hphp/runtime/base/shared-string.cpp

   1 /*
   2    +----------------------------------------------------------------------+
   3    | HipHop for PHP                                                       |
   4    +----------------------------------------------------------------------+
   5    | Copyright (c) 2010-2014 Facebook, Inc. (http://www.facebook.com)     |
   6    +----------------------------------------------------------------------+
   7    | This source file is subject to version 3.01 of the PHP license,      |
   8    | that is bundled with this package in the file LICENSE, and is        |
   9    | available through the world-wide-web at the following url:           |
  10    | http://www.php.net/license/3_01.txt                                  |
  11    | If you did not receive a copy of the PHP license and are unable to   |
  12    | obtain it through the world-wide-web, please send a note to          |
  13    | license@php.net so we can mail you a copy immediately.               |
  14    +----------------------------------------------------------------------+
  15 */
  16
  17 #include "hphp/runtime/base/shared-string.h"
  18
  19 namespace HPHP {
  20 ///////////////////////////////////////////////////////////////////////////////
  21
  22 SharedStringData::InternMap SharedStringData::s_intern;
  23
  24 SharedStringData::SharedStringData(const std::string &data) : m_data(data) {
  25   m_count = 1;
  26 }
  27
  28 int SharedStringData::decAtomicCount() const {
  29   assert(m_count > 0);
  30   int cur = m_count.fetch_and_decrement() - 1;
  31   if (cur == 0) {
  32     // Only left in intern map. While this data is still in the
  33     // the map we consider this data dying. All new Creates will
  34     // overwrite the SharedStringData* in the slot and not use this one.
  35     InternMap::accessor acc;
  36     bool found = s_intern.find(acc, m_data);
  37     assert(m_count == 0);
  38     // May not be found or may not be acc->second if other thread overwrote.
  39     // Safe to just delete self.
  40     if (found && acc->second == this) {
  41       s_intern.erase(acc);
  42     }
  43     return 0;
  44   }
  45   return 1;
  46 }
  47
  48 void SharedStringData::atomicRelease() {
  49   delete this;
  50 }
  51
  52 const std::string &SharedStringData::getString() const {
  53   return m_data;
  54 }
  55
  56 void SharedStringData::Create(InternMap::accessor &acc,
  57                               const std::string &data) {
  58   if (s_intern.insert(acc, data)) {
  59     acc->second = new SharedStringData(acc->first);
  60     return;
  61   }
  62   // Danger is now that the data is dying. We must not acquire a reference
  63   // if it in that state.
  64   while (true) {
  65     int cur = acc->second->m_count;
  66     if (cur == 0) {
  67       acc->second = new SharedStringData(acc->first);
  68       break;
  69     }
  70     // Never change refcount of 0 to refcount of 1, impossible
  71     // to revive a dying SharedStringData.
  72     if (acc->second->m_count.compare_and_swap(cur + 1, cur) == cur) {
  73       break;
  74     }
  75     // Other thread must have inc/dec ref'd since we got cur
  76   }
  77 }
  78
  79 SharedString &SharedString::operator=(const std::string &data) {
  80   reset();
  81   SharedStringData::InternMap::accessor acc;
  82   SharedStringData::Create(acc, data);
  83   // Ref count already incremented in Create
  84   overwrite_unsafe(acc->second);
  85   return *this;
  86 }
  87
  88 ///////////////////////////////////////////////////////////////////////////////
  89 }