comparison third_party/json/json_batchallocator.h @ 0:add35537fdbb tip

Initial import

+// Copyright 2007-2010 Baptiste Lepilleur
+// Distributed under MIT license, or public domain if desired and
+// recognized in your jurisdiction.
+// See file LICENSE for detail or copy at http://jsoncpp.sourceforge.net/LICENSE
+
+#ifndef JSONCPP_BATCHALLOCATOR_H_INCLUDED
+# define JSONCPP_BATCHALLOCATOR_H_INCLUDED
+
+# include <stdlib.h>
+# include <assert.h>
+
+# ifndef JSONCPP_DOC_EXCLUDE_IMPLEMENTATION
+
+namespace Json {
+
+/* Fast memory allocator.
+ *
+ * This memory allocator allocates memory for a batch of object (specified by
+ * the page size, the number of object in each page).
+ *
+ * It does not allow the destruction of a single object. All the allocated objects
+ * can be destroyed at once. The memory can be either released or reused for future
+ * allocation.
+ * 
+ * The in-place new operator must be used to construct the object using the pointer
+ * returned by allocate.
+ */
+template<typename AllocatedType
+        ,const unsigned int objectPerAllocation>
+class BatchAllocator
+{
+public:
+   BatchAllocator( unsigned int objectsPerPage = 255 )
+      : freeHead_( 0 )
+      , objectsPerPage_( objectsPerPage )
+   {
+//      printf( "Size: %d => %s\n", sizeof(AllocatedType), typeid(AllocatedType).name() );
+      assert( sizeof(AllocatedType) * objectPerAllocation >= sizeof(AllocatedType *) ); // We must be able to store a slist in the object free space.
+      assert( objectsPerPage >= 16 );
+      batches_ = allocateBatch( 0 );   // allocated a dummy page
+      currentBatch_ = batches_;
+   }
+
+   ~BatchAllocator()
+   {
+      for ( BatchInfo *batch = batches_; batch;  )
+      {
+         BatchInfo *nextBatch = batch->next_;
+         free( batch );
+         batch = nextBatch;
+      }
+   }
+
+   /// allocate space for an array of objectPerAllocation object.
+   /// @warning it is the responsability of the caller to call objects constructors.
+   AllocatedType *allocate()
+   {
+      if ( freeHead_ ) // returns node from free list.
+      {
+         AllocatedType *object = freeHead_;
+         freeHead_ = *(AllocatedType **)object;
+         return object;
+      }
+      if ( currentBatch_->used_ == currentBatch_->end_ )
+      {
+         currentBatch_ = currentBatch_->next_;
+         while ( currentBatch_  &&  currentBatch_->used_ == currentBatch_->end_ )
+            currentBatch_ = currentBatch_->next_;
+
+         if ( !currentBatch_  ) // no free batch found, allocate a new one
+         { 
+            currentBatch_ = allocateBatch( objectsPerPage_ );
+            currentBatch_->next_ = batches_; // insert at the head of the list
+            batches_ = currentBatch_;
+         }
+      }
+      AllocatedType *allocated = currentBatch_->used_;
+      currentBatch_->used_ += objectPerAllocation;
+      return allocated;
+   }
+
+   /// Release the object.
+   /// @warning it is the responsability of the caller to actually destruct the object.
+   void release( AllocatedType *object )
+   {
+      assert( object != 0 );
+      *(AllocatedType **)object = freeHead_;
+      freeHead_ = object;
+   }
+
+private:
+   struct BatchInfo
+   {
+      BatchInfo *next_;
+      AllocatedType *used_;
+      AllocatedType *end_;
+      AllocatedType buffer_[objectPerAllocation];
+   };
+
+   // disabled copy constructor and assignement operator.
+   BatchAllocator( const BatchAllocator & );
+   void operator =( const BatchAllocator &);
+
+   static BatchInfo *allocateBatch( unsigned int objectsPerPage )
+   {
+      const unsigned int mallocSize = sizeof(BatchInfo) - sizeof(AllocatedType)* objectPerAllocation
+                                + sizeof(AllocatedType) * objectPerAllocation * objectsPerPage;
+      BatchInfo *batch = static_cast<BatchInfo*>( malloc( mallocSize ) );
+      batch->next_ = 0;
+      batch->used_ = batch->buffer_;
+      batch->end_ = batch->buffer_ + objectsPerPage;
+      return batch;
+   }
+
+   BatchInfo *batches_;
+   BatchInfo *currentBatch_;
+   /// Head of a single linked list within the allocated space of freeed object
+   AllocatedType *freeHead_;
+   unsigned int objectsPerPage_;
+};
+
+
+} // namespace Json
+
+# endif // ifndef JSONCPP_DOC_INCLUDE_IMPLEMENTATION
+
+#endif // JSONCPP_BATCHALLOCATOR_H_INCLUDED