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gecko-dev/js/public/Utility.h

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/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
* vim: set ts=8 sw=4 et tw=99 ft=cpp:
*
* ***** 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 SpiderMonkey JavaScript code.
*
* The Initial Developer of the Original Code is
* the Mozilla Foundation.
* Portions created by the Initial Developer are Copyright (C) 2011
* the Initial Developer. All Rights Reserved.
*
* Contributor(s):
*
* Alternatively, the contents of this file may be used under the terms of
* either 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 ***** */
#ifndef js_utility_h__
#define js_utility_h__
#include "mozilla/Assertions.h"
#include <stdlib.h>
#include <string.h>
#ifdef JS_OOM_DO_BACKTRACES
#include <stdio.h>
#include <execinfo.h>
#endif
#include "jstypes.h"
#ifdef __cplusplus
/* The public JS engine namespace. */
namespace JS {}
/* The mozilla-shared reusable template/utility namespace. */
namespace mozilla {}
/* The private JS engine namespace. */
namespace js {
/* The private namespace is a superset of the public/shared namespaces. */
using namespace JS;
using namespace mozilla;
} /* namespace js */
#endif /* __cplusplus */
JS_BEGIN_EXTERN_C
/*
* Pattern used to overwrite freed memory. If you are accessing an object with
* this pattern, you probably have a dangling pointer.
*/
#define JS_FREE_PATTERN 0xDA
#define JS_ASSERT(expr) MOZ_ASSERT(expr)
#define JS_ASSERT_IF(cond, expr) MOZ_ASSERT_IF(cond, expr)
#define JS_NOT_REACHED(reason) MOZ_NOT_REACHED(reason)
#define JS_ALWAYS_TRUE(expr) MOZ_ALWAYS_TRUE(expr)
#define JS_ALWAYS_FALSE(expr) MOZ_ALWAYS_FALSE(expr)
#ifdef DEBUG
# ifdef JS_THREADSAFE
# define JS_THREADSAFE_ASSERT(expr) JS_ASSERT(expr)
# else
# define JS_THREADSAFE_ASSERT(expr) ((void) 0)
# endif
#else
# define JS_THREADSAFE_ASSERT(expr) ((void) 0)
#endif
#define JS_STATIC_ASSERT(cond) MOZ_STATIC_ASSERT(cond, "JS_STATIC_ASSERT")
#define JS_STATIC_ASSERT_IF(cond, expr) MOZ_STATIC_ASSERT_IF(cond, expr, "JS_STATIC_ASSERT_IF")
/*
* 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);
/*
* Custom allocator support for SpiderMonkey
*/
#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(uint32_t) OOM_maxAllocations; /* set from shell/js.cpp */
extern JS_PUBLIC_DATA(uint32_t) OOM_counter; /* data race, who cares. */
#ifdef JS_OOM_DO_BACKTRACES
#define JS_OOM_BACKTRACE_SIZE 32
static JS_ALWAYS_INLINE void
PrintBacktrace()
{
void* OOM_trace[JS_OOM_BACKTRACE_SIZE];
char** OOM_traceSymbols = NULL;
int32_t OOM_traceSize = 0;
int32_t OOM_traceIdx = 0;
OOM_traceSize = backtrace(OOM_trace, JS_OOM_BACKTRACE_SIZE);
OOM_traceSymbols = backtrace_symbols(OOM_trace, OOM_traceSize);
if (!OOM_traceSymbols)
return;
for (OOM_traceIdx = 0; OOM_traceIdx < OOM_traceSize; ++OOM_traceIdx) {
fprintf(stderr, "#%d %s\n", OOM_traceIdx, OOM_traceSymbols[OOM_traceIdx]);
}
free(OOM_traceSymbols);
}
#define JS_OOM_EMIT_BACKTRACE() \
do {\
fprintf(stderr, "Forcing artificial memory allocation function failure:\n");\
PrintBacktrace();\
} while (0)
# else
# define JS_OOM_EMIT_BACKTRACE() do {} while(0)
#endif /* JS_OOM_DO_BACKTRACES */
# define JS_OOM_POSSIBLY_FAIL() \
do \
{ \
if (++OOM_counter > OOM_maxAllocations) { \
JS_OOM_EMIT_BACKTRACE();\
return NULL; \
} \
} while (0)
# define JS_OOM_POSSIBLY_FAIL_REPORT(cx) \
do \
{ \
if (++OOM_counter > OOM_maxAllocations) { \
JS_OOM_EMIT_BACKTRACE();\
js_ReportOutOfMemory(cx);\
return NULL; \
} \
} while (0)
# else
# define JS_OOM_POSSIBLY_FAIL() do {} while(0)
# define JS_OOM_POSSIBLY_FAIL_REPORT(cx) do {} while(0)
# endif /* DEBUG */
/*
* 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 */
/*
* Replace bit-scanning code sequences with CPU-specific instructions to
* speedup calculations of ceiling/floor log2.
*
* With GCC 3.4 or later we can use __builtin_clz for that, see bug 327129.
*
* SWS: Added MSVC intrinsic bitscan support. See bugs 349364 and 356856.
*/
#if defined(_WIN32) && (_MSC_VER >= 1300) && (defined(_M_IX86) || defined(_M_AMD64) || defined(_M_X64))
unsigned char _BitScanForward(unsigned long * Index, unsigned long Mask);
unsigned char _BitScanReverse(unsigned long * Index, unsigned long Mask);
# pragma intrinsic(_BitScanForward,_BitScanReverse)
__forceinline static int
__BitScanForward32(unsigned int val)
{
unsigned long idx;
_BitScanForward(&idx, (unsigned long)val);
return (int)idx;
}
__forceinline static int
__BitScanReverse32(unsigned int val)
{
unsigned long idx;
_BitScanReverse(&idx, (unsigned long)val);
return (int)(31-idx);
}
# define js_bitscan_ctz32(val) __BitScanForward32(val)
# define js_bitscan_clz32(val) __BitScanReverse32(val)
# define JS_HAS_BUILTIN_BITSCAN32
#if defined(_M_AMD64) || defined(_M_X64)
unsigned char _BitScanForward64(unsigned long * Index, unsigned __int64 Mask);
unsigned char _BitScanReverse64(unsigned long * Index, unsigned __int64 Mask);
# pragma intrinsic(_BitScanForward64,_BitScanReverse64)
__forceinline static int
__BitScanForward64(unsigned __int64 val)
{
unsigned long idx;
_BitScanForward64(&idx, val);
return (int)idx;
}
__forceinline static int
__BitScanReverse64(unsigned __int64 val)
{
unsigned long idx;
_BitScanReverse64(&idx, val);
return (int)(63-idx);
}
# define js_bitscan_ctz64(val) __BitScanForward64(val)
# define js_bitscan_clz64(val) __BitScanReverse64(val)
# define JS_HAS_BUILTIN_BITSCAN64
#endif
#elif (__GNUC__ >= 4) || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4)
# define js_bitscan_ctz32(val) __builtin_ctz(val)
# define js_bitscan_clz32(val) __builtin_clz(val)
# define JS_HAS_BUILTIN_BITSCAN32
# if (JS_BYTES_PER_WORD == 8)
# define js_bitscan_ctz64(val) __builtin_ctzll(val)
# define js_bitscan_clz64(val) __builtin_clzll(val)
# define JS_HAS_BUILTIN_BITSCAN64
# endif
#endif
/*
** Macro version of JS_CeilingLog2: Compute the log of the least power of
** 2 greater than or equal to _n. The result is returned in _log2.
*/
#ifdef JS_HAS_BUILTIN_BITSCAN32
/*
* Use intrinsic function or count-leading-zeros to calculate ceil(log2(_n)).
* The macro checks for "n <= 1" and not "n != 0" as js_bitscan_clz32(0) is
* undefined.
*/
# define JS_CEILING_LOG2(_log2,_n) \
JS_BEGIN_MACRO \
unsigned int j_ = (unsigned int)(_n); \
(_log2) = (j_ <= 1 ? 0 : 32 - js_bitscan_clz32(j_ - 1)); \
JS_END_MACRO
#else
# define JS_CEILING_LOG2(_log2,_n) \
JS_BEGIN_MACRO \
uint32_t j_ = (uint32_t)(_n); \
(_log2) = 0; \
if ((j_) & ((j_)-1)) \
(_log2) += 1; \
if ((j_) >> 16) \
(_log2) += 16, (j_) >>= 16; \
if ((j_) >> 8) \
(_log2) += 8, (j_) >>= 8; \
if ((j_) >> 4) \
(_log2) += 4, (j_) >>= 4; \
if ((j_) >> 2) \
(_log2) += 2, (j_) >>= 2; \
if ((j_) >> 1) \
(_log2) += 1; \
JS_END_MACRO
#endif
/*
** Macro version of JS_FloorLog2: Compute the log of the greatest power of
** 2 less than or equal to _n. The result is returned in _log2.
**
** This is equivalent to finding the highest set bit in the word.
*/
#ifdef JS_HAS_BUILTIN_BITSCAN32
/*
* Use js_bitscan_clz32 or count-leading-zeros to calculate floor(log2(_n)).
* Since js_bitscan_clz32(0) is undefined, the macro set the loweset bit to 1
* to ensure 0 result when _n == 0.
*/
# define JS_FLOOR_LOG2(_log2,_n) \
JS_BEGIN_MACRO \
(_log2) = 31 - js_bitscan_clz32(((unsigned int)(_n)) | 1); \
JS_END_MACRO
#else
# define JS_FLOOR_LOG2(_log2,_n) \
JS_BEGIN_MACRO \
uint32_t j_ = (uint32_t)(_n); \
(_log2) = 0; \
if ((j_) >> 16) \
(_log2) += 16, (j_) >>= 16; \
if ((j_) >> 8) \
(_log2) += 8, (j_) >>= 8; \
if ((j_) >> 4) \
(_log2) += 4, (j_) >>= 4; \
if ((j_) >> 2) \
(_log2) += 2, (j_) >>= 2; \
if ((j_) >> 1) \
(_log2) += 1; \
JS_END_MACRO
#endif
#if JS_BYTES_PER_WORD == 4
# ifdef JS_HAS_BUILTIN_BITSCAN32
# define js_FloorLog2wImpl(n) \
((size_t)(JS_BITS_PER_WORD - 1 - js_bitscan_clz32(n)))
# else
JS_PUBLIC_API(size_t) js_FloorLog2wImpl(size_t n);
# endif
#elif JS_BYTES_PER_WORD == 8
# ifdef JS_HAS_BUILTIN_BITSCAN64
# define js_FloorLog2wImpl(n) \
((size_t)(JS_BITS_PER_WORD - 1 - js_bitscan_clz64(n)))
# else
JS_PUBLIC_API(size_t) js_FloorLog2wImpl(size_t n);
# endif
#else
# error "NOT SUPPORTED"
#endif
/*
* Internal function.
* Compute the log of the least power of 2 greater than or equal to n. This is
* a version of JS_CeilingLog2 that operates on unsigned integers with
* CPU-dependant size.
*/
#define JS_CEILING_LOG2W(n) ((n) <= 1 ? 0 : 1 + JS_FLOOR_LOG2W((n) - 1))
/*
* Internal function.
* Compute the log of the greatest power of 2 less than or equal to n.
* This is a version of JS_FloorLog2 that operates on unsigned integers with
* CPU-dependant size and requires that n != 0.
*/
static MOZ_ALWAYS_INLINE size_t
JS_FLOOR_LOG2W(size_t n)
{
JS_ASSERT(n != 0);
return js_FloorLog2wImpl(n);
}
JS_END_EXTERN_C
#ifdef __cplusplus
#include <new>
/*
* User guide to memory management within SpiderMonkey:
*
* Quick tips:
*
* Allocation:
* - Prefer to allocate using JSContext:
* cx->{malloc_,realloc_,calloc_,new_,array_new}
*
* - If no JSContext is available, use a JSRuntime:
* rt->{malloc_,realloc_,calloc_,new_,array_new}
*
* - As a last resort, use unaccounted allocation ("OffTheBooks"):
* js::OffTheBooks::{malloc_,realloc_,calloc_,new_,array_new}
*
* 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_t numBytes64 = uint64_t(JSMinAlignment) + uint64_t(sizeof(T)) * uint64_t(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 {
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 JS_FRIEND_API(JSGuardObjectNotifier)
{
private:
bool* mStatementDone;
public:
JSGuardObjectNotifier() : mStatementDone(NULL) {}
~JSGuardObjectNotifier() {
*mStatementDone = true;
}
void setStatementDone(bool *aStatementDone) {
mStatementDone = aStatementDone;
}
};
class JS_FRIEND_API(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 {
/*
* "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; }
#if defined(__GXX_EXPERIMENTAL_CXX0X__) && defined(__clang__)
/*
* If MoveRef is used in a rvalue position (which is expected), we can
* end up in a situation where, without this ifdef, we would try to pass
* a T& to a move constructor, which fails. It is not clear if the compiler
* should instead use the copy constructor, but for now this lets us build
* with clang. See bug 689066 and llvm.org/pr11003 for the details.
* Note: We can probably remove MoveRef completely once we are comfortable
* using c++11.
*/
operator T&& () const { return static_cast<T&&>(*pointer); }
#else
operator T& () const { return *pointer; }
#endif
private:
T *pointer;
};
template<typename T>
MoveRef<T> Move(T &t) { return MoveRef<T>(t); }
template<typename T>
MoveRef<T> Move(const T &t) { return MoveRef<T>(const_cast<T &>(t)); }
/* Useful for implementing containers that assert non-reentrancy */
class ReentrancyGuard
{
/* ReentrancyGuard is not copyable. */
ReentrancyGuard(const ReentrancyGuard &);
void operator=(const ReentrancyGuard &);
#ifdef DEBUG
bool &entered;
#endif
public:
template <class T>
#ifdef DEBUG
ReentrancyGuard(T &obj)
: entered(obj.entered)
#else
ReentrancyGuard(T &/*obj*/)
#endif
{
#ifdef DEBUG
JS_ASSERT(!entered);
entered = true;
#endif
}
~ReentrancyGuard()
{
#ifdef DEBUG
entered = false;
#endif
}
};
/*
* Round x up to the nearest power of 2. This function assumes that the most
* significant bit of x is not set, which would lead to overflow.
*/
JS_ALWAYS_INLINE size_t
RoundUpPow2(size_t x)
{
return size_t(1) << JS_CEILING_LOG2W(x);
}
} /* namespace js */
namespace JS {
/*
* Methods for poisoning GC heap pointer words and checking for poisoned words.
* These are in this file for use in Value methods and so forth.
*
* If the moving GC hazard analysis is in use and detects a non-rooted stack
* pointer to a GC thing, one byte of that pointer is poisoned to refer to an
* invalid location. For both 32 bit and 64 bit systems, the fourth byte of the
* pointer is overwritten, to reduce the likelihood of accidentally changing
* a live integer value.
*/
inline void PoisonPtr(uintptr_t *v)
{
#if defined(JSGC_ROOT_ANALYSIS) && defined(DEBUG)
uint8_t *ptr = (uint8_t *) v + 3;
*ptr = JS_FREE_PATTERN;
#endif
}
template <typename T>
inline bool IsPoisonedPtr(T *v)
{
#if defined(JSGC_ROOT_ANALYSIS) && defined(DEBUG)
uint32_t mask = uintptr_t(v) & 0xff000000;
return mask == uint32_t(JS_FREE_PATTERN << 24);
#else
return false;
#endif
}
}
#endif /* defined(__cplusplus) */
/*
* This is SpiderMonkey's equivalent to |nsMallocSizeOfFun|.
*/
typedef size_t(*JSMallocSizeOfFun)(const void *p);
/* sixgill annotation defines */
#ifndef HAVE_STATIC_ANNOTATIONS
# define HAVE_STATIC_ANNOTATIONS
# ifdef XGILL_PLUGIN
# define STATIC_PRECONDITION(COND) __attribute__((precondition(#COND)))
# define STATIC_PRECONDITION_ASSUME(COND) __attribute__((precondition_assume(#COND)))
# define STATIC_POSTCONDITION(COND) __attribute__((postcondition(#COND)))
# define STATIC_POSTCONDITION_ASSUME(COND) __attribute__((postcondition_assume(#COND)))
# define STATIC_INVARIANT(COND) __attribute__((invariant(#COND)))
# define STATIC_INVARIANT_ASSUME(COND) __attribute__((invariant_assume(#COND)))
# define STATIC_PASTE2(X,Y) X ## Y
# define STATIC_PASTE1(X,Y) STATIC_PASTE2(X,Y)
# define STATIC_ASSERT(COND) \
JS_BEGIN_MACRO \
__attribute__((assert_static(#COND), unused)) \
int STATIC_PASTE1(assert_static_, __COUNTER__); \
JS_END_MACRO
# define STATIC_ASSUME(COND) \
JS_BEGIN_MACRO \
__attribute__((assume_static(#COND), unused)) \
int STATIC_PASTE1(assume_static_, __COUNTER__); \
JS_END_MACRO
# define STATIC_ASSERT_RUNTIME(COND) \
JS_BEGIN_MACRO \
__attribute__((assert_static_runtime(#COND), unused)) \
int STATIC_PASTE1(assert_static_runtime_, __COUNTER__); \
JS_END_MACRO
# else /* XGILL_PLUGIN */
# define STATIC_PRECONDITION(COND) /* nothing */
# define STATIC_PRECONDITION_ASSUME(COND) /* nothing */
# define STATIC_POSTCONDITION(COND) /* nothing */
# define STATIC_POSTCONDITION_ASSUME(COND) /* nothing */
# define STATIC_INVARIANT(COND) /* nothing */
# define STATIC_INVARIANT_ASSUME(COND) /* nothing */
# define STATIC_ASSERT(COND) JS_BEGIN_MACRO /* nothing */ JS_END_MACRO
# define STATIC_ASSUME(COND) JS_BEGIN_MACRO /* nothing */ JS_END_MACRO
# define STATIC_ASSERT_RUNTIME(COND) JS_BEGIN_MACRO /* nothing */ JS_END_MACRO
# endif /* XGILL_PLUGIN */
# define STATIC_SKIP_INFERENCE STATIC_INVARIANT(skip_inference())
#endif /* HAVE_STATIC_ANNOTATIONS */
#endif /* js_utility_h__ */
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