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src: clamp idle_diff before computing proc_diff #372

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src: clamp idle_diff before computing proc_diff #372

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10 changes: 10 additions & 0 deletions src/nsolid/nsolid_api.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -611,6 +611,10 @@ void EnvInst::uv_metrics_cb_(nsuv::ns_prepare* handle, EnvInst* envinst) {
// Use the previous values to calculate the values for this loop iteration.
loop_duration = metrics_cb_time - envinst->prev_metrics_cb_time_;
loop_idle_time = idle_time - envinst->prev_loop_idle_time_;
// Clamp loop_idle_time to avoid unsigned underflow in loop_proc_time when
// clock skew causes idle_time to be slightly larger than loop_duration.
if (loop_idle_time > loop_duration)
loop_idle_time = loop_duration;
loop_proc_time = loop_duration - loop_idle_time;
events_procd = metrics->events - envinst->prev_events_processed_;
events_waiting = metrics->events_waiting - envinst->prev_events_waiting_;
Expand Down Expand Up @@ -2162,6 +2166,12 @@ void EnvInst::get_event_loop_stats_(EnvInst* envinst,
uint64_t loop_idle_time = uv_metrics_idle_time(envinst->event_loop());
uint64_t loop_diff = stor->current_hrtime_ - stor->prev_call_time_;
uint64_t idle_diff = loop_idle_time - stor->prev_idle_time_;
// On some platforms the clocks backing loop_diff and idle_diff can differ by
// a few hundred nanoseconds when the loop is nearly 100% idle, making
// idle_diff slightly larger than loop_diff. Clamp to avoid unsigned
// underflow in proc_diff and bogus utilization values.
if (idle_diff > loop_diff)
idle_diff = loop_diff;
uint64_t proc_diff = loop_diff - idle_diff;
uint64_t count_diff = metrics->loop_count - stor->loop_iterations;
auto entry_exit = envinst->provider_times();
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