[NativeTiming] Clear exceptions after calling JNI methods (#67)

When running `make run-ptests`, the output log is *spammed*:

	WARNING in native method: JNI call made without checking exceptions when required to from CallStaticVoidMethod

Over a million times [^0].

Call `JNIEnv::ExcceptionClear()` after every `JNIEnv::Call*Method()`
invocation so that any pending exception is cleared (there *won't* be
a pending exception, but the JVM doesn't care), which removes all of
these warning messages.

[^0]: *Probably*. 100,000 iterations across over 12 steps should
    exceed a million, unless you're on Android and the iteration count
		is instead 1,000.

Author: jonpryor

tests/NativeTiming/timing.c

@@ -229,80 +229,98 @@ foo_get_native_jni_timings (JNIEnv *env, int count, jclass klass, jobject self,
 		obj3 = (*env)->NewObject(env, Object_class, Object_init);
 
 	start = current_time_millis ();
-	for (i = 0; i < count; i++)
+	for (i = 0; i < count; i++) {
 		(*env)->CallStaticVoidMethod (env, klass, Timing_StaticVoidMethod);
+		(*env)->ExceptionClear (env);
+	}
 	end = current_time_millis ();
 
 	jniTimes [0] = end - start;
 	_log ("# NativeTiming: foo/timing: static void    method invoke: %10lli ms | average: %10f ms\n",
 			jniTimes [0], jniTimes [0] / (double) count);
 
 	start = current_time_millis ();
-	for (i = 0; i < count; i++)
+	for (i = 0; i < count; i++) {
 		(*env)->CallStaticIntMethod (env, klass, Timing_StaticIntMethod);
+		(*env)->ExceptionClear (env);
+	}
 	end = current_time_millis ();
 
 	jniTimes [1] = end - start;
 	_log ("# NativeTiming: foo/timing: static int     method invoke: %10lli ms | average: %10f ms\n",
 			jniTimes [1], jniTimes [1] / (double) count);
 
 	start = current_time_millis ();
-	for (i = 0; i < count; i++)
+	for (i = 0; i < count; i++) {
 		(*env)->CallStaticObjectMethod (env, klass, Timing_StaticObjectMethod);
+		(*env)->ExceptionClear (env);
+	}
 	end = current_time_millis ();
 
 	jniTimes [2] = end - start;
 	_log ("# NativeTiming: foo/timing: static Object  method invoke: %10lli ms | average: %10f ms\n",
 			jniTimes [2], jniTimes [2] / (double) count);
 
 	start = current_time_millis ();
-	for (i = 0; i < count; i++)
+	for (i = 0; i < count; i++) {
 		(*env)->CallVoidMethod (env, self, Timing_VirtualVoidMethod);
+		(*env)->ExceptionClear (env);
+	}
 	end = current_time_millis ();
 
 	jniTimes [3] = end - start;
 	_log ("# NativeTiming: foo/timing: virtual void   method invoke: %10lli ms | average: %10f ms\n",
 			jniTimes [3], jniTimes [3] / (double) count);
 
 	start = current_time_millis ();
-	for (i = 0; i < count; i++)
+	for (i = 0; i < count; i++) {
 		(*env)->CallIntMethod (env, self, Timing_VirtualIntMethod);
+		(*env)->ExceptionClear (env);
+	}
 	end = current_time_millis ();
 
 	jniTimes [4] = end - start;
 	_log ("# NativeTiming: foo/timing: virtual int    method invoke: %10lli ms | average: %10f ms\n",
 			jniTimes [4], jniTimes [4] / (double) count);
 
 	start = current_time_millis ();
-	for (i = 0; i < count; i++)
+	for (i = 0; i < count; i++) {
 		(*env)->CallObjectMethod (env, self, Timing_VirtualObjectMethod);
+		(*env)->ExceptionClear (env);
+	}
 	end = current_time_millis ();
 
 	jniTimes [5] = end - start;
 	_log ("# NativeTiming: foo/timing: virtual Object method invoke: %10lli ms | average: %10f ms\n",
 			jniTimes [5], jniTimes [5] / (double) count);
 
 	start = current_time_millis ();
-	for (i = 0; i < count; i++)
+	for (i = 0; i < count; i++) {
 		(*env)->CallNonvirtualVoidMethod (env, self, klass, Timing_FinalVoidMethod);
+		(*env)->ExceptionClear (env);
+	}
 	end = current_time_millis ();
 
 	jniTimes [6] = end - start;
 	_log ("# NativeTiming: foo/timing: final void     method invoke: %10lli ms | average: %10f ms\n",
 			jniTimes [6], jniTimes [6] / (double) count);
 
 	start = current_time_millis ();
-	for (i = 0; i < count; i++)
+	for (i = 0; i < count; i++) {
 		(*env)->CallNonvirtualIntMethod (env, self, klass, Timing_FinalIntMethod);
+		(*env)->ExceptionClear (env);
+	}
 	end = current_time_millis ();
 
 	jniTimes [7] = end - start;
 	_log ("# NativeTiming: foo/timing: final int      method invoke: %10lli ms | average: %10f ms\n",
 			jniTimes [7], jniTimes [7] / (double) count);
 
 	start = current_time_millis ();
-	for (i = 0; i < count; i++)
+	for (i = 0; i < count; i++) {
 		(*env)->CallNonvirtualObjectMethod (env, self, klass, Timing_FinalObjectMethod);
+		(*env)->ExceptionClear (env);
+	}
 	end = current_time_millis ();
 
 	jniTimes [8] = end - start;
@@ -312,26 +330,32 @@ foo_get_native_jni_timings (JNIEnv *env, int count, jclass klass, jobject self,
 
 
 	start = current_time_millis ();
-	for (i = 0; i < count; i++)
+	for (i = 0; i < count; i++) {
 		(*env)->CallStaticVoidMethod (env, klass, Timing_StaticVoidMethod1Args, obj1);
+		(*env)->ExceptionClear (env);
+	}
 	end = current_time_millis ();
 
 	jniTimes [9] = end - start;
 	_log ("# NativeTiming: foo/timing: static void o1 method invoke: %10lli ms | average: %10f ms\n",
 			jniTimes [9], jniTimes [9] / (double) count);
 
 	start = current_time_millis ();
-	for (i = 0; i < count; i++)
+	for (i = 0; i < count; i++) {
 		(*env)->CallStaticVoidMethod (env, klass, Timing_StaticVoidMethod2Args, obj1, obj2);
+		(*env)->ExceptionClear (env);
+	}
 	end = current_time_millis ();
 
 	jniTimes [10] = end - start;
 	_log ("# NativeTiming: foo/timing: static void o2 method invoke: %10lli ms | average: %10f ms\n",
 			jniTimes [10], jniTimes [10] / (double) count);
 
 	start = current_time_millis ();
-	for (i = 0; i < count; i++)
+	for (i = 0; i < count; i++) {
 		(*env)->CallStaticVoidMethod (env, klass, Timing_StaticVoidMethod3Args, obj1, obj2, obj3);
+		(*env)->ExceptionClear (env);
+	}
 	end = current_time_millis ();
 
 	jniTimes [11] = end - start;
@@ -341,26 +365,32 @@ foo_get_native_jni_timings (JNIEnv *env, int count, jclass klass, jobject self,
 
 
 	start = current_time_millis ();
-	for (i = 0; i < count; i++)
+	for (i = 0; i < count; i++) {
 		(*env)->CallStaticVoidMethod (env, klass, Timing_StaticVoidMethod1IArgs, 42);
+		(*env)->ExceptionClear (env);
+	}
 	end = current_time_millis ();
 
 	jniTimes [12] = end - start;
 	_log ("# NativeTiming: foo/timing: static void i1 method invoke: %10lli ms | average: %10f ms\n",
 			jniTimes [12], jniTimes [12] / (double) count);
 
 	start = current_time_millis ();
-	for (i = 0; i < count; i++)
+	for (i = 0; i < count; i++) {
 		(*env)->CallStaticVoidMethod (env, klass, Timing_StaticVoidMethod2IArgs, 42, 42);
+		(*env)->ExceptionClear (env);
+	}
 	end = current_time_millis ();
 
 	jniTimes [13] = end - start;
 	_log ("# NativeTiming: foo/timing: static void i2 method invoke: %10lli ms | average: %10f ms\n",
 			jniTimes [13], jniTimes [13] / (double) count);
 
 	start = current_time_millis ();
-	for (i = 0; i < count; i++)
+	for (i = 0; i < count; i++) {
 		(*env)->CallStaticVoidMethod (env, klass, Timing_StaticVoidMethod3IArgs, 42, 42, 42);
+		(*env)->ExceptionClear (env);
+	}
 	end = current_time_millis ();
 
 	jniTimes [14] = end - start;