Re: Heap memory available (W32 console app in Visual C++)
Igor Tandetnik a ?crit :
Why not
p1 = malloc(wanted1);
if (p1) p2 = malloc(wanted2);
if (p1 && p2) {
// Process two blocks
} else {
if (p1) free(p1);
// switch to alternative method }
Because it's much more complicated and less elegant than what I have now:
--------
struct rec *p1, *p2;
int numrecs1 = ...;
if ( ! ( p1 = (struct rec *)malloc( wanted1 + wanted2 ) )
// switch to alternative method
p2 = p1 + numrecs1;
// continue
--------
You seem to misunderstand how critical sections work. All threads
accessing the same shared data must do so under the same critical
section, otherwise it won't help any. You can't enforce proper access
synchronization from just one thread - all threads must cooperate.
You seem to have a different understanding of "critical sections" from mine.
In my terms (as a low-level assembly language programmer, having written
a multi-tasking kernel) the start of a critical section is marked by a
mutex and until it is cleared no other thread can acquire the CPU.
During a critical section the question of co-operation and sharing data
therefore simply doesn't exist: that is the entire point.
Anyway, we still haven't determined whether the 'data' - the heap - is
really shared or not.
If one single process malloc()'s one byte (OK - it will probably take 4,
neatly aligned) is the entire Windows memory management system updated?
Now, how do you plan to get all other processes in the system to use
your critical section whenever they allocate memory?
I don't.
Firstly, memory management under Windows doesn't seem to be very
intelligent and I can't fix that.
Secondly the whole point of a critical section is to exclude access by
other threads; not to allow them to share it.
Of course not. But all processes do share the same physical memory
chips installed on the motherboard, and the same swap file on the
same physical hard drive. You don't really believe that you can start
1000 processes and each of them would magically have 2GB of free
memory available to it?
So if there is not enough memory available to start a new process with
'normal' reasonable memory requirements, the system should say so
immediately and refuse.
You think it's reasonable to let me start 1000 processes none of which
which can claim even 1kB of memory?
--
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