gecko/js/public/Tracer.h

/* -*- 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_Tracer_h
#define js_Tracer_h

#include "mozilla/NullPtr.h"
 
#include "jspubtd.h"

struct JSTracer;

namespace JS {
template <typename T> class Heap;
template <typename T> class TenuredHeap;
}

// Tracer callback, called for each traceable thing directly referenced by a
// particular object or runtime structure. It is the callback responsibility
// to ensure the traversal of the full object graph via calling eventually
// JS_TraceChildren on the passed thing. In this case the callback must be
// prepared to deal with cycles in the traversal graph.
//
// kind argument is one of JSTRACE_OBJECT, JSTRACE_STRING or a tag denoting
// internal implementation-specific traversal kind. In the latter case the only
// operations on thing that the callback can do is to call JS_TraceChildren or
// JS_GetTraceThingInfo.
//
// If eagerlyTraceWeakMaps is true, when we trace a WeakMap visit all
// of its mappings. This should be used in cases where the tracer
// wants to use the existing liveness of entries.
typedef void
(* JSTraceCallback)(JSTracer *trc, void **thingp, JSGCTraceKind kind);

// Callback that JSTraceOp implementation can provide to return a string
// describing the reference traced with JS_CallTracer.
typedef void
(* JSTraceNamePrinter)(JSTracer *trc, char *buf, size_t bufsize);

enum WeakMapTraceKind {
    DoNotTraceWeakMaps = 0,
    TraceWeakMapValues = 1,
    TraceWeakMapKeysValues = 2
};

struct JSTracer {
    JSRuntime           *runtime;
    JSTraceCallback     callback;
    JSTraceNamePrinter  debugPrinter;
    const void          *debugPrintArg;
    size_t              debugPrintIndex;
    WeakMapTraceKind    eagerlyTraceWeakMaps;
#ifdef JS_GC_ZEAL
    void                *realLocation;
#endif
};

// Set debugging information about a reference to a traceable thing to prepare
// for the following call to JS_CallTracer.
//
// When printer is null, arg must be const char * or char * C string naming
// the reference and index must be either (size_t)-1 indicating that the name
// alone describes the reference or it must be an index into some array vector
// that stores the reference.
//
// When printer callback is not null, the arg and index arguments are
// available to the callback as debugPrintArg and debugPrintIndex fields
// of JSTracer.
//
// The storage for name or callback's arguments needs to live only until
// the following call to JS_CallTracer returns.
//
# define JS_SET_TRACING_DETAILS(trc, printer, arg, index)                     \
    JS_BEGIN_MACRO                                                            \
        (trc)->debugPrinter = (printer);                                      \
        (trc)->debugPrintArg = (arg);                                         \
        (trc)->debugPrintIndex = (index);                                     \
    JS_END_MACRO

// Sets the real location for a marked reference, when passing the address
// directly is not feasable.
//
// FIXME: This is currently overcomplicated by our need to nest calls for Values
// stored as keys in hash tables, but will get simplified once we can rekey
// in-place.
//
#ifdef JS_GC_ZEAL
# define JS_SET_TRACING_LOCATION(trc, location)                               \
    JS_BEGIN_MACRO                                                            \
        if (!(trc)->realLocation || !(location))                              \
            (trc)->realLocation = (location);                                 \
    JS_END_MACRO
# define JS_UNSET_TRACING_LOCATION(trc)                                       \
    JS_BEGIN_MACRO                                                            \
        (trc)->realLocation = nullptr;                                        \
    JS_END_MACRO
#else
# define JS_SET_TRACING_LOCATION(trc, location)                               \
    JS_BEGIN_MACRO                                                            \
    JS_END_MACRO
# define JS_UNSET_TRACING_LOCATION(trc)                                       \
    JS_BEGIN_MACRO                                                            \
    JS_END_MACRO
#endif

// Convenience macro to describe the argument of JS_CallTracer using C string
// and index.
# define JS_SET_TRACING_INDEX(trc, name, index)                               \
    JS_SET_TRACING_DETAILS(trc, nullptr, name, index)

// Convenience macro to describe the argument of JS_CallTracer using C string.
# define JS_SET_TRACING_NAME(trc, name)                                       \
    JS_SET_TRACING_DETAILS(trc, nullptr, name, (size_t)-1)

// The JS_Call*Tracer 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_Call*Tracer 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_Call*Tracer will be updated to the object'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.
//
extern JS_PUBLIC_API(void)
JS_CallValueTracer(JSTracer *trc, JS::Value *valuep, const char *name);

extern JS_PUBLIC_API(void)
JS_CallIdTracer(JSTracer *trc, jsid *idp, const char *name);

extern JS_PUBLIC_API(void)
JS_CallObjectTracer(JSTracer *trc, JSObject **objp, const char *name);

extern JS_PUBLIC_API(void)
JS_CallStringTracer(JSTracer *trc, JSString **strp, const char *name);

extern JS_PUBLIC_API(void)
JS_CallScriptTracer(JSTracer *trc, JSScript **scriptp, const char *name);

extern JS_PUBLIC_API(void)
JS_CallHeapValueTracer(JSTracer *trc, JS::Heap<JS::Value> *valuep, const char *name);

extern JS_PUBLIC_API(void)
JS_CallHeapIdTracer(JSTracer *trc, JS::Heap<jsid> *idp, const char *name);

extern JS_PUBLIC_API(void)
JS_CallHeapObjectTracer(JSTracer *trc, JS::Heap<JSObject *> *objp, const char *name);

extern JS_PUBLIC_API(void)
JS_CallHeapStringTracer(JSTracer *trc, JS::Heap<JSString *> *strp, const char *name);

extern JS_PUBLIC_API(void)
JS_CallHeapScriptTracer(JSTracer *trc, JS::Heap<JSScript *> *scriptp, const char *name);

template <typename HashSetEnum>
inline void
JS_CallHashSetObjectTracer(JSTracer *trc, HashSetEnum &e, JSObject *const &key, const char *name)
{
    JSObject *updated = key;
    JS_SET_TRACING_LOCATION(trc, reinterpret_cast<void *>(&const_cast<JSObject *&>(key)));
    JS_CallObjectTracer(trc, &updated, name);
    if (updated != key)
        e.rekeyFront(key, updated);
}

// Trace an object that is known to always be tenured.  No post barriers are
// required in this case.
extern JS_PUBLIC_API(void)
JS_CallTenuredObjectTracer(JSTracer *trc, JS::TenuredHeap<JSObject *> *objp, const char *name);

// API for JSTraceCallback implementations.
extern JS_PUBLIC_API(void)
JS_TracerInit(JSTracer *trc, JSRuntime *rt, JSTraceCallback callback);

extern JS_PUBLIC_API(void)
JS_TraceChildren(JSTracer *trc, void *thing, JSGCTraceKind kind);

extern JS_PUBLIC_API(void)
JS_TraceRuntime(JSTracer *trc);

extern JS_PUBLIC_API(void)
JS_GetTraceThingInfo(char *buf, size_t bufsize, JSTracer *trc,
                     void *thing, JSGCTraceKind kind, bool includeDetails);

extern JS_PUBLIC_API(const char *)
JS_GetTraceEdgeName(JSTracer *trc, char *buffer, int bufferSize);

#endif /* js_Tracer_h */