/* -*- 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/. */

/*
 * GC-internal definitions.
 */

#ifndef gc_GCInternals_h
#define gc_GCInternals_h

#include "mozilla/ArrayUtils.h"
#include "mozilla/Maybe.h"
#include "mozilla/PodOperations.h"

#include "gc/RelocationOverlay.h"
#include "gc/Zone.h"
#include "vm/HelperThreads.h"
#include "vm/Runtime.h"

namespace js {
namespace gc {

void FinishGC(JSContext* cx);

/*
 * This class should be used by any code that needs to exclusive access to the
 * heap in order to trace through it...
 */
class MOZ_RAII AutoTraceSession
{
  public:
    explicit AutoTraceSession(JSRuntime* rt, JS::HeapState state = JS::HeapState::Tracing);
    ~AutoTraceSession();

    // Threads with an exclusive context can hit refillFreeList while holding
    // the exclusive access lock. To avoid deadlocking when we try to acquire
    // this lock during GC and the other thread is waiting, make sure we hold
    // the exclusive access lock during GC sessions.
    AutoLockForExclusiveAccess lock;

  protected:
    JSRuntime* runtime;

  private:
    AutoTraceSession(const AutoTraceSession&) = delete;
    void operator=(const AutoTraceSession&) = delete;

    JS::HeapState prevState;
    AutoGeckoProfilerEntry pseudoFrame;
};

class MOZ_RAII AutoPrepareForTracing
{
    mozilla::Maybe<AutoTraceSession> session_;

  public:
    AutoPrepareForTracing(JSContext* cx, ZoneSelector selector);
    AutoTraceSession& session() { return session_.ref(); }
};

AbortReason
IsIncrementalGCUnsafe(JSRuntime* rt);

#ifdef JS_GC_ZEAL

class MOZ_RAII AutoStopVerifyingBarriers
{
    GCRuntime* gc;
    bool restartPreVerifier;

  public:
    AutoStopVerifyingBarriers(JSRuntime* rt, bool isShutdown)
      : gc(&rt->gc)
    {
        if (gc->isVerifyPreBarriersEnabled()) {
            gc->endVerifyPreBarriers();
            restartPreVerifier = !isShutdown;
        } else {
            restartPreVerifier = false;
        }
    }

    ~AutoStopVerifyingBarriers() {
        // Nasty special case: verification runs a minor GC, which *may* nest
        // inside of an outer minor GC. This is not allowed by the
        // gc::Statistics phase tree. So we pause the "real" GC, if in fact one
        // is in progress.
        gcstats::PhaseKind outer = gc->stats().currentPhaseKind();
        if (outer != gcstats::PhaseKind::NONE)
            gc->stats().endPhase(outer);
        MOZ_ASSERT(gc->stats().currentPhaseKind() == gcstats::PhaseKind::NONE);

        if (restartPreVerifier)
            gc->startVerifyPreBarriers();

        if (outer != gcstats::PhaseKind::NONE)
            gc->stats().beginPhase(outer);
    }
};
#else
struct MOZ_RAII AutoStopVerifyingBarriers
{
    AutoStopVerifyingBarriers(JSRuntime*, bool) {}
};
#endif /* JS_GC_ZEAL */

#ifdef JSGC_HASH_TABLE_CHECKS
void CheckHashTablesAfterMovingGC(JSRuntime* rt);
void CheckHeapAfterGC(JSRuntime* rt);
#endif

struct MovingTracer : JS::CallbackTracer
{
    explicit MovingTracer(JSRuntime* rt) : CallbackTracer(rt, TraceWeakMapKeysValues) {}

    void onObjectEdge(JSObject** objp) override;
    void onShapeEdge(Shape** shapep) override;
    void onStringEdge(JSString** stringp) override;
    void onScriptEdge(JSScript** scriptp) override;
    void onLazyScriptEdge(LazyScript** lazyp) override;
    void onBaseShapeEdge(BaseShape** basep) override;
    void onScopeEdge(Scope** basep) override;
    void onRegExpSharedEdge(RegExpShared** sharedp) override;
    void onChild(const JS::GCCellPtr& thing) override {
        MOZ_ASSERT(!RelocationOverlay::isCellForwarded(thing.asCell()));
    }

#ifdef DEBUG
    TracerKind getTracerKind() const override { return TracerKind::Moving; }
#endif

  private:
    template <typename T>
    void updateEdge(T** thingp);
};

// Structure for counting how many times objects in a particular group have
// been tenured during a minor collection.
struct TenureCount
{
    ObjectGroup* group;
    int count;
};

// Keep rough track of how many times we tenure objects in particular groups
// during minor collections, using a fixed size hash for efficiency at the cost
// of potential collisions.
struct TenureCountCache
{
    static const size_t EntryShift = 4;
    static const size_t EntryCount = 1 << EntryShift;

    TenureCount entries[EntryCount];

    TenureCountCache() { mozilla::PodZero(this); }

    HashNumber hash(ObjectGroup* group) {
#if JS_BITS_PER_WORD == 32
        static const size_t ZeroBits = 3;
#else
        static const size_t ZeroBits = 4;
#endif

        uintptr_t word = uintptr_t(group);
        MOZ_ASSERT((word & ((1 << ZeroBits) - 1)) == 0);
        word >>= ZeroBits;
        return HashNumber((word >> EntryShift) ^ word);
    }

    TenureCount& findEntry(ObjectGroup* group) {
        return entries[hash(group) % EntryCount];
    }
};

struct MOZ_RAII AutoAssertNoNurseryAlloc
{
#ifdef DEBUG
    AutoAssertNoNurseryAlloc();
    ~AutoAssertNoNurseryAlloc();
#else
    AutoAssertNoNurseryAlloc() {}
#endif
};

/*
 * There are a couple of classes here that serve mostly as "tokens" indicating
 * that a condition holds. Some functions force the caller to possess such a
 * token because they would misbehave if the condition were false, and it is
 * far more clear to make the condition visible at the point where it can be
 * affected rather than just crashing in an assertion down in the place where
 * it is relied upon.
 */

/*
 * A class that serves as a token that the nursery in the current thread's zone
 * group is empty.
 */
class MOZ_RAII AutoAssertEmptyNursery
{
  protected:
    JSContext* cx;

    mozilla::Maybe<AutoAssertNoNurseryAlloc> noAlloc;

    // Check that the nursery is empty.
    void checkCondition(JSContext* cx);

    // For subclasses that need to empty the nursery in their constructors.
    AutoAssertEmptyNursery() : cx(nullptr) {
    }

  public:
    explicit AutoAssertEmptyNursery(JSContext* cx) : cx(nullptr) {
        checkCondition(cx);
    }

    AutoAssertEmptyNursery(const AutoAssertEmptyNursery& other) : AutoAssertEmptyNursery(other.cx)
    {
    }
};

/*
 * Evict the nursery upon construction. Serves as a token indicating that the
 * nursery is empty. (See AutoAssertEmptyNursery, above.)
 *
 * Note that this is very improper subclass of AutoAssertHeapBusy, in that the
 * heap is *not* busy within the scope of an AutoEmptyNursery. I will most
 * likely fix this by removing AutoAssertHeapBusy, but that is currently
 * waiting on jonco's review.
 */
class MOZ_RAII AutoEmptyNursery : public AutoAssertEmptyNursery
{
  public:
    explicit AutoEmptyNursery(JSContext* cx);
};

extern void
DelayCrossCompartmentGrayMarking(JSObject* src);

inline bool
IsOOMReason(JS::gcreason::Reason reason)
{
    return reason == JS::gcreason::LAST_DITCH ||
           reason == JS::gcreason::MEM_PRESSURE;
}

inline void
RelocationOverlay::forwardTo(Cell* cell)
{
    MOZ_ASSERT(!isForwarded());
    // The location of magic_ is important because it must never be valid to see
    // the value Relocated there in a GC thing that has not been moved.
    static_assert(offsetof(RelocationOverlay, magic_) == offsetof(JSObject, group_) &&
                  offsetof(RelocationOverlay, magic_) == offsetof(js::Shape, base_) &&
                  offsetof(RelocationOverlay, magic_) == offsetof(JSString, d.u1.flags),
                  "RelocationOverlay::magic_ is in the wrong location");
    magic_ = Relocated;
    newLocation_ = cell;
}

} /* namespace gc */
} /* namespace js */

#endif /* gc_GCInternals_h */