gecko/js/src/jsutil.h

/* -*- Mode: C; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 *
 * ***** BEGIN LICENSE BLOCK *****
 * Version: MPL 1.1/GPL 2.0/LGPL 2.1
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 * http://www.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is Mozilla Communicator client code, released
 * March 31, 1998.
 *
 * The Initial Developer of the Original Code is
 * Netscape Communications Corporation.
 * Portions created by the Initial Developer are Copyright (C) 1998
 * the Initial Developer. All Rights Reserved.
 *
 * Contributor(s):
 *
 * Alternatively, the contents of this file may be used under the terms of
 * either of the GNU General Public License Version 2 or later (the "GPL"),
 * or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
 * in which case the provisions of the GPL or the LGPL are applicable instead
 * of those above. If you wish to allow use of your version of this file only
 * under the terms of either the GPL or the LGPL, and not to allow others to
 * use your version of this file under the terms of the MPL, indicate your
 * decision by deleting the provisions above and replace them with the notice
 * and other provisions required by the GPL or the LGPL. If you do not delete
 * the provisions above, a recipient may use your version of this file under
 * the terms of any one of the MPL, the GPL or the LGPL.
 *
 * ***** END LICENSE BLOCK ***** */

/*
 * PR assertion checker.
 */

#ifndef jsutil_h___
#define jsutil_h___

#include "jstypes.h"
#include "mozilla/Util.h"
#include <stdlib.h>
#include <string.h>

JS_BEGIN_EXTERN_C

#define JS_CRASH_UNLESS(__cond)                                                 \
    JS_BEGIN_MACRO                                                              \
        if (!(__cond)) {                                                        \
            *(int *)(uintptr_t)0xccadbeef = 0;                                  \
            ((void(*)())0)(); /* More reliable, but doesn't say CCADBEEF */     \
        }                                                                       \
    JS_END_MACRO

#define JS_FREE_PATTERN 0xDA

#ifdef JS_CRASH_DIAGNOSTICS

#define JS_POISON(p, val, size) memset((p), (val), (size))

#define JS_OPT_ASSERT(expr)                                                   \
    ((expr) ? (void)0 : JS_Assert(#expr, __FILE__, __LINE__))

#define JS_OPT_ASSERT_IF(cond, expr)                                          \
    ((!(cond) || (expr)) ? (void)0 : JS_Assert(#expr, __FILE__, __LINE__))

#else

#define JS_POISON(p, val, size) ((void) 0)
#define JS_OPT_ASSERT(expr) ((void) 0)
#define JS_OPT_ASSERT_IF(cond, expr) ((void) 0)

#endif /* JS_CRASH_DIAGNOSTICS */

#ifdef DEBUG

#define JS_ASSERT(expr)                                                       \
    ((expr) ? (void)0 : JS_Assert(#expr, __FILE__, __LINE__))

#define JS_ASSERT_IF(cond, expr)                                              \
    ((!(cond) || (expr)) ? (void)0 : JS_Assert(#expr, __FILE__, __LINE__))

#define JS_NOT_REACHED(reason)                                                \
    JS_Assert(reason, __FILE__, __LINE__)

#define JS_ALWAYS_TRUE(expr) JS_ASSERT(expr)

#define JS_ALWAYS_FALSE(expr) JS_ASSERT(!(expr))

# ifdef JS_THREADSAFE
# define JS_THREADSAFE_ASSERT(expr) JS_ASSERT(expr) 
# else
# define JS_THREADSAFE_ASSERT(expr) ((void) 0)
# endif

#else

#define JS_ASSERT(expr)         ((void) 0)
#define JS_ASSERT_IF(cond,expr) ((void) 0)
#define JS_NOT_REACHED(reason)
#define JS_ALWAYS_TRUE(expr)    ((void) (expr))
#define JS_ALWAYS_FALSE(expr)    ((void) (expr))
#define JS_THREADSAFE_ASSERT(expr) ((void) 0)

#endif /* defined(DEBUG) */

/*
 * Compile-time assert. "cond" must be a constant expression.
 * The macro can be used only in places where an "extern" declaration is
 * allowed.
 */

#ifdef __SUNPRO_CC
/*
 * Sun Studio C++ compiler has a bug
 * "sizeof expression not accepted as size of array parameter"
 * It happens when js_static_assert() function is declared inside functions.
 * The bug number is 6688515. It is not public yet.
 * Therefore, for Sun Studio, declare js_static_assert as an array instead.
 */
#define JS_STATIC_ASSERT(cond) extern char js_static_assert[(cond) ? 1 : -1]
#else
#ifdef __COUNTER__
    #define JS_STATIC_ASSERT_GLUE1(x,y) x##y
    #define JS_STATIC_ASSERT_GLUE(x,y) JS_STATIC_ASSERT_GLUE1(x,y)
    #define JS_STATIC_ASSERT(cond)                                            \
        typedef int JS_STATIC_ASSERT_GLUE(js_static_assert, __COUNTER__)[(cond) ? 1 : -1]
#else
    #define JS_STATIC_ASSERT(cond) extern void js_static_assert(int arg[(cond) ? 1 : -1])
#endif
#endif

#define JS_STATIC_ASSERT_IF(cond, expr) JS_STATIC_ASSERT(!(cond) || (expr))

/*
 * Abort the process in a non-graceful manner. This will cause a core file,
 * call to the debugger or other moral equivalent as well as causing the
 * entire process to stop.
 */
extern JS_PUBLIC_API(void) JS_Abort(void);

#ifdef DEBUG
# define JS_BASIC_STATS 1
#endif

#ifdef JS_BASIC_STATS

#include <stdio.h>

typedef struct JSBasicStats {
    uint32      num;
    uint32      max;
    double      sum;
    double      sqsum;
    uint32      logscale;           /* logarithmic scale: 0 (linear), 2, 10 */
    uint32      hist[11];
} JSBasicStats;

#define JS_INIT_STATIC_BASIC_STATS  {0,0,0,0,0,{0,0,0,0,0,0,0,0,0,0,0}}
#define JS_BASIC_STATS_INIT(bs)     memset((bs), 0, sizeof(JSBasicStats))

#define JS_BASIC_STATS_ACCUM(bs,val)                                          \
    JS_BasicStatsAccum(bs, val)

#define JS_MeanAndStdDevBS(bs,sigma)                                          \
    JS_MeanAndStdDev((bs)->num, (bs)->sum, (bs)->sqsum, sigma)

extern void
JS_BasicStatsAccum(JSBasicStats *bs, uint32 val);

extern double
JS_MeanAndStdDev(uint32 num, double sum, double sqsum, double *sigma);

extern void
JS_DumpBasicStats(JSBasicStats *bs, const char *title, FILE *fp);

extern void
JS_DumpHistogram(JSBasicStats *bs, FILE *fp);

#else

#define JS_BASIC_STATS_ACCUM(bs,val) /* nothing */

#endif /* JS_BASIC_STATS */


#if defined(DEBUG_notme) && defined(XP_UNIX)

typedef struct JSCallsite JSCallsite;

struct JSCallsite {
    uint32      pc;
    char        *name;
    const char  *library;
    int         offset;
    JSCallsite  *parent;
    JSCallsite  *siblings;
    JSCallsite  *kids;
    void        *handy;
};

extern JS_FRIEND_API(JSCallsite *)
JS_Backtrace(int skip);

extern JS_FRIEND_API(void)
JS_DumpBacktrace(JSCallsite *trace);
#endif

#if defined JS_USE_CUSTOM_ALLOCATOR

#include "jscustomallocator.h"

#else

#ifdef DEBUG
/*
 * In order to test OOM conditions, when the shell command-line option
 * |-A NUM| is passed, we fail continuously after the NUM'th allocation.
 */
extern JS_PUBLIC_DATA(JSUint32) OOM_maxAllocations; /* set from shell/js.cpp */
extern JS_PUBLIC_DATA(JSUint32) OOM_counter; /* data race, who cares. */
#define JS_OOM_POSSIBLY_FAIL() \
    do \
    { \
        if (OOM_counter++ >= OOM_maxAllocations) { \
            return NULL; \
        } \
    } while (0)

#else
#define JS_OOM_POSSIBLY_FAIL() do {} while(0)
#endif

/*
 * SpiderMonkey code should not be calling these allocation functions directly.
 * Instead, all calls should go through JSRuntime, JSContext or OffTheBooks.
 * However, js_free() can be called directly.
 */
static JS_INLINE void* js_malloc(size_t bytes) {
    JS_OOM_POSSIBLY_FAIL();
    return malloc(bytes);
}

static JS_INLINE void* js_calloc(size_t bytes) {
    JS_OOM_POSSIBLY_FAIL();
    return calloc(bytes, 1);
}

static JS_INLINE void* js_realloc(void* p, size_t bytes) {
    JS_OOM_POSSIBLY_FAIL();
    return realloc(p, bytes);
}

static JS_INLINE void js_free(void* p) {
    free(p);
}
#endif/* JS_USE_CUSTOM_ALLOCATOR */

JS_END_EXTERN_C



#ifdef __cplusplus

/* 
 * User guide to memory management within SpiderMonkey:
 *
 * Quick tips:
 *
 *   Allocation:
 *   - Prefer to allocate using JSContext:
 *       cx->{malloc_,realloc_,calloc_,new_,new_array}
 *
 *   - If no JSContext is available, use a JSRuntime:
 *       rt->{malloc_,realloc_,calloc_,new_,new_array}
 *
 *   - As a last resort, use unaccounted allocation ("OffTheBooks"):
 *       js::OffTheBooks::{malloc_,realloc_,calloc_,new_,new_array}
 *
 *   Deallocation:
 *   - When the deallocation occurs on a slow path, use:
 *       Foreground::{free_,delete_,array_delete}
 *
 *   - Otherwise deallocate on a background thread using a JSContext:
 *       cx->{free_,delete_,array_delete}
 *  
 *   - If no JSContext is available, use a JSRuntime:
 *       rt->{free_,delete_,array_delete}
 *
 *   - As a last resort, use UnwantedForeground deallocation:
 *       js::UnwantedForeground::{free_,delete_,array_delete}
 *
 * General tips:
 *
 *   - Mixing and matching these allocators is allowed (you may free memory
 *     allocated by any allocator, with any deallocator).
 * 
 *   - Never, ever use normal C/C++ memory management:
 *       malloc, free, new, new[], delete, operator new, etc.
 *
 *   - Never, ever use low-level SpiderMonkey allocators:
 *       js_malloc(), js_free(), js_calloc(), js_realloc()
 *     Their use is reserved for the other memory managers.
 *
 *   - Classes which have private constructors or destructors should have
 *     JS_DECLARE_ALLOCATION_FRIENDS_FOR_PRIVATE_CONSTRUCTOR added to their
 *     declaration.
 * 
 * Details:
 *
 *   Using vanilla new/new[] is unsafe in SpiderMonkey because they throw on
 *   failure instead of returning NULL, which is what SpiderMonkey expects.
 *   (Even overriding them is unsafe, as the system's C++ runtime library may
 *   throw, which we do not support. We also can't just use the 'nothrow'
 *   variant of new/new[], because we want to mediate *all* allocations
 *   within SpiderMonkey, to satisfy any embedders using
 *   JS_USE_CUSTOM_ALLOCATOR.)
 *
 *   JSContexts and JSRuntimes keep track of memory allocated, and use this
 *   accounting to schedule GC. OffTheBooks does not. We'd like to remove
 *   OffTheBooks allocations as much as possible (bug 636558).
 *
 *   On allocation failure, a JSContext correctly reports an error, which a
 *   JSRuntime and OffTheBooks does not.
 *
 *   A JSContext deallocates in a background thread. A JSRuntime might
 *   deallocate in the background in the future, but does not now. Foreground
 *   deallocation is preferable on slow paths. UnwantedForeground deallocations
 *   occur where we have no JSContext or JSRuntime, and the deallocation is not
 *   on a slow path. We want to remove UnwantedForeground deallocations (bug
 *   636561).
 *
 *   JS_DECLARE_ALLOCATION_FRIENDS_FOR_PRIVATE_CONSTRUCTOR makes the allocation
 *   classes friends with your class, giving them access to private
 *   constructors and destructors.
 *
 *   |make check| does a source level check on the number of uses OffTheBooks,
 *   UnwantedForeground, js_malloc, js_free etc, to prevent regressions. If you
 *   really must add one, update Makefile.in, and run |make check|.
 *
 *   |make check| also statically prevents the use of vanilla new/new[].
 */

#define JS_NEW_BODY(allocator, t, parms)                                       \
    void *memory = allocator(sizeof(t));                                       \
    return memory ? new(memory) t parms : NULL;

/*
 * Given a class which should provide new_() methods, add
 * JS_DECLARE_NEW_METHODS (see JSContext for a usage example). This
 * adds new_()s with up to 12 parameters. Add more versions of new_ below if
 * you need more than 12 parameters.  
 *
 * Note: Do not add a ; at the end of a use of JS_DECLARE_NEW_METHODS,
 * or the build will break.
 */
#define JS_DECLARE_NEW_METHODS(ALLOCATOR, QUALIFIERS)\
    template <class T>\
    QUALIFIERS T *new_() {\
        JS_NEW_BODY(ALLOCATOR, T, ())\
    }\
\
    template <class T, class P1>\
    QUALIFIERS T *new_(P1 p1) {\
        JS_NEW_BODY(ALLOCATOR, T, (p1))\
    }\
\
    template <class T, class P1, class P2>\
    QUALIFIERS T *new_(P1 p1, P2 p2) {\
        JS_NEW_BODY(ALLOCATOR, T, (p1, p2))\
    }\
\
    template <class T, class P1, class P2, class P3>\
    QUALIFIERS T *new_(P1 p1, P2 p2, P3 p3) {\
        JS_NEW_BODY(ALLOCATOR, T, (p1, p2, p3))\
    }\
\
    template <class T, class P1, class P2, class P3, class P4>\
    QUALIFIERS T *new_(P1 p1, P2 p2, P3 p3, P4 p4) {\
        JS_NEW_BODY(ALLOCATOR, T, (p1, p2, p3, p4))\
    }\
\
    template <class T, class P1, class P2, class P3, class P4, class P5>\
    QUALIFIERS T *new_(P1 p1, P2 p2, P3 p3, P4 p4, P5 p5) {\
        JS_NEW_BODY(ALLOCATOR, T, (p1, p2, p3, p4, p5))\
    }\
\
    template <class T, class P1, class P2, class P3, class P4, class P5, class P6>\
    QUALIFIERS T *new_(P1 p1, P2 p2, P3 p3, P4 p4, P5 p5, P6 p6) {\
        JS_NEW_BODY(ALLOCATOR, T, (p1, p2, p3, p4, p5, p6))\
    }\
\
    template <class T, class P1, class P2, class P3, class P4, class P5, class P6, class P7>\
    QUALIFIERS T *new_(P1 p1, P2 p2, P3 p3, P4 p4, P5 p5, P6 p6, P7 p7) {\
        JS_NEW_BODY(ALLOCATOR, T, (p1, p2, p3, p4, p5, p6, p7))\
    }\
\
    template <class T, class P1, class P2, class P3, class P4, class P5, class P6, class P7, class P8>\
    QUALIFIERS T *new_(P1 p1, P2 p2, P3 p3, P4 p4, P5 p5, P6 p6, P7 p7, P8 p8) {\
        JS_NEW_BODY(ALLOCATOR, T, (p1, p2, p3, p4, p5, p6, p7, p8))\
    }\
\
    template <class T, class P1, class P2, class P3, class P4, class P5, class P6, class P7, class P8, class P9>\
    QUALIFIERS T *new_(P1 p1, P2 p2, P3 p3, P4 p4, P5 p5, P6 p6, P7 p7, P8 p8, P9 p9) {\
        JS_NEW_BODY(ALLOCATOR, T, (p1, p2, p3, p4, p5, p6, p7, p8, p9))\
    }\
\
    template <class T, class P1, class P2, class P3, class P4, class P5, class P6, class P7, class P8, class P9, class P10>\
    QUALIFIERS T *new_(P1 p1, P2 p2, P3 p3, P4 p4, P5 p5, P6 p6, P7 p7, P8 p8, P9 p9, P10 p10) {\
        JS_NEW_BODY(ALLOCATOR, T, (p1, p2, p3, p4, p5, p6, p7, p8, p9, p10))\
    }\
\
    template <class T, class P1, class P2, class P3, class P4, class P5, class P6, class P7, class P8, class P9, class P10, class P11>\
    QUALIFIERS T *new_(P1 p1, P2 p2, P3 p3, P4 p4, P5 p5, P6 p6, P7 p7, P8 p8, P9 p9, P10 p10, P11 p11) {\
        JS_NEW_BODY(ALLOCATOR, T, (p1, p2, p3, p4, p5, p6, p7, p8, p9, p10, p11))\
    }\
\
    template <class T, class P1, class P2, class P3, class P4, class P5, class P6, class P7, class P8, class P9, class P10, class P11, class P12>\
    QUALIFIERS T *new_(P1 p1, P2 p2, P3 p3, P4 p4, P5 p5, P6 p6, P7 p7, P8 p8, P9 p9, P10 p10, P11 p11, P12 p12) {\
        JS_NEW_BODY(ALLOCATOR, T, (p1, p2, p3, p4, p5, p6, p7, p8, p9, p10, p11, p12))\
    }\
    static const int JSMinAlignment = 8;\
    template <class T>\
    QUALIFIERS T *array_new(size_t n) {\
        /* The length is stored just before the vector memory. */\
        uint64 numBytes64 = uint64(JSMinAlignment) + uint64(sizeof(T)) * uint64(n);\
        size_t numBytes = size_t(numBytes64);\
        if (numBytes64 != numBytes) {\
            JS_ASSERT(0);   /* we want to know if this happens in debug builds */\
            return NULL;\
        }\
        void *memory = ALLOCATOR(numBytes);\
        if (!memory)\
            return NULL;\
        *(size_t *)memory = n;\
        memory = (void*)(uintptr_t(memory) + JSMinAlignment);\
        return new(memory) T[n];\
    }\


#define JS_DECLARE_DELETE_METHODS(DEALLOCATOR, QUALIFIERS)\
    template <class T>\
    QUALIFIERS void delete_(T *p) {\
        if (p) {\
            p->~T();\
            DEALLOCATOR(p);\
        }\
    }\
\
    template <class T>\
    QUALIFIERS void array_delete(T *p) {\
        if (p) {\
            void* p0 = (void *)(uintptr_t(p) - js::OffTheBooks::JSMinAlignment);\
            size_t n = *(size_t *)p0;\
            for (size_t i = 0; i < n; i++)\
                (p + i)->~T();\
            DEALLOCATOR(p0);\
        }\
    }


/*
 * In general, all allocations should go through a JSContext or JSRuntime, so
 * that the garbage collector knows how much memory has been allocated. In
 * cases where it is difficult to use a JSContext or JSRuntime, OffTheBooks can
 * be used, though this is undesirable.
 */
namespace js {
/* Import common mfbt declarations into "js". */
using namespace mozilla;

class OffTheBooks {
public:
    JS_DECLARE_NEW_METHODS(::js_malloc, JS_ALWAYS_INLINE static)

    static JS_INLINE void* malloc_(size_t bytes) {
        return ::js_malloc(bytes);
    }

    static JS_INLINE void* calloc_(size_t bytes) {
        return ::js_calloc(bytes);
    }

    static JS_INLINE void* realloc_(void* p, size_t bytes) {
        return ::js_realloc(p, bytes);
    }
};

/*
 * We generally prefer deallocating using JSContext because it can happen in
 * the background. On slow paths, we may prefer foreground allocation.
 */
class Foreground {
public:
    /* See parentheses comment above. */
    static JS_ALWAYS_INLINE void free_(void* p) {
        ::js_free(p);
    }

    JS_DECLARE_DELETE_METHODS(::js_free, JS_ALWAYS_INLINE static)
};

class UnwantedForeground : public Foreground {
};

} /* namespace js */

/*
 * Note lack of ; in JSRuntime below. This is intentional so "calling" this
 * looks "normal".
 */
#define JS_DECLARE_ALLOCATION_FRIENDS_FOR_PRIVATE_CONSTRUCTOR \
    friend class js::OffTheBooks;\
    friend class js::Foreground;\
    friend class js::UnwantedForeground;\
    friend struct ::JSContext;\
    friend struct ::JSRuntime


/**
 * The following classes are designed to cause assertions to detect
 * inadvertent use of guard objects as temporaries.  In other words,
 * when we have a guard object whose only purpose is its constructor and
 * destructor (and is never otherwise referenced), the intended use
 * might be:
 *     JSAutoTempValueRooter tvr(cx, 1, &val);
 * but is is easy to accidentally write:
 *     JSAutoTempValueRooter(cx, 1, &val);
 * which compiles just fine, but runs the destructor well before the
 * intended time.
 *
 * They work by adding (#ifdef DEBUG) an additional parameter to the
 * guard object's constructor, with a default value, so that users of
 * the guard object's API do not need to do anything.  The default value
 * of this parameter is a temporary object.  C++ (ISO/IEC 14882:1998),
 * section 12.2 [class.temporary], clauses 4 and 5 seem to assume a
 * guarantee that temporaries are destroyed in the reverse of their
 * construction order, but I actually can't find a statement that that
 * is true in the general case (beyond the two specific cases mentioned
 * there).  However, it seems to be true.
 *
 * These classes are intended to be used only via the macros immediately
 * below them:
 *   JS_DECL_USE_GUARD_OBJECT_NOTIFIER declares (ifdef DEBUG) a member
 *     variable, and should be put where a declaration of a private
 *     member variable would be placed.
 *   JS_GUARD_OBJECT_NOTIFIER_PARAM should be placed at the end of the
 *     parameters to each constructor of the guard object; it declares
 *     (ifdef DEBUG) an additional parameter.
 *   JS_GUARD_OBJECT_NOTIFIER_INIT is a statement that belongs in each
 *     constructor.  It uses the parameter declared by
 *     JS_GUARD_OBJECT_NOTIFIER_PARAM.
 */
#ifdef DEBUG
class JSGuardObjectNotifier
{
private:
    bool* mStatementDone;
public:
    JSGuardObjectNotifier() : mStatementDone(NULL) {}

    ~JSGuardObjectNotifier() {
        *mStatementDone = true;
    }

    void setStatementDone(bool *aStatementDone) {
        mStatementDone = aStatementDone;
    }
};

class JSGuardObjectNotificationReceiver
{
private:
    bool mStatementDone;
public:
    JSGuardObjectNotificationReceiver() : mStatementDone(false) {}

    ~JSGuardObjectNotificationReceiver() {
        /*
         * Assert that the guard object was not used as a temporary.
         * (Note that this assert might also fire if Init is not called
         * because the guard object's implementation is not using the
         * above macros correctly.)
         */
        JS_ASSERT(mStatementDone);
    }

    void Init(const JSGuardObjectNotifier &aNotifier) {
        /*
         * aNotifier is passed as a const reference so that we can pass a
         * temporary, but we really intend it as non-const
         */
        const_cast<JSGuardObjectNotifier&>(aNotifier).
            setStatementDone(&mStatementDone);
    }
};

#define JS_DECL_USE_GUARD_OBJECT_NOTIFIER \
    JSGuardObjectNotificationReceiver _mCheckNotUsedAsTemporary;
#define JS_GUARD_OBJECT_NOTIFIER_PARAM \
    , const JSGuardObjectNotifier& _notifier = JSGuardObjectNotifier()
#define JS_GUARD_OBJECT_NOTIFIER_PARAM_NO_INIT \
    , const JSGuardObjectNotifier& _notifier
#define JS_GUARD_OBJECT_NOTIFIER_PARAM0 \
    const JSGuardObjectNotifier& _notifier = JSGuardObjectNotifier()
#define JS_GUARD_OBJECT_NOTIFIER_INIT \
    JS_BEGIN_MACRO _mCheckNotUsedAsTemporary.Init(_notifier); JS_END_MACRO

#else /* defined(DEBUG) */

#define JS_DECL_USE_GUARD_OBJECT_NOTIFIER
#define JS_GUARD_OBJECT_NOTIFIER_PARAM
#define JS_GUARD_OBJECT_NOTIFIER_PARAM_NO_INIT
#define JS_GUARD_OBJECT_NOTIFIER_PARAM0
#define JS_GUARD_OBJECT_NOTIFIER_INIT JS_BEGIN_MACRO JS_END_MACRO

#endif /* !defined(DEBUG) */

namespace js {

template <class T>
JS_ALWAYS_INLINE static void
PodZero(T *t)
{
    memset(t, 0, sizeof(T));
}

template <class T>
JS_ALWAYS_INLINE static void
PodZero(T *t, size_t nelem)
{
    memset(t, 0, nelem * sizeof(T));
}

/*
 * Arrays implicitly convert to pointers to their first element, which is
 * dangerous when combined with the above PodZero definitions. Adding an
 * overload for arrays is ambiguous, so we need another identifier. The
 * ambiguous overload is left to catch mistaken uses of PodZero; if you get a
 * compile error involving PodZero and array types, use PodArrayZero instead.
 */
template <class T, size_t N> static void PodZero(T (&)[N]);          /* undefined */
template <class T, size_t N> static void PodZero(T (&)[N], size_t);  /* undefined */

template <class T, size_t N>
JS_ALWAYS_INLINE static void
PodArrayZero(T (&t)[N])
{
    memset(t, 0, N * sizeof(T));
}

template <class T>
JS_ALWAYS_INLINE static void
PodCopy(T *dst, const T *src, size_t nelem)
{
    /* Cannot find portable word-sized abs(). */
    JS_ASSERT_IF(dst >= src, size_t(dst - src) >= nelem);
    JS_ASSERT_IF(src >= dst, size_t(src - dst) >= nelem);

    if (nelem < 128) {
        for (const T *srcend = src + nelem; src != srcend; ++src, ++dst)
            *dst = *src;
    } else {
        memcpy(dst, src, nelem * sizeof(T));
    }
}

template <class T>
JS_ALWAYS_INLINE static bool
PodEqual(T *one, T *two, size_t len)
{
    if (len < 128) {
        T *p1end = one + len;
        for (T *p1 = one, *p2 = two; p1 != p1end; ++p1, ++p2) {
            if (*p1 != *p2)
                return false;
        }
        return true;
    }

    return !memcmp(one, two, len * sizeof(T));
}


/*
 * Ordinarily, a function taking a JSContext* 'cx' paremter reports errors on
 * the context. In some cases, functions optionally report and indicate this by
 * taking a nullable 'maybecx' parameter. In some cases, though, a function
 * always needs a 'cx', but optionally reports. This option is presented by the
 * MaybeReportError.
 */
enum MaybeReportError { REPORT_ERROR = true, DONT_REPORT_ERROR = false };

/*
 * "Move" References
 *
 * Some types can be copied much more efficiently if we know the original's
 * value need not be preserved --- that is, if we are doing a "move", not a
 * "copy". For example, if we have:
 *
 *   Vector<T> u;
 *   Vector<T> v(u);
 * 
 * the constructor for v must apply a copy constructor to each element of u ---
 * taking time linear in the length of u. However, if we know we will not need u
 * any more once v has been initialized, then we could initialize v very
 * efficiently simply by stealing u's dynamically allocated buffer and giving it
 * to v --- a constant-time operation, regardless of the size of u.
 *
 * Moves often appear in container implementations. For example, when we append
 * to a vector, we may need to resize its buffer. This entails moving each of
 * its extant elements from the old, smaller buffer to the new, larger buffer.
 * But once the elements have been migrated, we're just going to throw away the
 * old buffer; we don't care if they still have their values. So if the vector's
 * element type can implement "move" more efficiently than "copy", the vector
 * resizing should by all means use a "move" operation. Hash tables also need to
 * be resized.
 *
 * The details of the optimization, and whether it's worth applying, vary from
 * one type to the next. And while some constructor calls are moves, many really
 * are copies, and can't be optimized this way. So we need:
 *
 * 1) a way for a particular invocation of a copy constructor to say that it's
 *    really a move, and that the value of the original isn't important
 *    afterwards (althought it must still be safe to destroy); and
 *
 * 2) a way for a type (like Vector) to announce that it can be moved more
 *    efficiently than it can be copied, and provide an implementation of that
 *    move operation.
 *
 * The Move(T &) function takes a reference to a T, and returns an MoveRef<T>
 * referring to the same value; that's 1). An MoveRef<T> is simply a reference
 * to a T, annotated to say that a copy constructor applied to it may move that
 * T, instead of copying it. Finally, a constructor that accepts an MoveRef<T>
 * should perform a more efficient move, instead of a copy, providing 2).
 *
 * So, where we might define a copy constructor for a class C like this:
 *
 *   C(const C &rhs) { ... copy rhs to this ... }
 *
 * we would declare a move constructor like this:
 *
 *   C(MoveRef<C> rhs) { ... move rhs to this ... }
 *
 * And where we might perform a copy like this:
 *
 *   C c2(c1);
 *
 * we would perform a move like this:
 *
 *   C c2(Move(c1))
 * 
 * Note that MoveRef<T> implicitly converts to T &, so you can pass an
 * MoveRef<T> to an ordinary copy constructor for a type that doesn't support a
 * special move constructor, and you'll just get a copy. This means that
 * templates can use Move whenever they know they won't use the original value
 * any more, even if they're not sure whether the type at hand has a specialized
 * move constructor. If it doesn't, the MoveRef<T> will just convert to a T &,
 * and the ordinary copy constructor will apply.
 *
 * A class with a move constructor can also provide a move assignment operator,
 * which runs this's destructor, and then applies the move constructor to
 * *this's memory. A typical definition:
 *
 *   C &operator=(MoveRef<C> rhs) {
 *     this->~C();
 *     new(this) C(rhs);
 *     return *this;
 *   }
 *
 * With that in place, one can write move assignments like this:
 *
 *   c2 = Move(c1);
 *
 * This destroys c1, moves c1's value to c2, and leaves c1 in an undefined but
 * destructible state.
 *
 * This header file defines MoveRef and Move in the js namespace. It's up to
 * individual containers to annotate moves as such, by calling Move; and it's up
 * to individual types to define move constructors.
 *
 * One hint: if you're writing a move constructor where the type has members
 * that should be moved themselves, it's much nicer to write this:
 *
 *   C(MoveRef<C> c) : x(c->x), y(c->y) { }
 *
 * than the equivalent:
 *
 *   C(MoveRef<C> c) { new(&x) X(c->x); new(&y) Y(c->y); }
 *
 * especially since GNU C++ fails to notice that this does indeed initialize x
 * and y, which may matter if they're const.
 */
template<typename T>
class MoveRef {
  public:
    typedef T Referent;
    explicit MoveRef(T &t) : pointer(&t) { }
    T &operator*()  const { return *pointer; }
    T *operator->() const { return  pointer; }
    operator T &()  const { return *pointer; }
  private:
    T *pointer;
};

template<typename T>
MoveRef<T> Move(T &t) { return MoveRef<T>(t); }

} /* namespace js */

#endif /* defined(__cplusplus) */

#endif /* jsutil_h___ */