Merge branch 'java-director-thread-name'

* java-director-thread-name:
  Add changes entry for setting Java thread name
  Increased Java thread name size.
  Java directors - more generic thread name setting
  Use prctl method to get thread names, which is available on all NDK versions
  Actually, pthread_getname_np is only available in recent versions of Android (API level >= 26).
  Set thread name when attaching to Android JVM in SWIG Java director

CHANGES.current

@@ -7,6 +7,17 @@ the issue number to the end of the URL: https://github.com/swig/swig/issues/
 Version 4.0.0 (in progress)
 ===========================
 
+2018-12-20: hasinoff,wsfulton
+            [Java] #1334 Set Java thread name to native thread name when using directors.
+
+            Default is to use name "Thread-XXX" and is still works like this by default. However,
+            adding the following will turn on the thread name setting (works for more recent
+            versions of Linux and MacOS):
+
+            %begin %{
+            #define SWIG_JAVA_USE_THREAD_NAME
+            %}
+
 2018-12-20: chlandsi
             [Python] #1357. Fix overriding __new__ in Python 3.6.
 

Examples/test-suite/director_thread.i

@@ -7,6 +7,11 @@
 %module(directors="1") director_thread
 #endif
 
+%begin %{
+#define SWIG_JAVA_USE_THREAD_NAME
+//#define DEBUG_DIRECTOR_THREAD_NAME
+%}
+
 %{
 #ifdef _WIN32
 #include <windows.h>
@@ -89,10 +94,23 @@ extern "C" {
         fprintf(stderr, "pthread_create failed in run()\n");
         assert(0);
       }
+      int setname = pthread_setname_np(thread, "MyThreadName");
+      if (setname != 0) {
+        fprintf(stderr, "pthread_setname_np failed in run()\n");
+        assert(0);
+      }
 %#endif
       MilliSecondSleep(500);
     }
-    
+
+    static bool namedThread() {
+%#ifdef _WIN32
+      return false;
+%#else
+      return true;
+%#endif
+    }
+
     virtual void do_foo() {
       val += 1;
     }

Examples/test-suite/java/director_thread_runme.java

@@ -30,6 +30,12 @@ class director_thread_Derived extends Foo {
   }
 
   public void do_foo() {
+    // Not all operating systems can name threads, so only test on those that can
+    if (Foo.namedThread()) {
+      String threadName = Thread.currentThread().getName();
+      if (!threadName.equals("MyThreadName"))
+        throw new RuntimeException("Unexpected thread name: " + threadName);
+    }
     setVal(getVal() - 1);
   }
 }

Lib/java/director.swg

@@ -5,12 +5,52 @@
  * methods can be called from C++.
  * ----------------------------------------------------------------------------- */
 
-#if defined(DEBUG_DIRECTOR_OWNED) || defined(DEBUG_DIRECTOR_EXCEPTION)
+#if defined(DEBUG_DIRECTOR_OWNED) || defined(DEBUG_DIRECTOR_EXCEPTION) || defined(DEBUG_DIRECTOR_THREAD_NAME)
 #include <iostream>
 #endif
 
 #include <exception>
 
+#if defined(SWIG_JAVA_USE_THREAD_NAME)
+
+#if !defined(SWIG_JAVA_GET_THREAD_NAME)
+namespace Swig {
+  SWIGINTERN int GetThreadName(char *name, size_t len);
+}
+
+#if defined(__linux__)
+
+#include <sys/prctl.h>
+SWIGINTERN int Swig::GetThreadName(char *name, size_t len) {
+  (void)len;
+#if defined(PR_GET_NAME)
+  return prctl(PR_GET_NAME, (unsigned long)name, 0, 0, 0);
+#else
+  (void)name;
+  return 1;
+#endif
+}
+
+#elif defined(__unix__)
+
+#include <pthread.h>
+SWIGINTERN int Swig::GetThreadName(char *name, size_t len) {
+  return pthread_getname_np(pthread_self(), name, len);
+}
+
+#else
+
+SWIGINTERN int Swig::GetThreadName(char *name, size_t len) {
+  (void)len;
+  (void)name;
+  return 1;
+}
+#endif
+
+#endif
+
+#endif
+
 namespace Swig {
 
   /* Java object wrapper */
@@ -139,12 +179,27 @@ namespace Swig {
         void **jenv = (void **)&jenv_;
 #endif
         env_status = director_->swig_jvm_->GetEnv((void **)&jenv_, JNI_VERSION_1_2);
+        JavaVMAttachArgs args;
+        args.version = JNI_VERSION_1_2;
+        args.group = NULL;
+        args.name = NULL;
+#if defined(SWIG_JAVA_USE_THREAD_NAME)
+        char thread_name[64];  // MAX_TASK_COMM_LEN=16 is hard-coded in the Linux kernel and MacOS has MAXTHREADNAMESIZE=64.
+        if (Swig::GetThreadName(thread_name, sizeof(thread_name)) == 0) {
+          args.name = thread_name;
+#if defined(DEBUG_DIRECTOR_THREAD_NAME)
+          std::cout << "JNIEnvWrapper: thread name: " << thread_name << std::endl;
+        } else {
+          std::cout << "JNIEnvWrapper: Couldn't set Java thread name" << std::endl;
+#endif
+        }
+#endif
 #if defined(SWIG_JAVA_ATTACH_CURRENT_THREAD_AS_DAEMON)
         // Attach a daemon thread to the JVM. Useful when the JVM should not wait for
         // the thread to exit upon shutdown. Only for jdk-1.4 and later.
-        director_->swig_jvm_->AttachCurrentThreadAsDaemon(jenv, NULL);
+        director_->swig_jvm_->AttachCurrentThreadAsDaemon(jenv, &args);
 #else
-        director_->swig_jvm_->AttachCurrentThread(jenv, NULL);
+        director_->swig_jvm_->AttachCurrentThread(jenv, &args);
 #endif
       }
       ~JNIEnvWrapper() {