org.eclipse.viatra.query.runtime.api

Class AdvancedViatraQueryEngine

java.lang.Object

org.eclipse.viatra.query.runtime.api.ViatraQueryEngine

org.eclipse.viatra.query.runtime.api.AdvancedViatraQueryEngine

public abstract class AdvancedViatraQueryEngine
extends ViatraQueryEngine

Advanced interface to a VIATRA incremental evaluation engine.

You can create a new, private, unmanaged AdvancedViatraQueryEngine instance using createUnmanagedEngine(QueryScope). Additionally, you can access the advanced interface on any ViatraQueryEngine by from(ViatraQueryEngine).

While the default interface ViatraQueryEngine, is suitable for most users, this advanced interface provides more control over the engine. The most important added functionality is the following:

• You can have tighter control over the lifecycle of the engine, if you create a private, unmanaged engine instance. For instance, a (non-managed) engine can be disposed in order to detach from the EMF model and stop listening on update notifications. The indexes built previously in the engine can then be garbage collected, even if the model itself is retained. Total lifecycle control is only available for private, unmanaged engines (created using createUnmanagedEngine(QueryScope)); a managed engine (obtained via ViatraQueryEngine.on(QueryScope)) is shared among clients and can not be disposed or wiped.
• You can add and remove listeners to receive notification when the model or the match sets change.
• You can add and remove listeners to receive notification on engine lifecycle events, such as creation of new matchers. For instance, if you explicitly share a private, unmanaged engine between multiple sites, you should register a callback using addLifecycleListener(ViatraQueryEngineLifecycleListener) to learn when another client has called the destructive methods dispose() or wipe().

No Extend:

This class is not intended to be subclassed by clients.

Constructor Summary

Constructors

Constructor and Description
AdvancedViatraQueryEngine()

Method Summary

Modifier and Type	Method and Description
abstract void	addLifecycleListener(ViatraQueryEngineLifecycleListener listener) Add an engine lifecycle listener to this engine instance.
abstract <Match extends IPatternMatch> void	addMatchUpdateListener(ViatraQueryMatcher<Match> matcher, IMatchUpdateListener<? super Match> listener, boolean fireNow) Registers low-level callbacks for match appearance and disappearance on this pattern matcher.
abstract void	addModelUpdateListener(ViatraQueryModelUpdateListener listener) Add an model update event listener to this engine instance (that fires its callbacks according to its notification level).
static AdvancedViatraQueryEngine	createUnmanagedEngine(QueryScope scope) Creates a new unmanaged VIATRA Query engine to evaluate queries over a given scope specified by an QueryScope.
static AdvancedViatraQueryEngine	createUnmanagedEngine(QueryScope scope, ViatraQueryEngineOptions options) Creates a new unmanaged VIATRA Query engine to evaluate queries over a given scope specified by an QueryScope.
abstract <V> V	delayUpdatePropagation(java.util.concurrent.Callable<V> callable) The given callable will be executed, and all update propagation in stateful query backends will be delayed until the execution is done.
abstract void	dispose() Completely disconnects and dismantles the engine.
static AdvancedViatraQueryEngine	from(ViatraQueryEngine engine) Provides access to a given existing engine through the advanced interface.
abstract ViatraQueryEngineOptions	getEngineOptions() Returns the immutable ViatraQueryEngineOptions of the engine.
abstract <Matcher extends ViatraQueryMatcher<? extends IPatternMatch>> Matcher	getExistingMatcher(IQuerySpecification<Matcher> querySpecification, QueryEvaluationHint optionalOverrideHints) Access an existing pattern matcher based on a IQuerySpecification, and optional hints override.
abstract <Matcher extends ViatraQueryMatcher<? extends IPatternMatch>> Matcher	getMatcher(IQuerySpecification<Matcher> querySpecification, QueryEvaluationHint optionalEvaluationHints) Access a pattern matcher based on a IQuerySpecification, overriding some of the default query evaluation hints.
abstract IQueryBackend	getQueryBackend(IQueryBackendFactory iQueryBackendFactory) Provides access to the selected query backend component of the VIATRA Query engine.
abstract IQueryResultProvider	getResultProviderOfMatcher(ViatraQueryMatcher<? extends IPatternMatch> matcher) Return the underlying result provider for the given matcher.
abstract boolean	isManaged() Indicates whether the engine is managed, i.e.
abstract boolean	isTainted() Indicates whether the engine is in a tainted, inconsistent state due to some internal errors.
abstract boolean	isUpdatePropagationDelayed() Returns true if the update propagation in this engine is currently delayed, false otherwise.
abstract void	prepareGroup(IQueryGroup queryGroup, QueryEvaluationHint optionalEvaluationHints) Initializes matchers for a group of patterns as one step (optionally overriding some of the default query evaluation hints).
abstract void	removeLifecycleListener(ViatraQueryEngineLifecycleListener listener) Remove an existing lifecycle listener from this engine instance.
abstract <Match extends IPatternMatch> void	removeMatchUpdateListener(ViatraQueryMatcher<Match> matcher, IMatchUpdateListener<? super Match> listener) Remove an existing match update event listener to this engine instance.
abstract void	removeModelUpdateListener(ViatraQueryModelUpdateListener listener) Remove an existing model update event listener to this engine instance.
abstract void	wipe() Discards any pattern matcher caches and forgets known patterns.

Methods inherited from class org.eclipse.viatra.query.runtime.api.ViatraQueryEngine

getBaseIndex, getCurrentMatchers, getExistingMatcher, getMatcher, getMatcher, getRegisteredQuerySpecifications, getScope, on, on

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

AdvancedViatraQueryEngine

public AdvancedViatraQueryEngine()

Method Detail

createUnmanagedEngine

public static AdvancedViatraQueryEngine createUnmanagedEngine(QueryScope scope)
                                                       throws ViatraQueryException

Creates a new unmanaged VIATRA Query engine to evaluate queries over a given scope specified by an QueryScope.

Repeated invocations will return different instances, so other clients are unable to independently access and influence the returned engine. Note that unmanaged engines do not benefit from some performance improvements that stem from sharing incrementally maintained indices and caches between multiple clients using the same managed engine instance.

Client is responsible for the lifecycle of the returned engine, hence the usage of the advanced interface AdvancedViatraQueryEngine.

The match set of any patterns will be incrementally refreshed upon updates from this scope.

Parameters:

scope - the scope of query evaluation; the definition of the set of model elements that this engine is operates on. Provide e.g. a EMFScope for evaluating queries on an EMF model.

Returns:

the advanced interface to a newly created unmanaged engine

Throws:

ViatraQueryException

Since:

0.9

createUnmanagedEngine

public static AdvancedViatraQueryEngine createUnmanagedEngine(QueryScope scope,
                                                              ViatraQueryEngineOptions options)
                                                       throws ViatraQueryException

Creates a new unmanaged VIATRA Query engine to evaluate queries over a given scope specified by an QueryScope.

Repeated invocations will return different instances, so other clients are unable to independently access and influence the returned engine. Note that unmanaged engines do not benefit from some performance improvements that stem from sharing incrementally maintained indices and caches between multiple clients using the same managed engine instance.

Client is responsible for the lifecycle of the returned engine, hence the usage of the advanced interface AdvancedViatraQueryEngine.

The match set of any patterns will be incrementally refreshed upon updates from this scope.

Parameters:

scope - the scope of query evaluation; the definition of the set of model elements that this engine is operates on. Provide e.g. a EMFScope for evaluating queries on an EMF model.

Returns:

the advanced interface to a newly created unmanaged engine

Throws:

ViatraQueryException

Since:

1.4

from

public static AdvancedViatraQueryEngine from(ViatraQueryEngine engine)

Provides access to a given existing engine through the advanced interface.

Caveat: if the referenced engine is managed (i.e. created via ViatraQueryEngine.on(QueryScope)), the advanced methods dispose() and wipe() will not be allowed.

Parameters:

engine - the engine to access using the advanced interface

Returns:

a reference to the same engine conforming to the advanced interface

addLifecycleListener

public abstract void addLifecycleListener(ViatraQueryEngineLifecycleListener listener)

Add an engine lifecycle listener to this engine instance.

Parameters:

listener - the ViatraQueryEngineLifecycleListener that should listen to lifecycle events from this engine

removeLifecycleListener

public abstract void removeLifecycleListener(ViatraQueryEngineLifecycleListener listener)

Remove an existing lifecycle listener from this engine instance.

Parameters:

listener - the ViatraQueryEngineLifecycleListener that should not listen to lifecycle events from this engine anymore

addModelUpdateListener

public abstract void addModelUpdateListener(ViatraQueryModelUpdateListener listener)

Add an model update event listener to this engine instance (that fires its callbacks according to its notification level).

Parameters:

listener - the ViatraQueryModelUpdateListener that should listen to model update events from this engine.

removeModelUpdateListener

public abstract void removeModelUpdateListener(ViatraQueryModelUpdateListener listener)

Remove an existing model update event listener to this engine instance.

Parameters:

listener - the ViatraQueryModelUpdateListener that should not listen to model update events from this engine anymore

addMatchUpdateListener

public abstract <Match extends IPatternMatch> void addMatchUpdateListener(ViatraQueryMatcher<Match> matcher,
                                                                          IMatchUpdateListener<? super Match> listener,
                                                                          boolean fireNow)

Registers low-level callbacks for match appearance and disappearance on this pattern matcher.

Caution: This is a low-level callback that is invoked when the pattern matcher is not necessarily in a consistent state yet. Importantly, no model modification permitted during the callback. Most users should use the databinding support (ViatraObservables) or the event-driven API (EventDrivenVM) instead.

Performance note: expected to be much more efficient than polling at #addCallbackAfterUpdates(Runnable), but prone to "signal hazards", e.g. spurious match appearances that will disappear immediately afterwards.

The callback can be unregistered via #removeCallbackOnMatchUpdate(IMatchUpdateListener).

Parameters:

fireNow - if true, appearCallback will be immediately invoked on all current matches as a one-time effect. See also ViatraQueryMatcher.forEachMatch(IMatchProcessor).

listener - the listener that will be notified of each new match that appears or disappears, starting from now.

matcher - the ViatraQueryMatcher for which this listener should be active

removeMatchUpdateListener

public abstract <Match extends IPatternMatch> void removeMatchUpdateListener(ViatraQueryMatcher<Match> matcher,
                                                                             IMatchUpdateListener<? super Match> listener)

Remove an existing match update event listener to this engine instance.

Parameters:

matcher - the ViatraQueryMatcher for which this listener should not be active anymore

listener - the IMatchUpdateListener that should not receive the callbacks anymore

getMatcher

public abstract <Matcher extends ViatraQueryMatcher<? extends IPatternMatch>> Matcher getMatcher(IQuerySpecification<Matcher> querySpecification,
                                                                                                 QueryEvaluationHint optionalEvaluationHints)
                                                                                          throws ViatraQueryException

Access a pattern matcher based on a IQuerySpecification, overriding some of the default query evaluation hints. Multiple calls may return the same matcher depending on the actual evaluation hints.

It is guaranteed that this method will always return a matcher instance which is functionally compatible with the requested functionality (see IMatcherCapability). Otherwise, the query evaluator is free to ignore any hints.

For stateful query backends (Rete), hints may be effective only the first time a matcher is created.

Parameters:

querySpecification - a IQuerySpecification that describes a VIATRA query

optionalEvaluationHints - additional / overriding options on query evaluation; passing null means default options associated with the query

Returns:

a pattern matcher corresponding to the specification

Throws:

ViatraQueryException - if the matcher could not be initialized

Since:

0.9

prepareGroup

public abstract void prepareGroup(IQueryGroup queryGroup,
                                  QueryEvaluationHint optionalEvaluationHints)
                           throws ViatraQueryException

Initializes matchers for a group of patterns as one step (optionally overriding some of the default query evaluation hints). If some of the pattern matchers are already constructed in the engine, no task is performed for them.

This preparation step has the advantage that it prepares pattern matchers for an arbitrary number of patterns in a single-pass traversal of the model. This is typically more efficient than traversing the model each time an individual pattern matcher is initialized on demand. The performance benefit only manifests itself if the engine is not in wildcard mode.

Parameters:

queryGroup - a IQueryGroup identifying a set of VIATRA queries

optionalEvaluationHints - additional / overriding options on query evaluation; passing null means default options associated with each query

Throws:

ViatraQueryException - if there was an error in preparing the engine

Since:

0.9

isManaged

public abstract boolean isManaged()

Indicates whether the engine is managed, i.e. the default engine assigned to the given scope root by ViatraQueryEngine.on(QueryScope).

If the engine is managed, there may be other clients using it, as all calls to ViatraQueryEngine.on(QueryScope) return the same managed engine instance for a given scope root. Therefore the destructive methods wipe() and dispose() are not allowed.

On the other hand, if the engine is unmanaged (i.e. a private instance created using createUnmanagedEngine(QueryScope)), then wipe() and dispose() can be called. If you explicitly share a private, unmanaged engine between multiple sites, register a callback using addLifecycleListener(ViatraQueryEngineLifecycleListener) to learn when another client has called these destructive methods.

Returns:

true if the engine is managed, and therefore potentially shared with other clients querying the same EMF model

isTainted

public abstract boolean isTainted()

Indicates whether the engine is in a tainted, inconsistent state due to some internal errors. If true, results are no longer reliable; engine should be disposed.

The engine is in a tainted state if any of its internal processes report back a fatal error. The ViatraQueryEngineLifecycleListener interface provides a callback method for entering the tainted state.

Returns:

the tainted state

wipe

public abstract void wipe()

Discards any pattern matcher caches and forgets known patterns. The base index built directly on the underlying EMF model, however, is kept in memory to allow reuse when new pattern matchers are built. Use this method if you have e.g. new versions of the same patterns, to be matched on the same model.

Matcher objects will continue to return stale results. If no references are retained to the matchers, they can eventually be GC'ed.

Disallowed if the engine is managed (see isManaged()), as there may be other clients using it.

If you explicitly share a private, unmanaged engine between multiple sites, register a callback using addLifecycleListener(ViatraQueryEngineLifecycleListener) to learn when another client has called this destructive method.

Throws:

java.lang.UnsupportedOperationException - if engine is managed

dispose

public abstract void dispose()

Completely disconnects and dismantles the engine. Cannot be reversed.

Matcher objects will continue to return stale results. If no references are retained to the matchers or the engine, they can eventually be GC'ed, and they won't block the EMF model from being GC'ed anymore.

The base indexer (see ViatraQueryEngine.getBaseIndex()) built on the model will be disposed alongside the engine, unless the user has manually added listeners on the base index that were not removed yet.

Disallowed if the engine is managed (see isManaged()), as there may be other clients using it.

If you explicitly share a private, unmanaged engine between multiple sites, register a callback using addLifecycleListener(ViatraQueryEngineLifecycleListener) to learn when another client has called this destructive method.

Throws:

java.lang.UnsupportedOperationException - if engine is managed

getQueryBackend

public abstract IQueryBackend getQueryBackend(IQueryBackendFactory iQueryBackendFactory)
                                       throws ViatraQueryException

Provides access to the selected query backend component of the VIATRA Query engine.

Throws:

ViatraQueryException

No Reference:

for internal use only

getExistingMatcher

public abstract <Matcher extends ViatraQueryMatcher<? extends IPatternMatch>> Matcher getExistingMatcher(IQuerySpecification<Matcher> querySpecification,
                                                                                                         QueryEvaluationHint optionalOverrideHints)

Access an existing pattern matcher based on a IQuerySpecification, and optional hints override.

Parameters:

querySpecification - a IQuerySpecification that describes a VIATRA query specification

optionalOverrideHints - a QueryEvaluationHint that may override the pattern hints (can be null)

Returns:

a pattern matcher corresponding to the specification, null if a matcher does not exist yet.

Since:

1.4

getEngineOptions

public abstract ViatraQueryEngineOptions getEngineOptions()

Returns the immutable ViatraQueryEngineOptions of the engine.

Returns:

the engine options

Since:

1.4

getResultProviderOfMatcher

public abstract IQueryResultProvider getResultProviderOfMatcher(ViatraQueryMatcher<? extends IPatternMatch> matcher)

Return the underlying result provider for the given matcher.

Since:

1.4

No Reference:

This method is considered internal API

delayUpdatePropagation

public abstract <V> V delayUpdatePropagation(java.util.concurrent.Callable<V> callable)
                                      throws java.lang.reflect.InvocationTargetException

The given callable will be executed, and all update propagation in stateful query backends will be delayed until the execution is done. Within the callback, these backends will provide stale results.

It is optional for a IQueryBackend to support the delaying of update propagation; stateless backends will display up-to-date results. In this case, the given callable shall be executed, and the update propagation shall happen just like in non-delayed execution.

Example: in the Rete network, no messages will be propagated until the given callable is executed. After the execution of the callable, all accumulated messages will be delivered.

The purpose of this method is that stateful query backends may save work when multiple model modifications are performed within the callback that partially cancel each other out.

Parameters:

callable - the callable to be executed

Returns:

the result of the callable

Throws:

java.lang.reflect.InvocationTargetException

Since:

1.6

isUpdatePropagationDelayed

public abstract boolean isUpdatePropagationDelayed()

Returns true if the update propagation in this engine is currently delayed, false otherwise.

Since:

1.6

See Also:

#delayUpdatePropagation(Callable)}