/*
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
/**
* Support for an abstract context, modelled loosely after ThreadLocal
* but using a user-provided context instead of the current thread.
*
* <p>Within the compiler, a single Context is used for each
* invocation of the compiler. The context is then used to ensure a
* single copy of each compiler phase exists per compiler invocation.
*
* <p>The context can be used to assist in extending the compiler by
* extending its components. To do that, the extended component must
* be registered before the base component. We break initialization
* cycles by (1) registering a factory for the component rather than
* the component itself, and (2) a convention for a pattern of usage
* in which each base component registers itself by calling an
* instance method that is overridden in extended components. A base
* phase supporting extension would look something like this:
*
* <p><pre>
* public class Phase {
* protected static final Context.Key<Phase> phaseKey =
* new Context.Key<Phase>();
*
* public static Phase instance(Context context) {
* Phase instance = context.get(phaseKey);
* if (instance == null)
* // the phase has not been overridden
* instance = new Phase(context);
* return instance;
* }
*
* protected Phase(Context context) {
* context.put(phaseKey, this);
* // other intitialization follows...
* }
* }
* </pre>
*
* <p>In the compiler, we simply use Phase.instance(context) to get
* the reference to the phase. But in extensions of the compiler, we
* must register extensions of the phases to replace the base phase,
* and this must be done before any reference to the phase is accessed
* using Phase.instance(). An extended phase might be declared thus:
*
* <p><pre>
* public class NewPhase extends Phase {
* protected NewPhase(Context context) {
* super(context);
* }
* public static void preRegister(final Context context) {
* context.put(phaseKey, new Context.Factory<Phase>() {
* public Phase make() {
* return new NewPhase(context);
* }
* });
* }
* }
* </pre>
*
* <p>And is registered early in the extended compiler like this
*
* <p><pre>
* NewPhase.preRegister(context);
* </pre>
*
* <p><b>This is NOT part of any supported API.
* If you write code that depends on this, you do so at your own risk.
* This code and its internal interfaces are subject to change or
* deletion without notice.</b>
*/
public class Context {
/** The client creates an instance of this class for each key.
*/
public static class Key<T> {
// note: we inherit identity equality from Object.
}
/**
* The client can register a factory for lazy creation of the
* instance.
*/
public static interface Factory<T> {
};
/**
* The underlying map storing the data.
* We maintain the invariant that this table contains only
* mappings of the form
* Key<T> -> T or Key<T> -> Factory<T> */
/** Set the factory for the key in this context. */
checkState(ht);
throw new AssertionError("duplicate context value");
checkState(ft);
}
/** Set the value for the key in this context. */
throw new AssertionError("T extends Context.Factory");
checkState(ht);
throw new AssertionError("duplicate context value");
}
/** Get the value for the key in this context. */
checkState(ht);
if (o instanceof Factory<?>) {
if (o instanceof Factory<?>)
throw new AssertionError("T extends Context.Factory");
}
/* The following cast can't fail unless there was
* cheating elsewhere, because of the invariant on ht.
* Since we found a key of type Key<T>, the value must
* be of type T.
*/
return Context.<T>uncheckedCast(o);
}
public Context() {}
/**
* The table of preregistered factories.
*/
}
/*
* The key table, providing a unique Key<T> for each Class<T>.
*/
checkState(kt);
if (k == null) {
k = new Key<T>();
}
return k;
}
}
}
}
/**
* TODO: This method should be removed and Context should be made type safe.
* This can be accomplished by using class literals as type tokens.
*/
@SuppressWarnings("unchecked")
return (T)o;
}
public void dump() {
}
public void clear() {
}
if (t == null)
throw new IllegalStateException();
}
}