IORangeAllocator

Inherits from
OSObject
Availability
Available in OS X v10.0 and later.
Declared in
IORangeAllocator.h

Overview

A utility class to manage allocations from a range.

The IORangeAllocator class provides functions for allocating ranges, at a fixed or any offset, and freeing them back to a free list. It is useful for describing ranges of memory or address space without requiring storage in the memory - information describing the free elements is kept elsewhere. Ranges are described by a start offset and a size. IORangeAllocator is optionally protected against multithreaded access.

Tasks

Miscellaneous

Instance Methods

allocate

Allocates from the free list, at any offset.

virtual bool allocate( IORangeScalar size, IORangeScalar *result, IORangeScalar alignment = 0 );
Parameters
size

The size of the range requested.

result

The beginning of the range allocated is returned here on success.

alignment

If zero is passed, default to the allocators alignment, otherwise pass an alignment required for the allocation, for example 4096 to page align.

Return Value

Returns true if the allocation was successful, else false.

Discussion

This method allocates a range from the free list. The alignment will default to the alignment set when the allocator was created or may be set here.

allocateRange

Allocates from the free list, at a set offset.

virtual bool allocateRange( IORangeScalar start, IORangeScalar size );
Parameters
start

The beginning of the range requested.

size

The size of the range requested.

Return Value

Returns true if the allocation was successful, else false.

Discussion

This method allocates a range from the free list, given a set offset passed in.

deallocate

Deallocates a range to the free list.

virtual void deallocate( IORangeScalar start, IORangeScalar size );
Parameters
start

The beginning of the range requested.

size

Returns the size of the range requested.

Discussion

This method deallocates a range to the free list, given a the start offset and length passed in.

getFragmentCapacity

Accessor to return the number of free fragments in the range.

virtual UInt32 getFragmentCapacity( void );
Return Value

Returns the current capacity of free fragment list.

Discussion

This method returns the current capacity of the free fragment list.

getFragmentCount

Accessor to return the number of free fragments in the range.

virtual UInt32 getFragmentCount( void );
Return Value

Returns the count of free fragments.

Discussion

This method returns a count of free fragments. Each fragment describes a non-contiguous free range - deallocations will merge contiguous fragments together.

getFreeCount

Totals the sizes of the free fragments.

virtual IORangeScalar getFreeCount( void );
Return Value

Returns the total of the free fragments sizes.

Discussion

This method returns the total of the sizes of the fragments on the free list.

init

Standard initializer for IORangeAllocator.

virtual bool init( IORangeScalar endOfRange, IORangeScalar defaultAlignment, UInt32 capacity, IOOptionBits options );
Parameters
endOfRange

If the free list is to contain an initial fragment, set endOfRange to the last offset in the range, ie. size - 1, to create a free fragment for the range zero to endOfRange inclusive. If zero is passed, the free list will be initialized empty, and can be populated with calls to the deallocate method.

defaultAlignment

If this parameter is non-zero it specifies a required alignment for all allocations, for example pass 256 to align allocations on 256 byte boundaries. Zero or one specify unaligned allocations.

capacity

Sets the initial size of the free list in number of noncontiguous fragments. This value is also used for the capacityIncrement.

options

Pass kLocking if the instance can be used by multiple threads.

Return Value

Returns true if the instance is successfully initialized, false on failure.

Discussion

This method initializes an IORangeAllocator and optionally sets the free list to contain one fragment, from zero to an endOfRange parameter. The capacity in terms of free fragments and locking options are set for the instance.

setFragmentCapacityIncrement

Sets the count of fragments the free list will increase by when full.

virtual void setFragmentCapacityIncrement( UInt32 count );
Parameters
count

The number of fragments to increment the capacity by when the free list is full.

Discussion

This method sets the number of extra fragments the free list will expand to when full. It defaults to the initial capacity.

withRange

Standard factory method for IORangeAllocator.

static IORangeAllocator * withRange( IORangeScalar endOfRange, IORangeScalar defaultAlignment = 0, UInt32 capacity = 0, IOOptionBits options = 0 );
Parameters
endOfRange

If the free list is to contain an initial fragment, set endOfRange to the last offset in the range, ie. size - 1, to create a free fragment for the range zero to endOfRange inclusive. If zero is passed the free list will be initialized empty, and can be populated with calls to the deallocate method.

defaultAlignment

If this parameter is non-zero it specifies a required alignment for all allocations, for example pass 256 to align allocations on 256 byte boundaries. Zero or one specify unaligned allocations.

capacity

Sets the initial size of the free list in number of non-contiguous fragments. This value is also used for the capacityIncrement.

options

Pass kLocking if the instance can be used by multiple threads.

Return Value

Returns the new IORangeAllocator instance, to be released by the caller, or zero on failure.

Discussion

This method allocates and initializes an IORangeAllocator and optionally sets the free list to contain one fragment, from zero to an endOfRange parameter. The capacity in terms of free fragments and locking options are set for the instance.