gecko-dev/js/public/TracingAPI.h

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/* -*- 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_TracingAPI_h
#define js_TracingAPI_h
#include "jsalloc.h"
#include "js/HashTable.h"
#include "js/HeapAPI.h"
#include "js/TraceKind.h"
class JS_PUBLIC_API(JSTracer);
namespace JS {
class JS_PUBLIC_API(CallbackTracer);
template <typename T> class Heap;
template <typename T> class TenuredHeap;
/** Returns a static string equivalent of |kind|. */
JS_FRIEND_API(const char*)
GCTraceKindToAscii(JS::TraceKind kind);
} // namespace JS
enum WeakMapTraceKind {
/**
* Do not trace into weak map keys or values during traversal. Users must
* handle weak maps manually.
*/
DoNotTraceWeakMaps,
/**
* Do true ephemeron marking with a weak key lookup marking phase. This is
* the default for GCMarker.
*/
ExpandWeakMaps,
/**
* Trace through to all values, irrespective of whether the keys are live
* or not. Used for non-marking tracers.
*/
TraceWeakMapValues,
/**
* Trace through to all keys and values, irrespective of whether the keys
* are live or not. Used for non-marking tracers.
*/
TraceWeakMapKeysValues
};
class JS_PUBLIC_API(JSTracer)
{
public:
// Return the runtime set on the tracer.
JSRuntime* runtime() const { return runtime_; }
// Return the weak map tracing behavior currently set on this tracer.
WeakMapTraceKind weakMapAction() const { return weakMapAction_; }
enum class TracerKindTag {
// Marking path: a tracer used only for marking liveness of cells, not
// for moving them. The kind will transition to WeakMarking after
// everything reachable by regular edges has been marked.
Marking,
// Same as Marking, except we have now moved on to the "weak marking
// phase", in which every marked obj/script is immediately looked up to
// see if it is a weak map key (and therefore might require marking its
// weak map value).
WeakMarking,
// A tracer that traverses the graph for the purposes of moving objects
// from the nursery to the tenured area.
Tenuring,
// General-purpose traversal that invokes a callback on each cell.
// Traversing children is the responsibility of the callback.
Callback
};
bool isMarkingTracer() const { return tag_ == TracerKindTag::Marking || tag_ == TracerKindTag::WeakMarking; }
bool isWeakMarkingTracer() const { return tag_ == TracerKindTag::WeakMarking; }
bool isTenuringTracer() const { return tag_ == TracerKindTag::Tenuring; }
bool isCallbackTracer() const { return tag_ == TracerKindTag::Callback; }
inline JS::CallbackTracer* asCallbackTracer();
#ifdef DEBUG
bool checkEdges() { return checkEdges_; }
#endif
protected:
JSTracer(JSRuntime* rt, TracerKindTag tag,
WeakMapTraceKind weakTraceKind = TraceWeakMapValues)
: runtime_(rt)
, weakMapAction_(weakTraceKind)
#ifdef DEBUG
, checkEdges_(true)
#endif
, tag_(tag)
{}
#ifdef DEBUG
// Set whether to check edges are valid in debug builds.
void setCheckEdges(bool check) {
checkEdges_ = check;
}
#endif
private:
JSRuntime* runtime_;
WeakMapTraceKind weakMapAction_;
#ifdef DEBUG
bool checkEdges_;
#endif
protected:
TracerKindTag tag_;
};
namespace JS {
class AutoTracingName;
class AutoTracingIndex;
class AutoTracingCallback;
class JS_PUBLIC_API(CallbackTracer) : public JSTracer
{
public:
CallbackTracer(JSRuntime* rt, WeakMapTraceKind weakTraceKind = TraceWeakMapValues)
: JSTracer(rt, JSTracer::TracerKindTag::Callback, weakTraceKind),
contextName_(nullptr), contextIndex_(InvalidIndex), contextFunctor_(nullptr)
{}
CallbackTracer(JSContext* cx, WeakMapTraceKind weakTraceKind = TraceWeakMapValues);
// Override these methods to receive notification when an edge is visited
// with the type contained in the callback. The default implementation
// dispatches to the fully-generic onChild implementation, so for cases that
// do not care about boxing overhead and do not need the actual edges,
// just override the generic onChild.
virtual void onObjectEdge(JSObject** objp) { onChild(JS::GCCellPtr(*objp)); }
virtual void onStringEdge(JSString** strp) { onChild(JS::GCCellPtr(*strp)); }
virtual void onSymbolEdge(JS::Symbol** symp) { onChild(JS::GCCellPtr(*symp)); }
virtual void onScriptEdge(JSScript** scriptp) { onChild(JS::GCCellPtr(*scriptp)); }
virtual void onShapeEdge(js::Shape** shapep) {
onChild(JS::GCCellPtr(*shapep, JS::TraceKind::Shape));
}
virtual void onObjectGroupEdge(js::ObjectGroup** groupp) {
onChild(JS::GCCellPtr(*groupp, JS::TraceKind::ObjectGroup));
}
virtual void onBaseShapeEdge(js::BaseShape** basep) {
onChild(JS::GCCellPtr(*basep, JS::TraceKind::BaseShape));
}
virtual void onJitCodeEdge(js::jit::JitCode** codep) {
onChild(JS::GCCellPtr(*codep, JS::TraceKind::JitCode));
}
virtual void onLazyScriptEdge(js::LazyScript** lazyp) {
onChild(JS::GCCellPtr(*lazyp, JS::TraceKind::LazyScript));
}
virtual void onScopeEdge(js::Scope** scopep) {
onChild(JS::GCCellPtr(*scopep, JS::TraceKind::Scope));
}
// Override this method to receive notification when a node in the GC
// heap graph is visited.
virtual void onChild(const JS::GCCellPtr& thing) = 0;
// Access to the tracing context:
// When tracing with a JS::CallbackTracer, we invoke the callback with the
// edge location and the type of target. This is useful for operating on
// the edge in the abstract or on the target thing, satisfying most common
// use cases. However, some tracers need additional detail about the
// specific edge that is being traced in order to be useful. Unfortunately,
// the raw pointer to the edge that we provide is not enough information to
// infer much of anything useful about that edge.
//
// In order to better support use cases that care in particular about edges
// -- as opposed to the target thing -- tracing implementations are
// responsible for providing extra context information about each edge they
// trace, as it is traced. This contains, at a minimum, an edge name and,
// when tracing an array, the index. Further specialization can be achived
// (with some complexity), by associating a functor with the tracer so
// that, when requested, the user can generate totally custom edge
// descriptions.
// Returns the current edge's name. It is only valid to call this when
// inside the trace callback, however, the edge name will always be set.
const char* contextName() const { MOZ_ASSERT(contextName_); return contextName_; }
// Returns the current edge's index, if marked as part of an array of edges.
// This must be called only inside the trace callback. When not tracing an
// array, the value will be InvalidIndex.
const static size_t InvalidIndex = size_t(-1);
size_t contextIndex() const { return contextIndex_; }
// Build a description of this edge in the heap graph. This call may invoke
// the context functor, if set, which may inspect arbitrary areas of the
// heap. On the other hand, the description provided by this method may be
// substantially more accurate and useful than those provided by only the
// contextName and contextIndex.
void getTracingEdgeName(char* buffer, size_t bufferSize);
// The trace implementation may associate a callback with one or more edges
// using AutoTracingDetails. This functor is called by getTracingEdgeName
// and is responsible for providing a textual representation of the
// currently being traced edge. The callback has access to the full heap,
// including the currently set tracing context.
class ContextFunctor {
public:
virtual void operator()(CallbackTracer* trc, char* buf, size_t bufsize) = 0;
};
#ifdef DEBUG
enum class TracerKind { DoNotCare, Moving, GrayBuffering, VerifyTraceProtoAndIface };
virtual TracerKind getTracerKind() const { return TracerKind::DoNotCare; }
#endif
// In C++, overriding a method hides all methods in the base class with
// that name, not just methods with that signature. Thus, the typed edge
// methods have to have distinct names to allow us to override them
// individually, which is freqently useful if, for example, we only want to
// process only one type of edge.
void dispatchToOnEdge(JSObject** objp) { onObjectEdge(objp); }
void dispatchToOnEdge(JSString** strp) { onStringEdge(strp); }
void dispatchToOnEdge(JS::Symbol** symp) { onSymbolEdge(symp); }
void dispatchToOnEdge(JSScript** scriptp) { onScriptEdge(scriptp); }
void dispatchToOnEdge(js::Shape** shapep) { onShapeEdge(shapep); }
void dispatchToOnEdge(js::ObjectGroup** groupp) { onObjectGroupEdge(groupp); }
void dispatchToOnEdge(js::BaseShape** basep) { onBaseShapeEdge(basep); }
void dispatchToOnEdge(js::jit::JitCode** codep) { onJitCodeEdge(codep); }
void dispatchToOnEdge(js::LazyScript** lazyp) { onLazyScriptEdge(lazyp); }
void dispatchToOnEdge(js::Scope** scopep) { onScopeEdge(scopep); }
private:
friend class AutoTracingName;
const char* contextName_;
friend class AutoTracingIndex;
size_t contextIndex_;
friend class AutoTracingDetails;
ContextFunctor* contextFunctor_;
};
// Set the name portion of the tracer's context for the current edge.
class MOZ_RAII AutoTracingName
{
CallbackTracer* trc_;
const char* prior_;
public:
AutoTracingName(CallbackTracer* trc, const char* name) : trc_(trc), prior_(trc->contextName_) {
MOZ_ASSERT(name);
trc->contextName_ = name;
}
~AutoTracingName() {
MOZ_ASSERT(trc_->contextName_);
trc_->contextName_ = prior_;
}
};
// Set the index portion of the tracer's context for the current range.
class MOZ_RAII AutoTracingIndex
{
CallbackTracer* trc_;
public:
explicit AutoTracingIndex(JSTracer* trc, size_t initial = 0) : trc_(nullptr) {
if (trc->isCallbackTracer()) {
trc_ = trc->asCallbackTracer();
MOZ_ASSERT(trc_->contextIndex_ == CallbackTracer::InvalidIndex);
trc_->contextIndex_ = initial;
}
}
~AutoTracingIndex() {
if (trc_) {
MOZ_ASSERT(trc_->contextIndex_ != CallbackTracer::InvalidIndex);
trc_->contextIndex_ = CallbackTracer::InvalidIndex;
}
}
void operator++() {
if (trc_) {
MOZ_ASSERT(trc_->contextIndex_ != CallbackTracer::InvalidIndex);
++trc_->contextIndex_;
}
}
};
// Set a context callback for the trace callback to use, if it needs a detailed
// edge description.
class MOZ_RAII AutoTracingDetails
{
CallbackTracer* trc_;
public:
AutoTracingDetails(JSTracer* trc, CallbackTracer::ContextFunctor& func) : trc_(nullptr) {
if (trc->isCallbackTracer()) {
trc_ = trc->asCallbackTracer();
MOZ_ASSERT(trc_->contextFunctor_ == nullptr);
trc_->contextFunctor_ = &func;
}
}
~AutoTracingDetails() {
if (trc_) {
MOZ_ASSERT(trc_->contextFunctor_);
trc_->contextFunctor_ = nullptr;
}
}
};
} // namespace JS
JS::CallbackTracer*
JSTracer::asCallbackTracer()
{
MOZ_ASSERT(isCallbackTracer());
return static_cast<JS::CallbackTracer*>(this);
}
namespace JS {
// The JS::TraceEdge family of functions traces the given GC thing reference.
// This performs the tracing action configured on the given JSTracer: typically
// calling the JSTracer::callback or marking the thing as live.
//
// The argument to JS::TraceEdge is an in-out param: when the function returns,
// the garbage collector might have moved the GC thing. In this case, the
// reference passed to JS::TraceEdge will be updated to the thing's new
// location. Callers of this method are responsible for updating any state that
// is dependent on the object's address. For example, if the object's address
// is used as a key in a hashtable, then the object must be removed and
// re-inserted with the correct hash.
//
// Note that while |edgep| must never be null, it is fine for |*edgep| to be
// nullptr.
template <typename T>
extern JS_PUBLIC_API(void)
TraceEdge(JSTracer* trc, JS::Heap<T>* edgep, const char* name);
extern JS_PUBLIC_API(void)
TraceEdge(JSTracer* trc, JS::TenuredHeap<JSObject*>* edgep, const char* name);
// Edges that are always traced as part of root marking do not require
// incremental barriers. This function allows for marking non-barriered
// pointers, but asserts that this happens during root marking.
//
// Note that while |edgep| must never be null, it is fine for |*edgep| to be
// nullptr.
template <typename T>
extern JS_PUBLIC_API(void)
UnsafeTraceRoot(JSTracer* trc, T* edgep, const char* name);
extern JS_PUBLIC_API(void)
TraceChildren(JSTracer* trc, GCCellPtr thing);
using ZoneSet = js::HashSet<Zone*, js::DefaultHasher<Zone*>, js::SystemAllocPolicy>;
using CompartmentSet = js::HashSet<JSCompartment*, js::DefaultHasher<JSCompartment*>,
js::SystemAllocPolicy>;
/**
* Trace every value within |compartments| that is wrapped by a
* cross-compartment wrapper from a compartment that is not an element of
* |compartments|.
*/
extern JS_PUBLIC_API(void)
TraceIncomingCCWs(JSTracer* trc, const JS::CompartmentSet& compartments);
} // namespace JS
extern JS_PUBLIC_API(void)
JS_GetTraceThingInfo(char* buf, size_t bufsize, JSTracer* trc,
void* thing, JS::TraceKind kind, bool includeDetails);
namespace js {
// Trace an edge that is not a GC root and is not wrapped in a barriered
// wrapper for some reason.
//
// This method does not check if |*edgep| is non-null before tracing through
// it, so callers must check any nullable pointer before calling this method.
template <typename T>
extern JS_PUBLIC_API(void)
UnsafeTraceManuallyBarrieredEdge(JSTracer* trc, T* edgep, const char* name);
namespace gc {
// Return true if the given edge is not live and is about to be swept.
template <typename T>
extern JS_PUBLIC_API(bool)
EdgeNeedsSweep(JS::Heap<T>* edgep);
// Not part of the public API, but declared here so we can use it in GCPolicy
// which is.
template <typename T>
bool
IsAboutToBeFinalizedUnbarriered(T* thingp);
} // namespace gc
} // namespace js
#endif /* js_TracingAPI_h */