[newlib-cygwin/main] Cygwin: open_shared: always bump next_address

[Corinna Vinschen]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=7e332208a0987fd91bf1afc8fa7a5647b53a5670

commit 7e332208a0987fd91bf1afc8fa7a5647b53a5670
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 20:13:36 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.
    
    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 eb798c2ddb5f..e68b506a9fff 100644
--- a/winsup/cygwin/mm/shared.cc
+++ b/winsup/cygwin/mm/shared.cc
@@ -159,25 +159,21 @@ 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);