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Hex Dec Type/Val Lng Label (dup) Comments
---- ---- --------- ---- -------------- --------
0000 0 Structure FREBK FREE STORAGE BLOCK
This is a picture of how the fields in this DSECT are
actually used:
+----------------------------------------------------+
0 | FREHEADR |
+----------------------------------------------------+
8 : :
: (control block) :
: :
+----------------------------------------------------+
xx | FRETRALR |
| |
+----------------------------------------------------+
xx+10
The free storage header (FREHEADR) and free storage
trailer (FRETRALR) areas are maintained both for internal
functional uses and as debugging aids for free storage
related problems. The free storage header immediately
precedes the start of the free storage block returned in
response to an obtain free storage request (HCPGETST).
The trailer, when present (which is always, except for
Fast Allocated Blocks), follows the end of the free
storage requested by the caller (there may be a gap
between the end of the size of block requested by the
caller and the free storage trailer, as we round the
requested size up to a convenient boundary in certain
cases). The exact format and content of these fields
depends on the type of free storage being used and whether
the free storage block is active or inactive:
+- free storage block itself in here
|
V
<----FREHEADR-----> <-------------FRETRALR-------------->
Normal (non-subpooled):
In use (for undefined blocks, cbi == '<<<')
+--------+--------+ +--------+--------+--------+--------+
|0000rqsz| >>>> |-| >>> |-| <--obtainer->|
Normal subpooled (non-FAB) free storage:
In use (normal):
+--------+--------+ +--------+--------+--------+--------+
| >> rqsz|1 subbk@|-| > rqsz|0 subbk@|-| <--obtainer->|
Available (on collection pile):
+--------+--------+ +--------+--------+--------+--------+
| fpnt |0 subbk@|-| <--obtainer->|
Fast Allocated Block free storage:
In use (normal):
+--------+--------+ +--------+--------+--------+--------+
|sli 0FAB|1 subbk@|-|xxxxxxxx|xxxxxxxx|xxxxxxxx|xxxxxxxx|
+--------+--------+ +--------+--------+--------+--------+
In use (flagged for collection pile):
+--------+--------+ +--------+--------+--------+--------+
|sli 0FAB|0 subbk@|-|xxxxxxxx|xxxxxxxx|xxxxxxxx|xxxxxxxx|
+--------+--------+ +--------+--------+--------+--------+
Available (normal):
+--------+--------+ +--------+--------+--------+--------+
| fpnt |1 subbk@|-|xxxxxxxx|xxxxxxxx|xxxxxxxx|xxxxxxxx|
+--------+--------+ +--------+--------+--------+--------+
Available (on collection pile):
+--------+--------+ +--------+--------+--------+--------+
| fpnt |0 subbk@|-|xxxxxxxx|xxxxxxxx|xxxxxxxx|xxxxxxxx|
+--------+--------+ +--------+--------+--------+--------+
Notes : Free storage trailer not maintained and is
unreliable for Fast Allocated Blocks!
0000 0 Dbl-Word 8 FRESTRT (0) START OF VARIABLE LENGTH DATA
0000 0 Dbl-Word 8 FREHEADR FREE STORAGE BLOCK HEADER
00000008 FREHEADL *-FREHEADR LENGTH OF HEADER IN
BYTES
0000 0 Dbl-Word 8 FRETRALR (2) FREE STORAGE BLOCK TRAILER
00000010 FRETRALL *-FRETRALR LENGTH OF TRAILER IN
BYTES
00000003 FRERECL (FREHEADL+FRETRALL+7)/8 SIZE IN
DOUBLE WORDS
0000 0 Signed 4 FREESIZE (0) # OF DWORDS OF STORAGE REQUESTED
0000 0 Signed 2 FREHSPSE (0) Mini-eyecatcher for non-FAB SPS,
0 for normal non-subpooled free
storage, or SLI for FAB SPS:
0000 0 Signed 2 FREHFSLI System Location Identifier (SLI)
for Fast Allocated Block
subpooled free storage
0002 2 Signed 2 FREHSIZE Actual count of DWs requested
Notes : The maximum allowable size value for FREESIZE /
FREHSIZE is the number of doublewords which can fit
into a single 4K page (not counting the free storage
header and trailer), or 509 doublewords, x'1FD'. For
normal non-subpooled free storage, the high order
halfword of FREESIZE (aka FREHSPSE) must be zero; for
normal (non-FAB) subpooled free stg, FREHSPSE has the
mini- eyecatcher '>>' == x'6E6E'. For Fast Allocated
Block subpooled free storage, FREHSPSE contains the
System Location Identifier (SLI) number, which
identifies where in the system the block was obtained.
A FREHSIZE value of x'FAB' in active subpooled free
storage blocks is not a size, but is used to indicate
that the block is an active "fast allocated block".
0004 4 Signed 4 FRESUBBK (0) Address of SUBBK for subpool blk
The high order bit of FRESUBBK is
normally 1, and is set to 0 by
garbage collection (HCPFRFDX) to
indicate that the block should be
queued on the collection pile
when freed (to attempt to reclaim
the frame)
0004 4 Character 4 FREESFLG ALLOCATED BLOCK CHARACTER STRI
0000 0 Character 4 FREEID CONTROL BLOCK'S IDENTIFIER (THE
FIRST CHARACTER IS '<', AND
THE ID FOR UNDEFINED BLOCKS IS
'<<<<' )
0004 4 Signed 4 FREFSCBK (0) Addr of storage obtainers FSCBK
0004 4 Character 4 FREEEFLG CHARACTER STRING '<<<
0008 8 Signed 4 FREEDISP REQUEST'S OFFSET IN CALLING
MODULE (1ST HALF WORD = X'00 00')
000C 12 Character 4 FREEMOD MODULE ID OF CALLING MODULE THE
FIRST BYTE'S ALWAYS SET TO 0
0000 0 Signed 4 FREEPNT PNTR TO NEXT BLOCK IN FREE
STORAGE CHAIN OR 0 (IF
END-OF-CHAIN)
0004 4 Signed 4 FRETSIZE Size of available block in DWs or
the size in bytes for a larger
than subpool size block that is
on the free storage chain
Notes : For for subpooled free storage, FRETSIZE as such is
not used. Instead the address of the SUBBK which
represents this subpool remains here in the second
word of the free storage header (as field FRESUBBK).
Since the maximum allowable value for FRETSIZE for
normal (non-FAB) free storage is 509 (x'1FD'), any
larger value in this field indicates that the block
in question is in a frame used for subpooled free
storage (since SUBBKs can't reside in low prefix page
addresses like x'1FD' and below). However, in order
to use this fact to distinguish between types,
caution must be used, since the high order bit of the
SUBBK address is used as a free storage garbage
collection flag.
Also note that in *active* subpooled free storage
blocks, a value of x'FAB' in the actual requested
size in dws (in FREHSIZE) is not a size, but an
indicator that the block is an active "fast allocated
block" (the requested size is not kept for fast
allocated blocks, we know the actual size allocated
because we know which subpool it's from).
Note that the free storage trailer is not maintained, and
may not even exist in some cases, and is therefore
unreliable for available blocks that were last used as Fast
Allocated Blocks.
0000 0 Character 4 FRETID CONTROL BLOCK'S IDENTIFIER (THE
FIRST CHARACTER IS '<', AND
THE ID FOR UNDEFINED BLOCKS IS
'<<<<' ) THIS FIELD
IS PRESERVED FROM THE HCPFREE
CALL WHICH ORIGINALLY OBTAINED
THIS CONTROL BLOCK
0004 4 Character 4 FRETMOD MODID OF HCPFRET CALLER THE FIRST
BYTE'S ALWAYS SET TO 0
0008 8 Signed 2 FRETDISP DISPL INTO MODID OF HCPFRET CALL
000A 10 Bitstring 1 FREECALL (6) LOW-ORDER 2 BYTES OF "FREEDISP"
AND "FREEMOD PRESERVED FROM THE
HCPFREE CALL WHICH ORIGINALLY
OBTAINED THIS CONTROL BLOCK
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