
end
f = Foo.new
f.ivar = [1,2,3]
copy = f.ivar
f.ivar = 17
copy
=> [1,2,3]
f.ivar
=> 17
copy << 4
=> [1,2,3,4]
f.ivar
=> [1,2,3,4]
== SYNOPSIS:
require 'memcache'
require 'instantcache'
class Foo
include InstantCache
memcached_counter(:c1) # defaults to 0 if not already existant
memcached_accessor(InstantCache::PRIVATE, :private_a1)
def bar
@c1.increment
self.c1_increment
self.decrement(2)
end
end
InstantCache.cache_object = MemCache.new('127.0.0.1:11211')
foo = Foo.new
foo.c1 = 0
=> 0
foo.private_a1 = nil
=> nil
foo.bar
=> 0 # cell was incremented and then decremented
foo.bar = 21
=> 21
foo.bar
=> 21
foo.bar_increment(2)
=> 23
foo.bar_destroy!
=> nil
foo.bar
InstantCache::Destroyed: attempt to access destroyed variable
== REQUIREMENTS:
* Gem <tt>{versionomy}[https://rubygems.org/gems/versionomy]</tt>
* Gem <tt>{memcache-client}[https://rubygems.org/gems/memcache-client]</tt>
== INSTALL:
* gem install instantcache
== LICENSE:
(The Apache License V2)
Apache License
Version 2.0, January 2004
http://www.apache.org/licenses/
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