output/alsa: log when generating silence due to slow decoder

MPD used to do that when this code lived in the player thread, but it was removed by commit 98a7c62d; and the replacement code in the ALSA output plugin didn't have it.

output/alsa: log when generating silence due to slow decoder
f780ac41 · Max Kellermann · 61a72a5d · f780ac41 · f780ac41
Commit f780ac41 authored Jun 28, 2019 by Max Kellermann
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NEWS NEWS +1 -0

AlsaOutputPlugin.cxx src/output/plugins/AlsaOutputPlugin.cxx +6 -0

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--- a/NEWS
+++ b/NEWS
@@ -7,6 +7,7 @@ ver 0.21.11 (not yet released)
  - alsa: fix busy loop while draining
  - alsa: fix missing drain call
  - alsa: improve xrun-avoiding silence generator
+  - alsa: log when generating silence due to slow decoder
  - alsa, osx: fix distortions with DSD_U32 and DoP on 32 bit CPUs
 * protocol
  - fix "list" with multiple "group" levels

--- a/src/output/plugins/AlsaOutputPlugin.cxx
+++ b/src/output/plugins/AlsaOutputPlugin.cxx
@@ -27,6 +27,7 @@
 #include "../OutputAPI.hxx"
 #include "mixer/MixerList.hxx"
 #include "pcm/PcmExport.hxx"
+#include "system/PeriodClock.hxx"
 #include "thread/Mutex.hxx"
 #include "thread/Cond.hxx"
 #include "util/Manual.hxx"
@@ -65,6 +66,8 @@ class AlsaOutput final
 	 */
 	TimerEvent silence_timer;

+	PeriodClock throttle_silence_log;
+
 	Manual<PcmExport> pcm_export;

 	/**
@@ -1073,6 +1076,9 @@ try {
 			return;
 		}

+		if (throttle_silence_log.CheckUpdate(std::chrono::seconds(5)))
+			FormatWarning(alsa_output_domain, "Decoder is too slow; playing silence to avoid xrun");
+
 		/* insert some silence if the buffer has not enough
 		   data yet, to avoid ALSA xrun */
 		period_buffer.FillWithSilence(silence, out_frame_size);