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

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 * 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.  Oracle designates this

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

 * by Oracle 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package java.dyn;

import sun.dyn.Access;

import sun.dyn.MemberName;

import sun.dyn.CallSiteImpl;

/**

 * A {@code CallSite} reifies an {@code invokedynamic} instruction from bytecode,

 * and controls its linkage.

 * Every linked {@code CallSite} object corresponds to a distinct instance

 * of the {@code invokedynamic} instruction, and vice versa.

 * <p>

 * Every linked {@code CallSite} object has one state variable,

 * a {@link MethodHandle} reference called the {@code target}.

 * This reference is never null.  Though it can change its value

 * successive values must always have exactly the {@link MethodType method type}

 * called for by the bytecodes of the associated {@code invokedynamic} instruction

 * <p>

 * It is the responsibility of each class's

 * {@link Linkage#registerBootstrapMethod(Class, MethodHandle) bootstrap method}

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

 * The required {@link MethodType type} for the target method is a parameter

 * to each bootstrap method call.

 * <p>

 * 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>

 * A freshly-created {@code CallSite} object is not yet in a linked state.

 * An unlinked {@code CallSite} object reports null for its {@code callerClass}.

 * When the JVM receives a {@code CallSite} object from a bootstrap method,

 * it first ensures that its target is non-null and of the correct type.

 * The JVM then links the {@code CallSite} object to the call site instruction,

 * enabling the {@code callerClass} to return the class in which the instruction occurs.

 * <p>

 * Next, the JVM links the instruction to the {@code CallSite}, at which point

 * any further execution of the {@code invokedynamic} instruction implicitly

 * invokes the current target of the {@code CallSite} object.

 * After this two-way linkage, both the instruction and the {@code CallSite}

 * object are said to be linked.

 * <p>

 * This state of linkage continues until the method containing the

 * dynamic call site is garbage collected, or the dynamic call site

 * is invalidated by an explicit request.

 * <p>

 * Linkage happens once in the lifetime of any given {@code CallSite} object.

 * Because of call site invalidation, this linkage can be repeated for

 * a single {@code invokedynamic} instruction, with multiple {@code CallSite} objects.

 * When a {@code CallSite} is unlinked from an {@code invokedynamic} instruction,

 * the instruction is reset so that it is no longer associated with

 * the {@code CallSite} object, but the {@code CallSite} does not change

 * state.

 * <p>

 * Here is a sample use of call sites and bootstrap methods which links every

 * dynamic call site to print its arguments:

<blockquote><pre><!-- see indy-demo/src/PrintArgsDemo.java -->

private static void printArgs(Object... args) {

  System.out.println(java.util.Arrays.deepToString(args));

}

private static final MethodHandle printArgs;

static {

  MethodHandles.Lookup lookup = MethodHandles.lookup();

  Class thisClass = lookup.lookupClass();  // (who am I?)

  printArgs = lookup.findStatic(thisClass,

      "printArgs", MethodType.methodType(void.class, Object[].class));

  Linkage.registerBootstrapMethod("bootstrapDynamic");

}

private static CallSite bootstrapDynamic(Class caller, String name, MethodType type) {

  // ignore caller and name, but match the type:

  return new CallSite(MethodHandles.collectArguments(printArgs, type));

}

</pre></blockquote>

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

 * @author John Rose, JSR 292 EG

 */

public class CallSite

{

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

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

    private MemberName vmmethod; // supplied by the JVM (ref. to calling method)

    private int        vmindex;  // supplied by the JVM (BCI within calling method)

    // The actual payload of this call site:

    private MethodHandle target;

    // Remove this field for PFD and delete deprecated methods:

    private MemberName calleeNameRemoveForPFD;

    /**

     * Make a blank call site object.

     * Before it is returned from a bootstrap method, this {@code CallSite} object

     * must be provided with

     * a target method via a call to {@link CallSite#setTarget(MethodHandle) setTarget},

     * or by a subclass override of {@link CallSite#initialTarget(Class,String,MethodType) initialTarget}.

     */

    public CallSite() {

    }

    /**

     * Make a blank call site object, possibly equipped with an initial target method handle.

     * The initial target reference may be null, in which case the {@code CallSite} object

     * must be provided with a target method via a call to {@link CallSite#setTarget},

     * or by a subclass override of {@link CallSite#initialTarget}.

     * @param target the method handle which will be the initial target of the call site, or null if there is none yet

     */

    public CallSite(MethodHandle target) {

        this.target = target;

    }

    /** @deprecated transitional form defined in EDR but removed in PFD */

    public CallSite(Class<?> caller, String name, MethodType type) {

        this.calleeNameRemoveForPFD = new MemberName(caller, name, type);

    }

    /** @deprecated transitional form defined in EDR but removed in PFD */

    public Class<?> callerClass() {

        MemberName callee = this.calleeNameRemoveForPFD;

        return callee == null ? null : callee.getDeclaringClass();

    }

    /** @deprecated transitional form defined in EDR but removed in PFD */

    public String name() {

        MemberName callee = this.calleeNameRemoveForPFD;

        return callee == null ? null : callee.getName();

    }

    /** @deprecated transitional form defined in EDR but removed in PFD */

    public MethodType type() {

        MemberName callee = this.calleeNameRemoveForPFD;

        return callee == null ? (target == null ? null : target.type()) : callee.getMethodType();

    }

    /** @deprecated transitional form defined in EDR but removed in PFD */

    protected MethodHandle initialTarget() {

        return initialTarget(callerClass(), name(), type());

    }

    /** Report if the JVM has linked this {@code CallSite} object to a dynamic call site instruction.

     *  Once it is linked, it is never unlinked.

     */

    private boolean isLinked() {

        return vmmethod != null;

    }

    /** Called from JVM (or low-level Java code) after the BSM returns the newly created CallSite.

     *  The parameters are JVM-specific.

     */

    void initializeFromJVM(String name,

                           MethodType type,

                           MemberName callerMethod,

                           int        callerBCI) {

        if (this.isLinked()) {

            throw new InvokeDynamicBootstrapError("call site has already been linked to an invokedynamic instruction");

        }

        MethodHandle target = this.target;

        if (target == null) {

            this.target = target = this.initialTarget(callerMethod.getDeclaringClass(), name, type);

        }

        if (!target.type().equals(type)) {

            throw wrongTargetType(target, type);

        }

        this.vmindex  = callerBCI;

        this.vmmethod = callerMethod;

        assert(this.isLinked());

    }

    /**

     * 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>

     * The arguments are the same as those passed to the bootstrap method.

     * Thus, a bootstrap method is free to ignore the arguments and simply

     * create a "blank" {@code CallSite} object of an appropriate subclass.

     * <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(Class<?> callerClass, String name, MethodType type) {

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

    }

    /**

     * 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 target;

    }

    /**

     * Set the target method of this call site.

     * <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 newTarget the new target

     * @throws NullPointerException if the proposed new target is null

     * @throws WrongMethodTypeException if the call site is linked and the proposed new target

     *         has a method type that differs from the previous target

     */

    public void setTarget(MethodHandle newTarget) {

        MethodType newType = newTarget.type();  // null check!

        MethodHandle oldTarget = this.target;

        if (oldTarget == null) {

            // CallSite is not yet linked.

            assert(!isLinked());

            this.target = newTarget;  // might be null!

            return;

        }

        MethodType oldType = oldTarget.type();

        if (!newTarget.type().equals(oldType))

            throw wrongTargetType(newTarget, oldType);

        if (oldTarget != newTarget)

            CallSiteImpl.setCallSiteTarget(IMPL_TOKEN, this, newTarget);

    }

    private static WrongMethodTypeException wrongTargetType(MethodHandle target, MethodType type) {

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

    }

    /** Produce a printed representation that displays information about this call site

     *  that may be useful to the human reader.

     */

    @Override

    public String toString() {

        StringBuilder buf = new StringBuilder("CallSite#");

        buf.append(hashCode());

        if (!isLinked())

            buf.append("[unlinked]");

        else

            buf.append("[")

                .append("from ").append(vmmethod.getDeclaringClass().getName())

                .append(" : ").append(getTarget().type())

                .append(" => ").append(getTarget())

                .append("]");

        return buf.toString();

    }

}