- * {@code CallSite} is an abstract class which does not allow - * direct subclassing by users. It has three immediate, - * concrete subclasses that may be either instantiated or subclassed. - *
- * A non-constant call site may be relinked by changing its target. - * The new target must have the same {@linkplain MethodHandle#type() type} - * as the previous target. - * Thus, though a call site can be relinked to a series of - * successive targets, it cannot change its type. - *
- * Here is a sample use of call sites and bootstrap methods which links every - * dynamic call site to print its arguments: -
-static void test() throws Throwable {
- // THE FOLLOWING LINE IS PSEUDOCODE FOR A JVM INSTRUCTION
- InvokeDynamic[#bootstrapDynamic].baz("baz arg", 2, 3.14);
-}
-private static void printArgs(Object... args) {
- System.out.println(java.util.Arrays.deepToString(args));
-}
-private static final MethodHandle printArgs;
-static {
- MethodHandles.Lookup lookup = MethodHandles.lookup();
- Class thisClass = lookup.lookupClass(); // (who am I?)
- printArgs = lookup.findStatic(thisClass,
- "printArgs", MethodType.methodType(void.class, Object[].class));
-}
-private static CallSite bootstrapDynamic(MethodHandles.Lookup caller, String name, MethodType type) {
- // ignore caller and name, but match the type:
- return new ConstantCallSite(printArgs.asType(type));
-}
-- * Before this {@code CallSite} object is returned from a bootstrap method, - * it is usually provided with a more useful target method, - * via a call to {@link CallSite#setTarget(MethodHandle) setTarget}. - * @throws NullPointerException if the proposed type is null - */ - /*package-private*/ - CallSite(MethodType type) { - target = type.invokers().uninitializedCallSite(); - } - - /** - * Make a blank call site object, possibly equipped with an initial target method handle. - * @param target the method handle which will be the initial target of the call site - * @throws NullPointerException if the proposed target is null - */ - /*package-private*/ - CallSite(MethodHandle target) { - target.type(); // null check - this.target = target; - } - - /** - * Returns the type of this call site's target. - * Although targets may change, any call site's type is permanent, and can never change to an unequal type. - * The {@code setTarget} method enforces this invariant by refusing any new target that does - * not have the previous target's type. - * @return the type of the current target, which is also the type of any future target - */ - public MethodType type() { - return target.type(); - } - - /** Called from JVM (or low-level Java code) after the BSM returns the newly created CallSite. - * The parameters are JVM-specific. - */ - void initializeFromJVM(String name, - MethodType type, - MemberName callerMethod, - int callerBCI) { - if (this.vmmethod != null) { - // FIXME - throw new InvokeDynamicBootstrapError("call site has already been linked to an invokedynamic instruction"); - } - if (!this.type().equals(type)) { - throw wrongTargetType(target, type); - } - this.vmindex = callerBCI; - this.vmmethod = callerMethod; - } - - /** - * Returns the target method of the call site, according to the - * behavior defined by this call site's specific class. - * The immediate subclasses of {@code CallSite} document the - * class-specific behaviors of this method. - * - * @return the current linkage state of the call site, its target method handle - * @see ConstantCallSite - * @see VolatileCallSite - * @see #setTarget - * @see ConstantCallSite#getTarget - * @see MutableCallSite#getTarget - * @see VolatileCallSite#getTarget - */ - public abstract MethodHandle getTarget(); - - /** - * Updates the target method of this call site, according to the - * behavior defined by this call site's specific class. - * The immediate subclasses of {@code CallSite} document the - * class-specific behaviors of this method. - *
- * The type of the new target must be {@linkplain MethodType#equals equal to} - * the type of the old target. - * - * @param newTarget the new target - * @throws NullPointerException if the proposed new target is null - * @throws WrongMethodTypeException if the proposed new target - * has a method type that differs from the previous target - * @see CallSite#getTarget - * @see ConstantCallSite#setTarget - * @see MutableCallSite#setTarget - * @see VolatileCallSite#setTarget - */ - public abstract void setTarget(MethodHandle newTarget); - - void checkTargetChange(MethodHandle oldTarget, MethodHandle newTarget) { - MethodType oldType = oldTarget.type(); - MethodType newType = newTarget.type(); // null check! - if (!newType.equals(oldType)) - throw wrongTargetType(newTarget, oldType); - } - - private static WrongMethodTypeException wrongTargetType(MethodHandle target, MethodType type) { - return new WrongMethodTypeException(String.valueOf(target)+" should be of type "+type); - } - - /** - * Produce a method handle equivalent to an invokedynamic instruction - * which has been linked to this call site. - *
- * This method is equivalent to the following code: - *
- * - * @return a method handle which always invokes this call site's current target - */ - public abstract MethodHandle dynamicInvoker(); - - /*non-public*/ MethodHandle makeDynamicInvoker() { - MethodHandle getTarget = MethodHandleImpl.bindReceiver(GET_TARGET, this); - MethodHandle invoker = MethodHandles.exactInvoker(this.type()); - return MethodHandles.foldArguments(invoker, getTarget); - } - - private static final MethodHandle GET_TARGET; - static { - try { - GET_TARGET = IMPL_LOOKUP. - findVirtual(CallSite.class, "getTarget", MethodType.methodType(MethodHandle.class)); - } catch (ReflectiveOperationException ignore) { - throw new InternalError(); - } - } - - /** This guy is rolled into the default target if a MethodType is supplied to the constructor. */ - /*package-private*/ - static Empty uninitializedCallSite() { - throw new IllegalStateException("uninitialized call site"); - } - - // unsafe stuff: - private static final Unsafe unsafe = Unsafe.getUnsafe(); - private static final long TARGET_OFFSET; - - static { - try { - TARGET_OFFSET = unsafe.objectFieldOffset(CallSite.class.getDeclaredField("target")); - } catch (Exception ex) { throw new Error(ex); } - } - - /*package-private*/ - void setTargetNormal(MethodHandle newTarget) { - target = newTarget; - } - /*package-private*/ - MethodHandle getTargetVolatile() { - return (MethodHandle) unsafe.getObjectVolatile(this, TARGET_OFFSET); - } - /*package-private*/ - void setTargetVolatile(MethodHandle newTarget) { - unsafe.putObjectVolatile(this, TARGET_OFFSET, newTarget); - } - - // this implements the upcall from the JVM, MethodHandleNatives.makeDynamicCallSite: - static CallSite makeSite(MethodHandle bootstrapMethod, - // Callee information: - String name, MethodType type, - // Extra arguments for BSM, if any: - Object info, - // Caller information: - MemberName callerMethod, int callerBCI) { - Class callerClass = callerMethod.getDeclaringClass(); - Object caller; - if (bootstrapMethod.type().parameterType(0) == Class.class && TRANSITIONAL_BEFORE_PFD) - caller = callerClass; // remove for PFD - else - caller = IMPL_LOOKUP.in(callerClass); - if (bootstrapMethod == null && TRANSITIONAL_BEFORE_PFD) { - // If there is no bootstrap method, throw IncompatibleClassChangeError. - // This is a valid generic error type for resolution (JLS 12.3.3). - throw new IncompatibleClassChangeError - ("Class "+callerClass.getName()+" has not declared a bootstrap method for invokedynamic"); - } - CallSite site; - try { - Object binding; - info = maybeReBox(info); - if (info == null) { - binding = bootstrapMethod.invokeGeneric(caller, name, type); - } else if (!info.getClass().isArray()) { - binding = bootstrapMethod.invokeGeneric(caller, name, type, info); - } else { - Object[] argv = (Object[]) info; - maybeReBoxElements(argv); - if (3 + argv.length > 255) - throw new InvokeDynamicBootstrapError("too many bootstrap method arguments"); - MethodType bsmType = bootstrapMethod.type(); - if (bsmType.parameterCount() == 4 && bsmType.parameterType(3) == Object[].class) - binding = bootstrapMethod.invokeGeneric(caller, name, type, argv); - else - binding = MethodHandles.spreadInvoker(bsmType, 3) - .invokeGeneric(bootstrapMethod, caller, name, type, argv); - } - //System.out.println("BSM for "+name+type+" => "+binding); - if (binding instanceof CallSite) { - site = (CallSite) binding; - } else if (binding instanceof MethodHandle && TRANSITIONAL_BEFORE_PFD) { - // Transitional! - MethodHandle target = (MethodHandle) binding; - site = new ConstantCallSite(target); - } else { - throw new ClassCastException("bootstrap method failed to produce a CallSite"); - } - if (TRANSITIONAL_BEFORE_PFD) - PRIVATE_INITIALIZE_CALL_SITE.invokeExact(site, name, type, - callerMethod, callerBCI); - assert(site.getTarget() != null); - assert(site.getTarget().type().equals(type)); - } catch (Throwable ex) { - InvokeDynamicBootstrapError bex; - if (ex instanceof InvokeDynamicBootstrapError) - bex = (InvokeDynamicBootstrapError) ex; - else - bex = new InvokeDynamicBootstrapError("call site initialization exception", ex); - throw bex; - } - return site; - } - - private static final boolean TRANSITIONAL_BEFORE_PFD = true; // FIXME: remove for PFD - // booby trap to force removal after package rename: - static { if (TRANSITIONAL_BEFORE_PFD) assert(CallSite.class.getName().startsWith("java.dyn.")); } - - private static Object maybeReBox(Object x) { - if (x instanceof Integer) { - int xi = (int) x; - if (xi == (byte) xi) - x = xi; // must rebox; see JLS 5.1.7 - } - return x; - } - private static void maybeReBoxElements(Object[] xa) { - for (int i = 0; i < xa.length; i++) { - xa[i] = maybeReBox(xa[i]); - } - } - - // This method is private in CallSite because it touches private fields in CallSite. - // These private fields (vmmethod, vmindex) are specific to the JVM. - private static final MethodHandle PRIVATE_INITIALIZE_CALL_SITE; - static { - try { - PRIVATE_INITIALIZE_CALL_SITE = - !TRANSITIONAL_BEFORE_PFD ? null : - IMPL_LOOKUP.findVirtual(CallSite.class, "initializeFromJVM", - MethodType.methodType(void.class, - String.class, MethodType.class, - MemberName.class, int.class)); - } catch (ReflectiveOperationException ex) { - throw uncaughtException(ex); - } - } -}- * MethodHandle getTarget, invoker, result; - * getTarget = MethodHandles.publicLookup().bind(this, "getTarget", MethodType.methodType(MethodHandle.class)); - * invoker = MethodHandles.exactInvoker(this.type()); - * result = MethodHandles.foldArguments(invoker, getTarget) - *