From 3d79c94bb24ada0bbc167c99e07d71ed7320a875 Mon Sep 17 00:00:00 2001
From: Jason Volk <jason@zemos.net>
Date: Mon, 24 Dec 2018 17:58:57 -0800
Subject: [PATCH] ircd::ctx: Add ctx::parallel device.

---
 include/ircd/ctx/ctx.h      |   1 +
 include/ircd/ctx/parallel.h | 114 ++++++++++++++++++++++++++++++++++++
 2 files changed, 115 insertions(+)
 create mode 100644 include/ircd/ctx/parallel.h

diff --git a/include/ircd/ctx/ctx.h b/include/ircd/ctx/ctx.h
index 79746ea6d..b56fefbbe 100644
--- a/include/ircd/ctx/ctx.h
+++ b/include/ircd/ctx/ctx.h
@@ -96,6 +96,7 @@ namespace ircd::ctx
 #include "pool.h"
 #include "ole.h"
 #include "fault.h"
+#include "parallel.h"
 
 // Exports to ircd::
 namespace ircd
diff --git a/include/ircd/ctx/parallel.h b/include/ircd/ctx/parallel.h
new file mode 100644
index 000000000..4d3704e9a
--- /dev/null
+++ b/include/ircd/ctx/parallel.h
@@ -0,0 +1,114 @@
+// 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_PARALLEL_H
+
+namespace ircd::ctx
+{
+	template<class arg> class parallel;
+}
+
+template<class arg>
+struct ircd::ctx::parallel
+{
+	using closure = std::function<void (arg &)>;
+
+	pool *p {nullptr};
+	vector_view<arg> a;
+	closure c;
+	dock d;
+	std::exception_ptr eptr;
+	size_t snd {0};
+	size_t rcv {0};
+	size_t out {0};
+
+  public:
+	void wait_avail();
+	void wait_done();
+
+	void operator()(const arg &a);
+
+	parallel(pool &, vector_view<arg>, closure);
+	~parallel() noexcept;
+};
+
+template<class arg>
+ircd::ctx::parallel<arg>::parallel(pool &p,
+                                   vector_view<arg> a,
+                                   closure c)
+:p{&p}
+,a{std::move(a)}
+,c{std::move(c)}
+{
+	p.min(this->a.size());
+}
+
+template<class arg>
+ircd::ctx::parallel<arg>::~parallel()
+noexcept
+{
+	const uninterruptible::nothrow ui;
+	wait_done();
+}
+
+template<class arg>
+void
+ircd::ctx::parallel<arg>::operator()(const arg &a)
+{
+	wait_avail();
+	if(this->eptr)
+		std::rethrow_exception(this->eptr);
+
+	auto &p(*this->p);
+	this->a.at(snd++ % this->a.size()) = a;
+	out++;
+	p([this]()
+	mutable
+	{
+		auto &a
+		{
+			this->a.at(rcv++ % this->a.size())
+		};
+
+		if(!this->eptr) try
+		{
+			c(a);
+		}
+		catch(...)
+		{
+			this->eptr = std::current_exception();
+		}
+
+		out--;
+		d.notify_one();
+	});
+}
+
+template<class arg>
+void
+ircd::ctx::parallel<arg>::wait_avail()
+{
+	d.wait([this]
+	{
+		assert(snd >= rcv);
+		return out < a.size();
+	});
+}
+
+template<class arg>
+void
+ircd::ctx::parallel<arg>::wait_done()
+{
+	d.wait([this]
+	{
+		return !out;
+	});
+}