DosAllocHuge

This call allocates multiple segments as a huge block of memory.

DosAllocHuge

(NumSeg, Size, Selector, MaxNumSeg, AllocFlags)

NumSeg (USHORT) - input

Number of 65536-byte segments to be allocated.
Size (USHORT) - input
Number of bytes to be allocated in the last (non-65536-byte) segment. A value of zero indicates none.
Selector (PSEL) - output
Address where the selector of the first segment allocated is returned.
MaxNumSeg (USHORT) - input
Maximum number of 65536-byte segments this object occupies as a result of any subsequent DosReallocHuge (see DosReallocHuge.) If MaxNumSeg is 0, OS/2 assumes this segment will never be increased by DosReallocHuge beyond its original size, though it may be decreased. This value is ignored in the DOS mode.
AllocFlags (USHORT) - input
Bit indicators describing the characteristics of the segment allocated. The bits that can be set and their meanings are:

Bit

Description
15-4
Reserved and must be set to zero.
3
If segment is shared, it can be decreased in size by DosReallocHuge.
2
Segment may be discarded by the system in low memory situations.
1
Segment is shareable through DosGetSeg.
0
Segment is shareable through DosGiveSeg.
rc (USHORT) - return
Return code descriptions are:
• NO_ERROR 8
  ERROR_NOT_ENOUGH_MEMORY
  87
  ERROR_INVALID_PARAMETER
  212
  ERROR_LOCKED
  Remarks

  DosAllocHuge allows a process to allocate a large amount of memory by telling the system how many 64KB segments it needs and whether it requires an additional partial segment. The system allocates the memory, which is movable and swappable, and returns a selector to the first segment. When this selector is used with a call, the requested function is performed for the entire block of memory.

  Each segment of a huge memory allocation has a unique selector. To determine the remaining selectors of a huge memory allocation, issue DosGetHugeShift, which returns a shift count. To compute the next sequential selector, take the value 1 and shift it left by the number of bits specified in shift count. Use the resulting value as an increment to add to the previous selector, using the selector returned by DosAllocHuge as the first selector. For example:

  o

  Assume DosAllocHuge is issued with NumSeg equal to 3, and that the number 63 is returned for the selector of the first segment.
  o
  If DosGetHugeShift returns a shift count of 4, shifting the value "1" by this amount results in an increment of 16.
  o
  Adding this increment to selector number 63 produces 79 for the second selector. Adding the same increment to selector number 79 yields 95 for the third selector.

  Like single segment memory allocated with DosAllocSeg, huge memory can be designated as shareable by other processes and discardable by the system when no longer needed. Allocating a huge block of memory as discardable automatically locks the memory for use by the caller. When one segment of a huge allocation is discarded by the system, this forces the discard of all the other segments. See DosAllocSeg for more information relating to discardable and shared segments.

  Applications should be discretionary in claiming large memory when doing so can impair system performance. To test system memory availability, issue DosMemAvail. This call returns the size of the largest block of unallocated memory. Although this value can change at any time because of system activity , it can provide a good indication of the system memory state.

  Memory allocated by DosAllocHuge is freed by DosFreeSeg. One call to DosFreeSeg, passing the selector returned from a DosAllocHuge, frees all of the memory allocated.

  Note: This request may be issued from privilege level 2. However, the segment is allocated as a privilege level 3 segment.

  Family API Considerations

  Some options operate differently in the DOS mode than in the OS/2 mode. Therefore, the following considerations apply to DosAllocHuge when coding for the DOS mode:

  o

  Requested size value is rounded up to the next paragraph (16-byte)
  o
  Selector is the actual segment address allocated.

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