rpc: Add unloadwallet RPC

src/wallet/rpcwallet.cpp

@@ -3076,7 +3076,7 @@ static UniValue listwallets(const JSONRPCRequest& request)
     return obj;
 }
 
-UniValue loadwallet(const JSONRPCRequest& request)
+static UniValue loadwallet(const JSONRPCRequest& request)
 {
     if (request.fHelp || request.params.size() != 1)
         throw std::runtime_error(
@@ -3123,7 +3123,7 @@ UniValue loadwallet(const JSONRPCRequest& request)
     return obj;
 }
 
-UniValue createwallet(const JSONRPCRequest& request)
+static UniValue createwallet(const JSONRPCRequest& request)
 {
     if (request.fHelp || request.params.size() != 1) {
         throw std::runtime_error(
@@ -3170,6 +3170,55 @@ UniValue createwallet(const JSONRPCRequest& request)
     return obj;
 }
 
+static UniValue unloadwallet(const JSONRPCRequest& request)
+{
+    if (request.fHelp || request.params.size() > 1) {
+        throw std::runtime_error(
+            "unloadwallet ( \"wallet_name\" )\n"
+            "Unloads the wallet referenced by the request endpoint otherwise unloads the wallet specified in the argument.\n"
+            "Specifying the wallet name on a wallet endpoint is invalid."
+            "\nArguments:\n"
+            "1. \"wallet_name\"    (string, optional) The name of the wallet to unload.\n"
+            "\nExamples:\n"
+            + HelpExampleCli("unloadwallet", "wallet_name")
+            + HelpExampleRpc("unloadwallet", "wallet_name")
+        );
+    }
+
+    std::string wallet_name;
+    if (GetWalletNameFromJSONRPCRequest(request, wallet_name)) {
+        if (!request.params[0].isNull()) {
+            throw JSONRPCError(RPC_INVALID_PARAMETER, "Cannot unload the requested wallet");
+        }
+    } else {
+        wallet_name = request.params[0].get_str();
+    }
+
+    std::shared_ptr<CWallet> wallet = GetWallet(wallet_name);
+    if (!wallet) {
+        throw JSONRPCError(RPC_WALLET_NOT_FOUND, "Requested wallet does not exist or is not loaded");
+    }
+
+    // Release the "main" shared pointer and prevent further notifications.
+    // Note that any attempt to load the same wallet would fail until the wallet
+    // is destroyed (see CheckUniqueFileid).
+    if (!RemoveWallet(wallet)) {
+        throw JSONRPCError(RPC_MISC_ERROR, "Requested wallet already unloaded");
+    }
+    UnregisterValidationInterface(wallet.get());
+
+    // The wallet can be in use so it's not possible to explicitly unload here.
+    // Just notify the unload intent so that all shared pointers are released.
+    // The wallet will be destroyed once the last shared pointer is released.
+    wallet->NotifyUnload();
+
+    // There's no point in waiting for the wallet to unload.
+    // At this point this method should never fail. The unloading could only
+    // fail due to an unexpected error which would cause a process termination.
+
+    return NullUniValue;
+}
+
 static UniValue resendwallettransactions(const JSONRPCRequest& request)
 {
     std::shared_ptr<CWallet> const wallet = GetWalletForJSONRPCRequest(request);
@@ -4405,6 +4454,7 @@ static const CRPCCommand commands[] =
     { "wallet",             "settxfee",                         &settxfee,                      {"amount"} },
     { "wallet",             "signmessage",                      &signmessage,                   {"address","message"} },
     { "wallet",             "signrawtransactionwithwallet",     &signrawtransactionwithwallet,  {"hexstring","prevtxs","sighashtype"} },
+    { "wallet",             "unloadwallet",                     &unloadwallet,                  {"wallet_name"} },
     { "wallet",             "walletlock",                       &walletlock,                    {} },
     { "wallet",             "walletpassphrasechange",           &walletpassphrasechange,        {"oldpassphrase","newpassphrase"} },
     { "wallet",             "walletpassphrase",                 &walletpassphrase,              {"passphrase","timeout"} },

src/wallet/wallet.cpp

@@ -79,6 +79,15 @@ std::shared_ptr<CWallet> GetWallet(const std::string& name)
     return nullptr;
 }
 
+// Custom deleter for shared_ptr<CWallet>.
+static void ReleaseWallet(CWallet* wallet)
+{
+    LogPrintf("Releasing wallet %s\n", wallet->GetName());
+    wallet->BlockUntilSyncedToCurrentChain();
+    wallet->Flush();
+    delete wallet;
+}
+
 const uint32_t BIP32_HARDENED_KEY_LIMIT = 0x80000000;
 
 const uint256 CMerkleTx::ABANDON_HASH(uint256S("0000000000000000000000000000000000000000000000000000000000000001"));
@@ -1294,7 +1303,7 @@ void CWallet::BlockUntilSyncedToCurrentChain() {
         LOCK(cs_main);
         const CBlockIndex* initialChainTip = chainActive.Tip();
 
-        if (m_last_block_processed->GetAncestor(initialChainTip->nHeight) == initialChainTip) {
+        if (m_last_block_processed && m_last_block_processed->GetAncestor(initialChainTip->nHeight) == initialChainTip) {
             return;
         }
     }
@@ -4057,7 +4066,9 @@ std::shared_ptr<CWallet> CWallet::CreateWalletFromFile(const std::string& name,
 
     int64_t nStart = GetTimeMillis();
     bool fFirstRun = true;
-    std::shared_ptr<CWallet> walletInstance = std::make_shared<CWallet>(name, WalletDatabase::Create(path));
+    // TODO: Can't use std::make_shared because we need a custom deleter but
+    // should be possible to use std::allocate_shared.
+    std::shared_ptr<CWallet> walletInstance(new CWallet(name, WalletDatabase::Create(path)), ReleaseWallet);
     DBErrors nLoadWalletRet = walletInstance->LoadWallet(fFirstRun);
     if (nLoadWalletRet != DBErrors::LOAD_OK)
     {

src/wallet/wallet.h

@@ -1097,6 +1097,9 @@ public:
     //! Flush wallet (bitdb flush)
     void Flush(bool shutdown=false);
 
+    /** Wallet is about to be unloaded */
+    boost::signals2::signal<void ()> NotifyUnload;
+
     /**
      * Address book entry changed.
      * @note called with lock cs_wallet held.