Merge bitcoin#14993: rpc: Fix data race (UB) in InterruptRPC()

6c10037 rpc: Fix data race (UB) in InterruptRPC() (practicalswift)

Pull request description:

  Fix data race (UB) in `InterruptRPC()`.

  Before:

  ```
  $ ./configure --with-sanitizers=thread
  $ make
  $ test/functional/test_runner.py feature_shutdown.py
  …
  SUMMARY: ThreadSanitizer: data race rpc/server.cpp:314 in InterruptRPC()
  …
  ALL                 | ✖ Failed  | 2 s (accumulated)
  ```

  After:

  ```
  $ ./configure --with-sanitizers=thread
  $ make
  $ test/functional/test_runner.py feature_shutdown.py
  …
  ALL                 | ✓ Passed  | 3 s (accumulated)
  ```

Tree-SHA512: b139ca1a0480258f8caa7730cabd7783a821d906630f51487750a6b15b7842675ed679747e1ff1bdade77d248807e9d77bae7bb88da54d1df84a179cd9b9b987

src/rpc/server.cpp

@@ -28,7 +28,7 @@
 #include <memory> // for unique_ptr
 #include <unordered_map>
 
-static bool fRPCRunning = false;
+static std::atomic<bool> g_rpc_running{false};
 static bool fRPCInWarmup = true;
 static std::string rpcWarmupStatus("RPC server started");
 static RecursiveMutex cs_rpcWarmup;
@@ -328,7 +328,7 @@ bool CRPCTable::appendCommand(const std::string& name, const CRPCCommand* pcmd)
 bool StartRPC()
 {
  LogPrint(BCLog::RPC, "Starting RPC\n");
- fRPCRunning = true;
+ g_rpc_running = true;
  g_rpcSignals.Started();
  return true;
 }
@@ -337,7 +337,7 @@ void InterruptRPC()
 {
  LogPrint(BCLog::RPC, "Interrupting RPC\n");
  // Interrupt e.g. running longpolls
- fRPCRunning = false;
+ g_rpc_running = false;
 }
 
 void StopRPC()
@@ -350,7 +350,7 @@ void StopRPC()
 
 bool IsRPCRunning()
 {
- return fRPCRunning;
+ return g_rpc_running;
 }
 
 void SetRPCWarmupStatus(const std::string& newStatus)