cutGoldenThread

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Module

The attachGoldenThread/cutGoldenThread accessor is exported by the urn:org:ten60:netkernel:ext:sys module. Import this module to gain access to the accessor.

Syntax

URI

active:attachGoldenThread/cutGoldenThread

Argument	Rules	Description
operand	Mandatory	resource to which Golden Thread is attached
param	Mandatory	The Golden Thread's URI

Example Usage

DPML

<instr>
  <type>attachGoldenThread</type>
  <operand>var:myresource</operand>
  <param>goldenthread:1</param>
  <target>var:attachedResource</target>
</instr>

<instr>
  <type>cutGoldenThread</type>
  <param>goldenthread:1</param>
</instr>

NetKernel Foundation API

req=context.createSubRequest("active:attachGoldenThread/cutGoldenThread");
req.addArgument("operand", [resource representation, aspect, or URI] );
req.addArgument("param", [resource representation, aspect, or URI] );
result=context.issueSubRequest(req);

Purpose

NetKernel provides a dependency based cache. In typical NetKernel applications, resources are generated from a tree of dependent resources. If one of the resources expires then all dependent resources expire. In most NetKernel applications this happens transparently and automatically.

However, in certain circumstances, for example database queries, it is not possible to create a URI based dependency that will automatically expire. In the database example, if an update is performed to the underlying data, the query does not know the data it references has changed. The Golden Thread provides the NetKernel application developer a mechanism to manually notify the query when an update is performed.

A Golden Thread is simply a common dependency URI across any number of resources. It is attached with the attachGoldenThread accessor. Any number of dependent resources can be added to single Golden Thread URI. All will be cacheable and depend directly on the validity of the specified Golden Thread.

At any time the Golden Thread can be cut with the cutGoldenThread accessor. All resources linked by the Golden Thread will be immediately expired and the Kernel will discard cached value and/or rebuild the resources.

Note: normal NetKernel processing does not require the use of a Golden Thread. NetKernel automatically detect dependencies and invalidates dependent results if a resource expires. Golden Threads are necessary with legacy resource sources such as relational databases where a resource may become invalid by the action of the application (an update invalidates a query result) and for which the resource is generated outside of NetKernel's addressable URI space.

Example

Here's an example that attaches a Golden Thread to the results of a database Query for customers. Note the Golden Thread URI is not a real resource it is just a URI that is unique to this Thread. NetKernel will cache the result of the query.

<instr>
  <type>attachGoldenThread</type>
  <operand>var:myCustomerQueryResult</operand>
  <param>goldenthread:customerDB</param>
  <target>var:myCustomerQueryResult</target>
</instr>

Suppose we now update the database. We can invalidate all results attached to the Golden Thread by cutting it...

<instr>
  <type>cutGoldenThread</type>
  <param>goldenthread:customerDB</param>
</instr>

All resources attached to the customerDB Golden Thread will be immediately invalidated and will be removed from the cache.