Allow benchmarking of CpuBoundWork#CpuBoundWork() via additional out-param

lib/base/io-engine.cpp

@@ -34,6 +34,31 @@ CpuBoundWork::CpuBoundWork(boost::asio::yield_context yc)
 	}
 }
 
+/**
+ * Measures how long it takes to acquire a slot.
+ *
+ * @param yc Forwarded to the regular constructor.
+ * @param took Set to the time it took to acquire the slot.
+ */
+CpuBoundWork::CpuBoundWork(boost::asio::yield_context yc, Clock::duration& took)
+	: CpuBoundWork(std::move(yc), Clock::now(), took)
+{
+}
+
+/**
+ * An internal helper layer between the regular constructor and the one that measures how long it takes.
+ * This is necessary to get the start time before the regular constructor is called.
+ *
+ * @param yc Forwarded to the regular constructor.
+ * @param started The current time.
+ * @param took Set to the time it took to acquire the slot.
+ */
+CpuBoundWork::CpuBoundWork(boost::asio::yield_context yc, Clock::time_point started, Clock::duration& took)
+	: CpuBoundWork(std::move(yc))
+{
+	took = Clock::now() - started;
+}
+
 CpuBoundWork::~CpuBoundWork()
 {
 	if (!m_Done) {

lib/base/io-engine.hpp

@@ -8,6 +8,7 @@
 #include "base/logger.hpp"
 #include "base/shared-object.hpp"
 #include <atomic>
+#include <chrono>
 #include <exception>
 #include <memory>
 #include <thread>
@@ -29,8 +30,14 @@ namespace icinga
  */
 class CpuBoundWork
 {
+private:
+	using Clock = std::chrono::steady_clock;
+
+	CpuBoundWork(boost::asio::yield_context yc, Clock::time_point started, Clock::duration& took);
+
 public:
 	CpuBoundWork(boost::asio::yield_context yc);
+	CpuBoundWork(boost::asio::yield_context yc, Clock::duration& took);
 	CpuBoundWork(const CpuBoundWork&) = delete;
 	CpuBoundWork(CpuBoundWork&&) = delete;
 	CpuBoundWork& operator=(const CpuBoundWork&) = delete;