js/src/jsapi-tests/testDeduplication.cpp

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
   2  * vim: set ts=8 sts=2 et sw=2 tw=80:
   3  */
   4 /* This Source Code Form is subject to the terms of the Mozilla Public
   5  * License, v. 2.0. If a copy of the MPL was not distributed with this
   6  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   7
   8 #include <string.h>
   9
  10 #include "gc/GC.h"
  11
  12 #include "js/RootingAPI.h"
  13 #include "js/StableStringChars.h"
  14 #include "js/String.h"  // JS::StringToLinearString
  15
  16 #include "jsapi-tests/tests.h"
  17
  18 #include "vm/JSContext.h"
  19 #include "vm/StringType.h"
  20
  21 #include "vm/JSContext-inl.h"
  22
  23 static bool SameChars(JSContext* cx, JSString* str1, JSString* str2,
  24                       size_t offset) {
  25   JS::AutoCheckCannotGC nogc(cx);
  26
  27   const JS::Latin1Char* chars1 =
  28       JS::StringToLinearString(cx, str1)->latin1Chars(nogc);
  29   const JS::Latin1Char* chars2 =
  30       JS::StringToLinearString(cx, str2)->latin1Chars(nogc);
  31
  32   return chars1 == chars2 + offset;
  33 }
  34
  35 BEGIN_TEST(testDeduplication_ASSC) {
  36   // Test with a long enough string to avoid inline chars allocation.
  37   const char text[] =
  38       "Andthebeastshallcomeforthsurroundedbyaroilingcloudofvengeance."
  39       "Thehouseoftheunbelieversshallberazedandtheyshallbescorchedtoth"
  40       "eearth.Theirtagsshallblinkuntiltheendofdays.";
  41
  42   // Create a string to deduplicate later strings to.
  43   JS::RootedString original(cx);
  44   JS::RootedString str(cx);
  45   JS::RootedString dep(cx);
  46   JS::RootedString depdep(cx);
  47   JS::RootedString str2(cx);
  48   JS::RootedString dep2(cx);
  49   JS::RootedString depdep2(cx);
  50
  51   {
  52     // This test checks the behavior when GC is performed after allocating
  53     // all the following strings.
  54     // GC shouldn't happen in between them, even in compacting jobs.
  55     js::gc::AutoSuppressGC suppress(cx);
  56
  57     original = JS_NewStringCopyZ(cx, text);
  58     CHECK(original);
  59
  60     // Create a chain of dependent strings, with a base string whose contents
  61     // match `original`'s.
  62     str = JS_NewStringCopyZ(cx, text);
  63     CHECK(str);
  64
  65     dep = JS_NewDependentString(cx, str, 10, 100);
  66     CHECK(dep);
  67
  68     depdep = JS_NewDependentString(cx, dep, 10, 80);
  69     CHECK(depdep);
  70
  71     // Repeat. This one will not be prevented from deduplication.
  72     str2 = JS_NewStringCopyZ(cx, text);
  73     CHECK(str2);
  74
  75     dep2 = JS_NewDependentString(cx, str2, 10, 100);
  76     CHECK(dep2);
  77
  78     depdep2 = JS_NewDependentString(cx, dep2, 10, 80);
  79     CHECK(depdep2);
  80   }
  81
  82   // Initializing an AutoStableStringChars with `depdep` should prevent the
  83   // owner of its chars (`str`) from deduplication.
  84   JS::AutoStableStringChars stable(cx);
  85   CHECK(stable.init(cx, depdep));
  86
  87   const JS::Latin1Char* chars = stable.latin1Chars();
  88   CHECK(memcmp(chars, text + 20, 80 * sizeof(JS::Latin1Char)) == 0);
  89
  90   // `depdep` should share chars with `str` but not with `original`.
  91   CHECK(SameChars(cx, depdep, str, 20));
  92   CHECK(!SameChars(cx, depdep, original, 20));
  93
  94   // Same for `depdep2`.
  95   CHECK(SameChars(cx, depdep2, str2, 20));
  96   CHECK(!SameChars(cx, depdep2, original, 20));
  97
  98   // Do a minor GC that will deduplicate `str2` to `original`, and would have
  99   // deduplicated `str` as well if it weren't prevented by the
 100   // AutoStableStringChars.
 101   cx->minorGC(JS::GCReason::API);
 102
 103   // `depdep` should still share chars with `str` but not with `original`.
 104   CHECK(SameChars(cx, depdep, str, 20));
 105   CHECK(!SameChars(cx, depdep, original, 20));
 106
 107   // `depdep2` should now share chars with both `str` and `original`.
 108   CHECK(SameChars(cx, depdep2, str2, 20));
 109   CHECK(SameChars(cx, depdep2, original, 20));
 110
 111   return true;
 112 }
 113 END_TEST(testDeduplication_ASSC)