lldb/source/Utility/ConstString.cpp

   1 //===-- ConstString.cpp ---------------------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #include "lldb/Utility/ConstString.h"
  10
  11 #include "lldb/Utility/Stream.h"
  12
  13 #include "llvm/ADT/StringMap.h"
  14 #include "llvm/ADT/iterator.h"
  15 #include "llvm/Support/Allocator.h"
  16 #include "llvm/Support/DJB.h"
  17 #include "llvm/Support/FormatProviders.h"
  18 #include "llvm/Support/RWMutex.h"
  19 #include "llvm/Support/Threading.h"
  20
  21 #include <array>
  22 #include <utility>
  23
  24 #include <cinttypes>
  25 #include <cstdint>
  26 #include <cstring>
  27
  28 using namespace lldb_private;
  29
  30 class Pool {
  31 public:
  32   /// The default BumpPtrAllocatorImpl slab size.
  33   static const size_t AllocatorSlabSize = 4096;
  34   static const size_t SizeThreshold = AllocatorSlabSize;
  35   /// Every Pool has its own allocator which receives an equal share of
  36   /// the ConstString allocations. This means that when allocating many
  37   /// ConstStrings, every allocator sees only its small share of allocations and
  38   /// assumes LLDB only allocated a small amount of memory so far. In reality
  39   /// LLDB allocated a total memory that is N times as large as what the
  40   /// allocator sees (where N is the number of string pools). This causes that
  41   /// the BumpPtrAllocator continues a long time to allocate memory in small
  42   /// chunks which only makes sense when allocating a small amount of memory
  43   /// (which is true from the perspective of a single allocator). On some
  44   /// systems doing all these small memory allocations causes LLDB to spend
  45   /// a lot of time in malloc, so we need to force all these allocators to
  46   /// behave like one allocator in terms of scaling their memory allocations
  47   /// with increased demand. To do this we set the growth delay for each single
  48   /// allocator to a rate so that our pool of allocators scales their memory
  49   /// allocations similar to a single BumpPtrAllocatorImpl.
  50   ///
  51   /// Currently we have 256 string pools and the normal growth delay of the
  52   /// BumpPtrAllocatorImpl is 128 (i.e., the memory allocation size increases
  53   /// every 128 full chunks), so by changing the delay to 1 we get a
  54   /// total growth delay in our allocator collection of 256/1 = 256. This is
  55   /// still only half as fast as a normal allocator but we can't go any faster
  56   /// without decreasing the number of string pools.
  57   static const size_t AllocatorGrowthDelay = 1;
  58   typedef llvm::BumpPtrAllocatorImpl<llvm::MallocAllocator, AllocatorSlabSize,
  59                                      SizeThreshold, AllocatorGrowthDelay>
  60       Allocator;
  61   typedef const char *StringPoolValueType;
  62   typedef llvm::StringMap<StringPoolValueType, Allocator> StringPool;
  63   typedef llvm::StringMapEntry<StringPoolValueType> StringPoolEntryType;
  64
  65   static StringPoolEntryType &
  66   GetStringMapEntryFromKeyData(const char *keyData) {
  67     return StringPoolEntryType::GetStringMapEntryFromKeyData(keyData);
  68   }
  69
  70   static size_t GetConstCStringLength(const char *ccstr) {
  71     if (ccstr != nullptr) {
  72       // Since the entry is read only, and we derive the entry entirely from
  73       // the pointer, we don't need the lock.
  74       const StringPoolEntryType &entry = GetStringMapEntryFromKeyData(ccstr);
  75       return entry.getKey().size();
  76     }
  77     return 0;
  78   }
  79
  80   StringPoolValueType GetMangledCounterpart(const char *ccstr) const {
  81     if (ccstr != nullptr) {
  82       const uint8_t h = hash(llvm::StringRef(ccstr));
  83       llvm::sys::SmartScopedReader<false> rlock(m_string_pools[h].m_mutex);
  84       return GetStringMapEntryFromKeyData(ccstr).getValue();
  85     }
  86     return nullptr;
  87   }
  88
  89   const char *GetConstCString(const char *cstr) {
  90     if (cstr != nullptr)
  91       return GetConstCStringWithLength(cstr, strlen(cstr));
  92     return nullptr;
  93   }
  94
  95   const char *GetConstCStringWithLength(const char *cstr, size_t cstr_len) {
  96     if (cstr != nullptr)
  97       return GetConstCStringWithStringRef(llvm::StringRef(cstr, cstr_len));
  98     return nullptr;
  99   }
 100
 101   const char *GetConstCStringWithStringRef(llvm::StringRef string_ref) {
 102     if (string_ref.data()) {
 103       const uint8_t h = hash(string_ref);
 104
 105       {
 106         llvm::sys::SmartScopedReader<false> rlock(m_string_pools[h].m_mutex);
 107         auto it = m_string_pools[h].m_string_map.find(string_ref);
 108         if (it != m_string_pools[h].m_string_map.end())
 109           return it->getKeyData();
 110       }
 111
 112       llvm::sys::SmartScopedWriter<false> wlock(m_string_pools[h].m_mutex);
 113       StringPoolEntryType &entry =
 114           *m_string_pools[h]
 115                .m_string_map.insert(std::make_pair(string_ref, nullptr))
 116                .first;
 117       return entry.getKeyData();
 118     }
 119     return nullptr;
 120   }
 121
 122   const char *
 123   GetConstCStringAndSetMangledCounterPart(llvm::StringRef demangled,
 124                                           const char *mangled_ccstr) {
 125     const char *demangled_ccstr = nullptr;
 126
 127     {
 128       const uint8_t h = hash(demangled);
 129       llvm::sys::SmartScopedWriter<false> wlock(m_string_pools[h].m_mutex);
 130
 131       // Make or update string pool entry with the mangled counterpart
 132       StringPool &map = m_string_pools[h].m_string_map;
 133       StringPoolEntryType &entry = *map.try_emplace(demangled).first;
 134
 135       entry.second = mangled_ccstr;
 136
 137       // Extract the const version of the demangled_cstr
 138       demangled_ccstr = entry.getKeyData();
 139     }
 140
 141     {
 142       // Now assign the demangled const string as the counterpart of the
 143       // mangled const string...
 144       const uint8_t h = hash(llvm::StringRef(mangled_ccstr));
 145       llvm::sys::SmartScopedWriter<false> wlock(m_string_pools[h].m_mutex);
 146       GetStringMapEntryFromKeyData(mangled_ccstr).setValue(demangled_ccstr);
 147     }
 148
 149     // Return the constant demangled C string
 150     return demangled_ccstr;
 151   }
 152
 153   const char *GetConstTrimmedCStringWithLength(const char *cstr,
 154                                                size_t cstr_len) {
 155     if (cstr != nullptr) {
 156       const size_t trimmed_len = strnlen(cstr, cstr_len);
 157       return GetConstCStringWithLength(cstr, trimmed_len);
 158     }
 159     return nullptr;
 160   }
 161
 162   ConstString::MemoryStats GetMemoryStats() const {
 163     ConstString::MemoryStats stats;
 164     for (const auto &pool : m_string_pools) {
 165       llvm::sys::SmartScopedReader<false> rlock(pool.m_mutex);
 166       const Allocator &alloc = pool.m_string_map.getAllocator();
 167       stats.bytes_total += alloc.getTotalMemory();
 168       stats.bytes_used += alloc.getBytesAllocated();
 169     }
 170     return stats;
 171   }
 172
 173 protected:
 174   uint8_t hash(llvm::StringRef s) const {
 175     uint32_t h = llvm::djbHash(s);
 176     return ((h >> 24) ^ (h >> 16) ^ (h >> 8) ^ h) & 0xff;
 177   }
 178
 179   struct PoolEntry {
 180     mutable llvm::sys::SmartRWMutex<false> m_mutex;
 181     StringPool m_string_map;
 182   };
 183
 184   std::array<PoolEntry, 256> m_string_pools;
 185 };
 186
 187 // Frameworks and dylibs aren't supposed to have global C++ initializers so we
 188 // hide the string pool in a static function so that it will get initialized on
 189 // the first call to this static function.
 190 //
 191 // Note, for now we make the string pool a pointer to the pool, because we
 192 // can't guarantee that some objects won't get destroyed after the global
 193 // destructor chain is run, and trying to make sure no destructors touch
 194 // ConstStrings is difficult.  So we leak the pool instead.
 195 static Pool &StringPool() {
 196   static llvm::once_flag g_pool_initialization_flag;
 197   static Pool *g_string_pool = nullptr;
 198
 199   llvm::call_once(g_pool_initialization_flag,
 200                  []() { g_string_pool = new Pool(); });
 201
 202   return *g_string_pool;
 203 }
 204
 205 ConstString::ConstString(const char *cstr)
 206     : m_string(StringPool().GetConstCString(cstr)) {}
 207
 208 ConstString::ConstString(const char *cstr, size_t cstr_len)
 209     : m_string(StringPool().GetConstCStringWithLength(cstr, cstr_len)) {}
 210
 211 ConstString::ConstString(llvm::StringRef s)
 212     : m_string(StringPool().GetConstCStringWithStringRef(s)) {}
 213
 214 bool ConstString::operator<(ConstString rhs) const {
 215   if (m_string == rhs.m_string)
 216     return false;
 217
 218   llvm::StringRef lhs_string_ref(GetStringRef());
 219   llvm::StringRef rhs_string_ref(rhs.GetStringRef());
 220
 221   // If both have valid C strings, then return the comparison
 222   if (lhs_string_ref.data() && rhs_string_ref.data())
 223     return lhs_string_ref < rhs_string_ref;
 224
 225   // Else one of them was nullptr, so if LHS is nullptr then it is less than
 226   return lhs_string_ref.data() == nullptr;
 227 }
 228
 229 Stream &lldb_private::operator<<(Stream &s, ConstString str) {
 230   const char *cstr = str.GetCString();
 231   if (cstr != nullptr)
 232     s << cstr;
 233
 234   return s;
 235 }
 236
 237 size_t ConstString::GetLength() const {
 238   return Pool::GetConstCStringLength(m_string);
 239 }
 240
 241 bool ConstString::Equals(ConstString lhs, ConstString rhs,
 242                          const bool case_sensitive) {
 243   if (lhs.m_string == rhs.m_string)
 244     return true;
 245
 246   // Since the pointers weren't equal, and identical ConstStrings always have
 247   // identical pointers, the result must be false for case sensitive equality
 248   // test.
 249   if (case_sensitive)
 250     return false;
 251
 252   // perform case insensitive equality test
 253   llvm::StringRef lhs_string_ref(lhs.GetStringRef());
 254   llvm::StringRef rhs_string_ref(rhs.GetStringRef());
 255   return lhs_string_ref.equals_insensitive(rhs_string_ref);
 256 }
 257
 258 int ConstString::Compare(ConstString lhs, ConstString rhs,
 259                          const bool case_sensitive) {
 260   // If the iterators are the same, this is the same string
 261   const char *lhs_cstr = lhs.m_string;
 262   const char *rhs_cstr = rhs.m_string;
 263   if (lhs_cstr == rhs_cstr)
 264     return 0;
 265   if (lhs_cstr && rhs_cstr) {
 266     llvm::StringRef lhs_string_ref(lhs.GetStringRef());
 267     llvm::StringRef rhs_string_ref(rhs.GetStringRef());
 268
 269     if (case_sensitive) {
 270       return lhs_string_ref.compare(rhs_string_ref);
 271     } else {
 272       return lhs_string_ref.compare_insensitive(rhs_string_ref);
 273     }
 274   }
 275
 276   if (lhs_cstr)
 277     return +1; // LHS isn't nullptr but RHS is
 278   else
 279     return -1; // LHS is nullptr but RHS isn't
 280 }
 281
 282 void ConstString::Dump(Stream *s, const char *fail_value) const {
 283   if (s != nullptr) {
 284     const char *cstr = AsCString(fail_value);
 285     if (cstr != nullptr)
 286       s->PutCString(cstr);
 287   }
 288 }
 289
 290 void ConstString::DumpDebug(Stream *s) const {
 291   const char *cstr = GetCString();
 292   size_t cstr_len = GetLength();
 293   // Only print the parens if we have a non-nullptr string
 294   const char *parens = cstr ? "\"" : "";
 295   s->Printf("%*p: ConstString, string = %s%s%s, length = %" PRIu64,
 296             static_cast<int>(sizeof(void *) * 2),
 297             static_cast<const void *>(this), parens, cstr, parens,
 298             static_cast<uint64_t>(cstr_len));
 299 }
 300
 301 void ConstString::SetCString(const char *cstr) {
 302   m_string = StringPool().GetConstCString(cstr);
 303 }
 304
 305 void ConstString::SetString(llvm::StringRef s) {
 306   m_string = StringPool().GetConstCStringWithStringRef(s);
 307 }
 308
 309 void ConstString::SetStringWithMangledCounterpart(llvm::StringRef demangled,
 310                                                   ConstString mangled) {
 311   m_string = StringPool().GetConstCStringAndSetMangledCounterPart(
 312       demangled, mangled.m_string);
 313 }
 314
 315 bool ConstString::GetMangledCounterpart(ConstString &counterpart) const {
 316   counterpart.m_string = StringPool().GetMangledCounterpart(m_string);
 317   return (bool)counterpart;
 318 }
 319
 320 void ConstString::SetCStringWithLength(const char *cstr, size_t cstr_len) {
 321   m_string = StringPool().GetConstCStringWithLength(cstr, cstr_len);
 322 }
 323
 324 void ConstString::SetTrimmedCStringWithLength(const char *cstr,
 325                                               size_t cstr_len) {
 326   m_string = StringPool().GetConstTrimmedCStringWithLength(cstr, cstr_len);
 327 }
 328
 329 ConstString::MemoryStats ConstString::GetMemoryStats() {
 330   return StringPool().GetMemoryStats();
 331 }
 332
 333 void llvm::format_provider<ConstString>::format(const ConstString &CS,
 334                                                 llvm::raw_ostream &OS,
 335                                                 llvm::StringRef Options) {
 336   format_provider<StringRef>::format(CS.GetStringRef(), OS, Options);
 337 }