interfaces: refactor: move waitNext implementation to miner

- We now assert for a valid chainman and notifications once when
 invoking WaitAndCreateNewBlock function.

src/node/miner.cpp

@@ -16,11 +16,14 @@
 #include <consensus/validation.h>
 #include <deploymentstatus.h>
 #include <logging.h>
+#include <node/context.h>
+#include <node/kernel_notifications.h>
 #include <policy/feerate.h>
 #include <policy/policy.h>
 #include <pow.h>
 #include <primitives/transaction.h>
 #include <util/moneystr.h>
+#include <util/signalinterrupt.h>
 #include <util/time.h>
 #include <validation.h>
 
@@ -447,4 +450,93 @@ void AddMerkleRootAndCoinbase(CBlock& block, CTransactionRef coinbase, uint32_t
     block.nNonce = nonce;
     block.hashMerkleRoot = BlockMerkleRoot(block);
 }
+
+std::unique_ptr<CBlockTemplate> WaitAndCreateNewBlock(ChainstateManager& chainman,
+                                                      KernelNotifications& kernel_notifications,
+                                                      CTxMemPool* mempool,
+                                                      const std::unique_ptr<CBlockTemplate>& block_template,
+                                                      const BlockWaitOptions& options,
+                                                      const BlockAssembler::Options& assemble_options)
+{
+    // Delay calculating the current template fees, just in case a new block
+    // comes in before the next tick.
+    CAmount current_fees = -1;
+
+    // Alternate waiting for a new tip and checking if fees have risen.
+    // The latter check is expensive so we only run it once per second.
+    auto now{NodeClock::now()};
+    const auto deadline = now + options.timeout;
+    const MillisecondsDouble tick{1000};
+    const bool allow_min_difficulty{chainman.GetParams().GetConsensus().fPowAllowMinDifficultyBlocks};
+
+    do {
+        bool tip_changed{false};
+        {
+            WAIT_LOCK(kernel_notifications.m_tip_block_mutex, lock);
+            // Note that wait_until() checks the predicate before waiting
+            kernel_notifications.m_tip_block_cv.wait_until(lock, std::min(now + tick, deadline), [&]() EXCLUSIVE_LOCKS_REQUIRED(kernel_notifications.m_tip_block_mutex) {
+                AssertLockHeld(kernel_notifications.m_tip_block_mutex);
+                const auto tip_block{kernel_notifications.TipBlock()};
+                // We assume tip_block is set, because this is an instance
+                // method on BlockTemplate and no template could have been
+                // generated before a tip exists.
+                tip_changed = Assume(tip_block) && tip_block != block_template->block.hashPrevBlock;
+                return tip_changed || chainman.m_interrupt;
+            });
+        }
+
+        if (chainman.m_interrupt) return nullptr;
+        // At this point the tip changed, a full tick went by or we reached
+        // the deadline.
+
+        // Must release m_tip_block_mutex before locking cs_main, to avoid deadlocks.
+        LOCK(::cs_main);
+
+        // On test networks return a minimum difficulty block after 20 minutes
+        if (!tip_changed && allow_min_difficulty) {
+            const NodeClock::time_point tip_time{std::chrono::seconds{chainman.ActiveChain().Tip()->GetBlockTime()}};
+            if (now > tip_time + 20min) {
+                tip_changed = true;
+            }
+        }
+
+        /**
+         * We determine if fees increased compared to the previous template by generating
+         * a fresh template. There may be more efficient ways to determine how much
+         * (approximate) fees for the next block increased, perhaps more so after
+         * Cluster Mempool.
+         *
+         * We'll also create a new template if the tip changed during this iteration.
+         */
+        if (options.fee_threshold < MAX_MONEY || tip_changed) {
+            auto new_tmpl{BlockAssembler{
+                chainman.ActiveChainstate(),
+                mempool,
+                assemble_options}
+                              .CreateNewBlock()};
+
+            // If the tip changed, return the new template regardless of its fees.
+            if (tip_changed) return new_tmpl;
+
+            // Calculate the original template total fees if we haven't already
+            if (current_fees == -1) {
+                current_fees = 0;
+                for (CAmount fee : block_template->vTxFees) {
+                    current_fees += fee;
+                }
+            }
+
+            CAmount new_fees = 0;
+            for (CAmount fee : new_tmpl->vTxFees) {
+                new_fees += fee;
+                Assume(options.fee_threshold != MAX_MONEY);
+                if (new_fees >= current_fees + options.fee_threshold) return new_tmpl;
+            }
+        }
+
+        now = NodeClock::now();
+    } while (now < deadline);
+
+    return nullptr;
+}
 } // namespace node