Introduce osmo_gettid() API

This API wraps conventional gettid() linux-specific API, which even in
Linux itself is sometimes not properly supported/announced.

This API also allows future porting to other platforms if needed, and so
far falls back to getpid() if no gettid(9 can be found.

Code ported from osmo-trx.git, see commit 7a07de1efd4eb7cc11c33d3ad25cb2df70aa1ef1.

Related: OS#5027
Change-Id: Id7534beeb22fcd50813dab76dd68818e2ff87ec2

configure.ac

@@ -134,6 +134,16 @@ AC_DEFUN([CHECK_TM_INCLUDES_TM_GMTOFF], [
 
 CHECK_TM_INCLUDES_TM_GMTOFF
 
+# Check if gettid is available (despite not being documented in glibc doc,
+# it requires __USE_GNU on some systems)
+# C compiler is used since __USE_GNU seems to be always defined for g++.
+save_CPPFLAGS=$CPPFLAGS
+AC_LANG_PUSH(C)
+CPPFLAGS="$CPPFLAGS -D_GNU_SOURCE"
+AC_CHECK_FUNCS([gettid])
+AC_LANG_POP(C)
+CPPFLAGS=$save_CPPFLAGS
+
 dnl Check if We need to apply workaround for TLS bug on ARM platform for GCC < 7.3.0:
 ARG_ENABLE_DETECT_TLS_GCC_ARM_BUG
 

include/Makefile.am

@@ -53,6 +53,7 @@ nobase_include_HEADERS = \
                        osmocom/core/strrb.h \
                        osmocom/core/talloc.h \
                        osmocom/core/tdef.h \
+		       osmocom/core/thread.h \
                        osmocom/core/timer.h \
                        osmocom/core/timer_compat.h \
                        osmocom/core/utils.h \

include/osmocom/core/thread.h

@@ -0,0 +1,33 @@
+/*! \file thread.h
+ *  Compatibility header with some thread related helpers
+ */
+/*
+ * (C) 2021 by sysmocom - s.f.m.c. GmbH <info@sysmocom.de>
+ * All Rights Reserved
+ * Author: Pau Espin Pedrol <pespin@sysmocom.de>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU 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.
+ *
+ */
+
+/*! \defgroup thread Osmocom thread helpers
+ *  @{
+ * \file thread.h */
+
+#pragma once
+
+#include <sys/types.h>
+
+pid_t osmo_gettid(void);

src/Makefile.am

@@ -25,6 +25,7 @@ libosmocore_la_SOURCES = context.c timer.c timer_gettimeofday.c timer_clockgetti
 			 conv_acc.c conv_acc_generic.c sercomm.c prbs.c \
 			 isdnhdlc.c \
 			 tdef.c \
+			 thread.c \
 			 sockaddr_str.c \
 			 use_count.c \
 			 exec.c \

src/thread.c

@@ -0,0 +1,60 @@
+/*
+ * (C) 2021 by sysmocom s.f.m.c. GmbH <info@sysmocom.de>
+ * All Rights Reserved
+ *
+ * Author: Pau Espin Pedrol <pespin@sysmocom.de>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU 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.
+ *
+ */
+
+/*! \addtogroup thread
+ *  @{
+ * \file thread.c
+ */
+
+/*! \file thread.c
+ */
+
+#include "config.h"
+
+/* If HAVE_GETTID, then "_GNU_SOURCE" may need to be defined to use gettid() */
+#if HAVE_GETTID
+#define _GNU_SOURCE
+#endif
+#include <unistd.h>
+#include <sys/types.h>
+
+#include <osmocom/core/thread.h>
+
+/*! Wrapper around Linux's gettid() to make it easily accessible on different system versions.
+ * If the gettid() API cannot be found, it will use the syscall directly if
+ * available. If no syscall is found available, then getpid() is called as
+ * fallback. See 'man 2 gettid' for further and details information.
+ * \returns This call is always successful and returns returns the thread ID of
+ *          the calling thread (or the process ID of the current process if
+ *          gettid() or its syscall are unavailable in the system).
+ */
+pid_t osmo_gettid(void)
+{
+#if HAVE_GETTID
+	return gettid();
+#elif defined(LINUX) && defined(__NR_gettid)
+	return (pid_t) syscall(__NR_gettid);
+#else
+	#pragma message ("use pid as tid")
+	return getpid();
+#endif
+}