View source for DosLockSeg

==Description==
This call locks a discardable segment in memory.

==Syntax==
<PRE>
 DosLockSeg

    (Selector)
</PRE>

==Parameters==
;  Selector (SEL) - input : Selector of the segment to be locked.

==Return Code==
 rc (USHORT) - return

Return code descriptions are:

* 0          NO_ERROR
* 5          ERROR_ACCESS_DENIED
* 157        ERROR_DISCARDED

==Remarks==
Discardable segments are useful for holding objects that are accessed for short periods of time and that can be regenerated quickly if discarded. Examples are cache buffers for a data base package, saved bitmap images for obscured windows or precomputed display images for a word processing application.

Discardable memory is allocated by a call to DosAllocSeg or DosAllocHuge with AllocFlags bit 2 set. Upon allocation, the memory is automatically locked for access by the allocating process and cannot be discarded. After the segment is unlocked by a DosUnlockSeg request, the memory can be discarded by the memory manager to remedy a low memory situation. Once memory is discarded, a DosLockSeg call returns ERROR_DISCARDED. The memory is reallocated by a call to DosReallocSeg or DosReallocHuge. The reallocation request automatically locks the memory.

Memory allocated as discardable by a DosAllocSeg or DosAllocHuge request may also have been designated as shareable. Sharing processes that access the discardable shared memory with DosGetSeg have to lock the memory by calling DosLockSeg. See DosGetSeg for more information.

DosLockSeg and DosUnlockSeg calls may be nested. If DosLockSeg is called multiple times to lock a segment, the same number of calls must be made to DosUnlockSeg before the segment is unlocked. However, if a segment is locked 255 times, it becomes permanently locked. Additional calls to DosLockSeg and DosUnlockSeg have no effect on the segment's locked state.

This function is used on segments that have been allocated through DosAllocSeg with AllocFlags bit 2 (0100B) set. It may be also used on segments that are non-discardable, in which case it has no effect. 

==Example Code==
=== C Binding===
<PRE>
#define INCL_DOSMEMMGR

USHORT  rc = DosLockSeg(Selector);

SEL              Selector;      /* Selector to lock */

USHORT           rc;            /* return code */
</PRE>

===MASM Binding===
<PRE>
EXTRN  DosLockSeg:FAR
INCL_DOSMEMMGR      EQU 1

PUSH   WORD    Selector      ;Selector to lock
CALL   DosLockSeg

Returns WORD
</PRE>

==Related Functions==
* 

[[Category:The OS/2 API Project]]