Merge #21: Refactor ThreadName() to improve its portability

f1857e3 Refactor ThreadName() to improve its portability (Vasil Dimov)

Pull request description:

  * 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.

ACKs for top commit:
  ryanofsky:
    Tested ACK f1857e3. Thanks! This is working well for me now

Tree-SHA512: 7b57b67bb67ecac2e25d83a4c1a3cc0fb833a96c68af5082cc83b40f5c158e4ae36696f6a6bd13409b6d1754712b7ec3e69743acf6e88686497c8a6dc6a7a1da

Author: ryanofsky

CMakeLists.txt

@@ -4,9 +4,43 @@
 
 cmake_minimum_required(VERSION 3.0)
 project("Libmultiprocess" CXX)
+include(CMakePushCheckState)
 include(CTest)
+include(CheckCXXSourceCompiles)
 find_package(Boost)
 find_package(CapnProto)
+find_package(Threads REQUIRED)
+
+cmake_push_check_state()
+set(CMAKE_REQUIRED_LIBRARIES Threads::Threads)
+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)
+
+check_cxx_source_compiles("
+  #include <pthread.h>
+  int main(int argc, char** argv)
+  {
+    uint64_t tid;
+    pthread_threadid_np(NULL, &tid);
+    return 0;
+  }"
+  HAVE_PTHREAD_THREADID_NP)
+
+check_cxx_source_compiles("
+  #include <pthread.h>
+  #include <pthread_np.h>
+  int main(int argc, char** argv)
+  {
+    return pthread_getthreadid_np();
+  }"
+  HAVE_PTHREAD_GETTHREADID_NP)
+cmake_pop_check_state()
 
 capnp_generate_cpp(MP_PROXY_SRCS MP_PROXY_HDRS include/mp/proxy.capnp)
 

include/mp/config.h.in

@@ -8,4 +8,8 @@
 #cmakedefine CMAKE_INSTALL_PREFIX "@CMAKE_INSTALL_PREFIX@"
 #cmakedefine capnp_PREFIX "@capnp_PREFIX@"
 
+#cmakedefine HAVE_PTHREAD_GETNAME_NP @HAVE_PTHREAD_GETNAME_NP@
+#cmakedefine HAVE_PTHREAD_THREADID_NP @HAVE_PTHREAD_THREADID_NP@
+#cmakedefine HAVE_PTHREAD_GETTHREADID_NP @HAVE_PTHREAD_GETTHREADID_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>
@@ -13,12 +14,17 @@
 #include <sys/types.h>
 #include <sys/un.h>
 #include <sys/wait.h>
+#include <thread>
 #include <unistd.h>
 
 #if __linux__
 #include <syscall.h>
 #endif
 
+#ifdef HAVE_PTHREAD_GETTHREADID_NP
+#include <pthread_np.h>
+#endif // HAVE_PTHREAD_GETTHREADID_NP
+
 namespace mp {
 namespace {
 
@@ -37,16 +43,28 @@ 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;
+#endif // HAVE_PTHREAD_GETNAME_NP
+
+    std::ostringstream buffer;
+    buffer << (exe_name ? exe_name : "") << "-" << getpid() << "/" << thread_name << "-";
+
+    // Prefer platform specific thread ids over the standard C++11 ones because
+    // the former are shorter and are the same as what gdb prints "LWP ...".
 #if __linux__
-    tid = syscall(SYS_gettid);
-#else
+    buffer << syscall(SYS_gettid);
+#elif defined(HAVE_PTHREAD_THREADID_NP)
+    uint64_t tid = 0;
     pthread_threadid_np(NULL, &tid);
+    buffer << tid;
+#elif defined(HAVE_PTHREAD_GETTHREADID_NP)
+    buffer << pthread_getthreadid_np();
+#else
+    buffer << std::this_thread::get_id();
 #endif
-    std::ostringstream buffer;
-    buffer << (exe_name ? exe_name : "") << "-" << getpid() << "/" << thread_name << "-" << tid;
+
     return std::move(buffer.str());
 }