1 /*

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

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     9  * by Oracle in the LICENSE file that accompanied this code.

    10  *

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    13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

    14  * version 2 for more details (a copy is included in the LICENSE file that

    15  * accompanied this code).

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    17  * You should have received a copy of the GNU General Public License version

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    19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

    20  *

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    25 

    26 /*

    27  * This file is available under and governed by the GNU General Public

    28  * License version 2 only, as published by the Free Software Foundation.

    29  * However, the following notice accompanied the original version of this

    30  * file, and Oracle licenses the original version of this file under the BSD

    31  * license:

    32  */

    33 /*

    34    Copyright 2009-2013 Attila Szegedi

    35 

    36    Licensed under both the Apache License, Version 2.0 (the "Apache License")

    37    and the BSD License (the "BSD License"), with licensee being free to

    38    choose either of the two at their discretion.

    39 

    40    You may not use this file except in compliance with either the Apache

    41    License or the BSD License.

    42 

    43    If you choose to use this file in compliance with the Apache License, the

    44    following notice applies to you:

    45 

    46        You may obtain a copy of the Apache License at

    47 

    48            http://www.apache.org/licenses/LICENSE-2.0

    49 

    50        Unless required by applicable law or agreed to in writing, software

    51        distributed under the License is distributed on an "AS IS" BASIS,

    52        WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or

    53        implied. See the License for the specific language governing

    54        permissions and limitations under the License.

    55 

    56    If you choose to use this file in compliance with the BSD License, the

    57    following notice applies to you:

    58 

    59        Redistribution and use in source and binary forms, with or without

    60        modification, are permitted provided that the following conditions are

    61        met:

    62        * Redistributions of source code must retain the above copyright

    63          notice, this list of conditions and the following disclaimer.

    64        * Redistributions in binary form must reproduce the above copyright

    65          notice, this list of conditions and the following disclaimer in the

    66          documentation and/or other materials provided with the distribution.

    67        * Neither the name of the copyright holder nor the names of

    68          contributors may be used to endorse or promote products derived from

    69          this software without specific prior written permission.

    70 

    71        THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS

    72        IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED

    73        TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A

    74        PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL COPYRIGHT HOLDER

    75        BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR

    76        CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF

    77        SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR

    78        BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,

    79        WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR

    80        OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF

    81        ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

    82 */

    83 

    84 package jdk.dynalink;

    85 

    86 import java.lang.StackWalker.StackFrame;

    87 import java.lang.invoke.MethodHandle;

    88 import java.lang.invoke.MethodHandles;

    89 import java.lang.invoke.MethodType;

    90 import java.lang.invoke.MutableCallSite;

    91 import java.util.Objects;

    92 import jdk.dynalink.linker.GuardedInvocation;

    93 import jdk.dynalink.linker.GuardedInvocationTransformer;

    94 import jdk.dynalink.linker.GuardingDynamicLinker;

    95 import jdk.dynalink.linker.LinkRequest;

    96 import jdk.dynalink.linker.LinkerServices;

    97 import jdk.dynalink.linker.support.Lookup;

    98 import jdk.dynalink.linker.support.SimpleLinkRequest;

    99 import jdk.dynalink.support.ChainedCallSite;

   100 import jdk.dynalink.support.SimpleRelinkableCallSite;

   101 

   102 /**

   103  * The linker for {@link RelinkableCallSite} objects. A dynamic linker is a main

   104  * objects when using Dynalink, it coordinates linking of call sites with

   105  * linkers of available language runtimes that are represented by

   106  * {@link GuardingDynamicLinker} objects (you only need to deal with these if

   107  * you are yourself implementing a language runtime with its own object model

   108  * and/or type conversions). To use Dynalink, you have to create one or more

   109  * dynamic linkers using a {@link DynamicLinkerFactory}. Subsequently, you need

   110  * to invoke its {@link #link(RelinkableCallSite)} method from

   111  * {@code invokedynamic} bootstrap methods to let it manage all the call sites

   112  * they create. Usual usage would be to create at least one class per language

   113  * runtime to contain one linker instance as:

   114  * <pre>

   115  *

   116  * class MyLanguageRuntime {

   117  *     private static final GuardingDynamicLinker myLanguageLinker = new MyLanguageLinker();

   118  *     private static final DynamicLinker dynamicLinker = createDynamicLinker();

   119  *

   120  *     private static DynamicLinker createDynamicLinker() {

   121  *         final DynamicLinkerFactory factory = new DynamicLinkerFactory();

   122  *         factory.setPrioritizedLinker(myLanguageLinker);

   123  *         return factory.createLinker();

   124  *     }

   125  *

   126  *     public static CallSite bootstrap(MethodHandles.Lookup lookup, String name, MethodType type) {

   127  *         return dynamicLinker.link(

   128  *             new SimpleRelinkableCallSite(

   129  *                 new CallSiteDescriptor(lookup, parseOperation(name), type)));

   130  *     }

   131  *

   132  *     private static Operation parseOperation(String name) {

   133  *         ...

   134  *     }

   135  * }

   136  * </pre>

   137  * The above setup of one static linker instance is often too simple. You will

   138  * often have your language runtime have a concept of some kind of

   139  * "context class loader" and you will want to create one dynamic linker per

   140  * such class loader, to ensure it incorporates linkers for all other language

   141  * runtimes visible to that class loader (see

   142  * {@link DynamicLinkerFactory#setClassLoader(ClassLoader)}).

   143  * <p>

   144  * There are three components you need to provide in the above example:

   145  * <ul>

   146  *

   147  * <li>You are expected to provide a {@link GuardingDynamicLinker} for your own

   148  * language. If your runtime doesn't have its own object model or type

   149  * conversions, you don't need to implement a {@code GuardingDynamicLinker}; you

   150  * would simply not invoke the {@code setPrioritizedLinker} method on the factory.</li>

   151  *

   152  * <li>The performance of the programs can depend on your choice of the class to

   153  * represent call sites. The above example used

   154  * {@link SimpleRelinkableCallSite}, but you might want to use

   155  * {@link ChainedCallSite} instead. You'll need to experiment and decide what

   156  * fits your runtime the best. You can further subclass either of these or

   157  * implement your own.</li>

   158  *

   159  * <li>You also need to provide {@link CallSiteDescriptor}s to your call sites.

   160  * They are immutable objects that contain all the information about the call

   161  * site: the class performing the lookups, the operation being invoked, and the

   162  * method signature. You will have to supply your own scheme to encode and

   163  * decode operations in the call site name or static parameters, that is why

   164  * in the above example the {@code parseOperation} method is left unimplemented.</li>

   165  *

   166  * </ul>

   167  */

   168 public final class DynamicLinker {

   169     private static final String CLASS_NAME = DynamicLinker.class.getName();

   170     private static final String RELINK_METHOD_NAME = "relink";

   171 

   172     private static final String INITIAL_LINK_CLASS_NAME = "java.lang.invoke.MethodHandleNatives";

   173     private static final String INITIAL_LINK_METHOD_NAME = "linkCallSite";

   174     private static final String INVOKE_PACKAGE_PREFIX = "java.lang.invoke.";

   175 

   176     private static final StackWalker stackWalker = StackWalker.getInstance(StackWalker.Option.SHOW_HIDDEN_FRAMES);

   177 

   178     private final LinkerServices linkerServices;

   179     private final GuardedInvocationTransformer prelinkTransformer;

   180     private final boolean syncOnRelink;

   181     private final int unstableRelinkThreshold;

   182 

   183     /**

   184      * Creates a new dynamic linker.

   185      *

   186      * @param linkerServices the linkerServices used by the linker, created by the factory.

   187      * @param prelinkTransformer see {@link DynamicLinkerFactory#setPrelinkTransformer(GuardedInvocationTransformer)}

   188      * @param syncOnRelink see {@link DynamicLinkerFactory#setSyncOnRelink(boolean)}

   189      * @param unstableRelinkThreshold see {@link DynamicLinkerFactory#setUnstableRelinkThreshold(int)}

   190      */

   191     DynamicLinker(final LinkerServices linkerServices, final GuardedInvocationTransformer prelinkTransformer,

   192             final boolean syncOnRelink, final int unstableRelinkThreshold) {

   193         if(unstableRelinkThreshold < 0) {

   194             throw new IllegalArgumentException("unstableRelinkThreshold < 0");

   195         }

   196         this.linkerServices = linkerServices;

   197         this.prelinkTransformer = prelinkTransformer;

   198         this.syncOnRelink = syncOnRelink;

   199         this.unstableRelinkThreshold = unstableRelinkThreshold;

   200     }

   201 

   202     /**

   203      * Links an invokedynamic call site. It will install a method handle into

   204      * the call site that invokes the relinking mechanism of this linker. Next

   205      * time the call site is invoked, it will be linked for the actual arguments

   206      * it was invoked with.

   207      *

   208      * @param <T> the particular subclass of {@link RelinkableCallSite} for

   209      *        which to create a link.

   210      * @param callSite the call site to link.

   211      *

   212      * @return the callSite, for easy call chaining.

   213      */

   214     public <T extends RelinkableCallSite> T link(final T callSite) {

   215         callSite.initialize(createRelinkAndInvokeMethod(callSite, 0));

   216         return callSite;

   217     }

   218 

   219     /**

   220      * Returns the object representing the linker services of this class that

   221      * are normally exposed to individual {@link GuardingDynamicLinker

   222      * language-specific linkers}. While as a user of this class you normally

   223      * only care about the {@link #link(RelinkableCallSite)} method, in certain

   224      * circumstances you might want to use the lower level services directly;

   225      * either to lookup specific method handles, to access the type converters,

   226      * and so on.

   227      *

   228      * @return the object representing the linker services of this class.

   229      */

   230     public LinkerServices getLinkerServices() {

   231         return linkerServices;

   232     }

   233 

   234     private static final MethodHandle RELINK = Lookup.findOwnSpecial(MethodHandles.lookup(), RELINK_METHOD_NAME,

   235             MethodHandle.class, RelinkableCallSite.class, int.class, Object[].class);

   236 

   237     private MethodHandle createRelinkAndInvokeMethod(final RelinkableCallSite callSite, final int relinkCount) {

   238         // Make a bound MH of invoke() for this linker and call site

   239         final MethodHandle boundRelinker = MethodHandles.insertArguments(RELINK, 0, this, callSite, Integer.valueOf(

   240                 relinkCount));

   241         // Make a MH that gathers all arguments to the invocation into an Object[]

   242         final MethodType type = callSite.getDescriptor().getMethodType();

   243         final MethodHandle collectingRelinker = boundRelinker.asCollector(Object[].class, type.parameterCount());

   244         return MethodHandles.foldArguments(MethodHandles.exactInvoker(type), collectingRelinker.asType(

   245                 type.changeReturnType(MethodHandle.class)));

   246     }

   247 

   248     /**

   249      * Relinks a call site conforming to the invocation arguments.

   250      *

   251      * @param callSite the call site itself

   252      * @param arguments arguments to the invocation

   253      *

   254      * @return return the method handle for the invocation

   255      *

   256      * @throws Exception rethrows any exception thrown by the linkers

   257      */

   258     @SuppressWarnings("unused")

   259     private MethodHandle relink(final RelinkableCallSite callSite, final int relinkCount, final Object... arguments) throws Exception {

   260         final CallSiteDescriptor callSiteDescriptor = callSite.getDescriptor();

   261         final boolean unstableDetectionEnabled = unstableRelinkThreshold > 0;

   262         final boolean callSiteUnstable = unstableDetectionEnabled && relinkCount >= unstableRelinkThreshold;

   263         final LinkRequest linkRequest = new SimpleLinkRequest(callSiteDescriptor, callSiteUnstable, arguments);

   264 

   265         GuardedInvocation guardedInvocation = linkerServices.getGuardedInvocation(linkRequest);

   266 

   267         // None found - throw an exception

   268         if(guardedInvocation == null) {

   269             throw new NoSuchDynamicMethodException(callSiteDescriptor.toString());

   270         }

   271 

   272         // Make sure we transform the invocation before linking it into the call site. This is typically used to match the

   273         // return type of the invocation to the call site.

   274         guardedInvocation = prelinkTransformer.filter(guardedInvocation, linkRequest, linkerServices);

   275         Objects.requireNonNull(guardedInvocation);

   276 

   277         int newRelinkCount = relinkCount;

   278         // Note that the short-circuited "&&" evaluation below ensures we'll increment the relinkCount until

   279         // threshold + 1 but not beyond that. Threshold + 1 is treated as a special value to signal that resetAndRelink

   280         // has already executed once for the unstable call site; we only want the call site to throw away its current

   281         // linkage once, when it transitions to unstable.

   282         if(unstableDetectionEnabled && newRelinkCount <= unstableRelinkThreshold && newRelinkCount++ == unstableRelinkThreshold) {

   283             callSite.resetAndRelink(guardedInvocation, createRelinkAndInvokeMethod(callSite, newRelinkCount));

   284         } else {

   285             callSite.relink(guardedInvocation, createRelinkAndInvokeMethod(callSite, newRelinkCount));

   286         }

   287         if(syncOnRelink) {

   288             MutableCallSite.syncAll(new MutableCallSite[] { (MutableCallSite)callSite });

   289         }

   290         return guardedInvocation.getInvocation();

   291     }

   292 

   293     /**

   294      * Returns a stack trace element describing the location of the

   295      * {@code invokedynamic} call site currently being linked on the current

   296      * thread. The operation is potentially expensive as it needs to generate a

   297      * stack trace to inspect it and is intended for use in diagnostics code.

   298      * For "free-floating" call sites (not associated with an

   299      * {@code invokedynamic} instruction), the result is not well-defined.

   300      *

   301      * @return a stack trace element describing the location of the call site

   302      *         currently being linked, or null if it is not invoked while a call

   303      *         site is being linked.

   304      */

   305     public static StackTraceElement getLinkedCallSiteLocation() {

   306         return stackWalker.walk(s -> s

   307                 // Find one of our linking entry points on the stack...

   308                 .dropWhile(f -> !(isRelinkFrame(f) || isInitialLinkFrame(f)))

   309                 .skip(1)

   310                 // ... then look for the first thing calling it that isn't j.l.invoke

   311                 .dropWhile(f -> f.getClassName().startsWith(INVOKE_PACKAGE_PREFIX))

   312                 .findFirst()

   313                 .map(StackFrame::toStackTraceElement)

   314                 .orElse(null)

   315         );

   316     }

   317 

   318     /**

   319      * Returns {@code true} if the frame represents {@code MethodHandleNatives.linkCallSite()},

   320      * the frame immediately on top of the call site frame when the call site is

   321      * being linked for the first time.

   322      *

   323      * @param frame the frame

   324      *

   325      * @return {@code true} if this frame represents {@code MethodHandleNatives.linkCallSite()}.

   326      */

   327     private static boolean isInitialLinkFrame(final StackFrame frame) {

   328         return testFrame(frame, INITIAL_LINK_METHOD_NAME, INITIAL_LINK_CLASS_NAME);

   329     }

   330 

   331     /**

   332      * Returns {@code true} if the frame represents {@code DynamicLinker.relink()},

   333      * the frame immediately on top of the call site frame when the call site is

   334      * being relinked (linked for second and subsequent times).

   335      *

   336      * @param frame the frame

   337      *

   338      * @return {@code true} if this frame represents {@code DynamicLinker.relink()}.

   339      */

   340     private static boolean isRelinkFrame(final StackFrame frame) {

   341         return testFrame(frame, RELINK_METHOD_NAME, CLASS_NAME);

   342     }

   343 

   344     private static boolean testFrame(final StackFrame frame, final String methodName, final String className) {

   345         return methodName.equals(frame.getMethodName()) && className.equals(frame.getClassName());

   346     }

   347 }