Merge #12172: Bugfix: RPC: savemempool: Don't save until LoadMempool() is finished

cb1e319 Bugfix: RPC: savemempool: Don't save until LoadMempool() is finished (Jorge Timón)

Pull request description:

  Fixes https://github.com/bitcoin/bitcoin/issues/12142

  The tests are a little bit slow, mempool_persist.py goes from about 20 s to about 120 s in my hardware.
  Perhaps there's a better way to test this.

Tree-SHA512: 9e6c24b32a9cf3774e8f0bd81c035b0deb53fba5ac3eb2532d85900579d21cef8a1135b75a4fa0a9d883e3822eb35e7d4b47a0838abf99789039205041962629

src/init.cpp

@@ -115,7 +115,6 @@ static const char* FEE_ESTIMATES_FILENAME="fee_estimates.dat";
 //
 
 std::atomic<bool> fRequestShutdown(false);
-std::atomic<bool> fDumpMempoolLater(false);
 
 void StartShutdown()
 {
@@ -205,7 +204,7 @@ void Shutdown()
     threadGroup.interrupt_all();
     threadGroup.join_all();
 
-    if (fDumpMempoolLater && gArgs.GetArg("-persistmempool", DEFAULT_PERSIST_MEMPOOL)) {
+    if (g_is_mempool_loaded && gArgs.GetArg("-persistmempool", DEFAULT_PERSIST_MEMPOOL)) {
         DumpMempool();
     }
 
@@ -684,8 +683,8 @@ void ThreadImport(std::vector<fs::path> vImportFiles)
     } // End scope of CImportingNow
     if (gArgs.GetArg("-persistmempool", DEFAULT_PERSIST_MEMPOOL)) {
         LoadMempool();
-        fDumpMempoolLater = !fRequestShutdown;
     }
+    g_is_mempool_loaded = !fRequestShutdown;
 }
 
 /** Sanity checks

src/rpc/blockchain.cpp

@@ -1607,13 +1607,17 @@ UniValue savemempool(const JSONRPCRequest& request)
     if (request.fHelp || request.params.size() != 0) {
         throw std::runtime_error(
             "savemempool\n"
-            "\nDumps the mempool to disk.\n"
+            "\nDumps the mempool to disk. It will fail until the previous dump is fully loaded.\n"
             "\nExamples:\n"
             + HelpExampleCli("savemempool", "")
             + HelpExampleRpc("savemempool", "")
         );
     }
 
+    if (!g_is_mempool_loaded) {
+        throw JSONRPCError(RPC_MISC_ERROR, "The mempool was not loaded yet");
+    }
+
     if (!DumpMempool()) {
         throw JSONRPCError(RPC_MISC_ERROR, "Unable to dump mempool to disk");
     }

src/validation.cpp

@@ -227,6 +227,7 @@ CAmount maxTxFee = DEFAULT_TRANSACTION_MAXFEE;
 
 CBlockPolicyEstimator feeEstimator;
 CTxMemPool mempool(&feeEstimator);
+std::atomic_bool g_is_mempool_loaded{false};
 
 /** Constant stuff for coinbase transactions we create: */
 CScript COINBASE_FLAGS;

src/validation.h

@@ -158,6 +158,7 @@ extern CScript COINBASE_FLAGS;
 extern CCriticalSection cs_main;
 extern CBlockPolicyEstimator feeEstimator;
 extern CTxMemPool mempool;
+extern std::atomic_bool g_is_mempool_loaded;
 typedef std::unordered_map<uint256, CBlockIndex*, BlockHasher> BlockMap;
 extern BlockMap& mapBlockIndex;
 extern uint64_t nLastBlockTx;