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comparison: xpcom/base/CycleCollectedJSRuntime.cpp

xpcom/base/CycleCollectedJSRuntime.cpp

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1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
3 /* This Source Code Form is subject to the terms of the Mozilla Public
4 * License, v. 2.0. If a copy of the MPL was not distributed with this
5 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
6
7 // We're dividing JS objects into 3 categories:
8 //
9 // 1. "real" roots, held by the JS engine itself or rooted through the root
10 // and lock JS APIs. Roots from this category are considered black in the
11 // cycle collector, any cycle they participate in is uncollectable.
12 //
13 // 2. certain roots held by C++ objects that are guaranteed to be alive.
14 // Roots from this category are considered black in the cycle collector,
15 // and any cycle they participate in is uncollectable. These roots are
16 // traced from TraceNativeBlackRoots.
17 //
18 // 3. all other roots held by C++ objects that participate in cycle
19 // collection, held by us (see TraceNativeGrayRoots). Roots from this
20 // category are considered grey in the cycle collector; whether or not
21 // they are collected depends on the objects that hold them.
22 //
23 // Note that if a root is in multiple categories the fact that it is in
24 // category 1 or 2 that takes precedence, so it will be considered black.
25 //
26 // During garbage collection we switch to an additional mark color (gray)
27 // when tracing inside TraceNativeGrayRoots. This allows us to walk those
28 // roots later on and add all objects reachable only from them to the
29 // cycle collector.
30 //
31 // Phases:
32 //
33 // 1. marking of the roots in category 1 by having the JS GC do its marking
34 // 2. marking of the roots in category 2 by having the JS GC call us back
35 // (via JS_SetExtraGCRootsTracer) and running TraceNativeBlackRoots
36 // 3. marking of the roots in category 3 by TraceNativeGrayRoots using an
37 // additional color (gray).
38 // 4. end of GC, GC can sweep its heap
39 //
40 // At some later point, when the cycle collector runs:
41 //
42 // 5. walk gray objects and add them to the cycle collector, cycle collect
43 //
44 // JS objects that are part of cycles the cycle collector breaks will be
45 // collected by the next JS GC.
46 //
47 // If WantAllTraces() is false the cycle collector will not traverse roots
48 // from category 1 or any JS objects held by them. Any JS objects they hold
49 // will already be marked by the JS GC and will thus be colored black
50 // themselves. Any C++ objects they hold will have a missing (untraversed)
51 // edge from the JS object to the C++ object and so it will be marked black
52 // too. This decreases the number of objects that the cycle collector has to
53 // deal with.
54 // To improve debugging, if WantAllTraces() is true all JS objects are
55 // traversed.
56
57 #include "mozilla/CycleCollectedJSRuntime.h"
58 #include <algorithm>
59 #include "mozilla/ArrayUtils.h"
60 #include "mozilla/MemoryReporting.h"
61 #include "mozilla/dom/BindingUtils.h"
62 #include "mozilla/dom/DOMJSClass.h"
63 #include "mozilla/dom/ScriptSettings.h"
64 #include "jsprf.h"
65 #include "nsCycleCollectionNoteRootCallback.h"
66 #include "nsCycleCollectionParticipant.h"
67 #include "nsCycleCollector.h"
68 #include "nsDOMJSUtils.h"
69 #include "nsIException.h"
70 #include "nsThreadUtils.h"
71 #include "xpcpublic.h"
72
73 using namespace mozilla;
74 using namespace mozilla::dom;
75
76 namespace mozilla {
77
78 struct DeferredFinalizeFunctionHolder
79 {
80 DeferredFinalizeFunction run;
81 void *data;
82 };
83
84 class IncrementalFinalizeRunnable : public nsRunnable
85 {
86 typedef nsAutoTArray<DeferredFinalizeFunctionHolder, 16> DeferredFinalizeArray;
87 typedef CycleCollectedJSRuntime::DeferredFinalizerTable DeferredFinalizerTable;
88
89 CycleCollectedJSRuntime* mRuntime;
90 nsTArray<nsISupports*> mSupports;
91 DeferredFinalizeArray mDeferredFinalizeFunctions;
92 uint32_t mFinalizeFunctionToRun;
93
94 static const PRTime SliceMillis = 10; /* ms */
95
96 static PLDHashOperator
97 DeferredFinalizerEnumerator(DeferredFinalizeFunction& aFunction,
98 void*& aData,
99 void* aClosure);
100
101 public:
102 IncrementalFinalizeRunnable(CycleCollectedJSRuntime* aRt,
103 nsTArray<nsISupports*>& mSupports,
104 DeferredFinalizerTable& aFinalizerTable);
105 virtual ~IncrementalFinalizeRunnable();
106
107 void ReleaseNow(bool aLimited);
108
109 NS_DECL_NSIRUNNABLE
110 };
111
112 } // namespace mozilla
113
114 inline bool
115 AddToCCKind(JSGCTraceKind kind)
116 {
117 return kind == JSTRACE_OBJECT || kind == JSTRACE_SCRIPT;
118 }
119
120 static void
121 TraceWeakMappingChild(JSTracer* trc, void** thingp, JSGCTraceKind kind);
122
123 struct NoteWeakMapChildrenTracer : public JSTracer
124 {
125 NoteWeakMapChildrenTracer(JSRuntime *rt, nsCycleCollectionNoteRootCallback& cb)
126 : JSTracer(rt, TraceWeakMappingChild), mCb(cb)
127 {
128 }
129 nsCycleCollectionNoteRootCallback& mCb;
130 bool mTracedAny;
131 JSObject* mMap;
132 void* mKey;
133 void* mKeyDelegate;
134 };
135
136 static void
137 TraceWeakMappingChild(JSTracer* trc, void** thingp, JSGCTraceKind kind)
138 {
139 MOZ_ASSERT(trc->callback == TraceWeakMappingChild);
140 void* thing = *thingp;
141 NoteWeakMapChildrenTracer* tracer =
142 static_cast<NoteWeakMapChildrenTracer*>(trc);
143
144 if (kind == JSTRACE_STRING) {
145 return;
146 }
147
148 if (!xpc_IsGrayGCThing(thing) && !tracer->mCb.WantAllTraces()) {
149 return;
150 }
151
152 if (AddToCCKind(kind)) {
153 tracer->mCb.NoteWeakMapping(tracer->mMap, tracer->mKey, tracer->mKeyDelegate, thing);
154 tracer->mTracedAny = true;
155 } else {
156 JS_TraceChildren(trc, thing, kind);
157 }
158 }
159
160 struct NoteWeakMapsTracer : public js::WeakMapTracer
161 {
162 NoteWeakMapsTracer(JSRuntime* rt, js::WeakMapTraceCallback cb,
163 nsCycleCollectionNoteRootCallback& cccb)
164 : js::WeakMapTracer(rt, cb), mCb(cccb), mChildTracer(rt, cccb)
165 {
166 }
167 nsCycleCollectionNoteRootCallback& mCb;
168 NoteWeakMapChildrenTracer mChildTracer;
169 };
170
171 static void
172 TraceWeakMapping(js::WeakMapTracer* trc, JSObject* m,
173 void* k, JSGCTraceKind kkind,
174 void* v, JSGCTraceKind vkind)
175 {
176 MOZ_ASSERT(trc->callback == TraceWeakMapping);
177 NoteWeakMapsTracer* tracer = static_cast<NoteWeakMapsTracer* >(trc);
178
179 // If nothing that could be held alive by this entry is marked gray, return.
180 if ((!k || !xpc_IsGrayGCThing(k)) && MOZ_LIKELY(!tracer->mCb.WantAllTraces())) {
181 if (!v || !xpc_IsGrayGCThing(v) || vkind == JSTRACE_STRING) {
182 return;
183 }
184 }
185
186 // The cycle collector can only properly reason about weak maps if it can
187 // reason about the liveness of their keys, which in turn requires that
188 // the key can be represented in the cycle collector graph. All existing
189 // uses of weak maps use either objects or scripts as keys, which are okay.
190 MOZ_ASSERT(AddToCCKind(kkind));
191
192 // As an emergency fallback for non-debug builds, if the key is not
193 // representable in the cycle collector graph, we treat it as marked. This
194 // can cause leaks, but is preferable to ignoring the binding, which could
195 // cause the cycle collector to free live objects.
196 if (!AddToCCKind(kkind)) {
197 k = nullptr;
198 }
199
200 JSObject* kdelegate = nullptr;
201 if (k && kkind == JSTRACE_OBJECT) {
202 kdelegate = js::GetWeakmapKeyDelegate((JSObject*)k);
203 }
204
205 if (AddToCCKind(vkind)) {
206 tracer->mCb.NoteWeakMapping(m, k, kdelegate, v);
207 } else {
208 tracer->mChildTracer.mTracedAny = false;
209 tracer->mChildTracer.mMap = m;
210 tracer->mChildTracer.mKey = k;
211 tracer->mChildTracer.mKeyDelegate = kdelegate;
212
213 if (v && vkind != JSTRACE_STRING) {
214 JS_TraceChildren(&tracer->mChildTracer, v, vkind);
215 }
216
217 // The delegate could hold alive the key, so report something to the CC
218 // if we haven't already.
219 if (!tracer->mChildTracer.mTracedAny && k && xpc_IsGrayGCThing(k) && kdelegate) {
220 tracer->mCb.NoteWeakMapping(m, k, kdelegate, nullptr);
221 }
222 }
223 }
224
225 // This is based on the logic in TraceWeakMapping.
226 struct FixWeakMappingGrayBitsTracer : public js::WeakMapTracer
227 {
228 FixWeakMappingGrayBitsTracer(JSRuntime* rt)
229 : js::WeakMapTracer(rt, FixWeakMappingGrayBits)
230 {}
231
232 void
233 FixAll()
234 {
235 do {
236 mAnyMarked = false;
237 js::TraceWeakMaps(this);
238 } while (mAnyMarked);
239 }
240
241 private:
242
243 static void
244 FixWeakMappingGrayBits(js::WeakMapTracer* trc, JSObject* m,
245 void* k, JSGCTraceKind kkind,
246 void* v, JSGCTraceKind vkind)
247 {
248 MOZ_ASSERT(!JS::IsIncrementalGCInProgress(trc->runtime),
249 "Don't call FixWeakMappingGrayBits during a GC.");
250
251 FixWeakMappingGrayBitsTracer* tracer = static_cast<FixWeakMappingGrayBitsTracer*>(trc);
252
253 // If nothing that could be held alive by this entry is marked gray, return.
254 bool delegateMightNeedMarking = k && xpc_IsGrayGCThing(k);
255 bool valueMightNeedMarking = v && xpc_IsGrayGCThing(v) && vkind != JSTRACE_STRING;
256 if (!delegateMightNeedMarking && !valueMightNeedMarking) {
257 return;
258 }
259
260 if (!AddToCCKind(kkind)) {
261 k = nullptr;
262 }
263
264 if (delegateMightNeedMarking && kkind == JSTRACE_OBJECT) {
265 JSObject* kdelegate = js::GetWeakmapKeyDelegate((JSObject*)k);
266 if (kdelegate && !xpc_IsGrayGCThing(kdelegate)) {
267 if (JS::UnmarkGrayGCThingRecursively(k, JSTRACE_OBJECT)) {
268 tracer->mAnyMarked = true;
269 }
270 }
271 }
272
273 if (v && xpc_IsGrayGCThing(v) &&
274 (!k || !xpc_IsGrayGCThing(k)) &&
275 (!m || !xpc_IsGrayGCThing(m)) &&
276 vkind != JSTRACE_SHAPE) {
277 if (JS::UnmarkGrayGCThingRecursively(v, vkind)) {
278 tracer->mAnyMarked = true;
279 }
280 }
281 }
282
283 bool mAnyMarked;
284 };
285
286 struct Closure
287 {
288 Closure(nsCycleCollectionNoteRootCallback* aCb)
289 : mCycleCollectionEnabled(true), mCb(aCb)
290 {
291 }
292
293 bool mCycleCollectionEnabled;
294 nsCycleCollectionNoteRootCallback* mCb;
295 };
296
297 static void
298 CheckParticipatesInCycleCollection(void* aThing, const char* aName, void* aClosure)
299 {
300 Closure* closure = static_cast<Closure*>(aClosure);
301
302 if (closure->mCycleCollectionEnabled) {
303 return;
304 }
305
306 if (AddToCCKind(js::GCThingTraceKind(aThing)) &&
307 xpc_IsGrayGCThing(aThing))
308 {
309 closure->mCycleCollectionEnabled = true;
310 }
311 }
312
313 static PLDHashOperator
314 NoteJSHolder(void *holder, nsScriptObjectTracer *&tracer, void *arg)
315 {
316 Closure *closure = static_cast<Closure*>(arg);
317
318 bool noteRoot;
319 if (MOZ_UNLIKELY(closure->mCb->WantAllTraces())) {
320 noteRoot = true;
321 } else {
322 closure->mCycleCollectionEnabled = false;
323 tracer->Trace(holder, TraceCallbackFunc(CheckParticipatesInCycleCollection), closure);
324 noteRoot = closure->mCycleCollectionEnabled;
325 }
326
327 if (noteRoot) {
328 closure->mCb->NoteNativeRoot(holder, tracer);
329 }
330
331 return PL_DHASH_NEXT;
332 }
333
334 NS_IMETHODIMP
335 JSGCThingParticipant::Traverse(void* p, nsCycleCollectionTraversalCallback& cb)
336 {
337 CycleCollectedJSRuntime* runtime = reinterpret_cast<CycleCollectedJSRuntime*>
338 (reinterpret_cast<char*>(this) -
339 offsetof(CycleCollectedJSRuntime, mGCThingCycleCollectorGlobal));
340
341 runtime->TraverseGCThing(CycleCollectedJSRuntime::TRAVERSE_FULL,
342 p, js::GCThingTraceKind(p), cb);
343 return NS_OK;
344 }
345
346 // NB: This is only used to initialize the participant in
347 // CycleCollectedJSRuntime. It should never be used directly.
348 static JSGCThingParticipant sGCThingCycleCollectorGlobal;
349
350 NS_IMETHODIMP
351 JSZoneParticipant::Traverse(void* p, nsCycleCollectionTraversalCallback& cb)
352 {
353 CycleCollectedJSRuntime* runtime = reinterpret_cast<CycleCollectedJSRuntime*>
354 (reinterpret_cast<char*>(this) -
355 offsetof(CycleCollectedJSRuntime, mJSZoneCycleCollectorGlobal));
356
357 MOZ_ASSERT(!cb.WantAllTraces());
358 JS::Zone* zone = static_cast<JS::Zone*>(p);
359
360 runtime->TraverseZone(zone, cb);
361 return NS_OK;
362 }
363
364 static void
365 NoteJSChildTracerShim(JSTracer* aTrc, void** aThingp, JSGCTraceKind aTraceKind);
366
367 struct TraversalTracer : public JSTracer
368 {
369 TraversalTracer(JSRuntime *rt, nsCycleCollectionTraversalCallback& aCb)
370 : JSTracer(rt, NoteJSChildTracerShim, DoNotTraceWeakMaps), mCb(aCb)
371 {
372 }
373 nsCycleCollectionTraversalCallback& mCb;
374 };
375
376 static void
377 NoteJSChild(JSTracer* aTrc, void* aThing, JSGCTraceKind aTraceKind)
378 {
379 TraversalTracer* tracer = static_cast<TraversalTracer*>(aTrc);
380
381 // Don't traverse non-gray objects, unless we want all traces.
382 if (!xpc_IsGrayGCThing(aThing) && !tracer->mCb.WantAllTraces()) {
383 return;
384 }
385
386 /*
387 * This function needs to be careful to avoid stack overflow. Normally, when
388 * AddToCCKind is true, the recursion terminates immediately as we just add
389 * |thing| to the CC graph. So overflow is only possible when there are long
390 * chains of non-AddToCCKind GC things. Currently, this only can happen via
391 * shape parent pointers. The special JSTRACE_SHAPE case below handles
392 * parent pointers iteratively, rather than recursively, to avoid overflow.
393 */
394 if (AddToCCKind(aTraceKind)) {
395 if (MOZ_UNLIKELY(tracer->mCb.WantDebugInfo())) {
396 // based on DumpNotify in jsapi.cpp
397 if (tracer->debugPrinter()) {
398 char buffer[200];
399 tracer->debugPrinter()(aTrc, buffer, sizeof(buffer));
400 tracer->mCb.NoteNextEdgeName(buffer);
401 } else if (tracer->debugPrintIndex() != (size_t)-1) {
402 char buffer[200];
403 JS_snprintf(buffer, sizeof(buffer), "%s[%lu]",
404 static_cast<const char *>(tracer->debugPrintArg()),
405 tracer->debugPrintIndex());
406 tracer->mCb.NoteNextEdgeName(buffer);
407 } else {
408 tracer->mCb.NoteNextEdgeName(static_cast<const char*>(tracer->debugPrintArg()));
409 }
410 }
411 tracer->mCb.NoteJSChild(aThing);
412 } else if (aTraceKind == JSTRACE_SHAPE) {
413 JS_TraceShapeCycleCollectorChildren(aTrc, aThing);
414 } else if (aTraceKind != JSTRACE_STRING) {
415 JS_TraceChildren(aTrc, aThing, aTraceKind);
416 }
417 }
418
419 static void
420 NoteJSChildTracerShim(JSTracer* aTrc, void** aThingp, JSGCTraceKind aTraceKind)
421 {
422 NoteJSChild(aTrc, *aThingp, aTraceKind);
423 }
424
425 static void
426 NoteJSChildGrayWrapperShim(void* aData, void* aThing)
427 {
428 TraversalTracer* trc = static_cast<TraversalTracer*>(aData);
429 NoteJSChild(trc, aThing, js::GCThingTraceKind(aThing));
430 }
431
432 /*
433 * The cycle collection participant for a Zone is intended to produce the same
434 * results as if all of the gray GCthings in a zone were merged into a single node,
435 * except for self-edges. This avoids the overhead of representing all of the GCthings in
436 * the zone in the cycle collector graph, which should be much faster if many of
437 * the GCthings in the zone are gray.
438 *
439 * Zone merging should not always be used, because it is a conservative
440 * approximation of the true cycle collector graph that can incorrectly identify some
441 * garbage objects as being live. For instance, consider two cycles that pass through a
442 * zone, where one is garbage and the other is live. If we merge the entire
443 * zone, the cycle collector will think that both are alive.
444 *
445 * We don't have to worry about losing track of a garbage cycle, because any such garbage
446 * cycle incorrectly identified as live must contain at least one C++ to JS edge, and
447 * XPConnect will always add the C++ object to the CC graph. (This is in contrast to pure
448 * C++ garbage cycles, which must always be properly identified, because we clear the
449 * purple buffer during every CC, which may contain the last reference to a garbage
450 * cycle.)
451 */
452
453 // NB: This is only used to initialize the participant in
454 // CycleCollectedJSRuntime. It should never be used directly.
455 static const JSZoneParticipant sJSZoneCycleCollectorGlobal;
456
457 CycleCollectedJSRuntime::CycleCollectedJSRuntime(JSRuntime* aParentRuntime,
458 uint32_t aMaxbytes,
459 JSUseHelperThreads aUseHelperThreads)
460 : mGCThingCycleCollectorGlobal(sGCThingCycleCollectorGlobal),
461 mJSZoneCycleCollectorGlobal(sJSZoneCycleCollectorGlobal),
462 mJSRuntime(nullptr),
463 mJSHolders(512)
464 {
465 mozilla::dom::InitScriptSettings();
466
467 mJSRuntime = JS_NewRuntime(aMaxbytes, aUseHelperThreads, aParentRuntime);
468 if (!mJSRuntime) {
469 MOZ_CRASH();
470 }
471
472 if (!JS_AddExtraGCRootsTracer(mJSRuntime, TraceBlackJS, this)) {
473 MOZ_CRASH();
474 }
475 JS_SetGrayGCRootsTracer(mJSRuntime, TraceGrayJS, this);
476 JS_SetGCCallback(mJSRuntime, GCCallback, this);
477 JS_SetContextCallback(mJSRuntime, ContextCallback, this);
478 JS_SetDestroyZoneCallback(mJSRuntime, XPCStringConvert::FreeZoneCache);
479 JS_SetSweepZoneCallback(mJSRuntime, XPCStringConvert::ClearZoneCache);
480
481 nsCycleCollector_registerJSRuntime(this);
482 }
483
484 CycleCollectedJSRuntime::~CycleCollectedJSRuntime()
485 {
486 MOZ_ASSERT(mJSRuntime);
487 MOZ_ASSERT(!mDeferredFinalizerTable.Count());
488 MOZ_ASSERT(!mDeferredSupports.Length());
489
490 // Clear mPendingException first, since it might be cycle collected.
491 mPendingException = nullptr;
492
493 JS_DestroyRuntime(mJSRuntime);
494 mJSRuntime = nullptr;
495 nsCycleCollector_forgetJSRuntime();
496
497 mozilla::dom::DestroyScriptSettings();
498 }
499
500 size_t
501 CycleCollectedJSRuntime::SizeOfExcludingThis(MallocSizeOf aMallocSizeOf) const
502 {
503 size_t n = 0;
504
505 // nullptr for the second arg; we're not measuring anything hanging off the
506 // entries in mJSHolders.
507 n += mJSHolders.SizeOfExcludingThis(nullptr, aMallocSizeOf);
508
509 return n;
510 }
511
512 static PLDHashOperator
513 UnmarkJSHolder(void* holder, nsScriptObjectTracer*& tracer, void* arg)
514 {
515 tracer->CanSkip(holder, true);
516 return PL_DHASH_NEXT;
517 }
518
519 void
520 CycleCollectedJSRuntime::UnmarkSkippableJSHolders()
521 {
522 mJSHolders.Enumerate(UnmarkJSHolder, nullptr);
523 }
524
525 void
526 CycleCollectedJSRuntime::DescribeGCThing(bool aIsMarked, void* aThing,
527 JSGCTraceKind aTraceKind,
528 nsCycleCollectionTraversalCallback& aCb) const
529 {
530 if (!aCb.WantDebugInfo()) {
531 aCb.DescribeGCedNode(aIsMarked, "JS Object");
532 return;
533 }
534
535 char name[72];
536 uint64_t compartmentAddress = 0;
537 if (aTraceKind == JSTRACE_OBJECT) {
538 JSObject* obj = static_cast<JSObject*>(aThing);
539 compartmentAddress = (uint64_t)js::GetObjectCompartment(obj);
540 const js::Class* clasp = js::GetObjectClass(obj);
541
542 // Give the subclass a chance to do something
543 if (DescribeCustomObjects(obj, clasp, name)) {
544 // Nothing else to do!
545 } else if (js::IsFunctionObject(obj)) {
546 JSFunction* fun = JS_GetObjectFunction(obj);
547 JSString* str = JS_GetFunctionDisplayId(fun);
548 if (str) {
549 NS_ConvertUTF16toUTF8 fname(JS_GetInternedStringChars(str));
550 JS_snprintf(name, sizeof(name),
551 "JS Object (Function - %s)", fname.get());
552 } else {
553 JS_snprintf(name, sizeof(name), "JS Object (Function)");
554 }
555 } else {
556 JS_snprintf(name, sizeof(name), "JS Object (%s)",
557 clasp->name);
558 }
559 } else {
560 static const char trace_types[][11] = {
561 "Object",
562 "String",
563 "Script",
564 "LazyScript",
565 "IonCode",
566 "Shape",
567 "BaseShape",
568 "TypeObject",
569 };
570 static_assert(MOZ_ARRAY_LENGTH(trace_types) == JSTRACE_LAST + 1,
571 "JSTRACE_LAST enum must match trace_types count.");
572 JS_snprintf(name, sizeof(name), "JS %s", trace_types[aTraceKind]);
573 }
574
575 // Disable printing global for objects while we figure out ObjShrink fallout.
576 aCb.DescribeGCedNode(aIsMarked, name, compartmentAddress);
577 }
578
579 void
580 CycleCollectedJSRuntime::NoteGCThingJSChildren(void* aThing,
581 JSGCTraceKind aTraceKind,
582 nsCycleCollectionTraversalCallback& aCb) const
583 {
584 MOZ_ASSERT(mJSRuntime);
585 TraversalTracer trc(mJSRuntime, aCb);
586 JS_TraceChildren(&trc, aThing, aTraceKind);
587 }
588
589 void
590 CycleCollectedJSRuntime::NoteGCThingXPCOMChildren(const js::Class* aClasp, JSObject* aObj,
591 nsCycleCollectionTraversalCallback& aCb) const
592 {
593 MOZ_ASSERT(aClasp);
594 MOZ_ASSERT(aClasp == js::GetObjectClass(aObj));
595
596 if (NoteCustomGCThingXPCOMChildren(aClasp, aObj, aCb)) {
597 // Nothing else to do!
598 return;
599 }
600 // XXX This test does seem fragile, we should probably whitelist classes
601 // that do hold a strong reference, but that might not be possible.
602 else if (aClasp->flags & JSCLASS_HAS_PRIVATE &&
603 aClasp->flags & JSCLASS_PRIVATE_IS_NSISUPPORTS) {
604 NS_CYCLE_COLLECTION_NOTE_EDGE_NAME(aCb, "js::GetObjectPrivate(obj)");
605 aCb.NoteXPCOMChild(static_cast<nsISupports*>(js::GetObjectPrivate(aObj)));
606 } else {
607 const DOMClass* domClass = GetDOMClass(aObj);
608 if (domClass) {
609 NS_CYCLE_COLLECTION_NOTE_EDGE_NAME(aCb, "UnwrapDOMObject(obj)");
610 if (domClass->mDOMObjectIsISupports) {
611 aCb.NoteXPCOMChild(UnwrapDOMObject<nsISupports>(aObj));
612 } else if (domClass->mParticipant) {
613 aCb.NoteNativeChild(UnwrapDOMObject<void>(aObj),
614 domClass->mParticipant);
615 }
616 }
617 }
618 }
619
620 void
621 CycleCollectedJSRuntime::TraverseGCThing(TraverseSelect aTs, void* aThing,
622 JSGCTraceKind aTraceKind,
623 nsCycleCollectionTraversalCallback& aCb)
624 {
625 MOZ_ASSERT(aTraceKind == js::GCThingTraceKind(aThing));
626 bool isMarkedGray = xpc_IsGrayGCThing(aThing);
627
628 if (aTs == TRAVERSE_FULL) {
629 DescribeGCThing(!isMarkedGray, aThing, aTraceKind, aCb);
630 }
631
632 // If this object is alive, then all of its children are alive. For JS objects,
633 // the black-gray invariant ensures the children are also marked black. For C++
634 // objects, the ref count from this object will keep them alive. Thus we don't
635 // need to trace our children, unless we are debugging using WantAllTraces.
636 if (!isMarkedGray && !aCb.WantAllTraces()) {
637 return;
638 }
639
640 if (aTs == TRAVERSE_FULL) {
641 NoteGCThingJSChildren(aThing, aTraceKind, aCb);
642 }
643
644 if (aTraceKind == JSTRACE_OBJECT) {
645 JSObject* obj = static_cast<JSObject*>(aThing);
646 NoteGCThingXPCOMChildren(js::GetObjectClass(obj), obj, aCb);
647 }
648 }
649
650 struct TraverseObjectShimClosure {
651 nsCycleCollectionTraversalCallback& cb;
652 CycleCollectedJSRuntime* self;
653 };
654
655 void
656 CycleCollectedJSRuntime::TraverseZone(JS::Zone* aZone,
657 nsCycleCollectionTraversalCallback& aCb)
658 {
659 /*
660 * We treat the zone as being gray. We handle non-gray GCthings in the
661 * zone by not reporting their children to the CC. The black-gray invariant
662 * ensures that any JS children will also be non-gray, and thus don't need to be
663 * added to the graph. For C++ children, not representing the edge from the
664 * non-gray JS GCthings to the C++ object will keep the child alive.
665 *
666 * We don't allow zone merging in a WantAllTraces CC, because then these
667 * assumptions don't hold.
668 */
669 aCb.DescribeGCedNode(false, "JS Zone");
670
671 /*
672 * Every JS child of everything in the zone is either in the zone
673 * or is a cross-compartment wrapper. In the former case, we don't need to
674 * represent these edges in the CC graph because JS objects are not ref counted.
675 * In the latter case, the JS engine keeps a map of these wrappers, which we
676 * iterate over. Edges between compartments in the same zone will add
677 * unnecessary loop edges to the graph (bug 842137).
678 */
679 TraversalTracer trc(mJSRuntime, aCb);
680 js::VisitGrayWrapperTargets(aZone, NoteJSChildGrayWrapperShim, &trc);
681
682 /*
683 * To find C++ children of things in the zone, we scan every JS Object in
684 * the zone. Only JS Objects can have C++ children.
685 */
686 TraverseObjectShimClosure closure = { aCb, this };
687 js::IterateGrayObjects(aZone, TraverseObjectShim, &closure);
688 }
689
690 /* static */ void
691 CycleCollectedJSRuntime::TraverseObjectShim(void* aData, void* aThing)
692 {
693 TraverseObjectShimClosure* closure =
694 static_cast<TraverseObjectShimClosure*>(aData);
695
696 MOZ_ASSERT(js::GCThingTraceKind(aThing) == JSTRACE_OBJECT);
697 closure->self->TraverseGCThing(CycleCollectedJSRuntime::TRAVERSE_CPP, aThing,
698 JSTRACE_OBJECT, closure->cb);
699 }
700
701 void
702 CycleCollectedJSRuntime::TraverseNativeRoots(nsCycleCollectionNoteRootCallback& aCb)
703 {
704 // NB: This is here just to preserve the existing XPConnect order. I doubt it
705 // would hurt to do this after the JS holders.
706 TraverseAdditionalNativeRoots(aCb);
707
708 Closure closure(&aCb);
709 mJSHolders.Enumerate(NoteJSHolder, &closure);
710 }
711
712 /* static */ void
713 CycleCollectedJSRuntime::TraceBlackJS(JSTracer* aTracer, void* aData)
714 {
715 CycleCollectedJSRuntime* self = static_cast<CycleCollectedJSRuntime*>(aData);
716
717 self->TraceNativeBlackRoots(aTracer);
718 }
719
720 /* static */ void
721 CycleCollectedJSRuntime::TraceGrayJS(JSTracer* aTracer, void* aData)
722 {
723 CycleCollectedJSRuntime* self = static_cast<CycleCollectedJSRuntime*>(aData);
724
725 // Mark these roots as gray so the CC can walk them later.
726 self->TraceNativeGrayRoots(aTracer);
727 }
728
729 /* static */ void
730 CycleCollectedJSRuntime::GCCallback(JSRuntime* aRuntime,
731 JSGCStatus aStatus,
732 void* aData)
733 {
734 CycleCollectedJSRuntime* self = static_cast<CycleCollectedJSRuntime*>(aData);
735
736 MOZ_ASSERT(aRuntime == self->Runtime());
737
738 self->OnGC(aStatus);
739 }
740
741 /* static */ bool
742 CycleCollectedJSRuntime::ContextCallback(JSContext* aContext,
743 unsigned aOperation,
744 void* aData)
745 {
746 CycleCollectedJSRuntime* self = static_cast<CycleCollectedJSRuntime*>(aData);
747
748 MOZ_ASSERT(JS_GetRuntime(aContext) == self->Runtime());
749
750 return self->CustomContextCallback(aContext, aOperation);
751 }
752
753 struct JsGcTracer : public TraceCallbacks
754 {
755 virtual void Trace(JS::Heap<JS::Value> *p, const char *name, void *closure) const MOZ_OVERRIDE {
756 JS_CallHeapValueTracer(static_cast<JSTracer*>(closure), p, name);
757 }
758 virtual void Trace(JS::Heap<jsid> *p, const char *name, void *closure) const MOZ_OVERRIDE {
759 JS_CallHeapIdTracer(static_cast<JSTracer*>(closure), p, name);
760 }
761 virtual void Trace(JS::Heap<JSObject *> *p, const char *name, void *closure) const MOZ_OVERRIDE {
762 JS_CallHeapObjectTracer(static_cast<JSTracer*>(closure), p, name);
763 }
764 virtual void Trace(JS::TenuredHeap<JSObject *> *p, const char *name, void *closure) const MOZ_OVERRIDE {
765 JS_CallTenuredObjectTracer(static_cast<JSTracer*>(closure), p, name);
766 }
767 virtual void Trace(JS::Heap<JSString *> *p, const char *name, void *closure) const MOZ_OVERRIDE {
768 JS_CallHeapStringTracer(static_cast<JSTracer*>(closure), p, name);
769 }
770 virtual void Trace(JS::Heap<JSScript *> *p, const char *name, void *closure) const MOZ_OVERRIDE {
771 JS_CallHeapScriptTracer(static_cast<JSTracer*>(closure), p, name);
772 }
773 virtual void Trace(JS::Heap<JSFunction *> *p, const char *name, void *closure) const MOZ_OVERRIDE {
774 JS_CallHeapFunctionTracer(static_cast<JSTracer*>(closure), p, name);
775 }
776 };
777
778 static PLDHashOperator
779 TraceJSHolder(void* aHolder, nsScriptObjectTracer*& aTracer, void* aArg)
780 {
781 aTracer->Trace(aHolder, JsGcTracer(), aArg);
782
783 return PL_DHASH_NEXT;
784 }
785
786 void
787 CycleCollectedJSRuntime::TraceNativeGrayRoots(JSTracer* aTracer)
788 {
789 // NB: This is here just to preserve the existing XPConnect order. I doubt it
790 // would hurt to do this after the JS holders.
791 TraceAdditionalNativeGrayRoots(aTracer);
792
793 mJSHolders.Enumerate(TraceJSHolder, aTracer);
794 }
795
796 void
797 CycleCollectedJSRuntime::AddJSHolder(void* aHolder, nsScriptObjectTracer* aTracer)
798 {
799 mJSHolders.Put(aHolder, aTracer);
800 }
801
802 struct ClearJSHolder : TraceCallbacks
803 {
804 virtual void Trace(JS::Heap<JS::Value>* aPtr, const char*, void*) const MOZ_OVERRIDE
805 {
806 *aPtr = JSVAL_VOID;
807 }
808
809 virtual void Trace(JS::Heap<jsid>* aPtr, const char*, void*) const MOZ_OVERRIDE
810 {
811 *aPtr = JSID_VOID;
812 }
813
814 virtual void Trace(JS::Heap<JSObject*>* aPtr, const char*, void*) const MOZ_OVERRIDE
815 {
816 *aPtr = nullptr;
817 }
818
819 virtual void Trace(JS::TenuredHeap<JSObject*>* aPtr, const char*, void*) const MOZ_OVERRIDE
820 {
821 *aPtr = nullptr;
822 }
823
824 virtual void Trace(JS::Heap<JSString*>* aPtr, const char*, void*) const MOZ_OVERRIDE
825 {
826 *aPtr = nullptr;
827 }
828
829 virtual void Trace(JS::Heap<JSScript*>* aPtr, const char*, void*) const MOZ_OVERRIDE
830 {
831 *aPtr = nullptr;
832 }
833
834 virtual void Trace(JS::Heap<JSFunction*>* aPtr, const char*, void*) const MOZ_OVERRIDE
835 {
836 *aPtr = nullptr;
837 }
838 };
839
840 void
841 CycleCollectedJSRuntime::RemoveJSHolder(void* aHolder)
842 {
843 nsScriptObjectTracer* tracer = mJSHolders.Get(aHolder);
844 if (!tracer) {
845 return;
846 }
847 tracer->Trace(aHolder, ClearJSHolder(), nullptr);
848 mJSHolders.Remove(aHolder);
849 }
850
851 #ifdef DEBUG
852 bool
853 CycleCollectedJSRuntime::IsJSHolder(void* aHolder)
854 {
855 return mJSHolders.Get(aHolder, nullptr);
856 }
857
858 static void
859 AssertNoGcThing(void* aGCThing, const char* aName, void* aClosure)
860 {
861 MOZ_ASSERT(!aGCThing);
862 }
863
864 void
865 CycleCollectedJSRuntime::AssertNoObjectsToTrace(void* aPossibleJSHolder)
866 {
867 nsScriptObjectTracer* tracer = mJSHolders.Get(aPossibleJSHolder);
868 if (tracer) {
869 tracer->Trace(aPossibleJSHolder, TraceCallbackFunc(AssertNoGcThing), nullptr);
870 }
871 }
872 #endif
873
874 already_AddRefed<nsIException>
875 CycleCollectedJSRuntime::GetPendingException() const
876 {
877 nsCOMPtr<nsIException> out = mPendingException;
878 return out.forget();
879 }
880
881 void
882 CycleCollectedJSRuntime::SetPendingException(nsIException* aException)
883 {
884 mPendingException = aException;
885 }
886
887 nsCycleCollectionParticipant*
888 CycleCollectedJSRuntime::GCThingParticipant()
889 {
890 return &mGCThingCycleCollectorGlobal;
891 }
892
893 nsCycleCollectionParticipant*
894 CycleCollectedJSRuntime::ZoneParticipant()
895 {
896 return &mJSZoneCycleCollectorGlobal;
897 }
898
899 nsresult
900 CycleCollectedJSRuntime::TraverseRoots(nsCycleCollectionNoteRootCallback &aCb)
901 {
902 TraverseNativeRoots(aCb);
903
904 NoteWeakMapsTracer trc(mJSRuntime, TraceWeakMapping, aCb);
905 js::TraceWeakMaps(&trc);
906
907 return NS_OK;
908 }
909
910 /*
911 * Return true if there exists a JSContext with a default global whose current
912 * inner is gray. The intent is to look for JS Object windows. We don't merge
913 * system compartments, so we don't use them to trigger merging CCs.
914 */
915 bool
916 CycleCollectedJSRuntime::UsefulToMergeZones() const
917 {
918 if (!NS_IsMainThread()) {
919 return false;
920 }
921
922 JSContext* iter = nullptr;
923 JSContext* cx;
924 JSAutoRequest ar(nsContentUtils::GetSafeJSContext());
925 while ((cx = JS_ContextIterator(mJSRuntime, &iter))) {
926 // Skip anything without an nsIScriptContext.
927 nsIScriptContext* scx = GetScriptContextFromJSContext(cx);
928 JS::RootedObject obj(cx, scx ? scx->GetWindowProxyPreserveColor() : nullptr);
929 if (!obj) {
930 continue;
931 }
932 MOZ_ASSERT(js::IsOuterObject(obj));
933 // Grab the inner from the outer.
934 obj = JS_ObjectToInnerObject(cx, obj);
935 MOZ_ASSERT(!js::GetObjectParent(obj));
936 if (JS::GCThingIsMarkedGray(obj) &&
937 !js::IsSystemCompartment(js::GetObjectCompartment(obj))) {
938 return true;
939 }
940 }
941 return false;
942 }
943
944 void
945 CycleCollectedJSRuntime::FixWeakMappingGrayBits() const
946 {
947 FixWeakMappingGrayBitsTracer fixer(mJSRuntime);
948 fixer.FixAll();
949 }
950
951 bool
952 CycleCollectedJSRuntime::NeedCollect() const
953 {
954 return !js::AreGCGrayBitsValid(mJSRuntime);
955 }
956
957 void
958 CycleCollectedJSRuntime::Collect(uint32_t aReason) const
959 {
960 MOZ_ASSERT(aReason < JS::gcreason::NUM_REASONS);
961 JS::gcreason::Reason gcreason = static_cast<JS::gcreason::Reason>(aReason);
962
963 JS::PrepareForFullGC(mJSRuntime);
964 JS::GCForReason(mJSRuntime, gcreason);
965 }
966
967 void
968 CycleCollectedJSRuntime::DeferredFinalize(DeferredFinalizeAppendFunction aAppendFunc,
969 DeferredFinalizeFunction aFunc,
970 void* aThing)
971 {
972 void* thingArray = nullptr;
973 bool hadThingArray = mDeferredFinalizerTable.Get(aFunc, &thingArray);
974
975 thingArray = aAppendFunc(thingArray, aThing);
976 if (!hadThingArray) {
977 mDeferredFinalizerTable.Put(aFunc, thingArray);
978 }
979 }
980
981 void
982 CycleCollectedJSRuntime::DeferredFinalize(nsISupports* aSupports)
983 {
984 mDeferredSupports.AppendElement(aSupports);
985 }
986
987 void
988 CycleCollectedJSRuntime::DumpJSHeap(FILE* file)
989 {
990 js::DumpHeapComplete(Runtime(), file, js::CollectNurseryBeforeDump);
991 }
992
993
994 bool
995 ReleaseSliceNow(uint32_t aSlice, void* aData)
996 {
997 MOZ_ASSERT(aSlice > 0, "nonsensical/useless call with slice == 0");
998 nsTArray<nsISupports*>* items = static_cast<nsTArray<nsISupports*>*>(aData);
999
1000 uint32_t length = items->Length();
1001 aSlice = std::min(aSlice, length);
1002 for (uint32_t i = length; i > length - aSlice; --i) {
1003 // Remove (and NS_RELEASE) the last entry in "items":
1004 uint32_t lastItemIdx = i - 1;
1005
1006 nsISupports* wrapper = items->ElementAt(lastItemIdx);
1007 items->RemoveElementAt(lastItemIdx);
1008 NS_IF_RELEASE(wrapper);
1009 }
1010
1011 return items->IsEmpty();
1012 }
1013
1014 /* static */ PLDHashOperator
1015 IncrementalFinalizeRunnable::DeferredFinalizerEnumerator(DeferredFinalizeFunction& aFunction,
1016 void*& aData,
1017 void* aClosure)
1018 {
1019 DeferredFinalizeArray* array = static_cast<DeferredFinalizeArray*>(aClosure);
1020
1021 DeferredFinalizeFunctionHolder* function = array->AppendElement();
1022 function->run = aFunction;
1023 function->data = aData;
1024
1025 return PL_DHASH_REMOVE;
1026 }
1027
1028 IncrementalFinalizeRunnable::IncrementalFinalizeRunnable(CycleCollectedJSRuntime* aRt,
1029 nsTArray<nsISupports*>& aSupports,
1030 DeferredFinalizerTable& aFinalizers)
1031 : mRuntime(aRt),
1032 mFinalizeFunctionToRun(0)
1033 {
1034 this->mSupports.SwapElements(aSupports);
1035 DeferredFinalizeFunctionHolder* function = mDeferredFinalizeFunctions.AppendElement();
1036 function->run = ReleaseSliceNow;
1037 function->data = &this->mSupports;
1038
1039 // Enumerate the hashtable into our array.
1040 aFinalizers.Enumerate(DeferredFinalizerEnumerator, &mDeferredFinalizeFunctions);
1041 }
1042
1043 IncrementalFinalizeRunnable::~IncrementalFinalizeRunnable()
1044 {
1045 MOZ_ASSERT(this != mRuntime->mFinalizeRunnable);
1046 }
1047
1048 void
1049 IncrementalFinalizeRunnable::ReleaseNow(bool aLimited)
1050 {
1051 //MOZ_ASSERT(NS_IsMainThread());
1052 MOZ_ASSERT(mDeferredFinalizeFunctions.Length() != 0,
1053 "We should have at least ReleaseSliceNow to run");
1054 MOZ_ASSERT(mFinalizeFunctionToRun < mDeferredFinalizeFunctions.Length(),
1055 "No more finalizers to run?");
1056
1057 TimeDuration sliceTime = TimeDuration::FromMilliseconds(SliceMillis);
1058 TimeStamp started = TimeStamp::Now();
1059 bool timeout = false;
1060 do {
1061 const DeferredFinalizeFunctionHolder &function =
1062 mDeferredFinalizeFunctions[mFinalizeFunctionToRun];
1063 if (aLimited) {
1064 bool done = false;
1065 while (!timeout && !done) {
1066 /*
1067 * We don't want to read the clock too often, so we try to
1068 * release slices of 100 items.
1069 */
1070 done = function.run(100, function.data);
1071 timeout = TimeStamp::Now() - started >= sliceTime;
1072 }
1073 if (done) {
1074 ++mFinalizeFunctionToRun;
1075 }
1076 if (timeout) {
1077 break;
1078 }
1079 } else {
1080 function.run(UINT32_MAX, function.data);
1081 ++mFinalizeFunctionToRun;
1082 }
1083 } while (mFinalizeFunctionToRun < mDeferredFinalizeFunctions.Length());
1084
1085 if (mFinalizeFunctionToRun == mDeferredFinalizeFunctions.Length()) {
1086 MOZ_ASSERT(mRuntime->mFinalizeRunnable == this);
1087 mDeferredFinalizeFunctions.Clear();
1088 // NB: This may delete this!
1089 mRuntime->mFinalizeRunnable = nullptr;
1090 }
1091 }
1092
1093 NS_IMETHODIMP
1094 IncrementalFinalizeRunnable::Run()
1095 {
1096 if (mRuntime->mFinalizeRunnable != this) {
1097 /* These items were already processed synchronously in JSGC_END. */
1098 MOZ_ASSERT(!mSupports.Length());
1099 MOZ_ASSERT(!mDeferredFinalizeFunctions.Length());
1100 return NS_OK;
1101 }
1102
1103 ReleaseNow(true);
1104
1105 if (mDeferredFinalizeFunctions.Length()) {
1106 nsresult rv = NS_DispatchToCurrentThread(this);
1107 if (NS_FAILED(rv)) {
1108 ReleaseNow(false);
1109 }
1110 }
1111
1112 return NS_OK;
1113 }
1114
1115 void
1116 CycleCollectedJSRuntime::FinalizeDeferredThings(DeferredFinalizeType aType)
1117 {
1118 MOZ_ASSERT(!mFinalizeRunnable);
1119 mFinalizeRunnable = new IncrementalFinalizeRunnable(this,
1120 mDeferredSupports,
1121 mDeferredFinalizerTable);
1122
1123 // Everything should be gone now.
1124 MOZ_ASSERT(!mDeferredSupports.Length());
1125 MOZ_ASSERT(!mDeferredFinalizerTable.Count());
1126
1127 if (aType == FinalizeIncrementally) {
1128 NS_DispatchToCurrentThread(mFinalizeRunnable);
1129 } else {
1130 mFinalizeRunnable->ReleaseNow(false);
1131 MOZ_ASSERT(!mFinalizeRunnable);
1132 }
1133 }
1134
1135 void
1136 CycleCollectedJSRuntime::OnGC(JSGCStatus aStatus)
1137 {
1138 switch (aStatus) {
1139 case JSGC_BEGIN:
1140 nsCycleCollector_prepareForGarbageCollection();
1141 break;
1142 case JSGC_END:
1143 {
1144 /*
1145 * If the previous GC created a runnable to finalize objects
1146 * incrementally, and if it hasn't finished yet, finish it now. We
1147 * don't want these to build up. We also don't want to allow any
1148 * existing incremental finalize runnables to run after a
1149 * non-incremental GC, since they are often used to detect leaks.
1150 */
1151 if (mFinalizeRunnable) {
1152 mFinalizeRunnable->ReleaseNow(false);
1153 }
1154
1155 // Do any deferred finalization of native objects.
1156 FinalizeDeferredThings(JS::WasIncrementalGC(mJSRuntime) ? FinalizeIncrementally :
1157 FinalizeNow);
1158 break;
1159 }
1160 default:
1161 MOZ_CRASH();
1162 }
1163
1164 CustomGCCallback(aStatus);
1165 }

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