Removes use of static mutex in sqlcipher_extra_shutdown()

sjlombardo · sjlombardo · commit c8ce6f052d38 · 2025-05-09T12:45:40.000-04:00
The sqlcipher_extra_shutdown() function is called by sqlite3_shutdown() to cleanup internal SQLCipher resources. However, many applications do not call sqlite3_shutdown(). In order to ensure that SQLCipher resources are cleaned up even if sqlite3_shutdown() is omitted, sqlcipher_extra_shutdown() is also called from atexit and from a library finalizer (fini/DllMain). Previously, sqlcipher_extra_shutdown() internally locked a global static mutex prior to clean up. However, this introduced an edge case where, if the library was compiled with SQLITE_OMIT_AUTOINIT, and sqlite_shutdown() was called explicitly, a subsequent call to sqlcipher_extra_shutdown() from atexit or the finalizer could reallocate a new mutex that would never be freed. This change removes the use of the mutex from sqlcipher_extra_shutdown() entirely. The SQLite documentation makes it clear that sqlite3_shutdown() is NOT threadsafe (https://www.sqlite.org/c3ref/initialize.html) so an application must already guarantee that is called from a single thread. Other invocations of sqlcipher_extra_shutdown will also be called in a single-threaded context. As a result sqlcipher_extra_shutdown() should not need to make use of a mutext internally, and its removal solves the previous edge case problem.
diff --git a/src/sqlcipher.c b/src/sqlcipher.c
@@ -589,10 +589,6 @@ int sqlcipher_extra_init(const char* arg) {
 void sqlcipher_extra_shutdown(void) {
   int i = 0;
   sqlcipher_provider *provider = NULL;
-  sqlite3_mutex *mutex = sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_MASTER); 
-  if(mutex) {
-    sqlite3_mutex_enter(mutex);
-  }
 
   /* if sqlcipher hasn't been initialized or the shutdown already completed exit early */
   if(!sqlcipher_init || sqlcipher_shutdown) {
@@ -663,9 +659,6 @@ void sqlcipher_extra_shutdown(void) {
   sqlcipher_init = 0;
   sqlcipher_init_error = SQLITE_ERROR;
   sqlcipher_shutdown = 1;
-  if(mutex) {
-    sqlite3_mutex_leave(mutex);
-  }
 }
 
 static void sqlcipher_shield(unsigned char *in, int sz) {
