/*

 * 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

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

 *

 * 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.

 *

 */

package java.dyn;

import sun.dyn.util.BytecodeName;

import sun.dyn.Access;

import sun.dyn.CallSiteImpl;

import sun.dyn.MethodHandleImpl;

/**

 * An {@code invokedynamic} call site, as reified by the

 * containing class's bootstrap method.

 * Every call site object corresponds to a distinct instance

 * of the <code>invokedynamic</code> instruction, and vice versa.

 * Every call site has one state variable, called the {@code target}.

 * It is typed as a {@link MethodHandle}.  This state is never null, and

 * it is the responsibility of the bootstrap method to produce call sites

 * which have been pre-linked to an initial target method.

 * <p>

 * (Note:  The bootstrap method may elect to produce call sites of a

 * language-specific subclass of {@code CallSite}.  In such a case,

 * the subclass may claim responsibility for initializing its target to

 * a non-null value, by overriding {@link #initialTarget}.)

 * <p>

 * An {@code invokedynamic} instruction which has not yet been executed

 * is said to be <em>unlinked</em>.  When an unlinked call site is executed,

 * the containing class's bootstrap method is called to manufacture a call site,

 * for the instruction.  If the bootstrap method does not assign a non-null

 * value to the new call site's target variable, the method {@link #initialTarget}

 * is called to produce the new call site's first target method.

 * <p>

 * @see Linkage#registerBootstrapMethod(java.lang.Class, java.dyn.MethodHandle)

 * @author John Rose, JSR 292 EG

 */

public class CallSite

        // Note: This is an implementation inheritance hack, and will be removed

        // with a JVM change which moves the required hidden state onto this class.

        extends CallSiteImpl

{

    private static final Access IMPL_TOKEN = Access.getToken();

    /*

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

    private Object vmmethod;

    int callerMID, callerBCI;  // supplied by the JVM

    private MethodHandle target;

    final Object caller;  // usually a class

    final String name;

    final MethodType type;

    */

    /**

     * Make a call site given the parameters from a call to the bootstrap method.

     * The resulting call site is in an unlinked state, which means that before

     * it is returned from a bootstrap method call it must be provided with

     * a target method via a call to {@link CallSite#setTarget}.

     * @param caller the class in which the relevant {@code invokedynamic} instruction occurs

     * @param name the name specified by the {@code invokedynamic} instruction

     * @param type the method handle type derived from descriptor of the {@code invokedynamic} instruction

     */

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

        super(IMPL_TOKEN, caller, name, type);

    }

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

        site.callerMID = callerMID;

        site.callerBCI = callerBCI;

        site.ensureTarget();

    }

    private void ensureTarget() {

        // Note use of super, which accesses the field directly,

        // without deferring to possible subclass overrides.

        if (super.getTarget() == null) {

            super.setTarget(this.initialTarget());

            super.getTarget().type();  // provoke NPE if still null

        }

    }

    /**

     * 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}, which in turn causes the

     * linkage of the {@code invokedynamic} instruction to terminate

     * abnormally.

     */

    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 may not be null after the {@code CallSite} object is returned

     * from the bootstrap method of the {@code invokedynamic} instruction.

     * When an {@code invokedynamic} instruction is executed, the target method

     * of its associated {@code call site} object is invoked directly,

     * as if via {@link MethodHandle}{@code .invoke}.

     * <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 super.getTarget();

    }

    /**

     * 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 NullPointerException if the proposed new target is null

     * @throws WrongMethodTypeException if the proposed new target

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

     */

    public void setTarget(MethodHandle target) {

        checkTarget(target);

        super.setTarget(target);

    }

    protected void checkTarget(MethodHandle target) {

        target.type();  // provoke NPE

        if (!canSetTarget(target))

            throw new WrongMethodTypeException(String.valueOf(target)+target.type()+" should be of type "+type());

    }

    protected boolean canSetTarget(MethodHandle target) {

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

    }

    /**

     * Report the class containing the call site.

     * This is an immutable property of the call site, set from the first argument to the constructor.

     * @return class containing the call site

     */

    public Class<?> callerClass() {

        return (Class) caller;

    }

    /**

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

     * This is an immutable property of the call site, set from the second argument to the constructor.

     * <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 an immutable property of the call site, set from the third argument to the constructor.

     * @return method type specified by the call site

     */

    public MethodType type() {

        return type;

    }

    @Override

    public String toString() {

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

    }

    // Package-local constant:

    static final MethodHandle GET_TARGET = MethodHandleImpl.getLookup(IMPL_TOKEN).

            findVirtual(CallSite.class, "getTarget", MethodType.methodType(MethodHandle.class));

}