DXR is a code search and navigation tool aimed at making sense of large projects. It supports full-text and regex searches as well as structural queries.

Mercurial (b6057e17f856)

VCS Links

Line Code
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 * vim: set ts=8 sts=4 et sw=4 tw=99:
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef js_GCAPI_h
#define js_GCAPI_h

#include "mozilla/NullPtr.h"

#include "js/HeapAPI.h"
#include "js/RootingAPI.h"
#include "js/Value.h"

namespace js {
namespace gc {
class GCRuntime;
}
}

typedef enum JSGCMode {
    /* Perform only global GCs. */
    JSGC_MODE_GLOBAL = 0,

    /* Perform per-compartment GCs until too much garbage has accumulated. */
    JSGC_MODE_COMPARTMENT = 1,

    /*
     * Collect in short time slices rather than all at once. Implies
     * JSGC_MODE_COMPARTMENT.
     */
    JSGC_MODE_INCREMENTAL = 2
} JSGCMode;

namespace JS {

#define GCREASONS(D)                            \
    /* Reasons internal to the JS engine */     \
    D(API)                                      \
    D(MAYBEGC)                                  \
    D(DESTROY_RUNTIME)                          \
    D(DESTROY_CONTEXT)                          \
    D(LAST_DITCH)                               \
    D(TOO_MUCH_MALLOC)                          \
    D(ALLOC_TRIGGER)                            \
    D(DEBUG_GC)                                 \
    D(TRANSPLANT)                               \
    D(RESET)                                    \
    D(OUT_OF_NURSERY)                           \
    D(EVICT_NURSERY)                            \
    D(FULL_STORE_BUFFER)                        \
                                                \
    /* These are reserved for future use. */    \
    D(RESERVED0)                                \
    D(RESERVED1)                                \
    D(RESERVED2)                                \
    D(RESERVED3)                                \
    D(RESERVED4)                                \
    D(RESERVED5)                                \
    D(RESERVED6)                                \
    D(RESERVED7)                                \
    D(RESERVED8)                                \
    D(RESERVED9)                                \
    D(RESERVED10)                               \
    D(RESERVED11)                               \
    D(RESERVED12)                               \
    D(RESERVED13)                               \
    D(RESERVED14)                               \
    D(RESERVED15)                               \
    D(RESERVED16)                               \
    D(RESERVED17)                               \
    D(RESERVED18)                               \
    D(RESERVED19)                               \
                                                \
    /* Reasons from Firefox */                  \
    D(DOM_WINDOW_UTILS)                         \
    D(COMPONENT_UTILS)                          \
    D(MEM_PRESSURE)                             \
    D(CC_WAITING)                               \
    D(CC_FORCED)                                \
    D(LOAD_END)                                 \
    D(POST_COMPARTMENT)                         \
    D(PAGE_HIDE)                                \
    D(NSJSCONTEXT_DESTROY)                      \
    D(SET_NEW_DOCUMENT)                         \
    D(SET_DOC_SHELL)                            \
    D(DOM_UTILS)                                \
    D(DOM_IPC)                                  \
    D(DOM_WORKER)                               \
    D(INTER_SLICE_GC)                           \
    D(REFRESH_FRAME)                            \
    D(FULL_GC_TIMER)                            \
    D(SHUTDOWN_CC)                              \
    D(FINISH_LARGE_EVALUTE)

namespace gcreason {

/* GCReasons will end up looking like JSGC_MAYBEGC */
enum Reason {
#define MAKE_REASON(name) name,
    GCREASONS(MAKE_REASON)
#undef MAKE_REASON
    NO_REASON,
    NUM_REASONS,

    /*
     * For telemetry, we want to keep a fixed max bucket size over time so we
     * don't have to switch histograms. 100 is conservative; as of this writing
     * there are 26. But the cost of extra buckets seems to be low while the
     * cost of switching histograms is high.
     */
    NUM_TELEMETRY_REASONS = 100
};

} /* namespace gcreason */

/*
 * Zone GC:
 *
 * SpiderMonkey's GC is capable of performing a collection on an arbitrary
 * subset of the zones in the system. This allows an embedding to minimize
 * collection time by only collecting zones that have run code recently,
 * ignoring the parts of the heap that are unlikely to have changed.
 *
 * When triggering a GC using one of the functions below, it is first necessary
 * to select the zones to be collected. To do this, you can call
 * PrepareZoneForGC on each zone, or you can call PrepareForFullGC to select
 * all zones. Failing to select any zone is an error.
 */

/*
 * Schedule the given zone to be collected as part of the next GC.
 */
extern JS_FRIEND_API(void)
PrepareZoneForGC(Zone* zone);

/*
 * Schedule all zones to be collected in the next GC.
 */
extern JS_FRIEND_API(void)
PrepareForFullGC(JSRuntime* rt);

/*
 * When performing an incremental GC, the zones that were selected for the
 * previous incremental slice must be selected in subsequent slices as well.
 * This function selects those slices automatically.
 */
extern JS_FRIEND_API(void)
PrepareForIncrementalGC(JSRuntime* rt);

/*
 * Returns true if any zone in the system has been scheduled for GC with one of
 * the functions above or by the JS engine.
 */
extern JS_FRIEND_API(bool)
IsGCScheduled(JSRuntime* rt);

/*
 * Undoes the effect of the Prepare methods above. The given zone will not be
 * collected in the next GC.
 */
extern JS_FRIEND_API(void)
SkipZoneForGC(Zone* zone);

/*
 * Non-Incremental GC:
 *
 * The following functions perform a non-incremental GC.
 */

/*
 * Performs a non-incremental collection of all selected zones. Some objects
 * that are unreachable from the program may still be alive afterwards because
 * of internal references.
 */
extern JS_FRIEND_API(void)
GCForReason(JSRuntime* rt, gcreason::Reason reason);

/*
 * Perform a non-incremental collection after clearing caches and other
 * temporary references to objects. This will remove all unreferenced objects
 * in the system.
 */
extern JS_FRIEND_API(void)
ShrinkingGC(JSRuntime* rt, gcreason::Reason reason);

/*
 * Incremental GC:
 *
 * Incremental GC divides the full mark-and-sweep collection into multiple
 * slices, allowing client JavaScript code to run between each slice. This
 * allows interactive apps to avoid long collection pauses. Incremental GC does
 * not make collection take less time, it merely spreads that time out so that
 * the pauses are less noticable.
 *
 * For a collection to be carried out incrementally the following conditions
 * must be met:
 *  - The collection must be run by calling JS::IncrementalGC() rather than
 *    JS_GC().
 *  - The GC mode must have been set to JSGC_MODE_INCREMENTAL with
 *    JS_SetGCParameter().
 *  - All native objects that have their own trace hook must indicate that they
 *    implement read and write barriers with the JSCLASS_IMPLEMENTS_BARRIERS
 *    flag.
 *
 * Note: Even if incremental GC is enabled and working correctly,
 *       non-incremental collections can still happen when low on memory.
 */

/*
 * Begin an incremental collection and perform one slice worth of work or
 * perform a slice of an ongoing incremental collection. When this function
 * returns, the collection is not complete. This function must be called
 * repeatedly until !IsIncrementalGCInProgress(rt).
 *
 * Note: SpiderMonkey's GC is not realtime. Slices in practice may be longer or
 *       shorter than the requested interval.
 */
extern JS_FRIEND_API(void)
IncrementalGC(JSRuntime* rt, gcreason::Reason reason, int64_t millis = 0);

/*
 * If IsIncrementalGCInProgress(rt), this call finishes the ongoing collection
 * by performing an arbitrarily long slice. If !IsIncrementalGCInProgress(rt),
 * this is equivalent to GCForReason. When this function returns,
 * IsIncrementalGCInProgress(rt) will always be false.
 */
extern JS_FRIEND_API(void)
FinishIncrementalGC(JSRuntime* rt, gcreason::Reason reason);

enum GCProgress {
    /*
     * During non-incremental GC, the GC is bracketed by JSGC_CYCLE_BEGIN/END
     * callbacks. During an incremental GC, the sequence of callbacks is as
     * follows:
     *   JSGC_CYCLE_BEGIN, JSGC_SLICE_END  (first slice)
     *   JSGC_SLICE_BEGIN, JSGC_SLICE_END  (second slice)
     *   ...
     *   JSGC_SLICE_BEGIN, JSGC_CYCLE_END  (last slice)
     */

    GC_CYCLE_BEGIN,
    GC_SLICE_BEGIN,
    GC_SLICE_END,
    GC_CYCLE_END
};

struct JS_FRIEND_API(GCDescription) {
    bool isCompartment_;

    explicit GCDescription(bool isCompartment)
      : isCompartment_(isCompartment) {}

    jschar* formatMessage(JSRuntime* rt) const;
    jschar* formatJSON(JSRuntime* rt, uint64_t timestamp) const;
};

typedef void
(* GCSliceCallback)(JSRuntime* rt, GCProgress progress, const GCDescription& desc);

/*
 * The GC slice callback is called at the beginning and end of each slice. This
 * callback may be used for GC notifications as well as to perform additional
 * marking.
 */
extern JS_FRIEND_API(GCSliceCallback)
SetGCSliceCallback(JSRuntime* rt, GCSliceCallback callback);

/*
 * Incremental GC defaults to enabled, but may be disabled for testing or in
 * embeddings that have not yet implemented barriers on their native classes.
 * There is not currently a way to re-enable incremental GC once it has been
 * disabled on the runtime.
 */
extern JS_FRIEND_API(void)
DisableIncrementalGC(JSRuntime* rt);

/*
 * Returns true if incremental GC is enabled. Simply having incremental GC
 * enabled is not sufficient to ensure incremental collections are happening.
 * See the comment "Incremental GC" above for reasons why incremental GC may be
 * suppressed. Inspection of the "nonincremental reason" field of the
 * GCDescription returned by GCSliceCallback may help narrow down the cause if
 * collections are not happening incrementally when expected.
 */
extern JS_FRIEND_API(bool)
IsIncrementalGCEnabled(JSRuntime* rt);

/*
 * Returns true while an incremental GC is ongoing, both when actively
 * collecting and between slices.
 */
JS_FRIEND_API(bool)
IsIncrementalGCInProgress(JSRuntime* rt);

/*
 * Returns true when writes to GC things must call an incremental (pre) barrier.
 * This is generally only true when running mutator code in-between GC slices.
 * At other times, the barrier may be elided for performance.
 */
extern JS_FRIEND_API(bool)
IsIncrementalBarrierNeeded(JSRuntime* rt);

extern JS_FRIEND_API(bool)
IsIncrementalBarrierNeeded(JSContext* cx);

/*
 * Notify the GC that a reference to a GC thing is about to be overwritten.
 * These methods must be called if IsIncrementalBarrierNeeded.
 */
extern JS_FRIEND_API(void)
IncrementalReferenceBarrier(void* ptr, JSGCTraceKind kind);

extern JS_FRIEND_API(void)
IncrementalValueBarrier(const Value& v);

extern JS_FRIEND_API(void)
IncrementalObjectBarrier(JSObject* obj);

/*
 * Returns true if the most recent GC ran incrementally.
 */
extern JS_FRIEND_API(bool)
WasIncrementalGC(JSRuntime* rt);

/*
 * Generational GC:
 *
 * Note: Generational GC is not yet enabled by default. The following class
 *       is non-functional unless SpiderMonkey was configured with
 *       --enable-gcgenerational.
 */

/* Ensure that generational GC is disabled within some scope. */
class JS_FRIEND_API(AutoDisableGenerationalGC)
{
    js::gc::GCRuntime* gc;
#if defined(JSGC_GENERATIONAL) && defined(JS_GC_ZEAL)
    bool restartVerifier;
#endif

  public:
    explicit AutoDisableGenerationalGC(JSRuntime* rt);
    ~AutoDisableGenerationalGC();
};

/*
 * Returns true if generational allocation and collection is currently enabled
 * on the given runtime.
 */
extern JS_FRIEND_API(bool)
IsGenerationalGCEnabled(JSRuntime* rt);

/*
 * Returns the GC's "number". This does not correspond directly to the number
 * of GCs that have been run, but is guaranteed to be monotonically increasing
 * with GC activity.
 */
extern JS_FRIEND_API(size_t)
GetGCNumber();

/*
 * The GC does not immediately return the unused memory freed by a collection
 * back to the system incase it is needed soon afterwards. This call forces the
 * GC to return this memory immediately.
 */
extern JS_FRIEND_API(void)
ShrinkGCBuffers(JSRuntime* rt);

/*
 * Assert if a GC occurs while this class is live. This class does not disable
 * the static rooting hazard analysis.
 */
class JS_PUBLIC_API(AutoAssertOnGC)
{
#ifdef DEBUG
    js::gc::GCRuntime* gc;
    size_t gcNumber;

  public:
    AutoAssertOnGC();
    explicit AutoAssertOnGC(JSRuntime* rt);
    ~AutoAssertOnGC();

    static void VerifyIsSafeToGC(JSRuntime* rt);
#else
  public:
    AutoAssertOnGC() {}
    explicit AutoAssertOnGC(JSRuntime* rt) {}
    ~AutoAssertOnGC() {}

    static void VerifyIsSafeToGC(JSRuntime* rt) {}
#endif
};

/*
 * Disable the static rooting hazard analysis in the live region, but assert if
 * any GC occurs while this guard object is live. This is most useful to help
 * the exact rooting hazard analysis in complex regions, since it cannot
 * understand dataflow.
 *
 * Note: GC behavior is unpredictable even when deterministice and is generally
 *       non-deterministic in practice. The fact that this guard has not
 *       asserted is not a guarantee that a GC cannot happen in the guarded
 *       region. As a rule, anyone performing a GC unsafe action should
 *       understand the GC properties of all code in that region and ensure
 *       that the hazard analysis is correct for that code, rather than relying
 *       on this class.
 */
class JS_PUBLIC_API(AutoSuppressGCAnalysis) : public AutoAssertOnGC
{
  public:
    AutoSuppressGCAnalysis() : AutoAssertOnGC() {}
    explicit AutoSuppressGCAnalysis(JSRuntime* rt) : AutoAssertOnGC(rt) {}
};

/*
 * Place AutoCheckCannotGC in scopes that you believe can never GC. These
 * annotations will be verified both dynamically via AutoAssertOnGC, and
 * statically with the rooting hazard analysis (implemented by making the
 * analysis consider AutoCheckCannotGC to be a GC pointer, and therefore
 * complain if it is live across a GC call.) It is useful when dealing with
 * internal pointers to GC things where the GC thing itself may not be present
 * for the static analysis: e.g. acquiring inline chars from a JSString* on the
 * heap.
 */
class JS_PUBLIC_API(AutoCheckCannotGC) : public AutoAssertOnGC
{
  public:
    AutoCheckCannotGC() : AutoAssertOnGC() {}
    explicit AutoCheckCannotGC(JSRuntime* rt) : AutoAssertOnGC(rt) {}
};

class JS_PUBLIC_API(ObjectPtr)
{
    Heap<JSObject*> value;

  public:
    ObjectPtr() : value(nullptr) {}

    explicit ObjectPtr(JSObject* obj) : value(obj) {}

    /* Always call finalize before the destructor. */
    ~ObjectPtr() { MOZ_ASSERT(!value); }

    void finalize(JSRuntime* rt) {
        if (IsIncrementalBarrierNeeded(rt))
            IncrementalObjectBarrier(value);
        value = nullptr;
    }

    void init(JSObject* obj) { value = obj; }

    JSObject* get() const { return value; }

    void writeBarrierPre(JSRuntime* rt) {
        IncrementalObjectBarrier(value);
    }

    bool isAboutToBeFinalized();

    ObjectPtr& operator=(JSObject* obj) {
        IncrementalObjectBarrier(value);
        value = obj;
        return *this;
    }

    void trace(JSTracer* trc, const char* name);

    JSObject& operator*() const { return *value; }
    JSObject* operator->() const { return value; }
    operator JSObject*() const { return value; }
};

/*
 * Unsets the gray bit for anything reachable from |thing|. |kind| should not be
 * JSTRACE_SHAPE. |thing| should be non-null.
 */
extern JS_FRIEND_API(bool)
UnmarkGrayGCThingRecursively(void* thing, JSGCTraceKind kind);

/*
 * This should be called when an object that is marked gray is exposed to the JS
 * engine (by handing it to running JS code or writing it into live JS
 * data). During incremental GC, since the gray bits haven't been computed yet,
 * we conservatively mark the object black.
 */
static MOZ_ALWAYS_INLINE void
ExposeGCThingToActiveJS(void* thing, JSGCTraceKind kind)
{
    MOZ_ASSERT(kind != JSTRACE_SHAPE);

    shadow::Runtime* rt = js::gc::GetGCThingRuntime(thing);
#ifdef JSGC_GENERATIONAL
    /*
     * GC things residing in the nursery cannot be gray: they have no mark bits.
     * All live objects in the nursery are moved to tenured at the beginning of
     * each GC slice, so the gray marker never sees nursery things.
     */
    if (js::gc::IsInsideNursery((js::gc::Cell*)thing))
        return;
#endif
    if (IsIncrementalBarrierNeededOnGCThing(rt, thing, kind))
        IncrementalReferenceBarrier(thing, kind);
    else if (GCThingIsMarkedGray(thing))
        UnmarkGrayGCThingRecursively(thing, kind);
}

static MOZ_ALWAYS_INLINE void
ExposeValueToActiveJS(const Value& v)
{
    if (v.isMarkable())
        ExposeGCThingToActiveJS(v.toGCThing(), v.gcKind());
}

static MOZ_ALWAYS_INLINE void
ExposeObjectToActiveJS(JSObject* obj)
{
    ExposeGCThingToActiveJS(obj, JSTRACE_OBJECT);
}

/*
 * If a GC is currently marking, mark the object black.
 */
static MOZ_ALWAYS_INLINE void
MarkGCThingAsLive(JSRuntime* rt_, void* thing, JSGCTraceKind kind)
{
    shadow::Runtime* rt = shadow::Runtime::asShadowRuntime(rt_);
#ifdef JSGC_GENERATIONAL
    /*
     * Any object in the nursery will not be freed during any GC running at that time.
     */
    if (js::gc::IsInsideNursery((js::gc::Cell*)thing))
        return;
#endif
    if (IsIncrementalBarrierNeededOnGCThing(rt, thing, kind))
        IncrementalReferenceBarrier(thing, kind);
}

static MOZ_ALWAYS_INLINE void
MarkStringAsLive(Zone* zone, JSString* string)
{
    JSRuntime* rt = JS::shadow::Zone::asShadowZone(zone)->runtimeFromMainThread();
    MarkGCThingAsLive(rt, string, JSTRACE_STRING);
}

/*
 * Internal to Firefox.
 *
 * Note: this is not related to the PokeGC in nsJSEnvironment.
 */
extern JS_FRIEND_API(void)
PokeGC(JSRuntime* rt);

/*
 * Internal to Firefox.
 */
extern JS_FRIEND_API(void)
NotifyDidPaint(JSRuntime* rt);

} /* namespace JS */

#endif /* js_GCAPI_h */