/*

 * Copyright 2008-2009 Sun Microsystems, Inc.  All Rights Reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Sun designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Sun in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * 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.

 *

 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

 * CA 95054 USA or visit www.sun.com if you need additional information or

 * have any questions.

 */

package java.dyn;

import sun.dyn.util.BytecodeName;

/**

 * An <code>invokedynamic</code> call site, as reified to the bootstrap method.

 * Every instance of a call site corresponds to a distinct instance

 * of the <code>invokedynamic</code> instruction.

 * Call sites have state, one reference word, called the <code>target</code>,

 * and typed as a {@link MethodHandle}.  When this state is null (as it is

 * initially) the call site is in the unlinked state.  Otherwise, it is said

 * to be linked to its target.

 * <p>

 * When an unlinked call site is executed, a bootstrap routine is called

 * to finish the execution of the call site, and optionally to link

 * the call site.

 * <p>

 * @author John Rose, JSR 292 EG

 */

public class CallSite {

    // Fields used only by the JVM.  Do not use or change.

    private Object vmmethod;

    int callerMID, callerBCI;  // supplied by the JVM

    MethodHandle target;

    final Object caller;  // usually a class

    final String name;

    final MethodType type;

    public CallSite(Object caller, String name, MethodType type) {

        this.caller = caller;

        this.name = name;

        this.type = type;

    }

    private static void privateInitializeCallSite(CallSite site, int callerMID, int callerBCI) {

        site.callerMID = callerMID;

        site.callerBCI = callerBCI;

        if (site.target == null)

            site.setTarget(site.initialTarget());

    }

    /**

     * Just after a call site is created by a bootstrap method handle,

     * if the target has not been initialized by the factory method itself,

     * the method {@code initialTarget} is called to produce an initial

     * non-null target.  (Live call sites must never have null targets.)

     * <p>

     * If the bootstrap method itself does not initialize the call site,

     * this method must be overridden, because it just raises an

     * {@code InvokeDynamicBootstrapError}.

     */

    protected MethodHandle initialTarget() {

        throw new InvokeDynamicBootstrapError("target must be initialized before call site is linked: "+this);

    }

    /**

     * Report the current linkage state of the call site.  (This is mutable.)

     * The value is null if and only if the call site is currently unlinked.

     * When a linked call site is invoked, the target method is used directly.

     * When an unlinked call site is invoked, its bootstrap method receives

     * the call, as if via {@link Linkage#bootstrapInvokeDynamic}.

     * <p>

     * The interactions of {@code getTarget} with memory are the same

     * as of a read from an ordinary variable, such as an array element or a

     * non-volatile, non-final field.

     * <p>

     * In particular, the current thread may choose to reuse the result

     * of a previous read of the target from memory, and may fail to see

     * a recent update to the target by another thread.

     * @return the current linkage state of the call site

     * @see #setTarget

     */

    public MethodHandle getTarget() {

        return target;

    }

    /**

     * Link or relink the call site, by setting its target method.

     * <p>

     * The interactions of {@code setTarget} with memory are the same

     * as of a write to an ordinary variable, such as an array element or a

     * non-volatile, non-final field.

     * <p>

     * In particular, unrelated threads may fail to see the updated target

     * until they perform a read from memory.

     * Stronger guarantees can be created by putting appropriate operations

     * into the bootstrap method and/or the target methods used

     * at any given call site.

     * @param target the new target, or null if it is to be unlinked

     * @throws WrongMethodTypeException if the new target is not null

     *         and has a method type that differs from the call site's {@link #type}

     */

    public void setTarget(MethodHandle target) {

        checkTarget(target);

        this.target = target;

    }

    protected void checkTarget(MethodHandle target) {

        if (!canSetTarget(target))

            throw new WrongMethodTypeException(String.valueOf(target));

    }

    protected boolean canSetTarget(MethodHandle target) {

        return (target != null && target.type() == type());

    }

    /**

     * Report the class containing the call site.

     * This is immutable static context.

     * @return class containing the call site

     */

    public Class<?> callerClass() {

        return (Class) caller;

    }

    /**

     * Report the method name specified in the {@code invokedynamic} instruction.

     * This is immutable static context.

     * <p>

     * Note that the name is a JVM bytecode name, and as such can be any

     * non-empty string, as long as it does not contain certain "dangerous"

     * characters such as slash {@code '/'} and dot {@code '.'}.

     * See the Java Virtual Machine specification for more details.

     * <p>

     * Application such as a language runtimes may need to encode

     * arbitrary program element names and other configuration information

     * into the name.  A standard convention for doing this is

     * <a href="http://blogs.sun.com/jrose/entry/symbolic_freedom_in_the_vm">specified here</a>.

     * @return method name specified by the call site

     */

    public String name() {

        return name;

    }

    /**

     * Report the method name specified in the {@code invokedynamic} instruction,

     * as a series of components, individually demangled according to

     * the standard convention

     * <a href="http://blogs.sun.com/jrose/entry/symbolic_freedom_in_the_vm">specified here</a>.

     * <p>

     * Non-empty runs of characters between dangerous characters are demangled.

     * Each component is either a completely arbitrary demangled string,

     * or else a character constant for a punctuation character, typically ':'.

     * (In principle, the character can be any dangerous character that the

     * JVM lets through in a method name, such as '$' or ']'.

     * Runtime implementors are encouraged to use colon ':' for building

     * structured names.)

     * <p>

     * In the common case where the name contains no dangerous characters,

     * the result is an array whose only element array is the demangled

     * name at the call site.  Such a demangled name can be any sequence

     * of any number of any unicode characters.

     * @return method name components specified by the call site

     */

    public Object[] nameComponents() {

        return BytecodeName.parseBytecodeName(name);

    }

    /**

     * Report the resolved result and parameter types of this call site,

     * which are derived from its bytecode-level invocation descriptor.

     * The types are packaged into a {@link MethodType}.

     * Any linked target of this call site must be exactly this method type.

     * This is immutable static context.

     * @return method type specified by the call site

     */

    public MethodType type() {

        return type;

    }

    @Override

    public String toString() {

        return "CallSite#"+hashCode()+"["+name+type+" => "+target+"]";

    }

}