diff -r 000000000000 -r c880a8a8803b rt/emul/compact/src/main/java/java/lang/invoke/package-info.java --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/rt/emul/compact/src/main/java/java/lang/invoke/package-info.java Sat Aug 09 11:11:13 2014 +0200 @@ -0,0 +1,211 @@ +/* + * Copyright (c) 2008, 2013, Oracle and/or its affiliates. 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. 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. + */ + +/** + * The {@code java.lang.invoke} package contains dynamic language support provided directly by + * the Java core class libraries and virtual machine. + * + *
+ * As described in the Java Virtual Machine Specification, + * certain types in this package have special relations to dynamic + * language support in the virtual machine: + *
+ * Before the JVM can execute a dynamic call site (an {@code invokedynamic} instruction), + * the call site must first be linked. + * Linking is accomplished by calling a bootstrap method + * which is given the static information content of the call site, + * and which must produce a {@link java.lang.invoke.MethodHandle method handle} + * that gives the behavior of the call site. + *
+ * Each {@code invokedynamic} instruction statically specifies its own + * bootstrap method as a constant pool reference. + * The constant pool reference also specifies the call site's name and type descriptor, + * just like {@code invokevirtual} and the other invoke instructions. + *
+ * Linking starts with resolving the constant pool entry for the + * bootstrap method, and resolving a {@link java.lang.invoke.MethodType MethodType} object for + * the type descriptor of the dynamic call site. + * This resolution process may trigger class loading. + * It may therefore throw an error if a class fails to load. + * This error becomes the abnormal termination of the dynamic + * call site execution. + * Linkage does not trigger class initialization. + *
+ * The bootstrap method is invoked on at least three values: + *
+ * As documented in the JVM specification, all failures arising from + * the linkage of a dynamic call site are reported + * by a {@link java.lang.BootstrapMethodError BootstrapMethodError}, + * which is thrown as the abnormal termination of the dynamic call + * site execution. + * If this happens, the same error will the thrown for all subsequent + * attempts to execute the dynamic call site. + * + *
+ * If there are several such threads, the bootstrap method may be + * invoked in several threads concurrently. + * Therefore, bootstrap methods which access global application + * data must take the usual precautions against race conditions. + * In any case, every {@code invokedynamic} instruction is either + * unlinked or linked to a unique {@code CallSite} object. + *
+ * In an application which requires dynamic call sites with individually + * mutable behaviors, their bootstrap methods should produce distinct + * {@link java.lang.invoke.CallSite CallSite} objects, one for each linkage request. + * Alternatively, an application can link a single {@code CallSite} object + * to several {@code invokedynamic} instructions, in which case + * a change to the target method will become visible at each of + * the instructions. + *
+ * If several threads simultaneously execute a bootstrap method for a single dynamic + * call site, the JVM must choose one {@code CallSite} object and install it visibly to + * all threads. Any other bootstrap method calls are allowed to complete, but their + * results are ignored, and their dynamic call site invocations proceed with the originally + * chosen target object. + + *
+ * Discussion: + * These rules do not enable the JVM to duplicate dynamic call sites, + * or to issue “causeless” bootstrap method calls. + * Every dynamic call site transitions at most once from unlinked to linked, + * just before its first invocation. + * There is no way to undo the effect of a completed bootstrap method call. + * + *
+ * If a given {@code invokedynamic} instruction specifies no static arguments, + * the instruction's bootstrap method will be invoked on three arguments, + * conveying the instruction's caller class, name, and method type. + * If the {@code invokedynamic} instruction specifies one or more static arguments, + * those values will be passed as additional arguments to the method handle. + * (Note that because there is a limit of 255 arguments to any method, + * at most 251 extra arguments can be supplied, since the bootstrap method + * handle itself and its first three arguments must also be stacked.) + * The bootstrap method will be invoked as if by either {@code MethodHandle.invoke} + * or {@code invokeWithArguments}. (There is no way to tell the difference.) + *
+ * The normal argument conversion rules for {@code MethodHandle.invoke} apply to all stacked arguments. + * For example, if a pushed value is a primitive type, it may be converted to a reference by boxing conversion. + * If the bootstrap method is a variable arity method (its modifier bit {@code 0x0080} is set), + * then some or all of the arguments specified here may be collected into a trailing array parameter. + * (This is not a special rule, but rather a useful consequence of the interaction + * between {@code CONSTANT_MethodHandle} constants, the modifier bit for variable arity methods, + * and the {@link java.lang.invoke.MethodHandle#asVarargsCollector asVarargsCollector} transformation.) + *
+ * Given these rules, here are examples of legal bootstrap method declarations, + * given various numbers {@code N} of extra arguments. + * The first rows (marked {@code *}) will work for any number of extra arguments. + *
N | sample bootstrap method |
---|---|
* | CallSite bootstrap(Lookup caller, String name, MethodType type, Object... args) |
* | CallSite bootstrap(Object... args) |
* | CallSite bootstrap(Object caller, Object... nameAndTypeWithArgs) |
0 | CallSite bootstrap(Lookup caller, String name, MethodType type) |
0 | CallSite bootstrap(Lookup caller, Object... nameAndType) |
1 | CallSite bootstrap(Lookup caller, String name, MethodType type, Object arg) |
2 | CallSite bootstrap(Lookup caller, String name, MethodType type, Object... args) |
2 | CallSite bootstrap(Lookup caller, String name, MethodType type, String... args) |
2 | CallSite bootstrap(Lookup caller, String name, MethodType type, String x, int y) |
+ * As noted above, the actual method type of the bootstrap method can vary. + * For example, the fourth argument could be {@code MethodHandle}, + * if that is the type of the corresponding constant in + * the {@code CONSTANT_InvokeDynamic} entry. + * In that case, the {@code MethodHandle.invoke} call will pass the extra method handle + * constant as an {@code Object}, but the type matching machinery of {@code MethodHandle.invoke} + * will cast the reference back to {@code MethodHandle} before invoking the bootstrap method. + * (If a string constant were passed instead, by badly generated code, that cast would then fail, + * resulting in a {@code BootstrapMethodError}.) + *
+ * Note that, as a consequence of the above rules, the bootstrap method may accept a primitive + * argument, if it can be represented by a constant pool entry. + * However, arguments of type {@code boolean}, {@code byte}, {@code short}, or {@code char} + * cannot be created for bootstrap methods, since such constants cannot be directly + * represented in the constant pool, and the invocation of the bootstrap method will + * not perform the necessary narrowing primitive conversions. + *
+ * Extra bootstrap method arguments are intended to allow language implementors + * to safely and compactly encode metadata. + * In principle, the name and extra arguments are redundant, + * since each call site could be given its own unique bootstrap method. + * Such a practice is likely to produce large class files and constant pools. + * + * @author John Rose, JSR 292 EG + * @since 1.7 + */ + +package java.lang.invoke;