assert from java that jni code has an env

Rare crashes are happening inside the jni, in game_dispose(), when a
game's double-disposed. Adding a jni call to check if the thread about
to do a game_dispose() will fail then asserting its result in java
allows useful stack traces to come via Crittercism. Or should.

xwords4/android/XWords4/jni/xwjni.c

@@ -191,8 +191,8 @@ map_destroy( EnvThreadInfo* ti )
     pthread_mutex_destroy( &ti->mtxThreads );
 }
 
-JNIEnv*
-envForMe( EnvThreadInfo* ti, const char* caller )
+static JNIEnv*
+prvEnvForMe( EnvThreadInfo* ti )
 {
     JNIEnv* result = NULL;
     pthread_t self = pthread_self();
@@ -204,7 +204,15 @@ envForMe( EnvThreadInfo* ti, const char* caller )
         }
     }
     pthread_mutex_unlock( &ti->mtxThreads );
+    return result;
+}
+
+JNIEnv*
+envForMe( EnvThreadInfo* ti, const char* caller )
+{
+    JNIEnv* result = prvEnvForMe( ti );
     if( !result ) {
+        pthread_t self = pthread_self();
         XP_LOGF( "no env for %s (thread %x)", caller, (int)self );
         XP_ASSERT(0);
     }
@@ -1948,6 +1956,15 @@ Java_org_eehouse_android_xw4_jni_XwJNI_comms_1getStats
     return result;
 }
 
+JNIEXPORT jboolean JNICALL
+Java_org_eehouse_android_xw4_jni_XwJNI_haveEnv
+( JNIEnv* env, jclass C, jint jniGlobalPtr )
+{
+    JNIGlobalState* state = (JNIGlobalState*)jniGlobalPtr;
+    jboolean result = NULL != prvEnvForMe(&state->ti);
+    return result;
+}
+
 JNIEXPORT void JNICALL
 Java_org_eehouse_android_xw4_jni_XwJNI_server_1endGame
 ( JNIEnv* env, jclass C, GamePtrType gamePtr )

xwords4/android/XWords4/src/org/eehouse/android/xw4/XWApp.java

@@ -93,6 +93,7 @@ public class XWApp extends Application {
 
     // This is called on emulator only, but good for ensuring no memory leaks
     // by forcing JNI cleanup
+    @Override
     public void onTerminate()
     {
         DbgUtils.logf( "XwApp.onTerminate() called" );

xwords4/android/XWords4/src/org/eehouse/android/xw4/jni/XwJNI.java

@@ -43,7 +43,11 @@ public class XwJNI {
             retain();
         }
 
-        public int ptr() { Assert.assertTrue( 0 != m_ptr ); return m_ptr; }
+        public synchronized int ptr()
+        {
+            Assert.assertTrue( 0 != m_ptr );
+            return m_ptr;
+        }
 
         public synchronized GamePtr retain()
         {
@@ -62,7 +66,10 @@ public class XwJNI {
                             this, m_rowid, m_refCount );
             if ( 0 == m_refCount ) {
                 if ( 0 != m_ptr ) {
-                    game_dispose( this );
+                    if ( !haveEnv( getJNI().m_ptr ) ) {
+                        Assert.fail();
+                    }
+                    game_dispose( this ); // will crash if haveEnv fails
                     m_ptr = 0;
                 }
             }
@@ -484,4 +491,6 @@ public class XwJNI {
     private static native int dict_iter_init( int jniState, byte[] dict,
                                               String name, String path,
                                               JNIUtils jniu );
+
+    private static native boolean haveEnv( int jniState );
 }