In article <khg6f3$cfr$1...@reader2.panix.com>,
Grant Edwards <invalid@invalid.invalid> wrote:
> What I should have said was that there's no way to return to the OS
> memory obtained via calls to malloc() et al.
That's true (for certain values of "et al").
> and those are the calls that "good" C programmers (like the
> maintainers of CPython) use.
Well, there is mmap, which is exposed via the Python mmap module.
Python doesn't have anything like C++'s "placement new", so there's no
way to use that memory to hold generic Python objects, but you can
certainly use mmap to allocate a large chunk of memory, use it, and then
give it back to the OS. For example:
#!/usr/bin/env python
import mmap
import time
time.sleep(5)
f = open('my-500-mbyte-text-file')
data = mmap.mmap(f.fileno(), 0, prot=mmap.PROT_READ)
count = 0
while 1:
line = data.readline()
if not line:
break
count += 1
print count
time.sleep(5)
data.close()
time.sleep(5)
When I run that and watch the process size (like I did with the previous
example), you can see the process grow when mmap() is called, and shrink
again when the segment is closed.
I have to admit, in all the years I've been using Python, this is the
first time I've ever used the mmap module. Even for long running
processes, the automatic memory management that Python provides out of
the box has always been good enough for me. But, it's nice to know mmap
is there if I need to do something unusual.
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