java.lang.Object
jdk.dynalink.DynamicLinker
The linker for
RelinkableCallSite
objects. A dynamic linker is a main
objects when using Dynalink, it coordinates linking of call sites with
linkers of available language runtimes that are represented by
GuardingDynamicLinker
objects (you only need to deal with these if
you are yourself implementing a language runtime with its own object model
and/or type conversions). To use Dynalink, you have to create one or more
dynamic linkers using a DynamicLinkerFactory
. Subsequently, you need
to invoke its link(RelinkableCallSite)
method from
invokedynamic
bootstrap methods to let it manage all the call sites
they create. Usual usage would be to create at least one class per language
runtime to contain one linker instance as:
class MyLanguageRuntime { private static final GuardingDynamicLinker myLanguageLinker = new MyLanguageLinker(); private static final DynamicLinker dynamicLinker = createDynamicLinker(); private static DynamicLinker createDynamicLinker() { final DynamicLinkerFactory factory = new DynamicLinkerFactory(); factory.setPrioritizedLinker(myLanguageLinker); return factory.createLinker(); } public static CallSite bootstrap(MethodHandles.Lookup lookup, String name, MethodType type) { return dynamicLinker.link( new SimpleRelinkableCallSite( new CallSiteDescriptor(lookup, parseOperation(name), type))); } private static Operation parseOperation(String name) { ... } }The above setup of one static linker instance is often too simple. You will often have your language runtime have a concept of some kind of "context class loader" and you will want to create one dynamic linker per such class loader, to ensure it incorporates linkers for all other language runtimes visible to that class loader (see
DynamicLinkerFactory.setClassLoader(ClassLoader)
).
There are three components you need to provide in the above example:
- You are expected to provide a
GuardingDynamicLinker
for your own language. If your runtime doesn't have its own object model or type conversions, you don't need to implement aGuardingDynamicLinker
; you would simply not invoke thesetPrioritizedLinker
method on the factory. - The performance of the programs can depend on your choice of the class to
represent call sites. The above example used
SimpleRelinkableCallSite
, but you might want to useChainedCallSite
instead. You'll need to experiment and decide what fits your runtime the best. You can further subclass either of these or implement your own. - You also need to provide
CallSiteDescriptor
s to your call sites. They are immutable objects that contain all the information about the call site: the class performing the lookups, the operation being invoked, and the method signature. You will have to supply your own scheme to encode and decode operations in the call site name or static parameters, that is why in the above example theparseOperation
method is left unimplemented.
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Method Summary
Modifier and TypeMethodDescriptionstatic StackTraceElement
Returns a stack trace element describing the location of theinvokedynamic
call site currently being linked on the current thread.Returns the object representing the linker services of this class that are normally exposed to individuallanguage-specific linkers
.<T extends RelinkableCallSite>
Tlink
(T callSite) Links an invokedynamic call site.
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Method Details
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link
Links an invokedynamic call site. It will install a method handle into the call site that invokes the relinking mechanism of this linker. Next time the call site is invoked, it will be linked for the actual arguments it was invoked with.- Type Parameters:
T
- the particular subclass ofRelinkableCallSite
for which to create a link.- Parameters:
callSite
- the call site to link.- Returns:
- the callSite, for easy call chaining.
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getLinkerServices
Returns the object representing the linker services of this class that are normally exposed to individuallanguage-specific linkers
. While as a user of this class you normally only care about thelink(RelinkableCallSite)
method, in certain circumstances you might want to use the lower level services directly; either to lookup specific method handles, to access the type converters, and so on.- Returns:
- the object representing the linker services of this class.
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getLinkedCallSiteLocation
Returns a stack trace element describing the location of theinvokedynamic
call site currently being linked on the current thread. The operation is potentially expensive as it needs to generate a stack trace to inspect it and is intended for use in diagnostics code. For "free-floating" call sites (not associated with aninvokedynamic
instruction), the result is not well-defined.- Returns:
- a stack trace element describing the location of the call site currently being linked, or null if it is not invoked while a call site is being linked.
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