https://openjdk.java.net/ 
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
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 *
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 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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package org.graalvm.compiler.graph;


An entity that depends upon stable node identifiers. 
/**
 * An entity that depends upon {@linkplain Graph#maybeCompress() stable} node identifiers.
 */
class NodeIdAccessor {
    final Graph graph;
    final int epoch;

    NodeIdAccessor(Graph graph) {
        this.graph = graph;
        this.epoch = graph.compressions;
    }

    Graph getGraph() {
        return graph;
    }

    
Verifies that node identifiers have not changed since this object was created.

Throws:
Returns:true if the check succeeds
/**
     * Verifies that node identifiers have not changed since this object was created.
     *
     * @return true if the check succeeds
     * @throws VerificationError if the check fails
     */
    boolean verifyIdsAreStable() {
        int compressions = graph.compressions - epoch;
        if (compressions != 0) {
            throw new VerificationError("accessing node id in %s across %d graph compression%s", graph, compressions, compressions == 1 ? "" : "s");
        }
        return true;
    }

    
Gets the identifier for a node. If assertions are enabled, this method asserts that the
identifier is stable.

/**
     * Gets the identifier for a node. If assertions are enabled, this method asserts that the
     * identifier is stable.
     */
    int getNodeId(Node node) {
        assert verifyIdsAreStable();
        return node.id();
    }
}