Refactor ThreadName() to improve its portability

* Test for the presence of pthread_getname_np() during cmake time and
  only use it if it is available. At least FreeBSD does not have it.
  When not available, fall back to (the first 15 chars of) the
  executable name, as if pthread_setname_np() has never been called.

* Use std::this_thread::get_id() to retrieve the thread id in a portable
  way instead of pthread_threadid_np() or syscall() (none of which is
  available on FreeBSD but it has its own pthread_getthreadid_np()).
  C++11 is here to help.

* According to pthread_getname_np(3) the thread name length is
  restricted to 16 characters, including the terminating null byte.
  So reduce our thread_name[] from 17 to 16 chars.

Author: vasild

CMakeLists.txt

@@ -5,9 +5,19 @@
 cmake_minimum_required(VERSION 3.0)
 project("Libmultiprocess" CXX)
 include(CTest)
+include(CheckCXXSourceCompiles)
 find_package(Boost)
 find_package(CapnProto)
 
+check_cxx_source_compiles("
+  #include <pthread.h>
+  int main(int argc, char** argv)
+  {
+    char thread_name[16];
+    return pthread_getname_np(pthread_self(), thread_name, sizeof(thread_name));
+  }"
+  HAVE_PTHREAD_GETNAME_NP)
+
 capnp_generate_cpp(MP_PROXY_SRCS MP_PROXY_HDRS include/mp/proxy.capnp)
 
 set(MP_PUBLIC_HEADERS

include/mp/config.h.in

@@ -8,4 +8,6 @@
 #cmakedefine CMAKE_INSTALL_PREFIX "@CMAKE_INSTALL_PREFIX@"
 #cmakedefine capnp_PREFIX "@capnp_PREFIX@"
 
+#cmakedefine HAVE_PTHREAD_GETNAME_NP @HAVE_PTHREAD_GETNAME_NP@
+
 #endif // MP_CONFIG_H

src/mp/util.cpp

@@ -2,6 +2,7 @@
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
+#include <mp/config.h>
 #include <mp/util.h>
 
 #include <kj/array.h>
@@ -13,6 +14,7 @@
 #include <sys/types.h>
 #include <sys/un.h>
 #include <sys/wait.h>
+#include <thread>
 #include <unistd.h>
 
 #if __linux__
@@ -37,14 +39,17 @@ size_t MaxFd()
 
 std::string ThreadName(const char* exe_name)
 {
-    char thread_name[17] = {0};
+    char thread_name[16] = {0};
+#ifdef HAVE_PTHREAD_GETNAME_NP
     pthread_getname_np(pthread_self(), thread_name, sizeof(thread_name));
-    uint64_t tid = 0;
-#if __linux__
-    tid = syscall(SYS_gettid);
 #else
-    pthread_threadid_np(NULL, &tid);
-#endif
+    // By default, all the threads inherit the program name. So use that one
+    // if we don't have pthread_getname_np().
+    snprintf(thread_name, sizeof(thread_name), "%s", exe_name);
+#endif // HAVE_PTHREAD_GETNAME_NP
+
+    const auto tid = std::this_thread::get_id();
+
     std::ostringstream buffer;
     buffer << (exe_name ? exe_name : "") << "-" << getpid() << "/" << thread_name << "-" << tid;
     return std::move(buffer.str());