GuardedInvocation.java

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 * This file is available under and governed by the GNU General Public
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/*
   Copyright 2009-2013 Attila Szegedi

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   modification, are permitted provided that the following conditions are
   met:
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     notice, this list of conditions and the following disclaimer.
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     notice, this list of conditions and the following disclaimer in the
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   * Neither the name of the copyright holder nor the names of
     contributors may be used to endorse or promote products derived from
     this software without specific prior written permission.

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*/

package jdk.dynalink.linker;

import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodHandles;
import java.lang.invoke.MethodType;
import java.lang.invoke.SwitchPoint;
import java.util.List;
import java.util.Objects;
import java.util.function.Supplier;
import jdk.dynalink.CallSiteDescriptor;
import jdk.dynalink.linker.support.Guards;

/**
 * Represents a conditionally valid method handle. Usually produced as a return
 * value of
 * {@link GuardingDynamicLinker#getGuardedInvocation(LinkRequest, LinkerServices)}
 * and
 * {@link GuardingTypeConverterFactory#convertToType(Class, Class, Supplier)}.
 * It is an immutable tuple of an invocation method handle, a guard method
 * handle that defines the applicability of the invocation handle, zero or more
 * switch points that can be used for external invalidation of the invocation
 * handle, and an exception type that if thrown during an invocation of the
 * method handle also invalidates it. The invocation handle is suitable for
 * invocation if the guard handle returns true for its arguments, and as long
 * as any of the switch points are not invalidated, and as long as it does not
 * throw an exception of the designated type. The guard, the switch points, and
 * the exception type are all optional (a guarded invocation having none of them
 * is unconditionally valid).
 */
public class GuardedInvocation {
    private final MethodHandle invocation;
    private final MethodHandle guard;
    private final Class<? extends Throwable> exception;
    private final SwitchPoint[] switchPoints;

    /**
     * Creates a new unconditional guarded invocation. It is unconditional as it
     * has no invalidations.
     *
     * @param invocation the method handle representing the invocation. Must not
     * be null.
     * @throws NullPointerException if invocation is null.
     */
    public GuardedInvocation(final MethodHandle invocation) {
        this(invocation, null, (SwitchPoint)null, null);
    }

    /**
     * Creates a new guarded invocation, with a guard method handle.
     *
     * @param invocation the method handle representing the invocation. Must not
     * be null.
     * @param guard the method handle representing the guard. Must have be
     * compatible with the {@code invocation} handle as per
     * {@link MethodHandles#guardWithTest(MethodHandle, MethodHandle, MethodHandle)}.
     * For some useful guards, check out the {@link Guards} class. It can be
     * null to represent an unconditional invocation.
     * @throws NullPointerException if invocation is null.
     */
    public GuardedInvocation(final MethodHandle invocation, final MethodHandle guard) {
        this(invocation, guard, (SwitchPoint)null, null);
    }

    /**
     * Creates a new guarded invocation that can be invalidated by a switch
     * point.
     *
     * @param invocation the method handle representing the invocation. Must
     * not be null.
     * @param switchPoint the optional switch point that can be used to
     * invalidate this linkage. It can be null. If it is null, this represents
     * an unconditional invocation.
     * @throws NullPointerException if invocation is null.
     */
    public GuardedInvocation(final MethodHandle invocation, final SwitchPoint switchPoint) {
        this(invocation, null, switchPoint, null);
    }

    /**
     * Creates a new guarded invocation, with both a guard method handle and a
     * switch point that can be used to invalidate it.
     *
     * @param invocation the method handle representing the invocation. Must
     * not be null.
     * @param guard the method handle representing the guard. Must have be
     * compatible with the {@code invocation} handle as per
     * {@link MethodHandles#guardWithTest(MethodHandle, MethodHandle, MethodHandle)}.
     * For some useful guards, check out the {@link Guards} class. It can be
     * null. If both it and the switch point are null, this represents an
     * unconditional invocation.
     * @param switchPoint the optional switch point that can be used to
     * invalidate this linkage.
     * @throws NullPointerException if invocation is null.
     */
    public GuardedInvocation(final MethodHandle invocation, final MethodHandle guard, final SwitchPoint switchPoint) {
        this(invocation, guard, switchPoint, null);
    }

    /**
     * Creates a new guarded invocation, with a guard method handle, a
     * switch point that can be used to invalidate it, and an exception that if
     * thrown when invoked also invalidates it.
     *
     * @param invocation the method handle representing the invocation. Must not
     * be null.
     * @param guard the method handle representing the guard. Must have be
     * compatible with the {@code invocation} handle as per
     * {@link MethodHandles#guardWithTest(MethodHandle, MethodHandle, MethodHandle)}.
     * For some useful guards, check out the {@link Guards} class. It can be
     * null. If it and the switch point and the exception are all null, this
     * represents an unconditional invocation.
     * @param switchPoint the optional switch point that can be used to
     * invalidate this linkage.
     * @param exception the optional exception type that is when thrown by the
     * invocation also invalidates it.
     * @throws NullPointerException if invocation is null.
     */
    public GuardedInvocation(final MethodHandle invocation, final MethodHandle guard, final SwitchPoint switchPoint, final Class<? extends Throwable> exception) {
        this.invocation = Objects.requireNonNull(invocation);
        this.guard = guard;
        this.switchPoints = switchPoint == null ? null : new SwitchPoint[] { switchPoint };
        if (exception != null && !Throwable.class.isAssignableFrom(exception)) {
            throw new IllegalArgumentException(exception.getName() + " is not assignable from Throwable");
        }
        this.exception = exception;
    }

    /**
     * Creates a new guarded invocation, with a guard method handle, any number
     * of switch points that can be used to invalidate it, and an exception that
     * if thrown when invoked also invalidates it.
     *
     * @param invocation the method handle representing the invocation. Must not
     * be null.
     * @param guard the method handle representing the guard. Must have be
     * compatible with the {@code invocation} handle as per
     * {@link MethodHandles#guardWithTest(MethodHandle, MethodHandle, MethodHandle)}.
     * For some useful guards, check out the {@link Guards} class. It can be
     * null. If it and the exception are both null, and no switch points were
     * specified, this represents an unconditional invocation.
     * @param switchPoints optional switch points that can be used to
     * invalidate this linkage.
     * @param exception the optional exception type that is when thrown by the
     * invocation also invalidates it.
     * @throws NullPointerException if invocation is null.
     */
    public GuardedInvocation(final MethodHandle invocation, final MethodHandle guard, final SwitchPoint[] switchPoints, final Class<? extends Throwable> exception) {
        this.invocation = Objects.requireNonNull(invocation);
        this.guard = guard;
        this.switchPoints = switchPoints == null ? null : switchPoints.clone();
        if (exception != null && !Throwable.class.isAssignableFrom(exception)) {
            throw new IllegalArgumentException(exception.getName() + " is not assignable from Throwable");
        }
        this.exception = exception;
    }

    /**
     * Returns the invocation method handle.
     *
     * @return the invocation method handle. It will never be null.
     */
    public MethodHandle getInvocation() {
        return invocation;
    }

    /**
     * Returns the guard method handle.
     *
     * @return the guard method handle. Can be null.
     */
    public MethodHandle getGuard() {
        return guard;
    }

    /**
     * Returns the switch points that can be used to invalidate the linkage of
     * this invocation handle.
     *
     * @return the switch points that can be used to invalidate the linkage of
     * this invocation handle. Can be null.
     */
    public SwitchPoint[] getSwitchPoints() {
        return switchPoints == null ? null : switchPoints.clone();
    }

    /**
     * Returns the exception type that if thrown by the invocation should
     * invalidate the linkage of this guarded invocation.
     *
     * @return the exception type that if thrown should be used to invalidate
     * the linkage. Can be null.
     */
    public Class<? extends Throwable> getException() {
        return exception;
    }

    /**
     * Returns true if and only if this guarded invocation has at least one
     * invalidated switch point.
     * @return true if and only if this guarded invocation has at least one
     * invalidated switch point.
     */
    public boolean hasBeenInvalidated() {
        if (switchPoints == null) {
            return false;
        }
        for (final SwitchPoint sp : switchPoints) {
            if (sp.hasBeenInvalidated()) {
                return true;
            }
        }
        return false;
    }

    /**
     * Creates a new guarded invocation with different methods, preserving the switch point.
     *
     * @param newInvocation the new invocation
     * @param newGuard the new guard
     * @return a new guarded invocation with the replaced methods and the same switch point as this invocation.
     */
    public GuardedInvocation replaceMethods(final MethodHandle newInvocation, final MethodHandle newGuard) {
        return new GuardedInvocation(newInvocation, newGuard, switchPoints, exception);
    }

    /**
     * Create a new guarded invocation with an added switch point.
     * @param newSwitchPoint new switch point. Can be null in which case this
     * method return the current guarded invocation with no changes.
     * @return a guarded invocation with the added switch point.
     */
    public GuardedInvocation addSwitchPoint(final SwitchPoint newSwitchPoint) {
        if (newSwitchPoint == null) {
            return this;
        }

        final SwitchPoint[] newSwitchPoints;
        if (switchPoints != null) {
            newSwitchPoints = new SwitchPoint[switchPoints.length + 1];
            System.arraycopy(switchPoints, 0, newSwitchPoints, 0, switchPoints.length);
            newSwitchPoints[switchPoints.length] = newSwitchPoint;
        } else {
            newSwitchPoints = new SwitchPoint[] { newSwitchPoint };
        }

        return new GuardedInvocation(invocation, guard, newSwitchPoints, exception);
    }

    private GuardedInvocation replaceMethodsOrThis(final MethodHandle newInvocation, final MethodHandle newGuard) {
        if (newInvocation == invocation && newGuard == guard) {
            return this;
        }
        return replaceMethods(newInvocation, newGuard);
    }

    /**
     * Changes the type of the invocation, as if
     * {@link MethodHandle#asType(MethodType)} was applied to its invocation
     * and its guard, if it has one (with return type changed to boolean, and
     * parameter count potentially truncated for the guard). If the invocation
     * already is of the required type, returns this object.
     * @param newType the new type of the invocation.
     * @return a guarded invocation with the new type applied to it.
     */
    public GuardedInvocation asType(final MethodType newType) {
        return replaceMethodsOrThis(invocation.asType(newType), guard == null ? null : Guards.asType(guard, newType));
    }

    /**
     * Changes the type of the invocation, as if
     * {@link LinkerServices#asType(MethodHandle, MethodType)} was applied to
     * its invocation and its guard, if it has one (with return type changed to
     * boolean, and parameter count potentially truncated for the guard). If the
     * invocation already is of the required type, returns this object.
     * @param linkerServices the linker services to use for the conversion
     * @param newType the new type of the invocation.
     * @return a guarded invocation with the new type applied to it.
     */
    public GuardedInvocation asType(final LinkerServices linkerServices, final MethodType newType) {
        return replaceMethodsOrThis(linkerServices.asType(invocation, newType), guard == null ? null :
            Guards.asType(linkerServices, guard, newType));
    }

    /**
     * Changes the type of the invocation, as if
     * {@link LinkerServices#asTypeLosslessReturn(MethodHandle, MethodType)} was
     * applied to its invocation and
     * {@link LinkerServices#asType(MethodHandle, MethodType)} applied to its
     * guard, if it has one (with return type changed to boolean, and parameter
     * count potentially truncated for the guard). If the invocation doesn't
     * change its type, returns this object.
     * @param linkerServices the linker services to use for the conversion
     * @param newType the new type of the invocation.
     * @return a guarded invocation with the new type applied to it.
     */
    public GuardedInvocation asTypeSafeReturn(final LinkerServices linkerServices, final MethodType newType) {
        return replaceMethodsOrThis(linkerServices.asTypeLosslessReturn(invocation, newType), guard == null ? null :
            Guards.asType(linkerServices, guard, newType));
    }

    /**
     * Changes the type of the invocation, as if
     * {@link MethodHandle#asType(MethodType)} was applied to its invocation
     * and its guard, if it has one (with return type changed to boolean for
     * guard). If the invocation already is of the required type, returns this
     * object.
     * @param desc a call descriptor whose method type is adapted.
     * @return a guarded invocation with the new type applied to it.
     */
    public GuardedInvocation asType(final CallSiteDescriptor desc) {
        return asType(desc.getMethodType());
    }

    /**
     * Applies argument filters to both the invocation and the guard
     * (if it exists and has at least {@code pos + 1} parameters) with
     * {@link MethodHandles#filterArguments(MethodHandle, int, MethodHandle...)}.
     * @param pos the position of the first argument being filtered
     * @param filters the argument filters
     * @return a filtered invocation
     */
    public GuardedInvocation filterArguments(final int pos, final MethodHandle... filters) {
        return replaceMethods(MethodHandles.filterArguments(invocation, pos, filters),
                guard == null || pos >= guard.type().parameterCount() ?
                        guard : MethodHandles.filterArguments(guard, pos, filters));
    }

    /**
     * Makes an invocation that drops arguments in both the invocation and the
     * guard (if it exists and has at least {@code pos} parameters) with
     * {@link MethodHandles#dropArguments(MethodHandle, int, List)}.
     * @param pos the position of the first argument being dropped
     * @param valueTypes the types of the values being dropped
     * @return an invocation that drops arguments
     */
    public GuardedInvocation dropArguments(final int pos, final List<Class<?>> valueTypes) {
        return replaceMethods(MethodHandles.dropArguments(invocation, pos, valueTypes),
                guard == null || pos > guard.type().parameterCount() ?
                    guard : MethodHandles.dropArguments(guard, pos, valueTypes));
    }

    /**
     * Makes an invocation that drops arguments in both the invocation and the
     * guard (if it exists and has at least {@code pos} parameters) with
     * {@link MethodHandles#dropArguments(MethodHandle, int, Class...)}.
     * @param pos the position of the first argument being dropped
     * @param valueTypes the types of the values being dropped
     * @return an invocation that drops arguments
     */
    public GuardedInvocation dropArguments(final int pos, final Class<?>... valueTypes) {
        return replaceMethods(MethodHandles.dropArguments(invocation, pos, valueTypes),
                guard == null || pos > guard.type().parameterCount() ?
                        guard : MethodHandles.dropArguments(guard, pos, valueTypes));
    }


    /**
     * Composes the invocation, guard, switch points, and the exception into a
     * composite method handle that knows how to fall back when the guard fails
     * or the invocation is invalidated.
     * @param fallback the fallback method handle for when a switch point is
     * invalidated, a guard returns false, or invalidating exception is thrown.
     * @return a composite method handle.
     */
    public MethodHandle compose(final MethodHandle fallback) {
        return compose(fallback, fallback, fallback);
    }

    /**
     * Composes the invocation, guard, switch points, and the exception into a
     * composite method handle that knows how to fall back when the guard fails
     * or the invocation is invalidated.
     * @param switchpointFallback the fallback method handle in case a switch
     * point is invalidated.
     * @param guardFallback the fallback method handle in case guard returns
     * false.
     * @param catchFallback the fallback method in case the exception handler
     * triggers.
     * @return a composite method handle.
     */
    public MethodHandle compose(final MethodHandle guardFallback, final MethodHandle switchpointFallback, final MethodHandle catchFallback) {
        final MethodHandle guarded =
                guard == null ?
                        invocation :
                        MethodHandles.guardWithTest(
                                guard,
                                invocation,
                                guardFallback);

        final MethodHandle catchGuarded =
                exception == null ?
                        guarded :
                        MethodHandles.catchException(
                                guarded,
                                exception,
                                MethodHandles.dropArguments(
                                    catchFallback,
                                    0,
                                    exception));

        if (switchPoints == null) {
            return catchGuarded;
        }

        MethodHandle spGuarded = catchGuarded;
        for (final SwitchPoint sp : switchPoints) {
            spGuarded = sp.guardWithTest(spGuarded, switchpointFallback);
        }

        return spGuarded;
    }
}