From d8bf5b9fff2be75eea08b874c3d97754fc646845 Mon Sep 17 00:00:00 2001
From: Jason Volk <jason@zemos.net>
Date: Wed, 10 Apr 2019 14:50:34 -0700
Subject: [PATCH] ircd::ctx: Add a syscall_usage_warning to suite.

---
 include/ircd/ctx/ctx.h                   |  1 +
 include/ircd/ctx/syscall_usage_warning.h | 47 ++++++++++++++++++++++++
 ircd/ctx.cc                              | 41 +++++++++++++++++++++
 3 files changed, 89 insertions(+)
 create mode 100644 include/ircd/ctx/syscall_usage_warning.h

diff --git a/include/ircd/ctx/ctx.h b/include/ircd/ctx/ctx.h
index 4f42fe3a6..11a150200 100644
--- a/include/ircd/ctx/ctx.h
+++ b/include/ircd/ctx/ctx.h
@@ -74,6 +74,7 @@ namespace ircd::ctx
 #include "this_ctx.h"
 #include "stack_usage_assertion.h"
 #include "slice_usage_warning.h"
+#include "syscall_usage_warning.h"
 #include "critical_assertion.h"
 #include "critical_indicator.h"
 #include "exception_handler.h"
diff --git a/include/ircd/ctx/syscall_usage_warning.h b/include/ircd/ctx/syscall_usage_warning.h
new file mode 100644
index 000000000..6e7c3cbcc
--- /dev/null
+++ b/include/ircd/ctx/syscall_usage_warning.h
@@ -0,0 +1,47 @@
+// Matrix Construct
+//
+// Copyright (C) Matrix Construct Developers, Authors & Contributors
+// Copyright (C) 2016-2019 Jason Volk <jason@zemos.net>
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted, provided that the above
+// copyright notice and this permission notice is present in all copies. The
+// full license for this software is available in the LICENSE file.
+
+#pragma once
+#define HAVE_IRCD_CTX_SYSCALL_USAGE_WARNING_H
+
+namespace ircd::ctx::this_ctx
+{
+	struct syscall_usage_warning;
+}
+
+#ifndef NDEBUG
+struct ircd::ctx::this_ctx::syscall_usage_warning
+{
+	const string_view fmt;
+	const va_rtti ap;
+	ircd::prof::syscall_timer timer;
+
+	template<class... args>
+	syscall_usage_warning(const string_view &fmt, args&&... a)
+	:syscall_usage_warning{fmt, va_rtti{std::forward<args>(a)...}}
+	{}
+
+	explicit syscall_usage_warning(const string_view &fmt, va_rtti &&ap)
+	:fmt{fmt}
+	,ap{std::move(ap)}
+	{}
+
+	~syscall_usage_warning() noexcept;
+};
+#else
+struct ircd::ctx::this_ctx::syscall_usage_warning
+{
+	syscall_usage_warning(const string_view &fmt, ...)
+	{
+		// In at least gcc 6.3.0 20170519, template param packs are not DCE'ed
+		// so legacy varargs are used here.
+	}
+};
+#endif
diff --git a/ircd/ctx.cc b/ircd/ctx.cc
index a214e6e81..60521b548 100644
--- a/ircd/ctx.cc
+++ b/ircd/ctx.cc
@@ -854,6 +854,47 @@ noexcept
 }
 #endif
 
+///////////////////////////////////////////////////////////////////////////////
+//
+// ctx/syscall_usage_warning.h
+//
+
+#ifndef NDEBUG
+ircd::ctx::this_ctx::syscall_usage_warning::~syscall_usage_warning()
+noexcept
+{
+	const uint64_t total
+	{
+		timer.stopped?
+			timer.at():
+			timer.stop()
+	};
+
+	if(likely(!total))
+		return;
+
+	thread_local char buf[512];
+	const string_view reason
+	{
+		fmt::vsprintf{buf, fmt, ap}
+	};
+
+	thread_local char tmbuf[64];
+	log::dwarning
+	{
+		log, "context '%s' id:%lu watchdog: system call took %s :%s",
+		current?
+			name(cur()):
+		ios::handler::current?
+			name(*ios::handler::current):
+			"*"_sv,
+		current? id(cur()) : 0,
+		pretty_nanoseconds(tmbuf, total, true),
+		reason
+	};
+}
+#endif
+
 ///////////////////////////////////////////////////////////////////////////////
 //
 // ctx/slice_usage_warning.h