traeak commented on code in PR #13843:
URL: https://github.com/apache/trafficserver/pull/13843#discussion_r4287059734
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plugins/stats_over_http/stats_over_http.cc:
##########
@@ -1039,32 +885,104 @@ prometheus_v2_out_stats(stats_state *my_state)
APPEND_STAT_PROMETHEUS_NUMERIC("current_time_epoch_ms", "%" PRIu64,
ms_since_epoch());
}
-static void
-stats_process_write(TSCont contp, TSEvent event, stats_state *my_state)
+static std::shared_ptr<const cached_body>
+generate_body(stats_state *my_state)
{
- if (event == TS_EVENT_VCONN_WRITE_READY) {
- if (my_state->body_written == 0) {
- my_state->body_written = 1;
- switch (my_state->output_format) {
- case output_format_t::JSON_OUTPUT:
- json_out_stats(my_state);
- break;
- case output_format_t::CSV_OUTPUT:
- csv_out_stats(my_state);
- break;
- case output_format_t::PROMETHEUS_OUTPUT:
- prometheus_out_stats(my_state);
- break;
- case output_format_t::PROMETHEUS_V2_OUTPUT:
- prometheus_v2_out_stats(my_state);
- break;
- }
+ auto entry = std::make_shared<cached_body>();
+ entry->generated = std::chrono::steady_clock::now();
+
+ switch (my_state->output_format) {
+ case output_format_t::CSV_OUTPUT:
+ csv_out_stats(my_state);
+ break;
+ case output_format_t::PROMETHEUS_OUTPUT:
+ prometheus_out_stats(my_state);
+ break;
+ case output_format_t::PROMETHEUS_V2_OUTPUT:
+ prometheus_v2_out_stats(my_state);
+ break;
+ default:
+ json_out_stats(my_state);
+ break;
+ }
+
+ bool compressed = false;
+
+ switch (my_state->encoding) {
+ case encoding_format_t::GZIP:
+ compressed = gzip_compress(my_state->body, entry->body, GZIP_MODE);
+ break;
+ case encoding_format_t::DEFLATE:
+ compressed = gzip_compress(my_state->body, entry->body, DEFLATE_MODE);
+ break;
+#if HAVE_BROTLI_ENCODE_H
+ case encoding_format_t::BR:
+ compressed = br_compress(my_state->body, entry->body);
+ break;
+#endif
+ default:
+ break;
+ }
+
+ if (compressed) {
+ entry->encoding = my_state->encoding;
+ } else {
+ entry->encoding = encoding_format_t::NONE;
+ entry->body = std::move(my_state->body);
+ }
+ my_state->body.clear();
+ my_state->prometheus_v2_families.clear();
+ my_state->prometheus_v2_family_order.clear();
+
+ return entry;
+}
+
+// Return a fresh cached body if there is one. When it is stale, one request
regenerates it while concurrent requests are
+// served the stale copy, provided it is less than twice the TTL old. Older
copies are not served; those requests regenerate.
+static std::shared_ptr<const cached_body>
+get_body(stats_state *my_state)
+{
+ if (cache_ttl.count() <= 0) {
+ return generate_body(my_state);
+ }
+
+ auto &slot =
body_cache[static_cast<size_t>(my_state->output_format)][static_cast<size_t>(my_state->encoding)];
+ bool owner = false;
+
+ {
+ std::lock_guard lock(body_cache_mutex);
- if (my_state->encoding != encoding_format_t::NONE) {
- compress_out_stats(my_state);
+ if (slot.entry) {
+ auto age = std::chrono::steady_clock::now() - slot.entry->generated;
+
+ if (age < cache_ttl || (slot.refreshing && age < 2 * cache_ttl)) {
+ return slot.entry;
}
- TSVIONBytesSet(my_state->write_vio, my_state->output_bytes);
}
+ if (!slot.refreshing) {
+ slot.refreshing = true;
+ owner = true;
+ }
+ }
Review Comment:
this is no worse than the default mode of the plugin and is very unlikely to
happen. the amount of code including needing a blocking exclusive lock is not
worth it.
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