Merge #19300: wallet: Handle concurrent wallet loading

9b009fae6e qa: Test concurrent wallet loading (João Barbosa)
b9971ae585 wallet: Handle concurrent wallet loading (João Barbosa)

Pull request description:

  This PR handles concurrent wallet loading.

  This can be tested by running in parallel the following script a couple of times:
  ```sh
  for i in {1..10}
  do
    src/bitcoin-cli -regtest loadwallet foo
    src/bitcoin-cli -regtest unloadwallet foo
  done
  ```

  Eventually the error occurs:
  ```
  error code: -4
  error message:
  Wallet already being loading.
  ```

  For reference, loading and already loaded wallet gives:
  ```
  error code: -4
  error message:
  Wallet file verification failed. Error loading wallet w1. Duplicate -wallet filename specified.
  ```

  Fixes #19232.

ACKs for top commit:
  MarcoFalke:
    Concept ACK 9b009fae6e I have not reviewed the code
  hebasto:
    ACK 9b009fae6e, tested on Linux Mint 20 (x86_64):
  ryanofsky:
    Code review good-but-not-ideal ACK 9b009fae6e

Tree-SHA512: 0ccd77b03c0926e4c4e51efb31e193b93cb4b9ffe8bac6bb018f7344c55dfd939b873b8cf5e657dca73e6202eb75aa672de2acb787cc133184b0b3b51e47b972

test/functional/wallet_multiwallet.py

@@ -7,19 +7,36 @@
 Verify that a bitcoind node can load multiple wallet files
 """
 from decimal import Decimal
+from threading import Thread
 import os
 import shutil
 import time
 
+from test_framework.authproxy import JSONRPCException
 from test_framework.test_framework import BitcoinTestFramework
 from test_framework.test_node import ErrorMatch
 from test_framework.util import (
     assert_equal,
     assert_raises_rpc_error,
+    get_rpc_proxy,
 )
 
 FEATURE_LATEST = 169900
 
+got_loading_error = False
+def test_load_unload(node, name):
+    global got_loading_error
+    for i in range(10):
+        if got_loading_error:
+            return
+        try:
+            node.loadwallet(name)
+            node.unloadwallet(name)
+        except JSONRPCException as e:
+            if e.error['code'] == -4 and 'Wallet already being loading' in e.error['message']:
+                got_loading_error = True
+                return
+
 
 class MultiWalletTest(BitcoinTestFramework):
     def set_test_params(self):
@@ -212,6 +229,18 @@ class MultiWalletTest(BitcoinTestFramework):
         w2 = node.get_wallet_rpc(wallet_names[1])
         w2.getwalletinfo()
 
+        self.log.info("Concurrent wallet loading")
+        threads = []
+        for _ in range(3):
+            n = node.cli if self.options.usecli else get_rpc_proxy(node.url, 1, timeout=600, coveragedir=node.coverage_dir)
+            t = Thread(target=test_load_unload, args=(n, wallet_names[2], ))
+            t.start()
+            threads.append(t)
+        for t in threads:
+            t.join()
+        global got_loading_error
+        assert_equal(got_loading_error, True)
+
         self.log.info("Load remaining wallets")
         for wallet_name in wallet_names[2:]:
             loadwallet_name = self.nodes[0].loadwallet(wallet_name)