Always write sample events in EventPipe based on sample frequency. (d…

…otnet#58720)

* Always write sample events in EventPipe based on sample frequency.

If no managed frames (including helper frames) are located on stack,
sample was dropped and not emitted into EventPipe. This cause issues
in tooling that try to do thread time calculations based on sample,
especially in cases where embedded threads returned to native
code during several samples before calling back into runtime. In such
scenarios the last sampled event would be prolonged, giving false
information that that stackframe lasted much longer than it really did.

Always writing samples into EventPipe will also visualize time an attached
thread spend outside of runtime, not running managed code.

src/mono/mono/eventpipe/ep-rt-mono.c

@@ -2553,6 +2553,16 @@ ep_rt_mono_sample_profiler_write_sampling_event_for_threads (
 						// as second, re-classify current callstack to be executing managed code.
 						data->payload_data = EP_SAMPLE_PROFILER_SAMPLE_TYPE_MANAGED;
 					}
+					if (data->stack_walk_data.top_frame && ep_stack_contents_get_length (&data->stack_contents) == 0) {
+						// If no managed frames (including helper frames) are located on stack, mark sample as beginning in external code.
+						// This can happen on attached embedding threads returning to native code between runtime invokes.
+						// Make sure sample is still written into EventPipe for all attached threads even if they are currently not having
+						// any managed frames on stack. Prevents some tools applying thread time heuristics to prolong duration of last sample
+						// when embedding thread returns to native code. It also opens ability to visualize number of samples in unmanaged code
+						// on attached threads when executing outside of runtime. If tooling is not interested in these sample events, they are easy
+						// to identify and filter out.
+						data->payload_data = EP_SAMPLE_PROFILER_SAMPLE_TYPE_EXTERNAL;
+					}
 
 					sampled_thread_count++;
 				}
@@ -2570,7 +2580,7 @@ ep_rt_mono_sample_profiler_write_sampling_event_for_threads (
 	THREAD_INFO_TYPE adapter = { { 0 } };
 	for (uint32_t i = 0; i < sampled_thread_count; ++i) {
 		EventPipeSampleProfileStackWalkData *data = &g_array_index (_ep_rt_mono_sampled_thread_callstacks, EventPipeSampleProfileStackWalkData, i);
-		if (data->payload_data != EP_SAMPLE_PROFILER_SAMPLE_TYPE_ERROR && ep_stack_contents_get_length(&data->stack_contents) > 0) {
+		if ((data->stack_walk_data.top_frame && data->payload_data == EP_SAMPLE_PROFILER_SAMPLE_TYPE_EXTERNAL) || (data->payload_data != EP_SAMPLE_PROFILER_SAMPLE_TYPE_ERROR && ep_stack_contents_get_length (&data->stack_contents) > 0)) {
 			// Check if we have an async frame, if so we will need to make sure all frames are registered in regular jit info table.
 			// TODO: An async frame can contain wrapper methods (no way to check during stackwalk), we could skip writing profile event
 			// for this specific stackwalk or we could cleanup stack_frames before writing profile event.