Proposed tweak for issue with finding seedblock hash

This patch isn't needed if we always restrict block-sync-size to <= SEEDHASH_EPOCH_LAG.
But otherwise, this will allow syncing with larger block-sync-sizes.

src/cryptonote_core/blockchain.cpp

@@ -139,7 +139,9 @@ Blockchain::Blockchain(tx_memory_pool& tx_pool) :
   m_long_term_block_weights_cache_rolling_median(CRYPTONOTE_LONG_TERM_BLOCK_WEIGHT_WINDOW_SIZE),
   m_difficulty_for_next_block_top_hash(crypto::null_hash),
   m_difficulty_for_next_block(1),
-  m_btc_valid(false)
+  m_btc_valid(false),
+  m_batch_success(true),
+  m_prepare_height(0)
 {
   LOG_PRINT_L3("Blockchain::" << __func__);
 }
@@ -798,6 +800,13 @@ crypto::hash Blockchain::get_block_id_by_height(uint64_t height) const
   return null_hash;
 }
 //------------------------------------------------------------------
+crypto::hash Blockchain::get_pending_block_id_by_height(uint64_t height) const
+{
+  if (m_prepare_height && height >= m_prepare_height && height - m_prepare_height < m_prepare_nblocks)
+    return (*m_prepare_blocks)[height - m_prepare_height].hash;
+  return get_block_id_by_height(height);
+}
+//------------------------------------------------------------------
 bool Blockchain::get_block_by_hash(const crypto::hash &h, block &blk, bool *orphan) const
 {
   LOG_PRINT_L3("Blockchain::" << __func__);
@@ -4534,6 +4543,9 @@ bool Blockchain::prepare_handle_incoming_blocks(const std::vector<block_complete
       m_blocks_longhash_table.clear();
       uint64_t thread_height = height;
       tools::threadpool::waiter waiter;
+      m_prepare_height = height;
+      m_prepare_nblocks = blocks_entry.size();
+      m_prepare_blocks = &blocks;
       for (unsigned int i = 0; i < threads; i++)
       {
         unsigned nblocks = batches;
@@ -4544,6 +4556,7 @@ bool Blockchain::prepare_handle_incoming_blocks(const std::vector<block_complete
       }
 
       waiter.wait(&tpool);
+      m_prepare_height = 0;
 
       if (m_cancel)
          return false;

src/cryptonote_core/blockchain.h

@@ -205,6 +205,18 @@ namespace cryptonote
      */
     crypto::hash get_block_id_by_height(uint64_t height) const;
 
+    /**
+     * @brief gets a block's hash given a height
+     *
+     * Used only by prepare_handle_incoming_blocks. Will look in the list of incoming blocks
+     * if the height is contained there.
+     *
+     * @param height the height of the block
+     *
+     * @return the hash of the block at the requested height, or a zeroed hash if there is no such block
+     */
+    crypto::hash get_pending_block_id_by_height(uint64_t height) const;
+
     /**
      * @brief gets the block with a given hash
      *
@@ -1082,6 +1094,11 @@ namespace cryptonote
     std::shared_ptr<tools::Notify> m_block_notify;
     std::shared_ptr<tools::Notify> m_reorg_notify;
 
+    // for prepare_handle_incoming_blocks
+    uint64_t m_prepare_height;
+    uint64_t m_prepare_nblocks;
+    std::vector<block> *m_prepare_blocks;
+
     /**
      * @brief collects the keys for all outputs being "spent" as an input
      *

src/cryptonote_core/cryptonote_tx_utils.cpp

@@ -681,7 +681,7 @@ namespace cryptonote
       if (rx_needhash(height, &seed_height)) {
         crypto::hash hash;
         if (pbc != NULL)
-          hash = pbc->get_block_id_by_height(seed_height);
+          hash = pbc->get_pending_block_id_by_height(seed_height);
         else
           memset(&hash, 0, sizeof(hash));  // only happens when generating genesis block
         rx_seedhash(seed_height, hash.data, miners);