Problem: ZMQ background threads are unnamed

Solution: use pthread API to set the name. For now call every thread
"ZMQ b/g thread". Would be nice to number the I/O threads and name
explicitly the reaper thread, but in reality a bit of internal API
churn would be necessary, so perhaps it's not worth it.
This is useful when debugging a process with many threads.

CMakeLists.txt

@@ -323,6 +323,7 @@ zmq_check_tcp_keepidle ()
 zmq_check_tcp_keepintvl ()
 zmq_check_tcp_keepalive ()
 zmq_check_tcp_tipc ()
+zmq_check_pthread_setname ()
 
 
 if (    CMAKE_SYSTEM_NAME MATCHES "Linux"

builds/cmake/Modules/ZMQSourceRunChecks.cmake

@@ -176,3 +176,55 @@ int main(int argc, char *argv [])
 "
     ZMQ_HAVE_TIPC)
 endmacro()
+
+
+macro(zmq_check_pthread_setname)
+  message(STATUS "Checking pthread_setname signature")
+  set(SAVE_CMAKE_REQUIRED_FLAGS ${CMAKE_REQUIRED_FLAGS})
+  set(CMAKE_REQUIRED_FLAGS "-D_GNU_SOURCE -Werror -pthread")
+  check_c_source_runs(
+    "
+#include <pthread.h>
+
+int main(int argc, char *argv [])
+{
+    pthread_setname_np (\"foo\");
+    return 0;
+}
+"
+    ZMQ_HAVE_PTHREAD_SETNAME_1)
+  check_c_source_runs(
+    "
+#include <pthread.h>
+
+int main(int argc, char *argv [])
+{
+    pthread_setname_np (pthread_self(), \"foo\");
+    return 0;
+}
+"
+    ZMQ_HAVE_PTHREAD_SETNAME_2)
+  check_c_source_runs(
+    "
+#include <pthread.h>
+
+int main(int argc, char *argv [])
+{
+    pthread_setname_np (pthread_self(), \"foo\", (void *)0);
+    return 0;
+}
+"
+    ZMQ_HAVE_PTHREAD_SETNAME_3)
+  check_c_source_runs(
+    "
+#include <pthread.h>
+
+int main(int argc, char *argv [])
+{
+    pthread_set_name_np (pthread_self(), \"foo\");
+    return 0;
+}
+"
+    ZMQ_HAVE_PTHREAD_SET_NAME)
+  set(CMAKE_REQUIRED_FLAGS ${SAVE_CMAKE_REQUIRED_FLAGS})
+endmacro()

builds/cmake/platform.hpp.in

@@ -29,6 +29,10 @@
 #cmakedefine ZMQ_HAVE_TCP_KEEPIDLE
 #cmakedefine ZMQ_HAVE_TCP_KEEPINTVL
 #cmakedefine ZMQ_HAVE_TCP_KEEPALIVE
+#cmakedefine ZMQ_HAVE_PTHREAD_SETNAME_1
+#cmakedefine ZMQ_HAVE_PTHREAD_SETNAME_2
+#cmakedefine ZMQ_HAVE_PTHREAD_SETNAME_3
+#cmakedefine ZMQ_HAVE_PTHREAD_SET_NAME
 
 #cmakedefine ZMQ_HAVE_OPENPGM
 #cmakedefine ZMQ_MAKE_VALGRIND_HAPPY

configure.ac

@@ -589,6 +589,56 @@ AC_TYPE_SIGNAL
 AC_CHECK_FUNCS(perror gettimeofday clock_gettime memset socket getifaddrs freeifaddrs fork posix_memalign mkdtemp)
 AC_CHECK_HEADERS([alloca.h])
 
+# pthread_setname is non-posix, and there are at least 4 different implementations
+AC_MSG_CHECKING([whether signature of pthread_setname_np() has 1 argument])
+AC_COMPILE_IFELSE(
+	[AC_LANG_PROGRAM(
+		[[#include <pthread.h>]],
+		[[pthread_setname_np ("foo"); return 0;]])
+	],[
+		AC_MSG_RESULT([yes])
+		AC_DEFINE(ZMQ_HAVE_PTHREAD_SETNAME_1, [1],
+		    [Whether pthread_setname_np() has 1 argument])
+	],[
+		AC_MSG_RESULT([no])
+])
+AC_MSG_CHECKING([whether signature of pthread_setname_np() has 2 arguments])
+AC_COMPILE_IFELSE(
+	[AC_LANG_PROGRAM(
+		[[#include <pthread.h>]],
+		[[pthread_setname_np (pthread_self (), "foo"); return 0;]])
+	],[
+		AC_MSG_RESULT([yes])
+		AC_DEFINE(ZMQ_HAVE_PTHREAD_SETNAME_2, [1],
+		    [Whether pthread_setname_np() has 2 arguments])
+	],[
+		AC_MSG_RESULT([no])
+])
+AC_MSG_CHECKING([whether signature of pthread_setname_np() has 3 arguments])
+AC_COMPILE_IFELSE(
+	[AC_LANG_PROGRAM(
+		[[#include <pthread.h>]],
+		[[pthread_setname_np (pthread_self(), "foo", (void *)0); return 0;]])
+	],[
+		AC_MSG_RESULT([yes])
+		AC_DEFINE(ZMQ_HAVE_PTHREAD_SETNAME_3, [1],
+		    [Whether pthread_setname_np() has 3 arguments])
+	],[
+		AC_MSG_RESULT([no])
+])
+AC_MSG_CHECKING([whether pthread_set_name_np() exists])
+AC_COMPILE_IFELSE(
+	[AC_LANG_PROGRAM(
+		[[#include <pthread.h>]],
+		[[pthread_set_name_np (pthread_self(), "foo"); return 0;]])
+	],[
+		AC_MSG_RESULT([yes])
+		AC_DEFINE(ZMQ_HAVE_PTHREAD_SET_NAME, [1],
+		    [Whether pthread_set_name_np() exists])
+	],[
+		AC_MSG_RESULT([no])
+])
+
 LIBZMQ_CHECK_SOCK_CLOEXEC([
     AC_DEFINE([ZMQ_HAVE_SOCK_CLOEXEC],
         [1],

src/ctx.cpp

@@ -412,6 +412,7 @@ void zmq::ctx_t::start_thread (thread_t &thread_, thread_fn *tfn_, void *arg_) c
 {
     thread_.start(tfn_, arg_);
     thread_.setSchedulingParameters(thread_priority, thread_sched_policy);
+    thread_.setThreadName ("ZMQ b/g thread");
 }
 
 void zmq::ctx_t::send_command (uint32_t tid_, const command_t &command_)

src/thread.cpp

@@ -77,6 +77,12 @@ void zmq::thread_t::setSchedulingParameters(int priority_, int schedulingPolicy_
     LIBZMQ_UNUSED (schedulingPolicy_);
 }
 
+void zmq::thread_t::setThreadName(const char *name_)
+{
+    // not implemented
+    LIBZMQ_UNUSED (name_);
+}
+
 #else
 
 #include <signal.h>
@@ -159,4 +165,23 @@ void zmq::thread_t::setSchedulingParameters(int priority_, int schedulingPolicy_
 #endif
 }
 
+void zmq::thread_t::setThreadName(const char *name_)
+{
+    if (!name_)
+        return;
+
+#if defined(HAVE_PTHREAD_SETNAME_1)
+    int rc = pthread_setname_np(name_);
+    posix_assert (rc);
+#elif defined(HAVE_PTHREAD_SETNAME_2)
+    int rc = pthread_setname_np(descriptor, name_);
+    posix_assert (rc);
+#elif defined(HAVE_PTHREAD_SETNAME_3)
+    int rc = pthread_setname_np(descriptor, name_, NULL);
+    posix_assert (rc);
+#elif defined(HAVE_PTHREAD_SET_NAME)
+    pthread_set_name_np(descriptor, name_);
+#endif
+}
+
 #endif

src/thread.hpp

@@ -67,6 +67,10 @@ namespace zmq
         // pthread. Has no effect on other platforms.
         void setSchedulingParameters(int priority_, int schedulingPolicy_);
 
+        // Sets the thread name, 16 characters max including terminating NUL.
+        // Only implemented for pthread. Has no effect on other platforms.
+        void setThreadName(const char *name_);
+
         //  These are internal members. They should be private, however then
         //  they would not be accessible from the main C routine of the thread.
         thread_fn *tfn;