compat: Add sigwait dummy for NaCl

Implement a sigwait dummy for NaCl, which relies on:
- NaCl does never send SIGPIPE to to apps (see
https://codereview.chromium.org/288063004/)
- VLC uses sigwait exclusively to wait for SIGPIPE

If sigwait is asked to wait for anything else than SIGPIPE it will run
into an assertion failure, so that breakage would not be silent.

Signed-off-by: Julian Scheel <julian@jusst.de>
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

compat/sigwait.c

@@ -0,0 +1,49 @@
+/*****************************************************************************
+ * sigwait.c: POSIX sigwait() replacement
+ *****************************************************************************
+ * Copyright © 2017 VLC authors and VideoLAN
+ *
+ * Author: Julian Scheel <julian@jusst.de>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation; either version 2.1 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
+ *****************************************************************************/
+
+#ifdef HAVE_CONFIG_H
+# include <config.h>
+#endif
+
+#ifdef __native_client__
+/* NaCl has no working sigwait, but SIGPIPE, for which vlc uses sigwait
+ * currently, is never generated in NaCl. So for SIGPIPE it's safe to instantly
+ * return, for all others run into an assertion. */
+
+#include <assert.h>
+#include <signal.h>
+
+int sigwait(const sigset_t *set, int *sig)
+{
+    sigset_t s = *set;
+    if (sigemptyset(&s))
+        return 0;
+    assert(sigismember(&s, SIGPIPE));
+    sigdelset(&s, SIGPIPE);
+    assert(sigemptyset(&s));
+
+    *sig = SIGPIPE;
+    return 0;
+}
+#else
+# error sigwait not implemented on your platform!
+#endif

configure.ac

@@ -300,6 +300,7 @@ case "${host_os}" in
   *nacl*)
     SYS=nacl
     AC_DEFINE([_XOPEN_SOURCE], [700], [POSIX and XPG 7th edition])
+    AC_LIBOBJ([sigwait])
     ;;
   *)
     SYS="${host_os}"

include/vlc_fixups.h

@@ -107,6 +107,15 @@ extern "C" {
 # define VLC_NOTHROW
 #endif
 
+/* signal.h */
+#if !defined(HAVE_SIGWAIT) && defined(__native_client__)
+/* NaCl does not define sigwait in signal.h. We need to include it here to
+ * define sigwait, because sigset_t is allowed to be either an integral or a
+ * struct. */
+#include <signal.h>
+int sigwait(const sigset_t *set, int *sig);
+#endif
+
 /* stddef.h */
 #if !defined (__cplusplus) && !defined (HAVE_MAX_ALIGN_T)
 typedef struct {