Merge bitcoin/bitcoin#26618: rpc: Prevent unloading a wallet when rescanning

109cbb819d doc: Add release notes for #26618 (Aurèle Oulès)
b13902d2e4 rpc: Prevent unloading a wallet when rescanning (Aurèle Oulès)

Pull request description:

  Fixes #26463.

  This PR prevents a user from unloading a wallet if it is currently rescanning.

  To test:

  ```bash
  ./src/bitcoin-cli -testnet -named createwallet wallet_name=wo disable_private_keys=true
  ./src/bitcoin-cli -testnet -rpcwallet=wo importdescriptors '[{
    "desc": "addr(mmcuW74MyJUZuLnWXGQLoNXPrS9RbFz6gD)#tpnrahgc",
        "timestamp": 0,
        "active": false,
        "internal": false,
        "next": 0
  }]'
  ./src/bitcoin-cli -testnet unloadwallet wo
  error code: -4
  error message:
  Wallet is currently rescanning. Abort existing rescan or wait.

ACKs for top commit:
  achow101:
    ACK 109cbb819d
  w0xlt:
    ACK 109cbb819d
  kouloumos:
    ACK 109cbb819d
  promag:
    ACK 109cbb819d

Tree-SHA512: 15fdddf4cf9f3fa08f52069fe4a25a76e04a55bb2586b031bfb0393dce7f175dcdb52823e132a7dff6a894539beeb980a1aad2a792790be036be6977628149b2

doc/release-notes-26618.md

@@ -0,0 +1,4 @@
+RPC Wallet
+----------
+
+- RPC `unloadwallet` now fails if a rescan is in progress. (#26618)

src/wallet/rpc/wallet.cpp

@@ -445,13 +445,20 @@ static RPCHelpMan unloadwallet()
         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).
     std::vector<bilingual_str> warnings;
-    std::optional<bool> load_on_start = request.params[1].isNull() ? std::nullopt : std::optional<bool>(request.params[1].get_bool());
-    if (!RemoveWallet(context, wallet, load_on_start, warnings)) {
-        throw JSONRPCError(RPC_MISC_ERROR, "Requested wallet already unloaded");
+    {
+        WalletRescanReserver reserver(*wallet);
+        if (!reserver.reserve()) {
+            throw JSONRPCError(RPC_WALLET_ERROR, "Wallet is currently rescanning. Abort existing rescan or wait.");
+        }
+
+        // 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).
+        std::optional<bool> load_on_start = request.params[1].isNull() ? std::nullopt : std::optional<bool>(request.params[1].get_bool());
+        if (!RemoveWallet(context, wallet, load_on_start, warnings)) {
+            throw JSONRPCError(RPC_MISC_ERROR, "Requested wallet already unloaded");
+        }
     }
 
     UnloadWallet(std::move(wallet));