[newlib-cygwin] Cygwin: sigproc: Eliminate redundant copying of chld_procs

[Corinna Vinschen <corinna@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=b05b0b78fa91514473b092877da0f13be5a6b2c5

commit b05b0b78fa91514473b092877da0f13be5a6b2c5
Author: Corinna Vinschen <corinna@vinschen.de>
Date:   Fri Aug 28 19:34:52 2020 +0200

    Cygwin: sigproc: Eliminate redundant copying of chld_procs
    
    On PROC_EXEC_CLEANUP, the pinfo's in chld_procs are removed.
    This is done in a loop always removing the child with index 0.
    This, however, results in copying the last child's pinfo in
    chld_procs to position 0.  Do this for 100 children and you
    get 99 entirely useless copy operations.
    
    Fix this by calling remove_proc in reverse order.
    
    Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

Diff:
---
 winsup/cygwin/sigproc.cc | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/winsup/cygwin/sigproc.cc b/winsup/cygwin/sigproc.cc
index f46d3d0d8..aa946fb4c 100644
--- a/winsup/cygwin/sigproc.cc
+++ b/winsup/cygwin/sigproc.cc
@@ -299,8 +299,10 @@ proc_subproc (DWORD what, uintptr_t val)
       goto scan_wait;
 
     case PROC_EXEC_CLEANUP:
+      /* Cleanup backwards to eliminate redundant copying of chld_procs
+	 array members inside remove_proc. */
       while (chld_procs.count ())
-	remove_proc (0);
+	remove_proc (chld_procs.count () - 1);
       for (w = &waitq_head; w->next != NULL; w = w->next)
 	CloseHandle (w->next->ev);
       break;