Persist pack profile snapshots during timed captures

src/PackLib/PackProfile.cpp

@@ -4,12 +4,14 @@
 #include <array>
 #include <cctype>
 #include <chrono>
+#include <condition_variable>
 #include <filesystem>
 #include <fstream>
 #include <map>
 #include <mutex>
 #include <sstream>
 #include <string>
+#include <thread>
 #include <vector>
 
 #include <windows.h>
@@ -24,6 +26,7 @@ using Clock = std::chrono::steady_clock;
 constexpr const char* kPackProfileEnv = "M2PACK_PROFILE";
 constexpr const char* kPackProfileOutput = "log/pack_profile.txt";
 constexpr std::size_t kTopListLimit = 12;
+constexpr auto kSnapshotFlushInterval = std::chrono::seconds(1);
 
 struct LoadStats
 {
@@ -69,10 +72,15 @@ struct PackProfileState
 	std::map<std::string, MountStats> mount_by_format;
 	std::map<std::string, MountStats> mount_by_pack;
 	std::map<std::string, StageStats> stage_by_key;
+	bool snapshot_dirty = false;
+	bool stop_snapshot_thread = false;
+	std::condition_variable snapshot_cv;
+	std::thread snapshot_thread;
 	std::mutex mutex;
 
 	~PackProfileState()
 	{
+		StopSnapshotThread();
 		if (enabled)
 		{
 			std::lock_guard<std::mutex> lock(mutex);
@@ -80,6 +88,50 @@ struct PackProfileState
 		}
 	}
 
+	void StartSnapshotThread()
+	{
+		snapshot_thread = std::thread([this]() {
+			SnapshotLoop();
+		});
+	}
+
+	void StopSnapshotThread()
+	{
+		{
+			std::lock_guard<std::mutex> lock(mutex);
+			stop_snapshot_thread = true;
+		}
+		snapshot_cv.notify_all();
+		if (snapshot_thread.joinable())
+		{
+			snapshot_thread.join();
+		}
+	}
+
+	void SnapshotLoop()
+	{
+		std::unique_lock<std::mutex> lock(mutex);
+		for (;;)
+		{
+			const bool shouldStop = snapshot_cv.wait_for(
+				lock,
+				kSnapshotFlushInterval,
+				[this]() { return stop_snapshot_thread; });
+			if (shouldStop)
+			{
+				return;
+			}
+
+			if (!enabled || !snapshot_dirty)
+			{
+				continue;
+			}
+
+			WriteReportLocked("periodic");
+			snapshot_dirty = false;
+		}
+	}
+
 	void WriteReportLocked(std::string_view reason) const
 	{
 		std::error_code ec;
@@ -376,6 +428,9 @@ void InitializePackProfile(const char* commandLine)
 		.elapsed_us = 0,
 	});
 	g_pack_profile.WriteReportLocked("initialized");
+	g_pack_profile.snapshot_dirty = false;
+	g_pack_profile.stop_snapshot_thread = false;
+	g_pack_profile.StartSnapshotThread();
 }
 
 bool IsPackProfileEnabled()
@@ -402,6 +457,7 @@ void MarkPackProfilePhase(std::string_view phase)
 		.elapsed_us = CurrentElapsedUs(),
 	});
 	g_pack_profile.WriteReportLocked(PackProfileState::MakePhaseKey("phase", phase));
+	g_pack_profile.snapshot_dirty = false;
 }
 
 void RecordPackProfileMount(
@@ -429,6 +485,7 @@ void RecordPackProfileMount(
 	packStats.failures += ok ? 0 : 1;
 	packStats.entry_count += entryCount;
 	packStats.elapsed_us += elapsedUs;
+	g_pack_profile.snapshot_dirty = true;
 }
 
 void RecordPackProfileLoad(
@@ -459,6 +516,7 @@ void RecordPackProfileLoad(
 	update(g_pack_profile.load_by_phase_pack[
 		PackProfileState::MakePhaseKey(g_pack_profile.current_phase, PackProfileState::ParsePackLabel(packPath))]);
 	update(g_pack_profile.load_by_extension[PackProfileState::ParseExtension(requestPath)]);
+	g_pack_profile.snapshot_dirty = true;
 }
 
 void RecordPackProfileStage(
@@ -480,6 +538,7 @@ void RecordPackProfileStage(
 	stats.input_bytes += inputBytes;
 	stats.output_bytes += outputBytes;
 	stats.elapsed_us += elapsedUs;
+	g_pack_profile.snapshot_dirty = true;
 }
 
 void FlushPackProfileSnapshot(std::string_view reason)
@@ -491,4 +550,5 @@ void FlushPackProfileSnapshot(std::string_view reason)
 
 	std::lock_guard<std::mutex> lock(g_pack_profile.mutex);
 	g_pack_profile.WriteReportLocked(reason);
+	g_pack_profile.snapshot_dirty = false;
 }