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* [newlib-cygwin/cygwin-3_4-branch] Cygwin: open_shared: always bump next_address
@ 2023-01-18 19:35 Corinna Vinschen
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From: Corinna Vinschen @ 2023-01-18 19:35 UTC (permalink / raw)
To: cygwin-cvs
https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=0aa1c038196d04d0dfc8dc0f0f30e247e0c1e1e3
commit 0aa1c038196d04d0dfc8dc0f0f30e247e0c1e1e3
Author: Corinna Vinschen <corinna@vinschen.de>
AuthorDate: Wed Jan 18 19:59:48 2023 +0100
Commit: Corinna Vinschen <corinna@vinschen.de>
CommitDate: Wed Jan 18 20:17:23 2023 +0100
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.
Conflict: Missing backport of 31302b267b86 ("Cygwin: drop fixed addresses for standard shared regions")
Fixes: dc0fe7742b8c ("Cygwin: open_shared: try harder allocating a shared region")
Signed-off-by: Corinna Vinschen <corinna@vinschen.de>
Diff:
---
winsup/cygwin/mm/shared.cc | 20 ++++++++------------
1 file changed, 8 insertions(+), 12 deletions(-)
diff --git a/winsup/cygwin/mm/shared.cc b/winsup/cygwin/mm/shared.cc
index d23cc8e0e510..2ea3a4336351 100644
--- a/winsup/cygwin/mm/shared.cc
+++ b/winsup/cygwin/mm/shared.cc
@@ -184,25 +184,21 @@ 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)
{
- next_address += wincap.allocation_granularity ();
- if (next_address >= SHARED_REGIONS_ADDRESS_HIGH)
- {
- if (loop)
- break;
- next_address = SHARED_REGIONS_ADDRESS_LOW;
- loop = true;
- }
- addr = (void *) next_address;
+ if (!shared && loop)
+ break;
+ next_address = SHARED_REGIONS_ADDRESS_LOW;
+ loop = true;
}
}
while (!shared);
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