(with the friendly permission of the original author, Andreas Kleinert)
New in release 2.01:
- Added a workarount for stupid "SaferPatches" clones.
New in release 2.00:
- Rewritten in assembly language, much shorter file
- Tries a partial flush first, instead of removing
all libraries on failure.
- Removed unnecessary AllocVec patch since it calls
AllocP will be part of a major memory defragmentizer project still to be
published, called PoolMem. Please stay tuned!
Sometimes programs fail with a "not enough memory" error,
but after calling "avail flush" the same operation does
succeed without problems.
If AllocMem routine in the ROMs did not find enough memory,
it tries to flush disk based libraries and devices and,
afterwards, tries again to reallocate the memory.
However, due to a design flaw of the AllocMem() routine,
this memory flushing does not have the desired result some-
times - even though the libraries have been informed to
remove themselves, the memory is not available directly
afterwards. The AllocMem() call will fail anyways, EVEN THOUGH
the requiested memory will be available immediatly after completion
The reasons for this strange behaiviour are rather technical
and explained below, for the interested user.
This patch does ensure, that AllocMem/AllocVec won't
fail unless there's really no memory available, even
by flushing. This means:
- less "out of memory" failures
- less "bad behaviour" of bad programs, which don't
check results of AllocMem/AllocVec
- no more need to call "avail flush" by hand
from the shell
- thus no more "retry" operations after "avail flush"
- no more unused libraries/devices consuming memory
when it is already low
Note: Works now for all operating systems and all CPUs,
is no longer restricted to V37 or MC'20.
Usage: Try starting in the Shell/CLI.
If it does run stable, copy it into
your C: directory and add it
somewhere into your s:user-startup
You use this patch at your own risk.
No guarantee for anything.
Source code in assembly language included, requires the DevPac assembler
and my macro package at dev/asm/DvPkMacros.lha at the AmiNet.
All mentioned trademarks are subject to their owners.
The design flaw in AllocMem():
When looking closely at the ROM routine of AllocMem(), you'll
notice that a memory flush is TRIED if the first allocation
Why does AllocMem then fail, even though if enough memory
Consider the following situation:
A library has launched a sub-task for control of some of its
features. This sub-task could be used for disk I-O, for example.
If this hypothetical library has to be expunged, it can't do
this on its own because this will release memory of the sub-task
which is still running. This sub-task must be informed somehow
that its memory must go. While this is in principle simple to do -
just send a message to the sub task - the library can't wait for
an answer of the sub-task because this would brake the Forbid()
state, which is illegal at this point of the operation.
The only solution for the library is to leave the memory flush
to the sub task and to return to the low-memory handler of exec
WITHOUT trying to remove itself - leaving this to its sub-task.
On the other hand, since multitasking is still forbidden, there
is NO chance that this subtask will actually get a chance to
remove the library, leaving it in memory and causing the
allocation failure. EVEN THOUGH the library was informed to
get removed, there is no chance of doing this while flushing.
However, as soon as exec leaves the AllocMem routine, multi-
tasking will be turned on again, thus causing a task switch to
the subtask and NOW causing the removal of the library - to late
to have any effect.
AllocP tries to avoid this situation by calling AllocMem a
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