[newlib-cygwin] Cygwin: pty: Make slave read() thread-safe.

[Corinna Vinschen]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=f186f61d60b342c8167e652073bdc6e3f704a90a

commit f186f61d60b342c8167e652073bdc6e3f704a90a
Author: Takashi Yano via Cygwin-patches <cygwin-patches@cygwin.com>
Date:   Thu Jan 28 23:11:33 2021 +0900

    Cygwin: pty: Make slave read() thread-safe.
    
    - Currently slave read() is somehow not thread-safe. This patch
      fixes the issue.

Diff:
---
 winsup/cygwin/fhandler_tty.cc | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/winsup/cygwin/fhandler_tty.cc b/winsup/cygwin/fhandler_tty.cc
index 06fc19ac2..48b89ae77 100644
--- a/winsup/cygwin/fhandler_tty.cc
+++ b/winsup/cygwin/fhandler_tty.cc
@@ -1241,6 +1241,7 @@ fhandler_pty_slave::read (void *ptr, size_t& len)
 	time_to_wait = !vtime ? INFINITE : 100 * vtime;
     }
 
+wait_retry:
   while (len)
     {
       switch (cygwait (input_available_event, time_to_wait))
@@ -1319,6 +1320,11 @@ fhandler_pty_slave::read (void *ptr, size_t& len)
 	    }
 	  goto out;
 	}
+      if (!IsEventSignalled (input_available_event))
+	{ /* Maybe another thread has processed input. */
+	  ReleaseMutex (input_mutex);
+	  goto wait_retry;
+	}
 
       if (!bytes_available (bytes_in_pipe))
 	{