Add Mutex to global initialisation of generators (#371)

* Mutex lock initialization call

* add comment on mutex

---------

Co-authored-by: kevaundray <kevtheappdev@gmail.com>

cpp/src/barretenberg/crypto/pedersen_hash/pedersen_lookup.cpp

@@ -1,5 +1,7 @@
 #include "./pedersen_lookup.hpp"
 
+#include <mutex>
+
 #include "barretenberg/ecc/curves/grumpkin/grumpkin.hpp"
 
 namespace crypto {
@@ -10,6 +12,12 @@ std::array<std::vector<grumpkin::g1::affine_element>, NUM_PEDERSEN_TABLES> peder
 std::vector<grumpkin::g1::affine_element> pedersen_iv_table;
 std::array<grumpkin::g1::affine_element, NUM_PEDERSEN_TABLES> generators;
 
+// Mutex is not available in the WASM context.
+// WASM runs in a single-thread so this is acceptable.
+#if !defined(__wasm__)
+std::mutex init_mutex;
+#endif
+
 static bool inited = false;
 
 void init_single_lookup_table(const size_t index)
@@ -66,6 +74,11 @@ void init()
 {
     ASSERT(BITS_PER_TABLE < BITS_OF_BETA);
     ASSERT(BITS_PER_TABLE + BITS_OF_BETA < BITS_ON_CURVE);
+
+#if !defined(__wasm__)
+    const std::lock_guard<std::mutex> lock(init_mutex);
+#endif
+
     if (inited) {
         return;
     }