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package org.jruby.runtime.ivars;

/**
 * A lazy mechanism for accessing VariableAccessors for a given variable name.
 */
public final class VariableAccessorField {
    /** the name of the variable */
    private final String name;
    
    /** the accessor cached after it has been allocated */
    private volatile VariableAccessor variableAccessor = VariableAccessor.DUMMY_ACCESSOR;

    /**
     * Construct a new VariableAccessorField for the given named variable.
     * 
     * @param name the name of the variable
     */
    public VariableAccessorField(String name) {
        this.name = name;
    }

    /**
     * Retrieve the variable accessor for read.
     * 
     * @return the variable accessor appropriate for reads
     */
    public VariableAccessor getVariableAccessorForRead() {
        return variableAccessor;
    }

    /**
     * Retrieve the variable access for write.
     * 
     * @param tableMgr the VariableTableManager for which to allocate an
     * accessor, if it has not already been allocated.
     * @return the variable accessor appropriate for writes.
     */
    public VariableAccessor getVariableAccessorForWrite(VariableTableManager tableMgr) {
        VariableAccessor variableAccessor = this.variableAccessor;
        return variableAccessor != VariableAccessor.DUMMY_ACCESSOR ? variableAccessor : allocateVariableAccessor(tableMgr);
    }

    /**
     * Retrieve or allocate the variable accessor for this variable. This
     * version differs from getVariableAccessorForWrite only in its visibility
     * and the fact that it is synchronized against this field to ensure
     * volatile behavior of the variableAccessor field.
     * 
     * @param tableMgr the VariableTableManager for which to allocate an
     * accessor, if it has not already been allocated.
     * @return the variable accessor appropriate for writes
     */
    private synchronized VariableAccessor allocateVariableAccessor(VariableTableManager tableMgr) {
        VariableAccessor variableAccessor = this.variableAccessor;
        if (variableAccessor == VariableAccessor.DUMMY_ACCESSOR) {
            variableAccessor = this.variableAccessor = tableMgr.allocateVariableAccessor(name);
        }
        return variableAccessor;
    }
    
}
