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Cygwin: open_shared: always bump next_address 

The new loop in open_shared has a subtil performance problem.
Next_address is bumped only if mapping at this address
failed.  Every subsequent call to open_shared has a high probability
having to call MapViewOfFileEx twice, because next_address is still
set to the address of the last successful mapping.

Avoid this by bumping next_address every time.

While at it, fix a comment.

Fixes: dc0fe7742b ("Cygwin: open_shared: try harder allocating a shared region")
Signed-off-by: Corinna Vinschen <corinna@vinschen.de>
This commit is contained in:
Corinna Vinschen 2023-01-18 19:59:48 +01:00
parent e18743072b
commit 7e332208a0
1 changed files with 8 additions and 12 deletions
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10
winsup/cygwin/mm/shared.cc
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@ -159,26 +159,22 @@ open_shared (const WCHAR *name, int n, HANDLE& shared_h, DWORD size,
/* Locate shared regions in the area between SHARED_REGIONS_ADDRESS_LOW
and SHARED_REGIONS_ADDRESS_HIGH, retrying until we have a slot.
Don't use MapViewOfFile3 (loader deadlock during fork. */
Don't use MapViewOfFile3 (STATUS_DLL_INIT_FAILED during fork). */
bool loop = false;
addr = (void *) next_address;
do
{
addr = (void *) next_address;
shared = MapViewOfFileEx (shared_h, FILE_MAP_READ | FILE_MAP_WRITE,
0, 0, 0, addr);
if (!shared)
{
next_address += wincap.allocation_granularity ();
if (next_address >= SHARED_REGIONS_ADDRESS_HIGH)
{
if (loop)
if (!shared && loop)
break;
next_address = SHARED_REGIONS_ADDRESS_LOW;
loop = true;
}
addr = (void *) next_address;
}
}
while (!shared);