1 /*

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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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    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.internal.dynalink;

    85 

    86 import java.lang.invoke.MethodHandle;

    87 import java.lang.invoke.MethodHandles;

    88 import java.lang.invoke.MethodType;

    89 import java.lang.invoke.MutableCallSite;

    90 import java.util.Objects;

    91 import jdk.internal.dynalink.linker.GuardedInvocation;

    92 import jdk.internal.dynalink.linker.GuardedInvocationTransformer;

    93 import jdk.internal.dynalink.linker.GuardingDynamicLinker;

    94 import jdk.internal.dynalink.linker.LinkRequest;

    95 import jdk.internal.dynalink.linker.LinkerServices;

    96 import jdk.internal.dynalink.linker.support.Lookup;

    97 import jdk.internal.dynalink.linker.support.SimpleLinkRequest;

    98 import jdk.internal.dynalink.support.ChainedCallSite;

    99 import jdk.internal.dynalink.support.SimpleRelinkableCallSite;

   100 

   101 /**

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

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

   104  * linkers of available language runtimes that are represented by

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

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

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

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

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

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

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

   112  * runtime to contain one linker instance as:

   113  * <pre>

   114  *

   115  * class MyLanguageRuntime {

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

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

   118  *

   119  *     private static DynamicLinker createDynamicLinker() {

   120  *         final DynamicLinkerFactory factory = new DynamicLinkerFactory();

   121  *         factory.setPrioritizedLinker(myLanguageLinker);

   122  *         return factory.createLinker();

   123  *     }

   124  *

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

   126  *         return dynamicLinker.link(

   127  *             new SimpleRelinkableCallSite(

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

   129  *     }

   130  *

   131  *     private static Operation parseOperation(String name) {

   132  *         ...

   133  *     }

   134  * }

   135  * </pre>

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

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

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

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

   140  * runtimes visible to that class loader (see

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

   142  * <p>

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

   144  * <ul>

   145  *

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

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

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

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

   150  *

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

   152  * represent call sites. The above example used

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

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

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

   156  * implement your own.</li>

   157  *

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

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

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

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

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

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

   164  *

   165  * </ul>

   166  */

   167 public final class DynamicLinker {

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

   169     private static final String RELINK_METHOD_NAME = "relink";

   170 

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

   172     private static final String INITIAL_LINK_METHOD_NAME = "linkCallSite";

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

   174 

   175     private final LinkerServices linkerServices;

   176     private final GuardedInvocationTransformer prelinkTransformer;

   177     private final boolean syncOnRelink;

   178     private final int unstableRelinkThreshold;

   179 

   180     /**

   181      * Creates a new dynamic linker.

   182      *

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

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

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

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

   187      */

   188     DynamicLinker(final LinkerServices linkerServices, final GuardedInvocationTransformer prelinkTransformer,

   189             final boolean syncOnRelink, final int unstableRelinkThreshold) {

   190         if(unstableRelinkThreshold < 0) {

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

   192         }

   193         this.linkerServices = linkerServices;

   194         this.prelinkTransformer = prelinkTransformer;

   195         this.syncOnRelink = syncOnRelink;

   196         this.unstableRelinkThreshold = unstableRelinkThreshold;

   197     }

   198 

   199     /**

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

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

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

   203      * it was invoked with.

   204      *

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

   206      *        which to create a link.

   207      * @param callSite the call site to link.

   208      *

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

   210      */

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

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

   213         return callSite;

   214     }

   215 

   216     /**

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

   218      * are normally exposed to individual {@link GuardingDynamicLinker

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

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

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

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

   223      * and so on.

   224      *

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

   226      */

   227     public LinkerServices getLinkerServices() {

   228         return linkerServices;

   229     }

   230 

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

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

   233 

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

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

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

   237                 relinkCount));

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

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

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

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

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

   243     }

   244 

   245     /**

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

   247      *

   248      * @param callSite the call site itself

   249      * @param arguments arguments to the invocation

   250      *

   251      * @return return the method handle for the invocation

   252      *

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

   254      */

   255     @SuppressWarnings("unused")

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

   257         final CallSiteDescriptor callSiteDescriptor = callSite.getDescriptor();

   258         final boolean unstableDetectionEnabled = unstableRelinkThreshold > 0;

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

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

   261 

   262         GuardedInvocation guardedInvocation = linkerServices.getGuardedInvocation(linkRequest);

   263 

   264         // None found - throw an exception

   265         if(guardedInvocation == null) {

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

   267         }

   268 

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

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

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

   272         Objects.requireNonNull(guardedInvocation);

   273 

   274         int newRelinkCount = relinkCount;

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

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

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

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

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

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

   281         } else {

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

   283         }

   284         if(syncOnRelink) {

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

   286         }

   287         return guardedInvocation.getInvocation();

   288     }

   289 

   290     /**

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

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

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

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

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

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

   297      *

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

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

   300      *         site is being linked.

   301      */

   302     public static StackTraceElement getLinkedCallSiteLocation() {

   303         final StackTraceElement[] trace = new Throwable().getStackTrace();

   304         for(int i = 0; i < trace.length - 1; ++i) {

   305             final StackTraceElement frame = trace[i];

   306             // If we found any of our linking entry points on the stack...

   307             if(isRelinkFrame(frame) || isInitialLinkFrame(frame)) {

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

   309                 for (int j = i + 1; j < trace.length; ++j) {

   310                     final StackTraceElement frame2 = trace[j];

   311                     if (!frame2.getClassName().startsWith(INVOKE_PACKAGE_PREFIX)) {

   312                         return frame2;

   313                     }

   314                 }

   315             }

   316         }

   317         return null;

   318     }

   319 

   320     /**

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

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

   323      * being linked for the first time.

   324      *

   325      * @param frame the frame

   326      *

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

   328      */

   329     private static boolean isInitialLinkFrame(final StackTraceElement frame) {

   330         return testFrame(frame, INITIAL_LINK_METHOD_NAME, INITIAL_LINK_CLASS_NAME);

   331     }

   332 

   333     /**

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

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

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

   337      *

   338      * @param frame the frame

   339      *

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

   341      */

   342     private static boolean isRelinkFrame(final StackTraceElement frame) {

   343         return testFrame(frame, RELINK_METHOD_NAME, CLASS_NAME);

   344     }

   345 

   346     private static boolean testFrame(final StackTraceElement frame, final String methodName, final String className) {

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

   348     }

   349 }