Problem: new thread naming breaks build on !Linux and overwrites prefix

Solution: use the thread class function rather than one of the pthread
functions, and take into account the thread prefix context option

src/ctx.cpp

@@ -422,23 +422,15 @@ void zmq::thread_ctx_t::start_thread (thread_t &thread_,
                                       void *arg_,
                                       const char *name_) const
 {
-    static unsigned int nthreads_started = 0;
-
     thread_.setSchedulingParameters (_thread_priority, _thread_sched_policy,
                                      _thread_affinity_cpus);
 
     char namebuf[16];
-    snprintf(namebuf, sizeof(namebuf), "0MQ%s%s",
-             name_ ? ":" : "", name_ ? name_ : "");
-    thread_.start(tfn_, arg_, namebuf);
-#ifndef ZMQ_HAVE_ANDROID
-    std::ostringstream s;
-    if (!_thread_name_prefix.empty ())
-        s << _thread_name_prefix << "/";
-    s << "ZMQbg/" << nthreads_started;
-    thread_.setThreadName (s.str ().c_str ());
-#endif
-    nthreads_started++;
+    snprintf (namebuf, sizeof (namebuf), "%s%sZMQbg%s%s",
+              _thread_name_prefix.empty () ? "" : _thread_name_prefix.c_str (),
+              _thread_name_prefix.empty () ? "" : "/", name_ ? "/" : "",
+              name_ ? name_ : "");
+    thread_.start (tfn_, arg_, namebuf);
 }
 
 int zmq::thread_ctx_t::set (int option_, int optval_)

src/thread.cpp

@@ -179,7 +179,7 @@ static void *thread_routine (void *arg_)
 #endif
     zmq::thread_t *self = (zmq::thread_t *) arg_;
     self->applySchedulingParameters ();
-    pthread_setname_np(pthread_self(), self->_name.c_str());
+    self->setThreadName (self->_name.c_str ());
     self->_tfn (self->_arg);
     return NULL;
 }
@@ -311,20 +311,25 @@ void zmq::thread_t::setThreadName (const char *name_)
     if (!name_)
         return;
 
+        /* Fails with permission denied on Android 5/6 */
+#if defined(ZMQ_HAVE_ANDROID)
+    return;
+#endif
+
 #if defined(ZMQ_HAVE_PTHREAD_SETNAME_1)
     int rc = pthread_setname_np (name_);
     if (rc)
         return;
 #elif defined(ZMQ_HAVE_PTHREAD_SETNAME_2)
-    int rc = pthread_setname_np (_descriptor, name_);
+    int rc = pthread_setname_np (pthread_self (), name_);
     if (rc)
         return;
 #elif defined(ZMQ_HAVE_PTHREAD_SETNAME_3)
-    int rc = pthread_setname_np (_descriptor, name_, NULL);
+    int rc = pthread_setname_np (pthread_self (), name_, NULL);
     if (rc)
         return;
 #elif defined(ZMQ_HAVE_PTHREAD_SET_NAME)
-    pthread_set_name_np (_descriptor, name_);
+    pthread_set_name_np (pthread_self (), name_);
 #endif
 }