Assumption.java

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * accompanied this code).
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package com.oracle.truffle.api;

import com.oracle.truffle.api.nodes.InvalidAssumptionException;
import com.oracle.truffle.api.nodes.Node;

/**
 * An assumption is a global boolean flag that starts with the value true (i.e., the assumption is
 * valid) and can subsequently be invalidated (using {@link Assumption#invalidate()}). Once
 * invalidated, an assumption can never get valid again. Assumptions can be created using the
 * {@link TruffleRuntime#createAssumption()} or the {@link TruffleRuntime#createAssumption(String)}
 * method. The Truffle compiler has special knowledge of this class in order to produce efficient
 * machine code for checking an assumption in case the assumption object is a compile time constant.
 * Therefore, assumptions should be stored in final fields in Truffle nodes.
 *
 * All instances of classes implementing {@code Assumption} must be held in {@code final} fields for
 * compiler optimizations to take effect.
 * 
 * @since 0.8 or earlier
 */
public interface Assumption {

    /**
     * Checks that this assumption is still valid. The method throws an exception, if this is no
     * longer the case. This method is preferred over the {@link #isValid()} method when writing
     * guest language interpreter code. The catch block should perform a node rewrite (see
     * {@link Node#replace(Node)}) with a node that no longer relies on the assumption.
     *
     * @throws InvalidAssumptionException If the assumption is no longer valid.
     * @since 0.8 or earlier
     */
    void check() throws InvalidAssumptionException;

    /**
     * Checks whether the assumption is still valid.
     *
     * @return a boolean value indicating the validity of the assumption
     * @since 0.8 or earlier
     */
    boolean isValid();

    /**
     * Invalidates this assumption. Performs no operation, if the assumption is already invalid.
     * 
     * @since 0.8 or earlier
     */
    void invalidate();

    /**
     * A name for the assumption that is used for debug output.
     *
     * @return the name of the assumption
     * @since 0.8 or earlier
     */
    String getName();
}