+ /* The select(2) system call only guarantees a "sufficiently small write"
+ * can be made without blocking. And on Linux the read might block too
+ * in certain cases, although I don't know if any of them can occur here.
+ * Regardless, set all the pipes to non-blocking to avoid T184171.
+ */
+ foreach ( $pipes as $pipe ) {
+ stream_set_blocking( $pipe, false );
+ }
+