1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000
1.2 +++ b/src/share/vm/code/dependencies.hpp Sat Dec 01 00:00:00 2007 +0000
1.3 @@ -0,0 +1,550 @@
1.4 +/*
1.5 + * Copyright 2005-2006 Sun Microsystems, Inc. All Rights Reserved.
1.6 + * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
1.7 + *
1.8 + * This code is free software; you can redistribute it and/or modify it
1.9 + * under the terms of the GNU General Public License version 2 only, as
1.10 + * published by the Free Software Foundation.
1.11 + *
1.12 + * This code is distributed in the hope that it will be useful, but WITHOUT
1.13 + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
1.14 + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
1.15 + * version 2 for more details (a copy is included in the LICENSE file that
1.16 + * accompanied this code).
1.17 + *
1.18 + * You should have received a copy of the GNU General Public License version
1.19 + * 2 along with this work; if not, write to the Free Software Foundation,
1.20 + * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
1.21 + *
1.22 + * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
1.23 + * CA 95054 USA or visit www.sun.com if you need additional information or
1.24 + * have any questions.
1.25 + *
1.26 + */
1.27 +
1.28 +//** Dependencies represent assertions (approximate invariants) within
1.29 +// the class hierarchy. An example is an assertion that a given
1.30 +// method is not overridden; another example is that a type has only
1.31 +// one concrete subtype. Compiled code which relies on such
1.32 +// assertions must be discarded if they are overturned by changes in
1.33 +// the class hierarchy. We can think of these assertions as
1.34 +// approximate invariants, because we expect them to be overturned
1.35 +// very infrequently. We are willing to perform expensive recovery
1.36 +// operations when they are overturned. The benefit, of course, is
1.37 +// performing optimistic optimizations (!) on the object code.
1.38 +//
1.39 +// Changes in the class hierarchy due to dynamic linking or
1.40 +// class evolution can violate dependencies. There is enough
1.41 +// indexing between classes and nmethods to make dependency
1.42 +// checking reasonably efficient.
1.43 +
1.44 +class ciEnv;
1.45 +class nmethod;
1.46 +class OopRecorder;
1.47 +class xmlStream;
1.48 +class CompileLog;
1.49 +class DepChange;
1.50 +class No_Safepoint_Verifier;
1.51 +
1.52 +class Dependencies: public ResourceObj {
1.53 + public:
1.54 + // Note: In the comments on dependency types, most uses of the terms
1.55 + // subtype and supertype are used in a "non-strict" or "inclusive"
1.56 + // sense, and are starred to remind the reader of this fact.
1.57 + // Strict uses of the terms use the word "proper".
1.58 + //
1.59 + // Specifically, every class is its own subtype* and supertype*.
1.60 + // (This trick is easier than continually saying things like "Y is a
1.61 + // subtype of X or X itself".)
1.62 + //
1.63 + // Sometimes we write X > Y to mean X is a proper supertype of Y.
1.64 + // The notation X > {Y, Z} means X has proper subtypes Y, Z.
1.65 + // The notation X.m > Y means that Y inherits m from X, while
1.66 + // X.m > Y.m means Y overrides X.m. A star denotes abstractness,
1.67 + // as *I > A, meaning (abstract) interface I is a super type of A,
1.68 + // or A.*m > B.m, meaning B.m implements abstract method A.m.
1.69 + //
1.70 + // In this module, the terms "subtype" and "supertype" refer to
1.71 + // Java-level reference type conversions, as detected by
1.72 + // "instanceof" and performed by "checkcast" operations. The method
1.73 + // Klass::is_subtype_of tests these relations. Note that "subtype"
1.74 + // is richer than "subclass" (as tested by Klass::is_subclass_of),
1.75 + // since it takes account of relations involving interface and array
1.76 + // types.
1.77 + //
1.78 + // To avoid needless complexity, dependencies involving array types
1.79 + // are not accepted. If you need to make an assertion about an
1.80 + // array type, make the assertion about its corresponding element
1.81 + // types. Any assertion that might change about an array type can
1.82 + // be converted to an assertion about its element type.
1.83 + //
1.84 + // Most dependencies are evaluated over a "context type" CX, which
1.85 + // stands for the set Subtypes(CX) of every Java type that is a subtype*
1.86 + // of CX. When the system loads a new class or interface N, it is
1.87 + // responsible for re-evaluating changed dependencies whose context
1.88 + // type now includes N, that is, all super types of N.
1.89 + //
1.90 + enum DepType {
1.91 + end_marker = 0,
1.92 +
1.93 + // An 'evol' dependency simply notes that the contents of the
1.94 + // method were used. If it evolves (is replaced), the nmethod
1.95 + // must be recompiled. No other dependencies are implied.
1.96 + evol_method,
1.97 + FIRST_TYPE = evol_method,
1.98 +
1.99 + // A context type CX is a leaf it if has no proper subtype.
1.100 + leaf_type,
1.101 +
1.102 + // An abstract class CX has exactly one concrete subtype CC.
1.103 + abstract_with_unique_concrete_subtype,
1.104 +
1.105 + // The type CX is purely abstract, with no concrete subtype* at all.
1.106 + abstract_with_no_concrete_subtype,
1.107 +
1.108 + // The concrete CX is free of concrete proper subtypes.
1.109 + concrete_with_no_concrete_subtype,
1.110 +
1.111 + // Given a method M1 and a context class CX, the set MM(CX, M1) of
1.112 + // "concrete matching methods" in CX of M1 is the set of every
1.113 + // concrete M2 for which it is possible to create an invokevirtual
1.114 + // or invokeinterface call site that can reach either M1 or M2.
1.115 + // That is, M1 and M2 share a name, signature, and vtable index.
1.116 + // We wish to notice when the set MM(CX, M1) is just {M1}, or
1.117 + // perhaps a set of two {M1,M2}, and issue dependencies on this.
1.118 +
1.119 + // The set MM(CX, M1) can be computed by starting with any matching
1.120 + // concrete M2 that is inherited into CX, and then walking the
1.121 + // subtypes* of CX looking for concrete definitions.
1.122 +
1.123 + // The parameters to this dependency are the method M1 and the
1.124 + // context class CX. M1 must be either inherited in CX or defined
1.125 + // in a subtype* of CX. It asserts that MM(CX, M1) is no greater
1.126 + // than {M1}.
1.127 + unique_concrete_method, // one unique concrete method under CX
1.128 +
1.129 + // An "exclusive" assertion concerns two methods or subtypes, and
1.130 + // declares that there are at most two (or perhaps later N>2)
1.131 + // specific items that jointly satisfy the restriction.
1.132 + // We list all items explicitly rather than just giving their
1.133 + // count, for robustness in the face of complex schema changes.
1.134 +
1.135 + // A context class CX (which may be either abstract or concrete)
1.136 + // has two exclusive concrete subtypes* C1, C2 if every concrete
1.137 + // subtype* of CX is either C1 or C2. Note that if neither C1 or C2
1.138 + // are equal to CX, then CX itself must be abstract. But it is
1.139 + // also possible (for example) that C1 is CX (a concrete class)
1.140 + // and C2 is a proper subtype of C1.
1.141 + abstract_with_exclusive_concrete_subtypes_2,
1.142 +
1.143 + // This dependency asserts that MM(CX, M1) is no greater than {M1,M2}.
1.144 + exclusive_concrete_methods_2,
1.145 +
1.146 + // This dependency asserts that no instances of class or it's
1.147 + // subclasses require finalization registration.
1.148 + no_finalizable_subclasses,
1.149 +
1.150 + TYPE_LIMIT
1.151 + };
1.152 + enum {
1.153 + LG2_TYPE_LIMIT = 4, // assert(TYPE_LIMIT <= (1<<LG2_TYPE_LIMIT))
1.154 +
1.155 + // handy categorizations of dependency types:
1.156 + all_types = ((1<<TYPE_LIMIT)-1) & ((-1)<<FIRST_TYPE),
1.157 + non_ctxk_types = (1<<evol_method),
1.158 + ctxk_types = all_types & ~non_ctxk_types,
1.159 +
1.160 + max_arg_count = 3, // current maximum number of arguments (incl. ctxk)
1.161 +
1.162 + // A "context type" is a class or interface that
1.163 + // provides context for evaluating a dependency.
1.164 + // When present, it is one of the arguments (dep_context_arg).
1.165 + //
1.166 + // If a dependency does not have a context type, there is a
1.167 + // default context, depending on the type of the dependency.
1.168 + // This bit signals that a default context has been compressed away.
1.169 + default_context_type_bit = (1<<LG2_TYPE_LIMIT)
1.170 + };
1.171 +
1.172 + static const char* dep_name(DepType dept);
1.173 + static int dep_args(DepType dept);
1.174 + static int dep_context_arg(DepType dept) {
1.175 + return dept_in_mask(dept, ctxk_types)? 0: -1;
1.176 + }
1.177 +
1.178 + private:
1.179 + // State for writing a new set of dependencies:
1.180 + GrowableArray<int>* _dep_seen; // (seen[h->ident] & (1<<dept))
1.181 + GrowableArray<ciObject*>* _deps[TYPE_LIMIT];
1.182 +
1.183 + static const char* _dep_name[TYPE_LIMIT];
1.184 + static int _dep_args[TYPE_LIMIT];
1.185 +
1.186 + static bool dept_in_mask(DepType dept, int mask) {
1.187 + return (int)dept >= 0 && dept < TYPE_LIMIT && ((1<<dept) & mask) != 0;
1.188 + }
1.189 +
1.190 + bool note_dep_seen(int dept, ciObject* x) {
1.191 + assert(dept < BitsPerInt, "oob");
1.192 + int x_id = x->ident();
1.193 + assert(_dep_seen != NULL, "deps must be writable");
1.194 + int seen = _dep_seen->at_grow(x_id, 0);
1.195 + _dep_seen->at_put(x_id, seen | (1<<dept));
1.196 + // return true if we've already seen dept/x
1.197 + return (seen & (1<<dept)) != 0;
1.198 + }
1.199 +
1.200 + bool maybe_merge_ctxk(GrowableArray<ciObject*>* deps,
1.201 + int ctxk_i, ciKlass* ctxk);
1.202 +
1.203 + void sort_all_deps();
1.204 + size_t estimate_size_in_bytes();
1.205 +
1.206 + // Initialize _deps, etc.
1.207 + void initialize(ciEnv* env);
1.208 +
1.209 + // State for making a new set of dependencies:
1.210 + OopRecorder* _oop_recorder;
1.211 +
1.212 + // Logging support
1.213 + CompileLog* _log;
1.214 +
1.215 + address _content_bytes; // everything but the oop references, encoded
1.216 + size_t _size_in_bytes;
1.217 +
1.218 + public:
1.219 + // Make a new empty dependencies set.
1.220 + Dependencies(ciEnv* env) {
1.221 + initialize(env);
1.222 + }
1.223 +
1.224 + private:
1.225 + // Check for a valid context type.
1.226 + // Enforce the restriction against array types.
1.227 + static void check_ctxk(ciKlass* ctxk) {
1.228 + assert(ctxk->is_instance_klass(), "java types only");
1.229 + }
1.230 + static void check_ctxk_concrete(ciKlass* ctxk) {
1.231 + assert(is_concrete_klass(ctxk->as_instance_klass()), "must be concrete");
1.232 + }
1.233 + static void check_ctxk_abstract(ciKlass* ctxk) {
1.234 + check_ctxk(ctxk);
1.235 + assert(!is_concrete_klass(ctxk->as_instance_klass()), "must be abstract");
1.236 + }
1.237 +
1.238 + void assert_common_1(DepType dept, ciObject* x);
1.239 + void assert_common_2(DepType dept, ciKlass* ctxk, ciObject* x);
1.240 + void assert_common_3(DepType dept, ciKlass* ctxk, ciObject* x, ciObject* x2);
1.241 +
1.242 + public:
1.243 + // Adding assertions to a new dependency set at compile time:
1.244 + void assert_evol_method(ciMethod* m);
1.245 + void assert_leaf_type(ciKlass* ctxk);
1.246 + void assert_abstract_with_unique_concrete_subtype(ciKlass* ctxk, ciKlass* conck);
1.247 + void assert_abstract_with_no_concrete_subtype(ciKlass* ctxk);
1.248 + void assert_concrete_with_no_concrete_subtype(ciKlass* ctxk);
1.249 + void assert_unique_concrete_method(ciKlass* ctxk, ciMethod* uniqm);
1.250 + void assert_abstract_with_exclusive_concrete_subtypes(ciKlass* ctxk, ciKlass* k1, ciKlass* k2);
1.251 + void assert_exclusive_concrete_methods(ciKlass* ctxk, ciMethod* m1, ciMethod* m2);
1.252 + void assert_has_no_finalizable_subclasses(ciKlass* ctxk);
1.253 +
1.254 + // Define whether a given method or type is concrete.
1.255 + // These methods define the term "concrete" as used in this module.
1.256 + // For this module, an "abstract" class is one which is non-concrete.
1.257 + //
1.258 + // Future optimizations may allow some classes to remain
1.259 + // non-concrete until their first instantiation, and allow some
1.260 + // methods to remain non-concrete until their first invocation.
1.261 + // In that case, there would be a middle ground between concrete
1.262 + // and abstract (as defined by the Java language and VM).
1.263 + static bool is_concrete_klass(klassOop k); // k is instantiable
1.264 + static bool is_concrete_method(methodOop m); // m is invocable
1.265 + static Klass* find_finalizable_subclass(Klass* k);
1.266 +
1.267 + // These versions of the concreteness queries work through the CI.
1.268 + // The CI versions are allowed to skew sometimes from the VM
1.269 + // (oop-based) versions. The cost of such a difference is a
1.270 + // (safely) aborted compilation, or a deoptimization, or a missed
1.271 + // optimization opportunity.
1.272 + //
1.273 + // In order to prevent spurious assertions, query results must
1.274 + // remain stable within any single ciEnv instance. (I.e., they must
1.275 + // not go back into the VM to get their value; they must cache the
1.276 + // bit in the CI, either eagerly or lazily.)
1.277 + static bool is_concrete_klass(ciInstanceKlass* k); // k appears instantiable
1.278 + static bool is_concrete_method(ciMethod* m); // m appears invocable
1.279 + static bool has_finalizable_subclass(ciInstanceKlass* k);
1.280 +
1.281 + // As a general rule, it is OK to compile under the assumption that
1.282 + // a given type or method is concrete, even if it at some future
1.283 + // point becomes abstract. So dependency checking is one-sided, in
1.284 + // that it permits supposedly concrete classes or methods to turn up
1.285 + // as really abstract. (This shouldn't happen, except during class
1.286 + // evolution, but that's the logic of the checking.) However, if a
1.287 + // supposedly abstract class or method suddenly becomes concrete, a
1.288 + // dependency on it must fail.
1.289 +
1.290 + // Checking old assertions at run-time (in the VM only):
1.291 + static klassOop check_evol_method(methodOop m);
1.292 + static klassOop check_leaf_type(klassOop ctxk);
1.293 + static klassOop check_abstract_with_unique_concrete_subtype(klassOop ctxk, klassOop conck,
1.294 + DepChange* changes = NULL);
1.295 + static klassOop check_abstract_with_no_concrete_subtype(klassOop ctxk,
1.296 + DepChange* changes = NULL);
1.297 + static klassOop check_concrete_with_no_concrete_subtype(klassOop ctxk,
1.298 + DepChange* changes = NULL);
1.299 + static klassOop check_unique_concrete_method(klassOop ctxk, methodOop uniqm,
1.300 + DepChange* changes = NULL);
1.301 + static klassOop check_abstract_with_exclusive_concrete_subtypes(klassOop ctxk, klassOop k1, klassOop k2,
1.302 + DepChange* changes = NULL);
1.303 + static klassOop check_exclusive_concrete_methods(klassOop ctxk, methodOop m1, methodOop m2,
1.304 + DepChange* changes = NULL);
1.305 + static klassOop check_has_no_finalizable_subclasses(klassOop ctxk,
1.306 + DepChange* changes = NULL);
1.307 + // A returned klassOop is NULL if the dependency assertion is still
1.308 + // valid. A non-NULL klassOop is a 'witness' to the assertion
1.309 + // failure, a point in the class hierarchy where the assertion has
1.310 + // been proven false. For example, if check_leaf_type returns
1.311 + // non-NULL, the value is a subtype of the supposed leaf type. This
1.312 + // witness value may be useful for logging the dependency failure.
1.313 + // Note that, when a dependency fails, there may be several possible
1.314 + // witnesses to the failure. The value returned from the check_foo
1.315 + // method is chosen arbitrarily.
1.316 +
1.317 + // The 'changes' value, if non-null, requests a limited spot-check
1.318 + // near the indicated recent changes in the class hierarchy.
1.319 + // It is used by DepStream::spot_check_dependency_at.
1.320 +
1.321 + // Detecting possible new assertions:
1.322 + static klassOop find_unique_concrete_subtype(klassOop ctxk);
1.323 + static methodOop find_unique_concrete_method(klassOop ctxk, methodOop m);
1.324 + static int find_exclusive_concrete_subtypes(klassOop ctxk, int klen, klassOop k[]);
1.325 + static int find_exclusive_concrete_methods(klassOop ctxk, int mlen, methodOop m[]);
1.326 +
1.327 + // Create the encoding which will be stored in an nmethod.
1.328 + void encode_content_bytes();
1.329 +
1.330 + address content_bytes() {
1.331 + assert(_content_bytes != NULL, "encode it first");
1.332 + return _content_bytes;
1.333 + }
1.334 + size_t size_in_bytes() {
1.335 + assert(_content_bytes != NULL, "encode it first");
1.336 + return _size_in_bytes;
1.337 + }
1.338 +
1.339 + OopRecorder* oop_recorder() { return _oop_recorder; }
1.340 + CompileLog* log() { return _log; }
1.341 +
1.342 + void copy_to(nmethod* nm);
1.343 +
1.344 + void log_all_dependencies();
1.345 + void log_dependency(DepType dept, int nargs, ciObject* args[]) {
1.346 + write_dependency_to(log(), dept, nargs, args);
1.347 + }
1.348 + void log_dependency(DepType dept,
1.349 + ciObject* x0,
1.350 + ciObject* x1 = NULL,
1.351 + ciObject* x2 = NULL) {
1.352 + if (log() == NULL) return;
1.353 + ciObject* args[max_arg_count];
1.354 + args[0] = x0;
1.355 + args[1] = x1;
1.356 + args[2] = x2;
1.357 + assert(2 < max_arg_count, "");
1.358 + log_dependency(dept, dep_args(dept), args);
1.359 + }
1.360 +
1.361 + static void write_dependency_to(CompileLog* log,
1.362 + DepType dept,
1.363 + int nargs, ciObject* args[],
1.364 + klassOop witness = NULL);
1.365 + static void write_dependency_to(CompileLog* log,
1.366 + DepType dept,
1.367 + int nargs, oop args[],
1.368 + klassOop witness = NULL);
1.369 + static void write_dependency_to(xmlStream* xtty,
1.370 + DepType dept,
1.371 + int nargs, oop args[],
1.372 + klassOop witness = NULL);
1.373 + static void print_dependency(DepType dept,
1.374 + int nargs, oop args[],
1.375 + klassOop witness = NULL);
1.376 +
1.377 + private:
1.378 + // helper for encoding common context types as zero:
1.379 + static ciKlass* ctxk_encoded_as_null(DepType dept, ciObject* x);
1.380 +
1.381 + static klassOop ctxk_encoded_as_null(DepType dept, oop x);
1.382 +
1.383 + public:
1.384 + // Use this to iterate over an nmethod's dependency set.
1.385 + // Works on new and old dependency sets.
1.386 + // Usage:
1.387 + //
1.388 + // ;
1.389 + // Dependencies::DepType dept;
1.390 + // for (Dependencies::DepStream deps(nm); deps.next(); ) {
1.391 + // ...
1.392 + // }
1.393 + //
1.394 + // The caller must be in the VM, since oops are not wrapped in handles.
1.395 + class DepStream {
1.396 + private:
1.397 + nmethod* _code; // null if in a compiler thread
1.398 + Dependencies* _deps; // null if not in a compiler thread
1.399 + CompressedReadStream _bytes;
1.400 +#ifdef ASSERT
1.401 + size_t _byte_limit;
1.402 +#endif
1.403 +
1.404 + // iteration variables:
1.405 + DepType _type;
1.406 + int _xi[max_arg_count+1];
1.407 +
1.408 + void initial_asserts(size_t byte_limit) NOT_DEBUG({});
1.409 +
1.410 + inline oop recorded_oop_at(int i);
1.411 + // => _code? _code->oop_at(i): *_deps->_oop_recorder->handle_at(i)
1.412 +
1.413 + klassOop check_dependency_impl(DepChange* changes);
1.414 +
1.415 + public:
1.416 + DepStream(Dependencies* deps)
1.417 + : _deps(deps),
1.418 + _code(NULL),
1.419 + _bytes(deps->content_bytes())
1.420 + {
1.421 + initial_asserts(deps->size_in_bytes());
1.422 + }
1.423 + DepStream(nmethod* code)
1.424 + : _deps(NULL),
1.425 + _code(code),
1.426 + _bytes(code->dependencies_begin())
1.427 + {
1.428 + initial_asserts(code->dependencies_size());
1.429 + }
1.430 +
1.431 + bool next();
1.432 +
1.433 + DepType type() { return _type; }
1.434 + int argument_count() { return dep_args(type()); }
1.435 + int argument_index(int i) { assert(0 <= i && i < argument_count(), "oob");
1.436 + return _xi[i]; }
1.437 + oop argument(int i); // => recorded_oop_at(argument_index(i))
1.438 + klassOop context_type();
1.439 +
1.440 + methodOop method_argument(int i) {
1.441 + oop x = argument(i);
1.442 + assert(x->is_method(), "type");
1.443 + return (methodOop) x;
1.444 + }
1.445 + klassOop type_argument(int i) {
1.446 + oop x = argument(i);
1.447 + assert(x->is_klass(), "type");
1.448 + return (klassOop) x;
1.449 + }
1.450 +
1.451 + // The point of the whole exercise: Is this dep is still OK?
1.452 + klassOop check_dependency() {
1.453 + return check_dependency_impl(NULL);
1.454 + }
1.455 + // A lighter version: Checks only around recent changes in a class
1.456 + // hierarchy. (See Universe::flush_dependents_on.)
1.457 + klassOop spot_check_dependency_at(DepChange& changes);
1.458 +
1.459 + // Log the current dependency to xtty or compilation log.
1.460 + void log_dependency(klassOop witness = NULL);
1.461 +
1.462 + // Print the current dependency to tty.
1.463 + void print_dependency(klassOop witness = NULL, bool verbose = false);
1.464 + };
1.465 + friend class Dependencies::DepStream;
1.466 +
1.467 + static void print_statistics() PRODUCT_RETURN;
1.468 +};
1.469 +
1.470 +// A class hierarchy change coming through the VM (under the Compile_lock).
1.471 +// The change is structured as a single new type with any number of supers
1.472 +// and implemented interface types. Other than the new type, any of the
1.473 +// super types can be context types for a relevant dependency, which the
1.474 +// new type could invalidate.
1.475 +class DepChange : public StackObj {
1.476 + private:
1.477 + enum ChangeType {
1.478 + NO_CHANGE = 0, // an uninvolved klass
1.479 + Change_new_type, // a newly loaded type
1.480 + Change_new_sub, // a super with a new subtype
1.481 + Change_new_impl, // an interface with a new implementation
1.482 + CHANGE_LIMIT,
1.483 + Start_Klass = CHANGE_LIMIT // internal indicator for ContextStream
1.484 + };
1.485 +
1.486 + // each change set is rooted in exactly one new type (at present):
1.487 + KlassHandle _new_type;
1.488 +
1.489 + void initialize();
1.490 +
1.491 + public:
1.492 + // notes the new type, marks it and all its super-types
1.493 + DepChange(KlassHandle new_type)
1.494 + : _new_type(new_type)
1.495 + {
1.496 + initialize();
1.497 + }
1.498 +
1.499 + // cleans up the marks
1.500 + ~DepChange();
1.501 +
1.502 + klassOop new_type() { return _new_type(); }
1.503 +
1.504 + // involves_context(k) is true if k is new_type or any of the super types
1.505 + bool involves_context(klassOop k);
1.506 +
1.507 + // Usage:
1.508 + // for (DepChange::ContextStream str(changes); str.next(); ) {
1.509 + // klassOop k = str.klass();
1.510 + // switch (str.change_type()) {
1.511 + // ...
1.512 + // }
1.513 + // }
1.514 + class ContextStream : public StackObj {
1.515 + private:
1.516 + DepChange& _changes;
1.517 + friend class DepChange;
1.518 +
1.519 + // iteration variables:
1.520 + ChangeType _change_type;
1.521 + klassOop _klass;
1.522 + objArrayOop _ti_base; // i.e., transitive_interfaces
1.523 + int _ti_index;
1.524 + int _ti_limit;
1.525 +
1.526 + // start at the beginning:
1.527 + void start() {
1.528 + klassOop new_type = _changes.new_type();
1.529 + _change_type = (new_type == NULL ? NO_CHANGE: Start_Klass);
1.530 + _klass = new_type;
1.531 + _ti_base = NULL;
1.532 + _ti_index = 0;
1.533 + _ti_limit = 0;
1.534 + }
1.535 +
1.536 + ContextStream(DepChange& changes)
1.537 + : _changes(changes)
1.538 + { start(); }
1.539 +
1.540 + public:
1.541 + ContextStream(DepChange& changes, No_Safepoint_Verifier& nsv)
1.542 + : _changes(changes)
1.543 + // the nsv argument makes it safe to hold oops like _klass
1.544 + { start(); }
1.545 +
1.546 + bool next();
1.547 +
1.548 + klassOop klass() { return _klass; }
1.549 + };
1.550 + friend class DepChange::ContextStream;
1.551 +
1.552 + void print();
1.553 +};
