LCOV - code coverage report
Current view: directory - xpcom/ds - nsFixedSizeAllocator.h (source / functions) Found Hit Coverage
Test: app.info Lines: 5 0 0.0 %
Date: 2012-06-02 Functions: 2 0 0.0 %

       1                 : /* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
       2                 : /* ***** BEGIN LICENSE BLOCK *****
       3                 :  * Version: MPL 1.1/GPL 2.0/LGPL 2.1
       4                 :  *
       5                 :  * The contents of this file are subject to the Mozilla Public License Version
       6                 :  * 1.1 (the "License"); you may not use this file except in compliance with
       7                 :  * the License. You may obtain a copy of the License at
       8                 :  * http://www.mozilla.org/MPL/
       9                 :  *
      10                 :  * Software distributed under the License is distributed on an "AS IS" basis,
      11                 :  * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
      12                 :  * for the specific language governing rights and limitations under the
      13                 :  * License.
      14                 :  *
      15                 :  * The Original Code is mozilla.org code.
      16                 :  *
      17                 :  * The Initial Developer of the Original Code is
      18                 :  * Netscape Communications Corporation.
      19                 :  * Portions created by the Initial Developer are Copyright (C) 1998
      20                 :  * the Initial Developer. All Rights Reserved.
      21                 :  *
      22                 :  * Contributor(s):
      23                 :  *   Chris Waterson <waterson@netscape.com
      24                 :  *
      25                 :  * Alternatively, the contents of this file may be used under the terms of
      26                 :  * either of the GNU General Public License Version 2 or later (the "GPL"),
      27                 :  * or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
      28                 :  * in which case the provisions of the GPL or the LGPL are applicable instead
      29                 :  * of those above. If you wish to allow use of your version of this file only
      30                 :  * under the terms of either the GPL or the LGPL, and not to allow others to
      31                 :  * use your version of this file under the terms of the MPL, indicate your
      32                 :  * decision by deleting the provisions above and replace them with the notice
      33                 :  * and other provisions required by the GPL or the LGPL. If you do not delete
      34                 :  * the provisions above, a recipient may use your version of this file under
      35                 :  * the terms of any one of the MPL, the GPL or the LGPL.
      36                 :  *
      37                 :  * ***** END LICENSE BLOCK ***** */
      38                 : 
      39                 : /*
      40                 : 
      41                 :   A simple fixed-size allocator that allocates its memory from an
      42                 :   arena.
      43                 : 
      44                 :   Although the allocator can handle blocks of any size, its
      45                 :   preformance will degrade rapidly if used to allocate blocks of
      46                 :   arbitrary size. Ideally, it should be used to allocate and recycle a
      47                 :   large number of fixed-size blocks.
      48                 : 
      49                 :   Here is a typical usage pattern:
      50                 : 
      51                 :     #include NEW_H // You'll need this!
      52                 :     #include "nsFixedSizeAllocator.h"
      53                 : 
      54                 :     // Say this is the object you want to allocate a ton of
      55                 :     class Foo {
      56                 :     public:
      57                 :       // Implement placement new & delete operators that will
      58                 :       // use the fixed size allocator.
      59                 :       static Foo *
      60                 :       Create(nsFixedSizeAllocator &aAllocator)
      61                 :       {
      62                 :         void *place = aAllocator.Alloc(sizeof(Foo));
      63                 :         return place ? ::new (place) Foo() : nsnull;
      64                 :       }
      65                 : 
      66                 :       static void
      67                 :       Destroy(nsFixedSizeAllocator &aAllocator, Foo *aFoo)
      68                 :       {
      69                 :         aFoo->~Foo();
      70                 :         aAllocator.Free(aFoo, sizeof(Foo));
      71                 :       }
      72                 : 
      73                 :       // ctor & dtor
      74                 :       Foo() {}
      75                 :       ~Foo() {}
      76                 :     };
      77                 : 
      78                 : 
      79                 :     int main(int argc, char* argv[])
      80                 :     {
      81                 :       // Somewhere in your code, you'll need to create an
      82                 :       // nsFixedSizeAllocator object and initialize it:
      83                 :       nsFixedSizeAllocator pool;
      84                 : 
      85                 :       // The fixed size allocator will support multiple fixed sizes.
      86                 :       // This array lists an initial set of sizes that the allocator
      87                 :       // should be prepared to support. In our case, there's just one,
      88                 :       // which is Foo.
      89                 :       static const size_t kBucketSizes[]
      90                 :         = { sizeof(Foo) }
      91                 : 
      92                 :       // This is the number of different "buckets" you'll need for
      93                 :       // fixed size objects. In our example, this will be "1".
      94                 :       static const PRInt32 kNumBuckets
      95                 :         = sizeof(kBucketSizes) / sizeof(size_t);
      96                 : 
      97                 :       // This is the intial size of the allocator, in bytes. We'll
      98                 :       // assume that we want to start with space for 1024 Foo objects.
      99                 :       static const PRInt32 kInitialPoolSize =
     100                 :         NS_SIZE_IN_HEAP(sizeof(Foo)) * 1024;
     101                 : 
     102                 :       // Initialize (or re-initialize) the pool
     103                 :       pool.Init("TheFooPool", kBucketSizes, kNumBuckets, kInitialPoolSize);
     104                 : 
     105                 :       // Now we can use the pool.
     106                 : 
     107                 :       // Create a new Foo object using the pool:
     108                 :       Foo* foo = Foo::Create(pool);
     109                 :       if (! foo) {
     110                 :         // uh oh, out of memory!
     111                 :       }
     112                 : 
     113                 :       // Delete the object. The memory used by `foo' is recycled in
     114                 :       // the pool, and placed in a freelist
     115                 :       Foo::Destroy(foo);
     116                 : 
     117                 :       // Create another foo: this one will be allocated from the
     118                 :       // free-list
     119                 :       foo = Foo::Create(pool);
     120                 : 
     121                 :       // When pool is destroyed, all of its memory is automatically
     122                 :       // freed. N.B. it will *not* call your objects' destructors! In
     123                 :       // this case, foo's ~Foo() method would never be called.
     124                 :     }
     125                 : 
     126                 : */
     127                 : 
     128                 : #ifndef nsFixedSizeAllocator_h__
     129                 : #define nsFixedSizeAllocator_h__
     130                 : 
     131                 : #include "nscore.h"
     132                 : #include "nsError.h"
     133                 : #include "plarena.h"
     134                 : 
     135                 : #define NS_SIZE_IN_HEAP(_size) (_size)
     136                 : 
     137                 : class nsFixedSizeAllocator
     138                 : {
     139                 : protected:
     140                 :     PLArenaPool mPool;
     141                 : 
     142                 :     struct Bucket;
     143                 :     struct FreeEntry;
     144                 :   
     145                 :     friend struct Bucket;
     146                 :     friend struct FreeEntry;
     147                 : 
     148                 :     struct FreeEntry {
     149                 :         FreeEntry* mNext;
     150                 :     };
     151                 : 
     152                 :     struct Bucket {
     153                 :         size_t     mSize;
     154                 :         FreeEntry* mFirst;
     155                 :         Bucket*    mNext;
     156                 :     };
     157                 : 
     158                 :     Bucket* mBuckets;
     159                 : 
     160                 :     Bucket *
     161                 :     AddBucket(size_t aSize);
     162                 : 
     163                 :     Bucket *
     164                 :     FindBucket(size_t aSize);
     165                 : 
     166                 : public:
     167               0 :     nsFixedSizeAllocator() : mBuckets(nsnull) {}
     168                 : 
     169               0 :     ~nsFixedSizeAllocator() {
     170               0 :         if (mBuckets)
     171               0 :             PL_FinishArenaPool(&mPool);
     172               0 :     }
     173                 : 
     174                 :     /**
     175                 :      * Initialize the fixed size allocator. 'aName' is used to tag
     176                 :      * the underlying PLArena object for debugging and measurement
     177                 :      * purposes. 'aNumBuckets' specifies the number of elements in
     178                 :      * 'aBucketSizes', which is an array of integral block sizes
     179                 :      * that this allocator should be prepared to handle.
     180                 :      */
     181                 :     nsresult
     182                 :     Init(const char* aName,
     183                 :          const size_t* aBucketSizes,
     184                 :          PRInt32 aNumBuckets,
     185                 :          PRInt32 aInitialSize,
     186                 :          PRInt32 aAlign = 0);
     187                 : 
     188                 :     /**
     189                 :      * Allocate a block of memory 'aSize' bytes big.
     190                 :      */
     191                 :     void* Alloc(size_t aSize);
     192                 : 
     193                 :     /**
     194                 :      * Free a pointer allocated using a fixed-size allocator
     195                 :      */
     196                 :     void Free(void* aPtr, size_t aSize);
     197                 : };
     198                 : 
     199                 : 
     200                 : 
     201                 : #endif // nsFixedSizeAllocator_h__

Generated by: LCOV version 1.7