|
Derivation: THREAD level STACK storage
THREADSTACK
controls the allocation of the thread's stack storage for both the
upward and downward-growing stacks, except the initial thread in a
multithreaded application. If the thread attribute object does not
provide an explicit stack size, then the allocation values can be
inherited from the STACK option or specified explicitly on the THREADSTACK
option.
The default
values for non-CICS applications is THREADSTACK(OFF,4K,4K,ANYWHERE,KEEP,128K,128K).
THREADSTACK
is ignored under CICS®.
Syntax
.-OFF-.
>>-THREADSTack--(--+-----+--,--+-------------+--,--------------->
'-ON--' '-usinit_size-'
.-ANYWHERE-. .-KEEP-.
>--+-------------+--,--+----------+--,--+------+--,------------->
'-usincr_size-' +-ANY------+ '-FREE-'
'-BELOW----'
>--+-------------+--,--+-------------+--)----------------------><
'-dsinit_size-' '-dsincr_size-'
- OFF
- Indicates that the allocation suboptions of the STACK runtime
option are used for thread stack allocation. Any other suboption specified
with THREADSTACK is ignored.
- ON
- Controls the stack allocation for each thread, except the initial
thread, in a multithreaded environment.
- usinit_size
- Determines the size of the initial upward-growing stack segment.
The storage is contiguous. You specify the usinit_size value
as n, nK, or nM
bytes of storage. The actual amount of allocated storage is rounded
up to the nearest multiple of 8 bytes.
The usinit_size value
can be preceded by a minus sign. In environments other than CICS, if you specify a negative
number Language Environment uses
all available storage minus the amount specified for the initial stack
segment.
A size of "0" or "-0" requests half of the largest
block of contiguous storage in the region below the 16-MB line.
- usincr_size
- Determines the minimum size of any subsequent increment to the
upward-growing stack area. You can specify this value as n, nK,
or nM bytes of storage. The actual amount
of allocated storage is the larger of two values— usincr_size or
the requested size—rounded up to the nearest multiple of 8 bytes
If
you specify usincr_size as 0, only the amount
of the storage needed at the time of the request, rounded up to the
nearest multiple of 8 bytes, is obtained.
The requested size
is the amount of storage a routine needs for a stack frame. For example,
if the requested size is 9000 bytes, usincr_size is
specified as 8K, and the initial stack segment is full, Language Environment gets
a 9000 byte stack increment from the operating system to satisfy the
request. If the requested size is smaller than 8K, Language Environment gets
an 8K stack increment from the operating system.
- ANYWHERE | ANY
- Specifies that stack storage can be allocated anywhere in storage.
On systems that support bimodal addressing, storage can be allocated
either above or below the 16M line. If there is no storage available
above the line, Language Environment acquires
storage below the line. On systems that do not support bimodal addressing
(for example, when VM/ESA is
initial program loaded in 370 mode) Language Environment ignores
this option and places the stack storage below 16M.
- BELOW
- Specifies that the stack storage must be allocated below the 16M
line in storage that is accessible to 24–bit addressing.
- KEEP
- Specifies that storage allocated to stack increments is not released
when the last of the storage in the stack increment is freed.
- FREE
- Specifies that storage allocated to stack increments is released
when the last of the storage in the stack is freed. The initial stack
segment is never released until the enclave terminates.
- dsinit_size
- Determines the size of the initial downward-growing stack segment.
The storage is contiguous. You specify the init_size value as n, nK,
or nM bytes of storage. The actual amount
of allocated storage is rounded up to the nearest multiple of 16 bytes.
- dsincr_size
- Determines the minimum size of any subsequent increment to the
downward-growing stack area. You can specify this value as n, nK,
or nM bytes of storage. The actual amount
of allocated storage is the larger of two values-- incr_size or
the requested size--rounded up to the nearest multiple of 16 bytes.
Usage notes - The dsinit_size and dsincr_size values
are the amounts of storage that can be used for downward-growing
stack frames (plus the stack header, approximately 20 bytes). The
actual size of the storage getmained will be 4K (8K if a 4K page alignment
cannot be guaranteed) larger to accommodate the guard page.
- The downward-growing stack is only initialized in a XPLINK supported
environment, that is, batch, TSO, z/OS UNIX, and only
when a XPLINK application
is active in the enclave. Otherwise the suboptions for the downward-growing
stack are ignored.
- All storage allocated to THREADSTACK segments are freed when the
thread terminates.
- The initial stack segment of the thread is never released until
the thread terminates, regardless of the KEEP/FREE state.
- You can specify suboptions with THREADSTACK(OFF,...), but they
are ignored. If you override the THREADSTACK(OFF,...) suboption with
THREADSTACK(ON) and you omit suboptions, then the suboptions you
specified with THREADSTACK(OFF,...) remain in effect. If you respecify
THREADSTACK(OFF,...) with different suboptions, they override the
defaults.
- PL/I MTF consideration—THREADSTACK(ON,4K, 4K, BELOW, KEEP,,) provides
PL/I compatibility for stack storage allocation and management for
each subtask in the application.
- PL/I considerations—For multitasking or multithreaded environments,
the stack size for a subtask or non-Initial Process Thread (non-IPT)
is taken from the THREADSTACK option unless THREADSTACK(OFF) is
specified. THREADSTACK(OFF) specifies that the values in the STACK
option be used.
- In the multithreaded environment, you can explicitly specify the
stack size in the thread attribute object; it will be used instead
of the value specified with THREADSTACK or STACK.
- The THREADSTACK option replaces the NONIPTSTACK and NONONIPTSTACK options.
|