DosAllocHuge
Bindings: C, MASM
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:
0 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.
Created using Inf-PHP v.2 (c) 2003 Yuri Prokushev
Created using Inf-HTML v.0.9b (c) 1995 Peter Childs