wallet: use Mutex for g_sqlite_mutex instead of GlobalMutex

Using `Mutex` provides stronger guarantee than `GlobalMutex` wrt Clang's
thread safety analysis. Thus it is better to reduce the usage of
`GlobalMutex` in favor of `Mutex`.

Using `Mutex` for `g_sqlite_mutex` is ok because its usage is limited in
`wallet/sqlite.cpp` and it does not require propagating the negative
annotations to not relevant code.

src/wallet/sqlite.cpp

@@ -23,9 +23,6 @@
 namespace wallet {
 static constexpr int32_t WALLET_SCHEMA_VERSION = 0;
 
-static GlobalMutex g_sqlite_mutex;
-static int g_sqlite_count GUARDED_BY(g_sqlite_mutex) = 0;
-
 static void ErrorLogCallback(void* arg, int code, const char* msg)
 {
     // From sqlite3_config() documentation for the SQLITE_CONFIG_LOG option:
@@ -83,6 +80,9 @@ static void SetPragma(sqlite3* db, const std::string& key, const std::string& va
     }
 }
 
+Mutex SQLiteDatabase::g_sqlite_mutex;
+int SQLiteDatabase::g_sqlite_count = 0;
+
 SQLiteDatabase::SQLiteDatabase(const fs::path& dir_path, const fs::path& file_path, const DatabaseOptions& options, bool mock)
     : WalletDatabase(), m_mock(mock), m_dir_path(fs::PathToString(dir_path)), m_file_path(fs::PathToString(file_path)), m_use_unsafe_sync(options.use_unsafe_sync)
 {
@@ -146,6 +146,8 @@ SQLiteDatabase::~SQLiteDatabase()
 
 void SQLiteDatabase::Cleanup() noexcept
 {
+    AssertLockNotHeld(g_sqlite_mutex);
+
     Close();
 
     LOCK(g_sqlite_mutex);

src/wallet/sqlite.h

@@ -5,6 +5,7 @@
 #ifndef BITCOIN_WALLET_SQLITE_H
 #define BITCOIN_WALLET_SQLITE_H
 
+#include <sync.h>
 #include <wallet/db.h>
 
 #include <sqlite3.h>
@@ -63,7 +64,16 @@ private:
 
     const std::string m_file_path;
 
-    void Cleanup() noexcept;
+    /**
+     * This mutex protects SQLite initialization and shutdown.
+     * sqlite3_config() and sqlite3_shutdown() are not thread-safe (sqlite3_initialize() is).
+     * Concurrent threads that execute SQLiteDatabase::SQLiteDatabase() should have just one
+     * of them do the init and the rest wait for it to complete before all can proceed.
+     */
+    static Mutex g_sqlite_mutex;
+    static int g_sqlite_count GUARDED_BY(g_sqlite_mutex);
+
+    void Cleanup() noexcept EXCLUSIVE_LOCKS_REQUIRED(!g_sqlite_mutex);
 
 public:
     SQLiteDatabase() = delete;