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* heap.cc (sbrk): Add a FIXME comment to VirtualFree call. Fix memory 

reservation and commit strategy when more memory is requested than
	available on the heap.  Release newly reserved memory if commiting
	it fails.  Add more comments to explain what we do.
This commit is contained in:
Corinna Vinschen 2013-08-30 20:01:10 +00:00
parent a723366660
commit b03bd1f41c
1 changed files with 43 additions and 18 deletions
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47
winsup/cygwin/heap.cc
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@ -245,7 +245,7 @@ extern "C" void *
sbrk (ptrdiff_t n)
{
char *newtop, *newbrk;
SIZE_T commitbytes, newbrksize;
SIZE_T commitbytes, newbrksize, reservebytes;
if (n == 0)
return cygheap->user_heap.ptr; /* Just wanted to find current cygheap->user_heap.ptr address */
@ -261,6 +261,9 @@ sbrk (ptrdiff_t n)
{ /* Freeing memory */
assert (newtop < cygheap->user_heap.top);
n = (char *) cygheap->user_heap.top - newtop;
/* FIXME: This doesn't work if we cross a virtual memory reservation
border. If that happens, we have to free the space in multiple
VirtualFree calls, aligned to the former reservation borders. */
if (VirtualFree (newtop, n, MEM_DECOMMIT)) /* Give it back to OS */
goto good;
goto err; /* Didn't take */
@ -277,27 +280,49 @@ sbrk (ptrdiff_t n)
reserved. */
if (newtop <= cygheap->user_heap.max)
{
if (VirtualAlloc (cygheap->user_heap.top, commitbytes, MEM_COMMIT, PAGE_READWRITE) != NULL)
if (VirtualAlloc (cygheap->user_heap.top, commitbytes,
MEM_COMMIT, PAGE_READWRITE) != NULL)
goto good;
}
/* Couldn't allocate memory. Maybe we can reserve some more.
Reserve either the maximum of the standard cygwin_shared->heap_chunk_size ()
or the requested amount. Then attempt to actually allocate it. */
if ((newbrksize = cygheap->user_heap.chunk) < commitbytes)
newbrksize = commitbytes;
/* The remainder of the existing heap is too small to fulfil the memory
request. We have to extend the heap, so we reserve some more memory
and then commit the remainder of the old heap, if any, and the rest of
the required space from the extended heap. */
if ((VirtualAlloc (cygheap->user_heap.top, newbrksize,
/* Reserve either the maximum of the standard heap chunk size
or the requested amount. Then attempt to actually allocate it. */
reservebytes = commitbytes - ((ptrdiff_t) cygheap->user_heap.max
- (ptrdiff_t) cygheap->user_heap.top);
commitbytes -= reservebytes;
if ((newbrksize = cygheap->user_heap.chunk) < reservebytes)
newbrksize = reservebytes;
if (VirtualAlloc (cygheap->user_heap.max, newbrksize,
MEM_RESERVE, PAGE_NOACCESS)
|| VirtualAlloc (cygheap->user_heap.top, newbrksize = commitbytes,
|| VirtualAlloc (cygheap->user_heap.max, newbrksize = reservebytes,
MEM_RESERVE, PAGE_NOACCESS))
&& VirtualAlloc (cygheap->user_heap.top, commitbytes,
MEM_COMMIT, PAGE_READWRITE) != NULL)
{
/* Now commit the requested memory. Windows keeps all virtual
reservations separate, so we can't commit the two regions in a single,
combined call or we suffer an ERROR_INVALID_ADDRESS. The same error
is returned when trying to VirtualAlloc 0 bytes, which would occur if
the existing heap was already full. */
if ((!commitbytes || VirtualAlloc (cygheap->user_heap.top, commitbytes,
MEM_COMMIT, PAGE_READWRITE))
&& VirtualAlloc (cygheap->user_heap.max, reservebytes,
MEM_COMMIT, PAGE_READWRITE))
{
cygheap->user_heap.max = (char *) cygheap->user_heap.max
+ pround (newbrksize);
goto good;
}
/* If committing the memory failed, we must free the extendend reserved
region, otherwise any other try to fetch memory (for instance by using
mmap) may fail just because we still reserve memory we don't even know
about. */
VirtualFree (cygheap->user_heap.max, newbrksize, MEM_RELEASE);
}
err:
set_errno (ENOMEM);