Perf top: Add ability to detect new threads dynamically during 'perf top -p 'pid'' is running

index 68cd61e..54c9cc1 100644
@@ -882,7 +882,7 @@ static void perf_top__mmap_read(struct perf_top *top)
 		perf_top__mmap_read_idx(top, i);
 }
 
-static void perf_top__start_counters(struct perf_top *top)
+static int perf_top__start_counters(struct perf_top *top)
 {
 	struct perf_evsel *counter, *first;
 	struct perf_evlist *evlist = top->evlist;

@@ -929,6 +929,10 @@ try_again:
 				     group_fd) < 0) {
 			int err = errno;
 
+			if (err == ESRCH) {
+				return err;
+			}
+
 			if (err == EPERM || err == EACCES) {
 				ui__error_paranoid();
 				goto out_err;

@@ -994,7 +998,7 @@ try_again:
 		goto out_err;
 	}
 
-	return;
+	return 0;
 
 out_err:
 	exit_browser(0);

@@ -1018,6 +1022,77 @@ static int perf_top__setup_sample_type(struct perf_top *top)
 	return 0;
 }
 
+static int thread_map_cmp(struct thread_map *threads_a,
+			  struct thread_map *threads_b)
+{
+	int i, j;
+
+	if (threads_a->nr != threads_b->nr) {
+		return 1;
+	} else {
+		for (i = 0; i < threads_b->nr; i++) {
+			for (j = 0; j < threads_a->nr; j++)
+				if (threads_b->map[i] == threads_a->map[j])
+					break;
+
+			if (j == threads_a->nr)
+				return 1;
+		}
+
+		return 0;
+	}
+}
+
+static void check_new_threads(struct perf_top *top)
+{
+	struct thread_map *new_thread_map;
+	struct perf_evsel *counter;
+	struct perf_evlist *evlist = top->evlist;
+
+retry:
+	new_thread_map = thread_map__new_str(top->target.pid, top->target.tid,
+					     top->target.uid);
+	if (!new_thread_map)
+		return;
+
+	if (thread_map_cmp(top->evlist->threads, new_thread_map) == 0) {
+		free(new_thread_map);
+		return;
+	} else {
+		list_for_each_entry(counter, &evlist->entries, node) {
+			perf_evsel__close(counter, top->evlist->cpus->nr,
+					  top->evlist->threads->nr);
+		}
+
+		if (top->evlist->mmap)
+			perf_evlist__munmap(top->evlist);
+
+		if (top->evlist->pollfd) {
+			free(top->evlist->pollfd);
+			top->evlist->pollfd = NULL;
+		}
+
+		top->evlist->nr_fds = 0;
+
+		thread_map__delete(top->evlist->threads);
+		top->evlist->threads = new_thread_map;
+
+		if (perf_top__start_counters(top) == ESRCH) {
+			while (thread_map_cmp(top->evlist->threads,
+					      new_thread_map) == 0) {
+				new_thread_map = thread_map__new_str(top->target.pid,
+								     top->target.tid,
+								     top->target.uid);
+				if (!new_thread_map)
+					return;
+			}
+			goto retry;
+		}
+
+		return;
+	}
+}
+
 static int __cmd_top(struct perf_top *top)
 {
 	pthread_t thread;

@@ -1067,7 +1142,12 @@ static int __cmd_top(struct perf_top *top)
 	}
 
 	while (1) {
-		u64 hits = top->samples;
+		u64 hits;
+
+		if (perf_target__has_task(&top->target))
+			check_new_threads(top);
+
+		hits = top->samples;
 
 		perf_top__mmap_read(top);
 

index 9b38681..293eca7 100644
@@ -452,6 +452,8 @@ void perf_evlist__munmap(struct perf_evlist *evlist)
 
 	free(evlist->mmap);
 	evlist->mmap = NULL;
+
+	evlist->nr_mmaps = 0;
 }
 
 static int perf_evlist__alloc_mmap(struct perf_evlist *evlist)