DSL VS10 / Locking policies
***Disclaimer: This information applies to Visual Studio 2010 Beta 1 only.***
Another new feature of the new version of the DSL toolkit is the ability to locks certain operations in a DSL. The idea is that we can define locking policies for a DSL and those policies are executed at runtime to constraint specific operations such as Add/Delete/Update etc.
These locking policies can be defined at three different levels , Store, Partition and ModelElement respectively.
Defining our own locking policies
It is really simple to create our own policy class, we just need to create a class that inherits from ILockingPolicy.
Then we need to define the locks that we are going to return, and for that we have three levels of granularity:
- Store
- Partition
- ModelElement
Locks are transitive following the “Store –> Partition –> ModelElement” object hierarchy.
That means that if we set locks at the Store level, those locks also apply to the Partition and the ModelElement levels.
The lock types are:
public class MyLockingPolicy : ILockingPolicy
{
public Locks RefineLocks(ModelElement element, Locks proposedLocks)
{
return proposedLocks;
}
public Locks RefineLocks(Partition partition, Locks proposedLocks)
{
return proposedLocks;
}
public Locks RefineLocks(Store store, Locks proposedLocks)
{
// TODO: return corresponding locks and they will also apply to Partition and ModelElement
}
}
Injecting our own ILockingPolicy
The Store class constructor sets the locking policy by querying for a ILockingPolicy service. That means that one possible way to inject our own locking policy is to override the GetService method and return our policy class:
internal partial class MyDocData
{
private ILockingPolicy myLockingPolicy;
public override object GetService(Type serviceType)
{
if (serviceType == typeof(SLockingPolicy) || serviceType == typeof(ILockingPolicy))
{
if (myLockingPolicy == null)
{
myLockingPolicy = new MyLockingPolicy();
}
return myLockingPolicy;
}
return base.GetService(serviceType);
}
}
At runtime the DSL infrastructure will query for existing locks using a set of extension methods located in the new ImmutabilityExtensionMethods class and constraint or not an operation accordingly.
The hardware model sample
I published a sample that shows how to lock a DSL.
The scenario is that there are two personas:
- Developer: He uses the VS full IDE to author a hardware model.
- Architect: He uses an Isolated shell to review the model and cannot do any modifications to it.
The locks are being set by detecting the shell SKU.
Pablo
