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Issue #1738 - Part 1: Improve performance of JSON stringify
- Use some pointer voodoo and instead of stringbuffer append() - Use a lookup table instead of char comparisons for chr < 256 - Stop using a Hashtable/MovableCellHasher for JSON CycleDetector
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Moonchild
roytam1
parent
ebf2abb0e3
commit
feab62b009
3 changed files with 111 additions and 90 deletions
181
js/src/json.cpp
181
js/src/json.cpp
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@ -39,78 +39,81 @@ const Class js::JSONClass = {
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JSCLASS_HAS_CACHED_PROTO(JSProto_JSON)
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};
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static inline bool
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IsQuoteSpecialCharacter(char16_t c)
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/* ES5 15.12.3 Quote.
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* Requires that the destination has enough space allocated for src after escaping
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* (that is, `2 + 6 * (srcEnd - srcBegin)` characters).
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*/
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template <typename SrcCharT, typename DstCharT>
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static MOZ_ALWAYS_INLINE RangedPtr<DstCharT>
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InfallibleQuote(RangedPtr<const SrcCharT> srcBegin, RangedPtr<const SrcCharT> srcEnd, RangedPtr<DstCharT> dstPtr)
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{
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static_assert('\b' < ' ', "'\\b' must be treated as special below");
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static_assert('\f' < ' ', "'\\f' must be treated as special below");
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static_assert('\n' < ' ', "'\\n' must be treated as special below");
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static_assert('\r' < ' ', "'\\r' must be treated as special below");
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static_assert('\t' < ' ', "'\\t' must be treated as special below");
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return c == '"' || c == '\\' || c < ' ';
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}
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/* ES5 15.12.3 Quote. */
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template <typename CharT>
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static bool
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Quote(StringBuffer& sb, JSLinearString* str)
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{
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size_t len = str->length();
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// Maps characters < 256 to the value that must follow the '\\' in the quoted string.
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// Entries with 'u' are handled as \\u00xy, and entries with 0 are not escaped in any way.
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// Characters >= 256 are all assumed to be unescaped.
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static const Latin1Char escapeLookup[256] = {
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'u', 'u', 'u', 'u', 'u', 'u', 'u', 'u', 'b', 't',
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'n', 'u', 'f', 'r', 'u', 'u', 'u', 'u', 'u', 'u',
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'u', 'u', 'u', 'u', 'u', 'u', 'u', 'u', 'u', 'u',
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'u', 'u', 0, 0, '\"', 0, 0, 0, 0, 0,
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0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
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0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
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0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
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0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
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0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
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0, 0, '\\', // rest are all zeros
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};
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/* Step 1. */
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if (!sb.append('"'))
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return false;
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*dstPtr++ = '"';
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/* Step 2. */
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JS::AutoCheckCannotGC nogc;
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const RangedPtr<const CharT> buf(str->chars<CharT>(nogc), len);
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for (size_t i = 0; i < len; ++i) {
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/* Batch-append maximal character sequences containing no escapes. */
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size_t mark = i;
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do {
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if (IsQuoteSpecialCharacter(buf[i]))
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break;
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} while (++i < len);
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if (i > mark) {
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if (!sb.appendSubstring(str, mark, i - mark))
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return false;
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if (i == len)
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break;
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while (srcBegin != srcEnd) {
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SrcCharT c = *srcBegin++;
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size_t escapeIndex = c % sizeof(escapeLookup);
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Latin1Char escaped = escapeLookup[escapeIndex];
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if (MOZ_LIKELY((escapeIndex != size_t(c)) || !escaped)) {
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*dstPtr++ = c;
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continue;
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}
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char16_t c = buf[i];
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if (c == '"' || c == '\\') {
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if (!sb.append('\\') || !sb.append(c))
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return false;
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} else if (c == '\b' || c == '\f' || c == '\n' || c == '\r' || c == '\t') {
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char16_t abbrev = (c == '\b')
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? 'b'
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: (c == '\f')
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? 'f'
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: (c == '\n')
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? 'n'
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: (c == '\r')
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? 'r'
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: 't';
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if (!sb.append('\\') || !sb.append(abbrev))
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return false;
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} else {
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*dstPtr++ = '\\';
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*dstPtr++ = escaped;
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if (escaped == 'u') {
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MOZ_ASSERT(c < ' ');
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if (!sb.append("\\u00"))
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return false;
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MOZ_ASSERT((c >> 4) < 10);
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uint8_t x = c >> 4, y = c % 16;
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if (!sb.append(Latin1Char('0' + x)) ||
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!sb.append(Latin1Char(y < 10 ? '0' + y : 'a' + (y - 10))))
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{
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return false;
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}
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*dstPtr++ = '0';
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*dstPtr++ = '0';
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*dstPtr++ = '0' + x;
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*dstPtr++ = y < 10 ? '0' + y : 'a' + (y - 10);
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}
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}
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/* Steps 3-4. */
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return sb.append('"');
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*dstPtr++ = '"';
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return dstPtr;
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}
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template <typename SrcCharT, typename CharVectorT>
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static bool
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Quote(CharVectorT& sb, JSLinearString* str)
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{
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// We resize the backing buffer to the maximum size we could possibly need,
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// write the escaped string into it, and shrink it back to the size we ended
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// up needing.
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size_t len = str->length();
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size_t sbInitialLen = sb.length();
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if (!sb.growByUninitialized(len * 6 + 2))
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return false;
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typedef typename CharVectorT::ElementType DstCharT;
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JS::AutoCheckCannotGC nogc;
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RangedPtr<const SrcCharT> srcBegin{str->chars<SrcCharT>(nogc), len};
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RangedPtr<DstCharT> dstBegin{sb.begin(), sb.begin(), sb.end()};
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RangedPtr<DstCharT> dstEnd = InfallibleQuote(srcBegin, srcBegin + len, dstBegin + sbInitialLen);
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size_t newSize = dstEnd - dstBegin;
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sb.shrinkTo(newSize);
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return true;
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}
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static bool
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@ -120,14 +123,23 @@ Quote(JSContext* cx, StringBuffer& sb, JSString* str)
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if (!linear)
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return false;
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return linear->hasLatin1Chars()
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? Quote<Latin1Char>(sb, linear)
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: Quote<char16_t>(sb, linear);
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// Check if either has non-latin1 before calling ensure, so that the buffer's
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// hasEnsured flag is set if the converstion to twoByte was automatic.
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if (!sb.isUnderlyingBufferLatin1() || linear->hasTwoByteChars()) {
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if (!sb.ensureTwoByteChars())
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return false;
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}
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if (linear->hasTwoByteChars())
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return Quote<char16_t>(sb.rawTwoByteBuffer(), linear);
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return sb.isUnderlyingBufferLatin1()
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? Quote<Latin1Char>(sb.latin1Chars(), linear)
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: Quote<Latin1Char>(sb.rawTwoByteBuffer(), linear);
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}
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namespace {
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using ObjectSet = GCHashSet<JSObject*, MovableCellHasher<JSObject*>, SystemAllocPolicy>;
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using ObjectVector = GCVector<JSObject*, 8>;
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class StringifyContext
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{
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@ -138,7 +150,7 @@ class StringifyContext
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: sb(sb),
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gap(gap),
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replacer(cx, replacer),
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stack(cx),
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stack(cx, ObjectVector(cx)),
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propertyList(propertyList),
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depth(0),
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maybeSafely(maybeSafely)
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@ -147,14 +159,10 @@ class StringifyContext
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MOZ_ASSERT_IF(maybeSafely, gap.empty());
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}
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bool init() {
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return stack.init(8);
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}
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StringBuffer& sb;
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const StringBuffer& gap;
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RootedObject replacer;
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Rooted<ObjectSet> stack;
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Rooted<ObjectVector> stack;
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const AutoIdVector& propertyList;
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uint32_t depth;
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bool maybeSafely;
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@ -302,29 +310,34 @@ class CycleDetector
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{
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public:
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CycleDetector(StringifyContext* scx, HandleObject obj)
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: stack(&scx->stack), obj_(obj) {
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}
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: stack_(&scx->stack)
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, obj_(obj)
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, appended_(false)
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{}
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bool foundCycle(JSContext* cx) {
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auto addPtr = stack.lookupForAdd(obj_);
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if (addPtr) {
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JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr, JSMSG_JSON_CYCLIC_VALUE);
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return false;
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MOZ_ALWAYS_INLINE bool foundCycle(JSContext* cx) {
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JSObject* obj = obj_;
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for (JSObject* obj2 : stack_) {
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if (MOZ_UNLIKELY(obj == obj2)) {
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JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr, JSMSG_JSON_CYCLIC_VALUE);
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return false;
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}
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}
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if (!stack.add(addPtr, obj_)) {
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ReportOutOfMemory(cx);
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return false;
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}
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return true;
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appended_ = stack_.append(obj);
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return appended_;
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}
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~CycleDetector() {
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stack.remove(obj_);
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if (MOZ_LIKELY(appended_)) {
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MOZ_ASSERT(stack_.back() == obj_);
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stack_.popBack();
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}
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}
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private:
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MutableHandle<ObjectSet> stack;
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MutableHandle<ObjectVector> stack_;
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HandleObject obj_;
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bool appended_;
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};
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/* ES5 15.12.3 JO. */
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@ -747,8 +760,6 @@ js::Stringify(JSContext* cx, MutableHandleValue vp, JSObject* replacer_, const V
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/* Step 12. */
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StringifyContext scx(cx, sb, gap, replacer, propertyList,
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stringifyBehavior == StringifyBehavior::RestrictedSafe);
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if (!scx.init())
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return false;
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if (!PreprocessValue(cx, wrapper, HandleId(emptyId), vp, &scx))
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return false;
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if (IsFilteredValue(vp))
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