Module jdk.dynalink

Package jdk.dynalink.linker

Interface GuardingDynamicLinker

All Known Subinterfaces:

TypeBasedGuardingDynamicLinker

All Known Implementing Classes:

BeansLinker, CompositeGuardingDynamicLinker, CompositeTypeBasedGuardingDynamicLinker

public interface GuardingDynamicLinker

The base interface for language-specific dynamic linkers. Such linkers always have to produce method handles with guards, as the validity of the method handle for calls at a call site inevitably depends on some condition (at the very least, it depends on the receiver belonging to the language runtime of the linker). Language runtime implementors will normally implement the linking logic for their own language as one or more GuardingDynamicLinker classes. They will typically set them as prioritized linkers in the DynamicLinkerFactory they configure for themselves, and maybe also set some as fallback linkers to handle language-specific "property not found" etc. conditions.

Consider implementing TypeBasedGuardingDynamicLinker interface instead of this interface for those linkers that are based on the Java class of the objects. If you need to implement language-specific type conversions, have your GuardingDynamicLinker also implement the GuardingTypeConverterFactory interface.

Languages can export linkers to other language runtimes for automatic discovery using a GuardingDynamicLinkerExporter.

Method Summary

Modifier and Type	Method	Description
GuardedInvocation	getGuardedInvocation(LinkRequest linkRequest, LinkerServices linkerServices)	Creates a guarded invocation appropriate for a particular invocation with the specified arguments at a call site.

Method Detail

getGuardedInvocation

GuardedInvocation getGuardedInvocation(LinkRequest linkRequest,
                                       LinkerServices linkerServices)
                                throws Exception

Creates a guarded invocation appropriate for a particular invocation with the specified arguments at a call site.

Parameters:

linkRequest - the object describing the request for linking a particular invocation

linkerServices - linker services

Returns:

a guarded invocation with a method handle suitable for the arguments, as well as a guard condition that if fails should trigger relinking. Must return null if it can't resolve the invocation. If the returned invocation is unconditional (which is actually quite rare), the guard in the return value can be null. The invocation can also have any number of switch points for asynchronous invalidation of the linkage, as well as a Throwable subclass that describes an expected exception condition that also triggers relinking (often it is faster to rely on an infrequent but expected ClassCastException than on an always evaluated instanceof guard). While the linker must produce an invocation with parameter types matching those in the call site descriptor of the link request, it should not try to match the return type expected at the call site except when it can do it with only the conversions that lose neither precision nor magnitude, see LinkerServices.asTypeLosslessReturn(MethodHandle, MethodType) for further explanation.

Throws:

Exception - if the operation fails for whatever reason