intro.gml

开放源码的编译器open watcom 1.6.0版的源代码

.ev TEMP 
and 
.ev TMP 
environment variables specify the directory and drive
where a swap file is built by CauseWay's virtual memory manager (VMM)
when operating under DOS. Windows and OS/2 provide their own memory
management functions which override CauseWay's use of the 
.ev TEMP 
and 
.ev TMP
environment variables. The path indicated by 
.ev TEMP 
will be used under DOS
if both 
.ev TEMP
and 
.ev TMP 
environment variables exist. Both settings are
superseded by the 
.ev CAUSEWAY=SWAP 
environment variable setting.
.millust begin
SET TMP=C:\SWAP
.millust end
The example above directs the CauseWay DOS extender to create its swap
file, if any, in the C:\SWAP directory.
.np
If no 
.ev TEMP
, 
.ev TMP 
and 
.ev CAUSEWAY=SWAP 
settings are present or are invalid,
the current drive is used when creating a swap file.  If free drive
space is less than physical memory (extended and conventional) available
at startup, then the DOS extender VMM is disabled, no swap file is
created, and virtual memory is not available to the application.
.*
.section CAUSEWAY Environment Variable
.np
The 
.ev CAUSEWAY 
environment variable controls operation of the DOS extender
at application runtime.  Eleven (11) options are supported, although
they are ignored in a Windows or OS/2 DPMI environment.  Use any
combination of the options in the following format:
.millust begin
SET CAUSEWAY=[<setting_1>;][<setting_2>;][<setting_n>;]
.millust end
Items in square brackets ([ ]) are optional. Do not actually type the 
brackets if you use the optional items.  Items in brackets (< >) should 
be replaced with actual values, separated by semicolons.  Following is 
a description of the valid settings:
.np
.begnote
.note BIG1
.br
.ix 'BIG1 setting'
.ix 'DPMI host'
.ix 'INT 15h'
Force CauseWay to use an alternate method to
determine available extended memory under RAW memory environments (no
DPMI host, no HIMEM.SYS loaded), allowing CauseWay to see more than 64MB
of memory on machines which do not support more than 64MB under original
INT 15h method. This method uses INT 15h function 0e801h to determine
available extended memory, falling back to the original function if
0e801h fails. Note that old machines may not support this function and
there is a slight chance that some older machines may not work if this 
setting is used.
.*
.note DPMI
.br
.ix 'DPMI setting'
.ix 'DPMI'
Force DPMI rather than default VCPI usage
whenever possible (recommended for 386Max and BlueMax users).  The
memory manager must support DPMI or else this setting is ignored.
.*
.note EXTALL
.br
.ix 'EXTALL setting'
Force CauseWay to use all extended memory and
sub-allocate memory from the bottom up instead of the default top-down
approach.  This setting is most useful for processor intensive
environments which have a small hardware cache that does not cover the 
entire physical address range.  Use of this setting
means that no extended memory will be available for other programs while
the application is loaded (including shelling to DOS).
.*
.note HIMEM:<nnn>
.br
.ix 'HIMEM setting'
Set maximum physical (conventional plus extended)
memory that can be consumed by CauseWay where 
.mono <nnn> 
is the decimal number of
kilobytes that can be consumed.  If memory allocation requests exceed
this figure, CauseWay will use virtual memory, even if additional
physical memory is present.  If the HIMEM memory value exceeds available
physical memory, then memory allocations operate normally. For example,
HIMEM:2048 on a 4MB machine would force virtual memory use after 2MB of
memory allocations (including loading the executable file). The
remaining 2MB of memory could be used by other applications while the
CauseWay application is active.
.*
.note LOWMEM:<nnn>
.br
.ix 'LOWMEM setting'
.ix 'conventional memory'
Set DOS (conventional) memory to restrict it from use by
CauseWay.  This memory is in addition to the default 32KB low DOS memory
block reserved by CauseWay for use by any applications which need to
allocate DOS memory.  
.mono <nnn> 
is the decimal number of kilobytes to
reserve.  If there is not enough conventional memory to satisfy the
.mono <nnn> 
request value, then CauseWay will leave all conventional memory
free that is not required by the extender to operate. Note that this
option does not guarantee the amount of free DOS memory, just how much
needs to be free before CauseWay will consume DOS memory after
exhausting all extended memory.  For example, LOWMEM:200 will attempt to
reserve 200KB of DOS memory, even if CauseWay has exhausted all extended
memory and is using conventional memory to fill memory allocation requests.
.*
.note MAXMEM:<nn>
.br
.ix 'MAXMEM setting'
Set maximum linear address space provided by CauseWay where
.mono <nn> 
is the decimal number of megabytes of linear address space. This
setting is similar to HIMEM except that it includes any virtual memory.
For example, MAXMEM:32 on a 16MB memory system restricts VMM disk space
usage to 32MB, even if more disk space is present.  MAXMEM:8 on the same
system would restrict the application to 8MB of memory (all physical).
Note that the setting is in megabytes, rather than kilobytes used in the
LOWMEM and HIMEM options.
.*
.note NAME:<filename>
.br
.ix 'NAME setting'
Set a name, without a
pathspec, to use the virtual memory temporary swap file.  To set a path
for the swap file, use the 
.ev CAUSEWAY=SWAP
,
.ev TEMP
, or 
.ev TMP
environment variable. The filename
must be valid, 12 characters or less.  Additional characters are
truncated or invalidate the filename, depending upon how DOS handles it
(e.g., multiple periods make an invalid file name whereas a
five-character extension is truncated to three).  If the filename
specified is invalid, CauseWay shuts off virtual memory.  It makes no
further attempts for a temporary file name.  If a pre-existing file name
is specified, CauseWay overwrites the file.
.np
In conjunction with the PRE
setting, the NAME setting can be a very powerful tool.  Not only can no
clusters be lost due to reset/reboot, but the leftover temporary file
can be forced to a known name and location.  Erase the swap file prior
to running the application or leave it as a "permanent" swap file for
CauseWay.
.np
Note: In a multi-user or
muti-CauseWay application situation, do not use the NAME setting unless
it generates a unique file for each user and application.  Otherwise,
applications will be stepping on others' temporary files.
.*
.note NOEX
.br
.ix 'NOEX setting'
Force CauseWay to not patch the INT 21h, function
4bh (EXEC) vector to turn off CauseWay's INT 31h extensions when the
EXEC function is called. CauseWay normally turns off support of its INT
31h extensions with an EXEC call to be well behaved and avoid conflicts
with other extenders or programs which may add their own extensions to
INT 31h. However, if your CauseWay extended application shells out to
DOS and passes the shelled-to application a callback address pointing to
a routine within the parent CauseWay application, the callback will not
work properly if the protected mode code uses the CauseWay extensions.
With the NOEX setting present, CauseWay still supports its INT 31h
extensions for those users who need to operate with callbacks in this
fashion. Be aware that when the NOEX setting is present, CauseWay is
less "well-behaved" about other programs which might add their own INT
31h extensions.
.*
.note NOVM
.br
.ix 'NOVM setting'
.ix 'virtual memory'
Disable all virtual memory use by CauseWay.  If
physical memory is exhausted, CauseWay will fail  further memory
allocation requests.
.*
.note PRE:<nnn>
.br
.ix 'PRE setting'
Pre-allocates a swap file size, under non-DPMI
environments, at start-up, where
.mono <nnn> 
is file size in megabytes, not kilobytes (same as MAXMEM).
.np
There are at least two uses for this
feature.  First, to pre-allocate a virtual memory file size for
applications with a total memory allocation (including EXE image) that
does not exceed the set size.  For example:
.millust begin
SET CAUSEWAY=PRE:4
.millust end
pre-allocates a virtual memory file of
4MB.  If an enduser resets or powers off the computer while the
application is running and virtual memory is in use, the enduser's
machine will not have lost clusters.  There is only a 4MB temporary file
to find and erase.  If virtual memory usage exceeds 4MB, then SCANDISK
must be used to recover lost clusters above and beyond what was
pre-allocated.
.np
Secondly, PRE can be used to allow your
application to stake a claim to disk space before it needs it.
.np
PRE may be used in conjunction with MAXMEM
to ensure that virtual memory does not exceed the pre-allocation setting.
.*
.note SWAP:<path>
.br
.ix 'SWAP setting'
.ix 'swap file'
Set CauseWay's virtual memory manager swap file
path.  This path takes precedence for choosing the location of a swap
file over the 
.ev TEMP 
and 
.ev TMP 
environment variables.
.endnote
.endlevel