validation: Move FindFilesToPrune{,Manual} to BlockManager

[META] No behaviour change is intended in this commit.
[META] This commit should be followed up by removing the comments and
       assertions meant only to show that the change is correct.

Also stop FindFilesToPrune{,Manual} from unnecessary reaching for
::ChainActive() by passing in the necessary information.

src/validation.cpp

@@ -197,9 +197,6 @@ CBlockIndex* FindForkInGlobalIndex(const CChain& chain, const CBlockLocator& loc
 
 std::unique_ptr<CBlockTreeDB> pblocktree;
 
-// See definition for documentation
-static void FindFilesToPruneManual(ChainstateManager& chainman, std::set<int>& setFilesToPrune, int nManualPruneHeight);
-static void FindFilesToPrune(ChainstateManager& chainman, std::set<int>& setFilesToPrune, uint64_t nPruneAfterHeight);
 bool CheckInputScripts(const CTransaction& tx, TxValidationState &state, const CCoinsViewCache &inputs, unsigned int flags, bool cacheSigStore, bool cacheFullScriptStore, PrecomputedTransactionData& txdata, std::vector<CScriptCheck> *pvChecks = nullptr);
 static FILE* OpenUndoFile(const FlatFilePos &pos, bool fReadOnly = false);
 static FlatFileSeq BlockFileSeq();
@@ -2284,14 +2281,53 @@ bool CChainState::FlushStateToDisk(
         CoinsCacheSizeState cache_state = GetCoinsCacheSizeState(&m_mempool);
         LOCK(cs_LastBlockFile);
         if (fPruneMode && (fCheckForPruning || nManualPruneHeight > 0) && !fReindex) {
+            // Previously, we called the global function ::ChainActive() in
+            // FindFilesToPrune{,Manual} to get the tip height and to determine
+            // whether or not a tip even exists. Now, we are simply passing in
+            // m_chain.Height() (which returns -1 if the tip doesn't exist). To
+            // make sure we're not changing behaviour, let's check that
+            // ::ChainActive() is the same object as m_chain (not just
+            // identical).
+            //
+            // This comment and the following assert will be removed in a
+            // subsequent commit, as they're just meant to demonstrate
+            // correctness (you can run tests against it and see that nothing
+            // exit unexpectedly).
+            assert(std::addressof(::ChainActive()) == std::addressof(m_chain));
             if (nManualPruneHeight > 0) {
                 LOG_TIME_MILLIS_WITH_CATEGORY("find files to prune (manual)", BCLog::BENCH);
 
-                FindFilesToPruneManual(g_chainman, setFilesToPrune, nManualPruneHeight);
+                m_blockman.FindFilesToPruneManual(setFilesToPrune, nManualPruneHeight, m_chain.Height());
             } else {
                 LOG_TIME_MILLIS_WITH_CATEGORY("find files to prune", BCLog::BENCH);
 
-                FindFilesToPrune(g_chainman, setFilesToPrune, chainparams.PruneAfterHeight());
+                // Previously, we called the global function
+                // ::ChainstateActive() in FindFilesToPrune{,Manual} to get the
+                // IBD status. Now, we are simply passing in
+                // IsInitialBlockDownload(). To make sure we're not changing
+                // behaviour, let's check that ::ChainstateActive() is the same
+                // object as *this (not just identical).
+                //
+                // This comment and the following assert will be removed in a
+                // subsequent commit, as they're just meant to demonstrate
+                // correctness (you can run tests against it and see that
+                // nothing exit unexpectedly).
+                assert(std::addressof(::ChainstateActive()) == std::addressof(*this));
+
+                // Previously, we called PruneOneBlockFile on g_chainman's
+                // m_blockman in FindFilesToPrune{,Manual}. Now, we are instead
+                // calling PruneOneBlockFile on _our_ m_blockman. To make sure
+                // we're not changing behaviour, let's check that
+                // g_chainman.m_blockman is the same object as _our_ m_blockman
+                // (not just identical).
+                //
+                // This comment and the following assert will be removed in a
+                // subsequent commit, as they're just meant to demonstrate
+                // correctness (you can run tests against it and see that
+                // nothing exit unexpectedly).
+                assert(std::addressof(g_chainman.m_blockman) == std::addressof(m_blockman));
+
+                m_blockman.FindFilesToPrune(setFilesToPrune, chainparams.PruneAfterHeight(), m_chain.Height(), IsInitialBlockDownload());
                 fCheckForPruning = false;
             }
             if (!setFilesToPrune.empty()) {
@@ -3958,21 +3994,21 @@ void UnlinkPrunedFiles(const std::set<int>& setFilesToPrune)
 }
 
 /* Calculate the block/rev files to delete based on height specified by user with RPC command pruneblockchain */
-static void FindFilesToPruneManual(ChainstateManager& chainman, std::set<int>& setFilesToPrune, int nManualPruneHeight)
+void BlockManager::FindFilesToPruneManual(std::set<int>& setFilesToPrune, int nManualPruneHeight, int chain_tip_height)
 {
     assert(fPruneMode && nManualPruneHeight > 0);
 
     LOCK2(cs_main, cs_LastBlockFile);
-    if (::ChainActive().Tip() == nullptr)
+    if (chain_tip_height < 0)
         return;
 
     // last block to prune is the lesser of (user-specified height, MIN_BLOCKS_TO_KEEP from the tip)
-    unsigned int nLastBlockWeCanPrune = std::min((unsigned)nManualPruneHeight, ::ChainActive().Tip()->nHeight - MIN_BLOCKS_TO_KEEP);
+    unsigned int nLastBlockWeCanPrune = std::min((unsigned)nManualPruneHeight, chain_tip_height - MIN_BLOCKS_TO_KEEP);
     int count=0;
     for (int fileNumber = 0; fileNumber < nLastBlockFile; fileNumber++) {
         if (vinfoBlockFile[fileNumber].nSize == 0 || vinfoBlockFile[fileNumber].nHeightLast > nLastBlockWeCanPrune)
             continue;
-        chainman.m_blockman.PruneOneBlockFile(fileNumber);
+        PruneOneBlockFile(fileNumber);
         setFilesToPrune.insert(fileNumber);
         count++;
     }
@@ -4005,17 +4041,17 @@ void PruneBlockFilesManual(int nManualPruneHeight)
  *
  * @param[out]   setFilesToPrune   The set of file indices that can be unlinked will be returned
  */
-static void FindFilesToPrune(ChainstateManager& chainman, std::set<int>& setFilesToPrune, uint64_t nPruneAfterHeight)
+void BlockManager::FindFilesToPrune(std::set<int>& setFilesToPrune, uint64_t nPruneAfterHeight, int chain_tip_height, bool is_ibd)
 {
     LOCK2(cs_main, cs_LastBlockFile);
-    if (::ChainActive().Tip() == nullptr || nPruneTarget == 0) {
+    if (chain_tip_height < 0 || nPruneTarget == 0) {
         return;
     }
-    if ((uint64_t)::ChainActive().Tip()->nHeight <= nPruneAfterHeight) {
+    if ((uint64_t)chain_tip_height <= nPruneAfterHeight) {
         return;
     }
 
-    unsigned int nLastBlockWeCanPrune = ::ChainActive().Tip()->nHeight - MIN_BLOCKS_TO_KEEP;
+    unsigned int nLastBlockWeCanPrune = chain_tip_height - MIN_BLOCKS_TO_KEEP;
     uint64_t nCurrentUsage = CalculateCurrentUsage();
     // We don't check to prune until after we've allocated new space for files
     // So we should leave a buffer under our target to account for another allocation
@@ -4029,7 +4065,7 @@ static void FindFilesToPrune(ChainstateManager& chainman, std::set<int>& setFile
         // To avoid excessive prune events negating the benefit of high dbcache
         // values, we should not prune too rapidly.
         // So when pruning in IBD, increase the buffer a bit to avoid a re-prune too soon.
-        if (::ChainstateActive().IsInitialBlockDownload()) {
+        if (is_ibd) {
             // Since this is only relevant during IBD, we use a fixed 10%
             nBuffer += nPruneTarget / 10;
         }
@@ -4047,7 +4083,7 @@ static void FindFilesToPrune(ChainstateManager& chainman, std::set<int>& setFile
             if (vinfoBlockFile[fileNumber].nHeightLast > nLastBlockWeCanPrune)
                 continue;
 
-            chainman.m_blockman.PruneOneBlockFile(fileNumber);
+            PruneOneBlockFile(fileNumber);
             // Queue up the files for removal
             setFilesToPrune.insert(fileNumber);
             nCurrentUsage -= nBytesToPrune;

src/validation.h

@@ -356,7 +356,15 @@ struct CBlockIndexWorkComparator
  * This data is used mostly in `CChainState` - information about, e.g.,
  * candidate tips is not maintained here.
  */
-class BlockManager {
+class BlockManager
+{
+    friend CChainState;
+
+private:
+    // See definition for documentation
+    void FindFilesToPruneManual(std::set<int>& setFilesToPrune, int nManualPruneHeight, int chain_tip_height);
+    void FindFilesToPrune(std::set<int>& setFilesToPrune, uint64_t nPruneAfterHeight, int chain_tip_height, bool is_ibd);
+
 public:
     BlockMap m_block_index GUARDED_BY(cs_main);