refactor: Coroutine based webserver (#1699)

Code of new coroutine-based web server. The new server is not connected
to Clio and not ready to use yet.
For #919.

src/util/CoroutineGroup.cpp

@@ -0,0 +1,76 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2024, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#include "util/CoroutineGroup.hpp"
+
+#include "util/Assert.hpp"
+
+#include <boost/asio/spawn.hpp>
+#include <boost/asio/steady_timer.hpp>
+
+#include <cstddef>
+#include <functional>
+#include <optional>
+#include <utility>
+
+namespace util {
+
+CoroutineGroup::CoroutineGroup(boost::asio::yield_context yield, std::optional<int> maxChildren)
+    : timer_{yield.get_executor(), boost::asio::steady_timer::duration::max()}, maxChildren_{maxChildren}
+{
+}
+
+CoroutineGroup::~CoroutineGroup()
+{
+    ASSERT(childrenCounter_ == 0, "CoroutineGroup is destroyed without waiting for child coroutines to finish");
+}
+
+bool
+CoroutineGroup::spawn(boost::asio::yield_context yield, std::function<void(boost::asio::yield_context)> fn)
+{
+    if (maxChildren_.has_value() && childrenCounter_ >= *maxChildren_)
+        return false;
+
+    ++childrenCounter_;
+    boost::asio::spawn(yield, [this, fn = std::move(fn)](boost::asio::yield_context yield) {
+        fn(yield);
+        --childrenCounter_;
+        if (childrenCounter_ == 0)
+            timer_.cancel();
+    });
+    return true;
+}
+
+void
+CoroutineGroup::asyncWait(boost::asio::yield_context yield)
+{
+    if (childrenCounter_ == 0)
+        return;
+
+    boost::system::error_code error;
+    timer_.async_wait(yield[error]);
+}
+
+size_t
+CoroutineGroup::size() const
+{
+    return childrenCounter_;
+}
+
+}  // namespace util