INT 31H 0d00H: Allocate Shared Memory

                                                    Compatibility: DPMI 1.0+ 
 Expects: AX    0d00H
          ES:DI (or ES:EDI) address of 28-byte info structure (see below)
          ──────────────────────────────────────────────────────────────────
 Returns: CF    NC (clear) if successful; else AX = DPMI Error Code
          ES:DI (or ES:EDI) structure updated
          ──────────────────────────────────────────────────────────────────
    Info: This allocates a named block of memory that may be shared by DPMI
          clients.  This may be used for interprocess communication.

 DS:(E)DI this selector:offset must point to a 28-byte local structure
          defined as follows:

            Offset Size Contents
            ▀▀▀▀▀▀ ▀▀▀▀ ▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀
             +0      4  lReqSize     desired size of block, in bytes
             +4      4  lActualSize  actual size allocated (returned)
             +8      4  lHandle      handle for the allocation (returned)
            +0cH     4  lLinAddr     linear addr of allocation (returned)
            +10H     6  p48szName    48-bit address of ASCIIZ▲ name for
                                     the shared block.  First 4 bytes are
                                     the offset; the last 2 are selector.
            +16H     2  wRes1        reserved
            +18H     4  lRes2        reserved; must be 0
                    28               size of this structure

          On entry, you must fill in lReqSize and set p48szName to a 48-bit
          address of an ASCIIZ string that names the block.  The host
          fills-in lAllocSize, lHandle, and lLinAddr.

          For 16-bit clients, the high word of p48szName must be 0000H.

    Note: ■ The second and subsequent client to use this fn with the same
            ASCIIZ name, will be returned info about the initial
            allocation.  For such subsequent "allocations", the lReqSize
            field is ignored.  Be sure to check the lActualSize field on
            return.

          ■ The first client to allocate a named block will find that the
            first 16-bytes are 0.  It can gain exclusive ownership via
            INT 31H 0d02H, and store some non-zero values so that
            subsequent clients can tell that it has been initialized.

          ■ 0-length allocations are explicitly supported and can be used
            as a way to implement semaphores (see INT 31H 0d02H, for
            instance).

          ■ All of your shared memory allocations and serializations are
            freed by the host automatically when you terminate.

See Also: DPMI API
          INT 2fH: Multiplex Interrupt
          DOS Functions
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