CONTEXT: lazily evaluate frames to only actually assemble when needed

lib/base/context.cpp

@@ -3,14 +3,16 @@
 #include "base/context.hpp"
 #include <boost/thread/tss.hpp>
 #include <iostream>
+#include <sstream>
+#include <utility>
 
 using namespace icinga;
 
-static boost::thread_specific_ptr<std::vector<String>> l_Frames;
+static boost::thread_specific_ptr<std::vector<std::function<void(std::ostream&)>>> l_Frames;
 
-ContextFrame::ContextFrame(const String& message)
+ContextFrame::ContextFrame(std::function<void(std::ostream&)> message)
 {
-	GetFrames().emplace_back(message);
+	GetFrames().emplace_back(std::move(message));
 }
 
 ContextFrame::~ContextFrame()
@@ -18,17 +20,23 @@ ContextFrame::~ContextFrame()
 	GetFrames().pop_back();
 }
 
-std::vector<String>& ContextFrame::GetFrames()
+std::vector<std::function<void(std::ostream&)>>& ContextFrame::GetFrames()
 {
 	if (!l_Frames.get())
-		l_Frames.reset(new std::vector<String>());
+		l_Frames.reset(new std::vector<std::function<void(std::ostream&)>>());
 
 	return *l_Frames;
 }
 
 ContextTrace::ContextTrace()
-	: m_Frames(ContextFrame::GetFrames().rbegin(), ContextFrame::GetFrames().rend())
-{ }
+{
+	for (auto frame (ContextFrame::GetFrames().rbegin()); frame != ContextFrame::GetFrames().rend(); ++frame) {
+		std::ostringstream oss;
+
+		(*frame)(oss);
+		m_Frames.emplace_back(oss.str());
+	}
+}
 
 void ContextTrace::Print(std::ostream& fp) const
 {

lib/base/context.hpp

@@ -5,6 +5,7 @@
 
 #include "base/i2-base.hpp"
 #include "base/string.hpp"
+#include <functional>
 #include <vector>
 
 namespace icinga
@@ -33,18 +34,21 @@ std::ostream& operator<<(std::ostream& stream, const ContextTrace& trace);
 class ContextFrame
 {
 public:
-	ContextFrame(const String& message);
+	ContextFrame(std::function<void(std::ostream&)> message);
 	~ContextFrame();
 
 private:
-	static std::vector<String>& GetFrames();
+	static std::vector<std::function<void(std::ostream&)>>& GetFrames();
 
 	friend class ContextTrace;
 };
 
 /* The currentContextFrame variable has to be volatile in order to prevent
  * the compiler from optimizing it away. */
-#define CONTEXT(message) volatile icinga::ContextFrame currentContextFrame(message)
+#define CONTEXT(message) volatile icinga::ContextFrame currentContextFrame ([&](std::ostream& _CONTEXT_stream) { \
+_CONTEXT_stream << message; \
+})
+
 }
 
 #endif /* CONTEXT_H */

lib/icinga/dependency-apply.cpp

@@ -66,9 +66,7 @@ bool Dependency::EvaluateApplyRule(const Checkable::Ptr& checkable, const ApplyR
 {
 	auto& di (rule.GetDebugInfo());
 
-	std::ostringstream msgbuf;
-	msgbuf << "Evaluating 'apply' rule (" << di << ")";
-	CONTEXT(msgbuf.str());
+	CONTEXT("Evaluating 'apply' rule (" << di << ")");
 
 	Host::Ptr host;
 	Service::Ptr service;

lib/icinga/notification-apply.cpp

@@ -65,9 +65,7 @@ bool Notification::EvaluateApplyRule(const Checkable::Ptr& checkable, const Appl
 {
 	auto& di (rule.GetDebugInfo());
 
-	std::ostringstream msgbuf;
-	msgbuf << "Evaluating 'apply' rule (" << di << ")";
-	CONTEXT(msgbuf.str());
+	CONTEXT("Evaluating 'apply' rule (" << di << ")");
 
 	Host::Ptr host;
 	Service::Ptr service;

lib/icinga/scheduleddowntime-apply.cpp

@@ -64,9 +64,7 @@ bool ScheduledDowntime::EvaluateApplyRule(const Checkable::Ptr& checkable, const
 {
 	auto& di (rule.GetDebugInfo());
 
-	std::ostringstream msgbuf;
-	msgbuf << "Evaluating 'apply' rule (" << di << ")";
-	CONTEXT(msgbuf.str());
+	CONTEXT("Evaluating 'apply' rule (" << di << ")");
 
 	Host::Ptr host;
 	Service::Ptr service;

lib/icinga/service-apply.cpp

@@ -59,9 +59,7 @@ bool Service::EvaluateApplyRule(const Host::Ptr& host, const ApplyRule& rule, bo
 {
 	auto& di (rule.GetDebugInfo());
 
-	std::ostringstream msgbuf;
-	msgbuf << "Evaluating 'apply' rule (" << di << ")";
-	CONTEXT(msgbuf.str());
+	CONTEXT("Evaluating 'apply' rule (" << di << ")");
 
 	ScriptFrame frame(true);
 	if (rule.GetScope())