MDEV-21101 unexpected wait_timeout with pool-of-threads

Due to restricted size of the threadpool, execution of client queries can
be delayed (queued) for a while. This delay was interpreted as client
inactivity, and connection is closed, if client idle time + queue time
exceeds wait_timeout.

But users did not expect queue time to be included into wait_timeout.

This patch changes the behavior. We don't close connection anymore,
if there is some unread data present on connection,
even if wait_timeout is exceeded. Unread data means that client
was not idle, it sent a query, which we did not have time to process yet.

3 files changed, 27 insertions, 9 deletions

diff --git a/vio/vio_priv.h b/vio/vio_priv.h
index 71a0468e226..6780ec5664a 100644
--- a/vio/vio_priv.h
+++ b/vio/vio_priv.h
@@ -33,6 +33,7 @@ my_bool vio_is_connected_pipe(Vio *vio);
 int vio_close_pipe(Vio * vio);
 int cancel_io(HANDLE handle, DWORD thread_id);
 int vio_shutdown_pipe(Vio *vio,int how);
+uint vio_pending_pipe(Vio* vio);
 #endif
 
 #ifdef HAVE_SMEM
diff --git a/vio/viopipe.c b/vio/viopipe.c
index 84643935c13..5007599aa17 100644
--- a/vio/viopipe.c
+++ b/vio/viopipe.c
@@ -141,5 +141,11 @@ int vio_close_pipe(Vio *vio)
   DBUG_RETURN(ret);
 }
 
+/* return number of bytes readable from pipe.*/
+uint vio_pending_pipe(Vio *vio)
+{
+  DWORD bytes;
+  return PeekNamedPipe(vio->hPipe, NULL, 0, NULL, &bytes, NULL) ? bytes : 0;
+}
 #endif
 
diff --git a/vio/viosocket.c b/vio/viosocket.c
index d1a3eeb5c0d..6409aeb9899 100644
--- a/vio/viosocket.c
+++ b/vio/viosocket.c
@@ -1214,7 +1214,6 @@ my_bool vio_is_connected(Vio *vio)
   DBUG_RETURN(bytes ? TRUE : FALSE);
 }
 
-#ifndef DBUG_OFF
 
 /**
   Number of bytes in the read or socket buffer
@@ -1233,22 +1232,34 @@ ssize_t vio_pending(Vio *vio)
     return vio->read_end - vio->read_pos;
 
   /* Skip non-socket based transport types. */
-  if (vio->type == VIO_TYPE_TCPIP || vio->type == VIO_TYPE_SOCKET)
+  switch (vio->type)
   {
+  case VIO_TYPE_TCPIP:
+    /* fallthrough */
+  case VIO_TYPE_SOCKET:
     /* Obtain number of readable bytes in the socket buffer. */
     if (socket_peek_read(vio, &bytes))
       return -1;
-  }
+    return bytes;
 
-  /*
-    SSL not checked due to a yaSSL bug in SSL_pending that
-    causes it to attempt to read from the socket.
-  */
+  case VIO_TYPE_SSL:
+    bytes= (uint) SSL_pending(vio->ssl_arg);
+    if (bytes)
+      return bytes;
+    if (socket_peek_read(vio, &bytes))
+      return -1;
+    return bytes;
 
-  return (ssize_t) bytes;
+#ifdef _WIN32
+  case VIO_TYPE_NAMEDPIPE:
+    bytes= vio_pending_pipe(vio);
+    return bytes;
+#endif
+  default:
+    return -1;
+  }
 }
 
-#endif /* DBUG_OFF */
 
 /**
   Checks if the error code, returned by vio_getnameinfo(), means it was the