storage

storage : object

Parameter	Type		Description
Result	object	←	Catalog of shared objects and shared collections registered in storage

Description

The storage command returns the catalog of shared objects or shared collections that you have registered in the storage object on the current application.

The catalog returned by storage is automatically created by Qodly and is available to all processes of the application, including preemptive processes. There is one storage shared object per server.

Use the storage catalog to reference any shared objects or shared collections that you want to be used from any preemptive or standard process. To register a shared object or a shared collection in the catalog, add its reference to the shared object returned by storage.

Since the catalog returned by storage is a shared object, it follows the rules described in the Shared objects and shared collections section (but with some specificities):

• This object can only contain shared objects and shared collections. Trying to add other kinds of values (non-shared objects or collections, null, scalar values) will generate an error.
• Adding a property to this object must be surrounded by the use...end structure, otherwise an error is returned. Reading an attribute outside of a use...end structure is, however, possible.
• When surrounded by the use...end structure, first-level attributes of storage are locked for other processes.
• Unlike standard shared objects, the object returned by storage will NOT share its locking identifier with shared objects or collections added as attributes (and thus will not be locked).

Example 1

Initializing the storage object:

 use(storage)
    storage.counters = newSharedObject("customers",0,"invoices",0)
 end

Example 2

A standard way to set storage values:

 use(storage)
    storage.mydata: = newSharedObject
    use(storage.mydata)
       storage.mydata.prop1 = "Smith"
       storage.mydata.prop2 = 100
    end
 end

Example 3

storage allows implementing a singleton with a lazy initialization, as shown in the following example.

declare -> counterValue : integer var counter : object //create a reference to counter for the process

if(counter == null) //if this reference is null, get if from storage use(storage) //Use of storage needed only once! if(storage.counter == null) storage.counter = newSharedObject("operation",0) end counter = storage.counter //Get the reference of the counter shared object end end use(counter) //directly use the shared object counter (no need to use storage!) counter.operation = counter.operation+1 counterValue = counter.operation end

note

For more information about singleton patterns, you can refer to this Wikipedia page.