From 0a822212e17510cb992acd3a4a07d58cf65a1e51 Mon Sep 17 00:00:00 2001
From: Jason Volk <jason@zemos.net>
Date: Sat, 18 Aug 2018 19:28:39 -0700
Subject: [PATCH] ircd::ctx: Add latch (concurrency TS).

---
 include/ircd/ctx/ctx.h   |  1 +
 include/ircd/ctx/latch.h | 82 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 83 insertions(+)
 create mode 100644 include/ircd/ctx/latch.h

diff --git a/include/ircd/ctx/ctx.h b/include/ircd/ctx/ctx.h
index c4f1061d2..a69e5789f 100644
--- a/include/ircd/ctx/ctx.h
+++ b/include/ircd/ctx/ctx.h
@@ -77,6 +77,7 @@ namespace ircd::ctx
 #include "prof.h"
 #include "list.h"
 #include "dock.h"
+#include "latch.h"
 #include "queue.h"
 #include "mutex.h"
 #include "shared_mutex.h"
diff --git a/include/ircd/ctx/latch.h b/include/ircd/ctx/latch.h
new file mode 100644
index 000000000..da45b598d
--- /dev/null
+++ b/include/ircd/ctx/latch.h
@@ -0,0 +1,82 @@
+// Matrix Construct
+//
+// Copyright (C) Matrix Construct Developers, Authors & Contributors
+// Copyright (C) 2016-2018 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_LATCH_H
+
+namespace ircd::ctx
+{
+	class latch;
+}
+
+class ircd::ctx::latch
+{
+	mutable struct dock dock;
+	size_t count {0};
+
+  public:
+	bool is_ready() const noexcept;
+	void count_down(const size_t &n = 1);
+	void count_down_and_wait();
+	void wait() const;
+
+	latch(const size_t &count);
+	latch() = default;
+	latch(latch &&) = default;
+	latch(const latch &) = delete;
+	~latch() noexcept;
+};
+
+inline
+ircd::ctx::latch::latch(const size_t &count)
+:count{count}
+{}
+
+inline
+ircd::ctx::latch::~latch()
+noexcept
+{
+	assert(is_ready());
+}
+
+inline void
+ircd::ctx::latch::wait()
+const
+{
+	dock.wait([this]
+	{
+		return is_ready();
+	});
+}
+
+inline void
+ircd::ctx::latch::count_down_and_wait()
+{
+	if(--count == 0)
+		dock.notify_all();
+	else
+		wait();
+}
+
+inline void
+ircd::ctx::latch::count_down(const size_t &n)
+{
+	count -= n;
+	if(is_ready())
+		dock.notify_all();
+}
+
+
+inline bool
+ircd::ctx::latch::is_ready()
+const noexcept
+{
+	return count == 0;
+}