[newlib-cygwin/cygwin-3_5-branch] Cygwin: pipe: Fix a regression that raw_write() slows down

[Takashi Yano]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=37ab3e0d55e3ff3932509bfd2f2625c138b18866

commit 37ab3e0d55e3ff3932509bfd2f2625c138b18866
Author: Takashi Yano <takashi.yano@nifty.ne.jp>
Date:   Sun Sep 1 04:31:03 2024 +0900

    Cygwin: pipe: Fix a regression that raw_write() slows down
    
    After the commit 7f3c22532577, writing to pipe extremely slows down.
    This is because cygwait(select_sem, 10, cw_cancel) is called even
    when write operation is already completed. With this patch, the
    cygwait() is called only if the write operation is not completed.
    
    Addresses: https://cygwin.com/pipermail/cygwin/2024-August/256398.html
    Fixes: 7f3c22532577 ("Cygwin: pipe: handle signals explicitely in raw_write")
    Reported-by: Jim Reisert AD1C <jjreisert@alum.mit.edu>
    Reviewed-by: Corinna Vinschen <corinna@vinschen.de>
    Signed-off-by: Takashi Yano <takashi.yano@nifty.ne.jp>
    (cherry picked from commit f78009cb1ccf84cc343cf2441c76196461d87532)

Diff:
---
 winsup/cygwin/fhandler/pipe.cc | 6 ++++--
 winsup/cygwin/release/3.5.5    | 3 +++
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/winsup/cygwin/fhandler/pipe.cc b/winsup/cygwin/fhandler/pipe.cc
index 6658a23e7..997346877 100644
--- a/winsup/cygwin/fhandler/pipe.cc
+++ b/winsup/cygwin/fhandler/pipe.cc
@@ -503,8 +503,9 @@ fhandler_pipe_fifo::raw_write (const void *ptr, size_t len)
 		      raise (SIGPIPE);
 		      goto out;
 		    }
-		  else
-		    cygwait (select_sem, 10, cw_cancel);
+		  /* Break out on completion */
+		  if (waitret == WAIT_OBJECT_0)
+		    break;
 		  /* If we got a timeout in the blocking case, and we already
 		     did a short write, we got a signal in the previous loop. */
 		  if (waitret == WAIT_TIMEOUT && short_write_once)
@@ -512,6 +513,7 @@ fhandler_pipe_fifo::raw_write (const void *ptr, size_t len)
 		      waitret = WAIT_SIGNALED;
 		      break;
 		    }
+		  cygwait (select_sem, 10, cw_cancel);
 		}
 	      /* Loop in case of blocking write or SA_RESTART */
 	      while (waitret == WAIT_TIMEOUT || waitret == WAIT_SIGNALED);
diff --git a/winsup/cygwin/release/3.5.5 b/winsup/cygwin/release/3.5.5
index a98687c26..904119a38 100644
--- a/winsup/cygwin/release/3.5.5
+++ b/winsup/cygwin/release/3.5.5
@@ -4,3 +4,6 @@ Fixes:
 - Fix undesired behaviour of console master thread in win32-input-mode
   which is supported by Windows Termainal.
   Addresses: https://cygwin.com/pipermail/cygwin/2024-August/256380.html
+
+- Fix a regression in 3.5.4 that writing to pipe extremely slows down.
+  Addresses: https://cygwin.com/pipermail/cygwin/2024-August/256398.html