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Truffle is a multi-language framework for executing dynamic languages that achieves high performance when combined with Graal.
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package com.oracle.truffle.api.instrumentation;

import com.oracle.truffle.api.CompilerDirectives.CompilationFinal;

/**
 * Event node factories are factories of event nodes for a {@link EventContext program location}.
 * The factory might be invoked multiple times for one and the same source location but the location
 * does never change for a particular returned event node.
 *
 * 
 * For example it makes sense to register a performance counter on {@link #create(EventContext) }
 * and increment the counter in the {@link ExecutionEventNode} implementation. The counter can be
 * stored as a {@link CompilationFinal compilation final}, so no peak performance overhead persists
 * for looking up the counter on the fast path.
 * 
 * 
 * @since 0.12
 */
public interface ExecutionEventNodeFactory {

    /**
     * Returns a new instance of {@link ExecutionEventNode} for this particular source location.
     * This method might be invoked multiple times for one particular source location
     * {@link EventContext context}. The implementation must ensure that this is handled
     * accordingly.
     *
     * @param context the current context where this event node should get created.
     * @return a new event node instance, or null for no event node at the location
     * @since 0.12
     */
    ExecutionEventNode create(EventContext context);

}