From 9e0acde5cfa5eaca84839165e453ae3108f0ef81 Mon Sep 17 00:00:00 2001
From: Jason Volk <jason@zemos.net>
Date: Mon, 14 May 2018 16:53:28 -0700
Subject: [PATCH] ircd::db: Add cache entry iteration (experimental).

---
 include/ircd/db/cache.h |  5 +++++
 ircd/db.cc              | 44 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 49 insertions(+)

diff --git a/include/ircd/db/cache.h b/include/ircd/db/cache.h
index e2a91bae6..1d92a504c 100644
--- a/include/ircd/db/cache.h
+++ b/include/ircd/db/cache.h
@@ -36,4 +36,9 @@ namespace ircd::db
 	// Test if key exists
 	bool exists(rocksdb::Cache &, const string_view &key);
 	bool exists(rocksdb::Cache *const &, const string_view &key);
+
+	// Iterate the cache entries.
+	using cache_closure = std::function<void (const string_view &, const size_t &)>;
+	void for_each(rocksdb::Cache &, const cache_closure &);
+	void for_each(rocksdb::Cache *const &, const cache_closure &);
 }
diff --git a/ircd/db.cc b/ircd/db.cc
index bbf0f1f41..8e7da9b71 100644
--- a/ircd/db.cc
+++ b/ircd/db.cc
@@ -5074,6 +5074,50 @@ ircd::db::_seek_(rocksdb::Iterator &it,
 // cache.h
 //
 
+void
+ircd::db::for_each(rocksdb::Cache *const &cache,
+                   const cache_closure &closure)
+{
+	if(cache)
+		for_each(*cache, closure);
+}
+
+void
+ircd::db::for_each(rocksdb::Cache &cache,
+                   const cache_closure &closure)
+{
+	thread_local rocksdb::Cache *_cache;
+	_cache = &cache;
+
+	thread_local const cache_closure *_closure;
+	_closure = &closure;
+
+	cache.ApplyToAllCacheEntries([]
+	(void *const data, const size_t charge)
+	{
+		assert(_cache);
+		assert(_closure);
+		auto *const &handle
+		{
+			reinterpret_cast<rocksdb::Cache::Handle *>(data)
+		};
+
+		const void *const &value
+		{
+			_cache->Value(handle)
+		};
+
+		assert(value);
+		const auto &s
+		{
+			*reinterpret_cast<const rocksdb::Slice *>(value)
+		};
+
+		(*_closure)(slice(s), charge);
+	},
+	false);
+}
+
 bool
 ircd::db::exists(rocksdb::Cache *const &cache,
                  const string_view &key)