trace2: add global counter mechanism

Add global counters mechanism to Trace2.

The Trace2 counters mechanism adds the ability to create a set of
global counter variables and an API to increment them efficiently.
Counters can optionally report per-thread usage in addition to the sum
across all threads.

Counter events are emitted to the Trace2 logs when a thread exits and
at process exit.

Counters are an alternative to `data` and `data_json` events.

Counters are useful when you want to measure something across the life
of the process, when you don't want per-measurement events for
performance reasons, when the data does not fit conveniently within a
region, or when your control flow does not easily let you write the
final total.  For example, you might use this to report the number of
calls to unzip() or the number of de-delta steps during a checkout.

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 89 insertions, 0 deletions

diff --git a/t/helper/test-trace2.c b/t/helper/test-trace2.c
index f951b9e97d..1b092c6071 100644
--- a/t/helper/test-trace2.c
+++ b/t/helper/test-trace2.c
@@ -324,6 +324,92 @@ static int ut_101timer(int argc, const char **argv)
 }
 
 /*
+ * Single-threaded counter test.  Add several values to the TEST1 counter.
+ * The test script can verify that the final sum is reported in the "counter"
+ * event.
+ */
+static int ut_200counter(int argc, const char **argv)
+{
+	const char *usage_error =
+		"expect <v1> [<v2> [...]]";
+	int value;
+	int k;
+
+	if (argc < 1)
+		die("%s", usage_error);
+
+	for (k = 0; k < argc; k++) {
+		if (get_i(&value, argv[k]))
+			die("invalid value[%s] -- %s",
+			    argv[k], usage_error);
+		trace2_counter_add(TRACE2_COUNTER_ID_TEST1, value);
+	}
+
+	return 0;
+}
+
+/*
+ * Multi-threaded counter test.  Create seveal threads that each increment
+ * the TEST2 global counter.  The test script can verify that an individual
+ * "th_counter" event is generated with a partial sum for each thread and
+ * that a final aggregate "counter" event is generated.
+ */
+
+struct ut_201_data {
+	int v1;
+	int v2;
+};
+
+static void *ut_201counter_thread_proc(void *_ut_201_data)
+{
+	struct ut_201_data *data = _ut_201_data;
+
+	trace2_thread_start("ut_201");
+
+	trace2_counter_add(TRACE2_COUNTER_ID_TEST2, data->v1);
+	trace2_counter_add(TRACE2_COUNTER_ID_TEST2, data->v2);
+
+	trace2_thread_exit();
+	return NULL;
+}
+
+static int ut_201counter(int argc, const char **argv)
+{
+	const char *usage_error =
+		"expect <v1> <v2> <threads>";
+
+	struct ut_201_data data = { 0, 0 };
+	int nr_threads = 0;
+	int k;
+	pthread_t *pids = NULL;
+
+	if (argc != 3)
+		die("%s", usage_error);
+	if (get_i(&data.v1, argv[0]))
+		die("%s", usage_error);
+	if (get_i(&data.v2, argv[1]))
+		die("%s", usage_error);
+	if (get_i(&nr_threads, argv[2]))
+		die("%s", usage_error);
+
+	CALLOC_ARRAY(pids, nr_threads);
+
+	for (k = 0; k < nr_threads; k++) {
+		if (pthread_create(&pids[k], NULL, ut_201counter_thread_proc, &data))
+			die("failed to create thread[%d]", k);
+	}
+
+	for (k = 0; k < nr_threads; k++) {
+		if (pthread_join(pids[k], NULL))
+			die("failed to join thread[%d]", k);
+	}
+
+	free(pids);
+
+	return 0;
+}
+
+/*
  * Usage:
  *     test-tool trace2 <ut_name_1> <ut_usage_1>
  *     test-tool trace2 <ut_name_2> <ut_usage_2>
@@ -346,6 +432,9 @@ static struct unit_test ut_table[] = {
 
 	{ ut_100timer,    "100timer",  "<count> <ms_delay>" },
 	{ ut_101timer,    "101timer",  "<count> <ms_delay> <threads>" },
+
+	{ ut_200counter,  "200counter", "<v1> [<v2> [<v3> [...]]]" },
+	{ ut_201counter,  "201counter", "<v1> <v2> <threads>" },
 };
 /* clang-format on */