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, 45 insertions, 7 deletions

diff --git a/trace2.c b/trace2.c
index a93cab7c2b..279bddf53b 100644
--- a/trace2.c
+++ b/trace2.c
@@ -8,6 +8,7 @@
 #include "version.h"
 #include "trace2/tr2_cfg.h"
 #include "trace2/tr2_cmd_name.h"
+#include "trace2/tr2_ctr.h"
 #include "trace2/tr2_dst.h"
 #include "trace2/tr2_sid.h"
 #include "trace2/tr2_sysenv.h"
@@ -101,6 +102,22 @@ static void tr2_tgt_emit_a_timer(const struct tr2_timer_metadata *meta,
 			tgt_j->pfn_timer(meta, timer, is_final_data);
 }
 
+/*
+ * The signature of this function must match the pfn_counter
+ * method in the targets.
+ */
+static void tr2_tgt_emit_a_counter(const struct tr2_counter_metadata *meta,
+				   const struct tr2_counter *counter,
+				   int is_final_data)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_counter)
+			tgt_j->pfn_counter(meta, counter, is_final_data);
+}
+
 static int tr2main_exit_code;
 
 /*
@@ -132,20 +149,26 @@ static void tr2main_atexit_handler(void)
 	 * Some timers want per-thread details.  If the main thread
 	 * used one of those timers, emit the details now (before
 	 * we emit the aggregate timer values).
+	 *
+	 * Likewise for counters.
 	 */
 	tr2_emit_per_thread_timers(tr2_tgt_emit_a_timer);
+	tr2_emit_per_thread_counters(tr2_tgt_emit_a_counter);
 
 	/*
-	 * Add stopwatch timer data for the main thread to the final
-	 * totals.  And then emit the final timer values.
+	 * Add stopwatch timer and counter data for the main thread to
+	 * the final totals.  And then emit the final values.
 	 *
 	 * Technically, we shouldn't need to hold the lock to update
-	 * and output the final_timer_block (since all other threads
-	 * should be dead by now), but it doesn't hurt anything.
+	 * and output the final_timer_block and final_counter_block
+	 * (since all other threads should be dead by now), but it
+	 * doesn't hurt anything.
 	 */
 	tr2tls_lock();
 	tr2_update_final_timers();
+	tr2_update_final_counters();
 	tr2_emit_final_timers(tr2_tgt_emit_a_timer);
+	tr2_emit_final_counters(tr2_tgt_emit_a_counter);
 	tr2tls_unlock();
 
 	for_each_wanted_builtin (j, tgt_j)
@@ -582,16 +605,20 @@ void trace2_thread_exit_fl(const char *file, int line)
 	/*
 	 * Some timers want per-thread details.  If this thread used
 	 * one of those timers, emit the details now.
+	 *
+	 * Likewise for counters.
 	 */
 	tr2_emit_per_thread_timers(tr2_tgt_emit_a_timer);
+	tr2_emit_per_thread_counters(tr2_tgt_emit_a_counter);
 
 	/*
-	 * Add stopwatch timer data from the current (non-main) thread
-	 * to the final totals.  (We'll accumulate data for the main
-	 * thread later during "atexit".)
+	 * Add stopwatch timer and counter data from the current
+	 * (non-main) thread to the final totals.  (We'll accumulate
+	 * data for the main thread later during "atexit".)
 	 */
 	tr2tls_lock();
 	tr2_update_final_timers();
+	tr2_update_final_counters();
 	tr2tls_unlock();
 
 	for_each_wanted_builtin (j, tgt_j)
@@ -870,6 +897,17 @@ void trace2_timer_stop(enum trace2_timer_id tid)
 	tr2_stop_timer(tid);
 }
 
+void trace2_counter_add(enum trace2_counter_id cid, uint64_t value)
+{
+	if (!trace2_enabled)
+		return;
+
+	if (cid < 0 || cid >= TRACE2_NUMBER_OF_COUNTERS)
+		BUG("trace2_counter_add: invalid counter id: %d", cid);
+
+	tr2_counter_increment(cid, value);
+}
+
 const char *trace2_session_id(void)
 {
 	return tr2_sid_get();