Heap Allocation Strategy

The attributes associated with the default heap are defined by the system through a default allocation strategy. This allocation strategy defines attributes such as a heap creation size of 4K bytes and an extension size of 4K bytes. You cannot change this default allocation strategy.

However, you can control heaps that you explicitly create through the Create a Heap (CEECRHP) bindable API. You also can define an allocation strategy for explicitly created heaps through the Define Heap Allocation Strategy (CEE4DAS) bindable API. Then, when you explicitly create a heap, the heap attributes are provided by the allocation strategy that you defined. In this way you can define separate allocation strategies for one or more explicitly created heaps.

You can use the CEECRHP bindable API without defining an allocation strategy. In this case, the heap is defined by the attributes of the _CEE4ALC allocation strategy type. The _CEE4ALC allocation strategy type specifies a heap creation size of 4K bytes and an extension size of 4K bytes. The _CEE4ALC allocation strategy type contains the following attributes:

Max_Sngl_Alloc = 16MB - 64K  /* maximum size of a single allocation */
Min_Bdy        = 16          /* minimum boundary alignment of any allocation */
Crt_Size       = 4K          /* initial creation size of the heap */
Ext_Size       = 4K          /* the extension size of the heap */
Alloc_Strat    = 0           /* a choice for allocation strategy */
No_Mark        = 1           /* a group deallocation choice */
Blk_Xfer       = 0           /* a choice for block transfer of a heap */
PAG            = 0           /* a choice for heap creation in a PAG */
Alloc_Init     = 0           /* a choice for allocation initialization */
Init_Value     = 0x00        /* initialization value */

The attributes that are shown here illustrate the structure of the _CEE4ALC allocation strategy type. For information about all of the _CEE4ALC allocation strategy attributes, see the API topic collection in the Programming category of the IBM® i Information Center.