diff --git a/src/engine/hash.h b/src/engine/hash.h
index 4088894e3c..c478a14dfd 100644
--- a/src/engine/hash.h
+++ b/src/engine/hash.h
@@ -7,7 +7,8 @@
 /*  This file is ALSO:
  *  Copyright 2022 René Ferdinand Rivera Morell
  *  Distributed under the Boost Software License, Version 1.0.
- *  (See accompanying file LICENSE.txt or https://www.bfgroup.xyz/b2/LICENSE.txt)
+ *  (See accompanying file LICENSE.txt or
+ * https://www.bfgroup.xyz/b2/LICENSE.txt)
  */
 
 /*
@@ -18,8 +19,12 @@
 #define BOOST_JAM_HASH_H
 
 #include "config.h"
+
+#include "mem.h"
 #include "object.h"
 
+#include <mutex>
+
 /*
  * An opaque struct representing an item in the hash table. The first element of
  * every struct stored in the table must be an OBJECT * which is treated as the
@@ -34,31 +39,31 @@ typedef struct hashdata HASHDATA;
  *   datalen - item size
  *   name    - used for debugging
  */
-struct hash * hashinit( int32_t datalen, char const * name );
+struct hash * hashinit(int32_t datalen, char const * name);
 
 /*
  * hash_free() - free a hash table, given its handle
  */
-void hash_free( struct hash * );
-void hashdone( struct hash * );
+void hash_free(struct hash *);
+void hashdone(struct hash *);
 
-typedef void (* hashenumerate_f)( void *, void * );
+typedef void (*hashenumerate_f)(void *, void *);
 
 /*
  * hashenumerate() - call f(i, data) on each item, i in the hash table. The
  * enumeration order is unspecified.
  */
-void hashenumerate( struct hash *, void (* f)( void *, void * ), void * data );
+void hashenumerate(struct hash *, void (*f)(void *, void *), void * data);
 
 template <typename T, typename D>
-void hash_enumerate( struct hash * h, void (* f)(T *, D *), D * data)
+void hash_enumerate(struct hash * h, void (*f)(T *, D *), D * data)
 {
-    hashenumerate(h, reinterpret_cast<hashenumerate_f>(f), data);
+	hashenumerate(h, reinterpret_cast<hashenumerate_f>(f), data);
 }
 template <typename T, typename D>
-void hash_enumerate( struct hash * h, void (* f)(T *, D *))
+void hash_enumerate(struct hash * h, void (*f)(T *, D *))
 {
-    hashenumerate(h, reinterpret_cast<hashenumerate_f>(f), nullptr);
+	hashenumerate(h, reinterpret_cast<hashenumerate_f>(f), nullptr);
 }
 
 /*
@@ -76,24 +81,81 @@ void hash_enumerate( struct hash * h, void (* f)(T *, D *))
  *   - if the key is present then *found == 1 and the result is a pointer to the
  *     existing record.
  */
-HASHDATA * hash_insert( struct hash *, OBJECT * key, int32_t * found );
+HASHDATA * hash_insert(struct hash *, OBJECT * key, int32_t * found);
 
 /*
  * hash_find() - find a record in the table or NULL if none exists
  */
-HASHDATA * hash_find( struct hash *, OBJECT * key );
-
-struct hashstats {
-    int count;
-    int num_items;
-    int tab_size;
-    int item_size;
-    int sets;
-    int num_hashes;
+HASHDATA * hash_find(struct hash *, OBJECT * key);
+
+struct hashstats
+{
+	int count;
+	int num_items;
+	int tab_size;
+	int item_size;
+	int sets;
+	int num_hashes;
+};
+
+void hashstats_init(struct hashstats * stats);
+void hashstats_add(struct hashstats * stats, struct hash *);
+void hashstats_print(struct hashstats * stats, char const * name);
+
+namespace b2 { namespace core {
+
+template <typename T>
+struct concurrent_hash
+{
+	using key_type = b2::value_ptr;
+	using value_type = T;
+
+	concurrent_hash(const char * debug_name)
+	{
+		table = hashinit(sizeof(value_type), debug_name);
+	}
+
+	~concurrent_hash() { reset(); }
+
+	void reset()
+	{
+		std::lock_guard<std::mutex> guard(mutex);
+		if (table != nullptr)
+		{
+			hashenumerate(table, concurrent_hash::destroy_at, nullptr);
+			hashdone(table);
+			table = nullptr;
+		}
+	}
+
+	template <typename... Args>
+	std::pair<value_type *, bool> get(b2::value_ptr key, Args... args)
+	{
+		int found = 0;
+		std::lock_guard<std::mutex> guard(mutex);
+		value_type * val
+			= reinterpret_cast<value_type *>(hash_insert(table, key, &found));
+		if (found == 0) b2::jam::ctor_ptr<value_type>(val, args...);
+		return std::make_pair(val, found != 0);
+	}
+
+	template <typename F>
+	void guarded(F f)
+	{
+		std::lock_guard<std::mutex> guard(mutex);
+		f();
+	}
+
+	private:
+	std::mutex mutex;
+	hash * table = nullptr;
+
+	static void destroy_at(void * p, void * _)
+	{
+		b2::jam::dtor_ptr(static_cast<value_type *>(p));
+	}
 };
 
-void hashstats_init( struct hashstats * stats );
-void hashstats_add( struct hashstats * stats, struct hash * );
-void hashstats_print( struct hashstats * stats, char const * name );
+}} // namespace b2::core
 
 #endif