kjs/JSLock.h

   1 // -*- mode: c++; c-basic-offset: 4 -*-
   2 /*
   3  * This file is part of the KDE libraries
   4  * Copyright (C) 2005 Apple Computer, Inc.
   5  *
   6  * This library is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU Library General Public
   8  * License as published by the Free Software Foundation; either
   9  * version 2 of the License, or (at your option) any later version.
  10  *
  11  * This library is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14  * Library General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU Library General Public License
  17  * along with this library; see the file COPYING.LIB.  If not, write to
  18  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  19  * Boston, MA 02110-1301, USA.
  20  *
  21  */
  22
  23 #ifndef KJS_JSLock_h
  24 #define KJS_JSLock_h
  25
  26 #include <wtf/Assertions.h>
  27 #include <wtf/Noncopyable.h>
  28
  29 namespace KJS {
  30
  31     // To make it safe to use JavaScript on multiple threads, it is
  32     // important to lock before doing anything that allocates a
  33     // JavaScript data structure or that interacts with shared state
  34     // such as the protect count hash table. The simplest way to lock
  35     // is to create a local JSLock object in the scope where the lock
  36     // must be held. The lock is recursive so nesting is ok. The JSLock
  37     // object also acts as a convenience short-hand for running important
  38     // initialization routines.
  39
  40     // To avoid deadlock, sometimes it is necessary to temporarily
  41     // release the lock. Since it is recursive you actually have to
  42     // release all locks held by your thread. This is safe to do if
  43     // you are executing code that doesn't require the lock, and you
  44     // reacquire the right number of locks at the end. You can do this
  45     // by constructing a locally scoped JSLock::DropAllLocks object. The
  46     // DropAllLocks object takes care to release the JSLock only if your
  47     // thread acquired it to begin with.
  48
  49     class JSLock : Noncopyable {
  50     public:
  51         JSLock()
  52         {
  53             lock();
  54             registerThread();
  55         }
  56
  57         ~JSLock()
  58         {
  59             unlock();
  60         }
  61
  62         static void lock();
  63         static void unlock();
  64         static int lockCount();
  65         static bool currentThreadIsHoldingLock();
  66
  67         static void registerThread();
  68
  69         class DropAllLocks : Noncopyable {
  70         public:
  71             DropAllLocks();
  72             ~DropAllLocks();
  73
  74         private:
  75             int m_lockCount;
  76         };
  77     };
  78
  79 } // namespace
  80
  81 #endif // KJS_JSLock_h