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477 lines
25 KiB
477 lines
25 KiB
/*
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* Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved.
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* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*/
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package java.lang.invoke;
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import java.io.Serializable;
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import java.util.Arrays;
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/**
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* <p>Methods to facilitate the creation of simple "function objects" that
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* implement one or more interfaces by delegation to a provided {@link MethodHandle},
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* possibly after type adaptation and partial evaluation of arguments. These
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* methods are typically used as <em>bootstrap methods</em> for {@code invokedynamic}
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* call sites, to support the <em>lambda expression</em> and <em>method
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* reference expression</em> features of the Java Programming Language.
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*
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* <p>Indirect access to the behavior specified by the provided {@code MethodHandle}
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* proceeds in order through three phases:
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* <ul>
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* <li><em>Linkage</em> occurs when the methods in this class are invoked.
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* They take as arguments an interface to be implemented (typically a
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* <em>functional interface</em>, one with a single abstract method), a
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* name and signature of a method from that interface to be implemented, a
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* method handle describing the desired implementation behavior
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* for that method, and possibly other additional metadata, and produce a
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* {@link CallSite} whose target can be used to create suitable function
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* objects. Linkage may involve dynamically loading a new class that
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* implements the target interface. The {@code CallSite} can be considered a
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* "factory" for function objects and so these linkage methods are referred
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* to as "metafactories".</li>
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*
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* <li><em>Capture</em> occurs when the {@code CallSite}'s target is
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* invoked, typically through an {@code invokedynamic} call site,
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* producing a function object. This may occur many times for
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* a single factory {@code CallSite}. Capture may involve allocation of a
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* new function object, or may return an existing function object. The
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* behavior {@code MethodHandle} may have additional parameters beyond those
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* of the specified interface method; these are referred to as <em>captured
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* parameters</em>, which must be provided as arguments to the
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* {@code CallSite} target, and which may be early-bound to the behavior
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* {@code MethodHandle}. The number of captured parameters and their types
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* are determined during linkage.</li>
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*
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* <li><em>Invocation</em> occurs when an implemented interface method
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* is invoked on a function object. This may occur many times for a single
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* function object. The method referenced by the behavior {@code MethodHandle}
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* is invoked with the captured arguments and any additional arguments
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* provided on invocation, as if by {@link MethodHandle#invoke(Object...)}.</li>
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* </ul>
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*
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* <p>It is sometimes useful to restrict the set of inputs or results permitted
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* at invocation. For example, when the generic interface {@code Predicate<T>}
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* is parameterized as {@code Predicate<String>}, the input must be a
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* {@code String}, even though the method to implement allows any {@code Object}.
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* At linkage time, an additional {@link MethodType} parameter describes the
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* "instantiated" method type; on invocation, the arguments and eventual result
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* are checked against this {@code MethodType}.
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*
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* <p>This class provides two forms of linkage methods: a standard version
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* ({@link #metafactory(MethodHandles.Lookup, String, MethodType, MethodType, MethodHandle, MethodType)})
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* using an optimized protocol, and an alternate version
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* {@link #altMetafactory(MethodHandles.Lookup, String, MethodType, Object...)}).
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* The alternate version is a generalization of the standard version, providing
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* additional control over the behavior of the generated function objects via
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* flags and additional arguments. The alternate version adds the ability to
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* manage the following attributes of function objects:
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*
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* <ul>
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* <li><em>Bridging.</em> It is sometimes useful to implement multiple
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* variations of the method signature, involving argument or return type
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* adaptation. This occurs when multiple distinct VM signatures for a method
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* are logically considered to be the same method by the language. The
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* flag {@code FLAG_BRIDGES} indicates that a list of additional
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* {@code MethodType}s will be provided, each of which will be implemented
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* by the resulting function object. These methods will share the same
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* name and instantiated type.</li>
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*
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* <li><em>Multiple interfaces.</em> If needed, more than one interface
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* can be implemented by the function object. (These additional interfaces
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* are typically marker interfaces with no methods.) The flag {@code FLAG_MARKERS}
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* indicates that a list of additional interfaces will be provided, each of
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* which should be implemented by the resulting function object.</li>
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*
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* <li><em>Serializability.</em> The generated function objects do not
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* generally support serialization. If desired, {@code FLAG_SERIALIZABLE}
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* can be used to indicate that the function objects should be serializable.
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* Serializable function objects will use, as their serialized form,
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* instances of the class {@code SerializedLambda}, which requires additional
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* assistance from the capturing class (the class described by the
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* {@link MethodHandles.Lookup} parameter {@code caller}); see
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* {@link SerializedLambda} for details.</li>
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* </ul>
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*
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* <p>Assume the linkage arguments are as follows:
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* <ul>
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* <li>{@code invokedType} (describing the {@code CallSite} signature) has
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* K parameters of types (D1..Dk) and return type Rd;</li>
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* <li>{@code samMethodType} (describing the implemented method type) has N
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* parameters, of types (U1..Un) and return type Ru;</li>
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* <li>{@code implMethod} (the {@code MethodHandle} providing the
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* implementation has M parameters, of types (A1..Am) and return type Ra
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* (if the method describes an instance method, the method type of this
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* method handle already includes an extra first argument corresponding to
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* the receiver);</li>
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* <li>{@code instantiatedMethodType} (allowing restrictions on invocation)
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* has N parameters, of types (T1..Tn) and return type Rt.</li>
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* </ul>
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*
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* <p>Then the following linkage invariants must hold:
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* <ul>
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* <li>Rd is an interface</li>
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* <li>{@code implMethod} is a <em>direct method handle</em></li>
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* <li>{@code samMethodType} and {@code instantiatedMethodType} have the same
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* arity N, and for i=1..N, Ti and Ui are the same type, or Ti and Ui are
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* both reference types and Ti is a subtype of Ui</li>
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* <li>Either Rt and Ru are the same type, or both are reference types and
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* Rt is a subtype of Ru</li>
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* <li>K + N = M</li>
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* <li>For i=1..K, Di = Ai</li>
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* <li>For i=1..N, Ti is adaptable to Aj, where j=i+k</li>
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* <li>The return type Rt is void, or the return type Ra is not void and is
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* adaptable to Rt</li>
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* </ul>
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*
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* <p>Further, at capture time, if {@code implMethod} corresponds to an instance
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* method, and there are any capture arguments ({@code K > 0}), then the first
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* capture argument (corresponding to the receiver) must be non-null.
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*
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* <p>A type Q is considered adaptable to S as follows:
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* <table summary="adaptable types">
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* <tr><th>Q</th><th>S</th><th>Link-time checks</th><th>Invocation-time checks</th></tr>
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* <tr>
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* <td>Primitive</td><td>Primitive</td>
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* <td>Q can be converted to S via a primitive widening conversion</td>
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* <td>None</td>
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* </tr>
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* <tr>
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* <td>Primitive</td><td>Reference</td>
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* <td>S is a supertype of the Wrapper(Q)</td>
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* <td>Cast from Wrapper(Q) to S</td>
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* </tr>
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* <tr>
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* <td>Reference</td><td>Primitive</td>
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* <td>for parameter types: Q is a primitive wrapper and Primitive(Q)
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* can be widened to S
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* <br>for return types: If Q is a primitive wrapper, check that
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* Primitive(Q) can be widened to S</td>
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* <td>If Q is not a primitive wrapper, cast Q to the base Wrapper(S);
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* for example Number for numeric types</td>
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* </tr>
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* <tr>
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* <td>Reference</td><td>Reference</td>
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* <td>for parameter types: S is a supertype of Q
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* <br>for return types: none</td>
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* <td>Cast from Q to S</td>
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* </tr>
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* </table>
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*
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* @apiNote These linkage methods are designed to support the evaluation
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* of <em>lambda expressions</em> and <em>method references</em> in the Java
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* Language. For every lambda expressions or method reference in the source code,
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* there is a target type which is a functional interface. Evaluating a lambda
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* expression produces an object of its target type. The recommended mechanism
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* for evaluating lambda expressions is to desugar the lambda body to a method,
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* invoke an invokedynamic call site whose static argument list describes the
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* sole method of the functional interface and the desugared implementation
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* method, and returns an object (the lambda object) that implements the target
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* type. (For method references, the implementation method is simply the
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* referenced method; no desugaring is needed.)
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*
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* <p>The argument list of the implementation method and the argument list of
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* the interface method(s) may differ in several ways. The implementation
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* methods may have additional arguments to accommodate arguments captured by
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* the lambda expression; there may also be differences resulting from permitted
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* adaptations of arguments, such as casting, boxing, unboxing, and primitive
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* widening. (Varargs adaptations are not handled by the metafactories; these are
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* expected to be handled by the caller.)
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*
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* <p>Invokedynamic call sites have two argument lists: a static argument list
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* and a dynamic argument list. The static argument list is stored in the
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* constant pool; the dynamic argument is pushed on the operand stack at capture
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* time. The bootstrap method has access to the entire static argument list
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* (which in this case, includes information describing the implementation method,
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* the target interface, and the target interface method(s)), as well as a
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* method signature describing the number and static types (but not the values)
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* of the dynamic arguments and the static return type of the invokedynamic site.
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*
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* @implNote The implementation method is described with a method handle. In
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* theory, any method handle could be used. Currently supported are direct method
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* handles representing invocation of virtual, interface, constructor and static
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* methods.
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*/
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public class LambdaMetafactory {
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/** Flag for alternate metafactories indicating the lambda object
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* must be serializable */
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public static final int FLAG_SERIALIZABLE = 1 << 0;
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/**
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* Flag for alternate metafactories indicating the lambda object implements
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* other marker interfaces
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* besides Serializable
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*/
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public static final int FLAG_MARKERS = 1 << 1;
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/**
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* Flag for alternate metafactories indicating the lambda object requires
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* additional bridge methods
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*/
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public static final int FLAG_BRIDGES = 1 << 2;
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private static final Class<?>[] EMPTY_CLASS_ARRAY = new Class<?>[0];
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private static final MethodType[] EMPTY_MT_ARRAY = new MethodType[0];
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/**
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* Facilitates the creation of simple "function objects" that implement one
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* or more interfaces by delegation to a provided {@link MethodHandle},
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* after appropriate type adaptation and partial evaluation of arguments.
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* Typically used as a <em>bootstrap method</em> for {@code invokedynamic}
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* call sites, to support the <em>lambda expression</em> and <em>method
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* reference expression</em> features of the Java Programming Language.
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*
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* <p>This is the standard, streamlined metafactory; additional flexibility
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* is provided by {@link #altMetafactory(MethodHandles.Lookup, String, MethodType, Object...)}.
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* A general description of the behavior of this method is provided
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* {@link LambdaMetafactory above}.
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*
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* <p>When the target of the {@code CallSite} returned from this method is
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* invoked, the resulting function objects are instances of a class which
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* implements the interface named by the return type of {@code invokedType},
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* declares a method with the name given by {@code invokedName} and the
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* signature given by {@code samMethodType}. It may also override additional
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* methods from {@code Object}.
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*
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* @param caller Represents a lookup context with the accessibility
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* privileges of the caller. When used with {@code invokedynamic},
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* this is stacked automatically by the VM.
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* @param invokedName The name of the method to implement. When used with
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* {@code invokedynamic}, this is provided by the
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* {@code NameAndType} of the {@code InvokeDynamic}
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* structure and is stacked automatically by the VM.
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* @param invokedType The expected signature of the {@code CallSite}. The
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* parameter types represent the types of capture variables;
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* the return type is the interface to implement. When
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* used with {@code invokedynamic}, this is provided by
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* the {@code NameAndType} of the {@code InvokeDynamic}
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* structure and is stacked automatically by the VM.
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* In the event that the implementation method is an
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* instance method and this signature has any parameters,
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* the first parameter in the invocation signature must
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* correspond to the receiver.
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* @param samMethodType Signature and return type of method to be implemented
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* by the function object.
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* @param implMethod A direct method handle describing the implementation
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* method which should be called (with suitable adaptation
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* of argument types, return types, and with captured
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* arguments prepended to the invocation arguments) at
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* invocation time.
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* @param instantiatedMethodType The signature and return type that should
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* be enforced dynamically at invocation time.
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* This may be the same as {@code samMethodType},
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* or may be a specialization of it.
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* @return a CallSite whose target can be used to perform capture, generating
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* instances of the interface named by {@code invokedType}
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* @throws LambdaConversionException If any of the linkage invariants
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* described {@link LambdaMetafactory above}
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* are violated
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*/
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public static CallSite metafactory(MethodHandles.Lookup caller,
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String invokedName,
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MethodType invokedType,
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MethodType samMethodType,
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MethodHandle implMethod,
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MethodType instantiatedMethodType)
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throws LambdaConversionException {
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AbstractValidatingLambdaMetafactory mf;
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mf = new InnerClassLambdaMetafactory(caller, invokedType,
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invokedName, samMethodType,
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implMethod, instantiatedMethodType,
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false, EMPTY_CLASS_ARRAY, EMPTY_MT_ARRAY);
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mf.validateMetafactoryArgs();
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return mf.buildCallSite();
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}
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/**
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* Facilitates the creation of simple "function objects" that implement one
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* or more interfaces by delegation to a provided {@link MethodHandle},
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* after appropriate type adaptation and partial evaluation of arguments.
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* Typically used as a <em>bootstrap method</em> for {@code invokedynamic}
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* call sites, to support the <em>lambda expression</em> and <em>method
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* reference expression</em> features of the Java Programming Language.
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*
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* <p>This is the general, more flexible metafactory; a streamlined version
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* is provided by {@link #metafactory(java.lang.invoke.MethodHandles.Lookup,
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* String, MethodType, MethodType, MethodHandle, MethodType)}.
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* A general description of the behavior of this method is provided
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* {@link LambdaMetafactory above}.
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*
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* <p>The argument list for this method includes three fixed parameters,
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* corresponding to the parameters automatically stacked by the VM for the
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* bootstrap method in an {@code invokedynamic} invocation, and an {@code Object[]}
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* parameter that contains additional parameters. The declared argument
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* list for this method is:
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*
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* <pre>{@code
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* CallSite altMetafactory(MethodHandles.Lookup caller,
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* String invokedName,
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* MethodType invokedType,
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* Object... args)
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* }</pre>
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*
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* <p>but it behaves as if the argument list is as follows:
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*
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* <pre>{@code
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* CallSite altMetafactory(MethodHandles.Lookup caller,
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* String invokedName,
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* MethodType invokedType,
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* MethodType samMethodType,
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* MethodHandle implMethod,
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* MethodType instantiatedMethodType,
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* int flags,
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* int markerInterfaceCount, // IF flags has MARKERS set
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* Class... markerInterfaces, // IF flags has MARKERS set
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* int bridgeCount, // IF flags has BRIDGES set
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* MethodType... bridges // IF flags has BRIDGES set
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* )
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* }</pre>
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*
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* <p>Arguments that appear in the argument list for
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* {@link #metafactory(MethodHandles.Lookup, String, MethodType, MethodType, MethodHandle, MethodType)}
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* have the same specification as in that method. The additional arguments
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* are interpreted as follows:
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* <ul>
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* <li>{@code flags} indicates additional options; this is a bitwise
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* OR of desired flags. Defined flags are {@link #FLAG_BRIDGES},
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* {@link #FLAG_MARKERS}, and {@link #FLAG_SERIALIZABLE}.</li>
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* <li>{@code markerInterfaceCount} is the number of additional interfaces
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* the function object should implement, and is present if and only if the
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* {@code FLAG_MARKERS} flag is set.</li>
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* <li>{@code markerInterfaces} is a variable-length list of additional
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* interfaces to implement, whose length equals {@code markerInterfaceCount},
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* and is present if and only if the {@code FLAG_MARKERS} flag is set.</li>
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* <li>{@code bridgeCount} is the number of additional method signatures
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* the function object should implement, and is present if and only if
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* the {@code FLAG_BRIDGES} flag is set.</li>
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* <li>{@code bridges} is a variable-length list of additional
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* methods signatures to implement, whose length equals {@code bridgeCount},
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* and is present if and only if the {@code FLAG_BRIDGES} flag is set.</li>
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* </ul>
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*
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* <p>Each class named by {@code markerInterfaces} is subject to the same
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* restrictions as {@code Rd}, the return type of {@code invokedType},
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* as described {@link LambdaMetafactory above}. Each {@code MethodType}
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* named by {@code bridges} is subject to the same restrictions as
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* {@code samMethodType}, as described {@link LambdaMetafactory above}.
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*
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* <p>When FLAG_SERIALIZABLE is set in {@code flags}, the function objects
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* will implement {@code Serializable}, and will have a {@code writeReplace}
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* method that returns an appropriate {@link SerializedLambda}. The
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* {@code caller} class must have an appropriate {@code $deserializeLambda$}
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* method, as described in {@link SerializedLambda}.
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*
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* <p>When the target of the {@code CallSite} returned from this method is
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* invoked, the resulting function objects are instances of a class with
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* the following properties:
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* <ul>
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* <li>The class implements the interface named by the return type
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* of {@code invokedType} and any interfaces named by {@code markerInterfaces}</li>
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* <li>The class declares methods with the name given by {@code invokedName},
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* and the signature given by {@code samMethodType} and additional signatures
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* given by {@code bridges}</li>
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* <li>The class may override methods from {@code Object}, and may
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* implement methods related to serialization.</li>
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* </ul>
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*
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* @param caller Represents a lookup context with the accessibility
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* privileges of the caller. When used with {@code invokedynamic},
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* this is stacked automatically by the VM.
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* @param invokedName The name of the method to implement. When used with
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* {@code invokedynamic}, this is provided by the
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* {@code NameAndType} of the {@code InvokeDynamic}
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* structure and is stacked automatically by the VM.
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* @param invokedType The expected signature of the {@code CallSite}. The
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* parameter types represent the types of capture variables;
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* the return type is the interface to implement. When
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* used with {@code invokedynamic}, this is provided by
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* the {@code NameAndType} of the {@code InvokeDynamic}
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* structure and is stacked automatically by the VM.
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* In the event that the implementation method is an
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* instance method and this signature has any parameters,
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* the first parameter in the invocation signature must
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* correspond to the receiver.
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* @param args An {@code Object[]} array containing the required
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* arguments {@code samMethodType}, {@code implMethod},
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* {@code instantiatedMethodType}, {@code flags}, and any
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* optional arguments, as described
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* {@link #altMetafactory(MethodHandles.Lookup, String, MethodType, Object...)} above}
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* @return a CallSite whose target can be used to perform capture, generating
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* instances of the interface named by {@code invokedType}
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* @throws LambdaConversionException If any of the linkage invariants
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* described {@link LambdaMetafactory above}
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* are violated
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*/
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public static CallSite altMetafactory(MethodHandles.Lookup caller,
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String invokedName,
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|
MethodType invokedType,
|
|
Object... args)
|
|
throws LambdaConversionException {
|
|
MethodType samMethodType = (MethodType)args[0];
|
|
MethodHandle implMethod = (MethodHandle)args[1];
|
|
MethodType instantiatedMethodType = (MethodType)args[2];
|
|
int flags = (Integer) args[3];
|
|
Class<?>[] markerInterfaces;
|
|
MethodType[] bridges;
|
|
int argIndex = 4;
|
|
if ((flags & FLAG_MARKERS) != 0) {
|
|
int markerCount = (Integer) args[argIndex++];
|
|
markerInterfaces = new Class<?>[markerCount];
|
|
System.arraycopy(args, argIndex, markerInterfaces, 0, markerCount);
|
|
argIndex += markerCount;
|
|
}
|
|
else
|
|
markerInterfaces = EMPTY_CLASS_ARRAY;
|
|
if ((flags & FLAG_BRIDGES) != 0) {
|
|
int bridgeCount = (Integer) args[argIndex++];
|
|
bridges = new MethodType[bridgeCount];
|
|
System.arraycopy(args, argIndex, bridges, 0, bridgeCount);
|
|
argIndex += bridgeCount;
|
|
}
|
|
else
|
|
bridges = EMPTY_MT_ARRAY;
|
|
|
|
boolean isSerializable = ((flags & FLAG_SERIALIZABLE) != 0);
|
|
if (isSerializable) {
|
|
boolean foundSerializableSupertype = Serializable.class.isAssignableFrom(invokedType.returnType());
|
|
for (Class<?> c : markerInterfaces)
|
|
foundSerializableSupertype |= Serializable.class.isAssignableFrom(c);
|
|
if (!foundSerializableSupertype) {
|
|
markerInterfaces = Arrays.copyOf(markerInterfaces, markerInterfaces.length + 1);
|
|
markerInterfaces[markerInterfaces.length-1] = Serializable.class;
|
|
}
|
|
}
|
|
|
|
AbstractValidatingLambdaMetafactory mf
|
|
= new InnerClassLambdaMetafactory(caller, invokedType,
|
|
invokedName, samMethodType,
|
|
implMethod,
|
|
instantiatedMethodType,
|
|
isSerializable,
|
|
markerInterfaces, bridges);
|
|
mf.validateMetafactoryArgs();
|
|
return mf.buildCallSite();
|
|
}
|
|
}
|