prevent Valkey crash when module is loaded twice (#415)

* prevent Valkey crash when module is loaded twice

Signed-off-by: Dmitry Polyakovsky <[email protected]>

* added utils::verifyLoadedOnlyOnce, calling it from VALKEY_MODULE

Signed-off-by: Dmitry Polyakovsky <[email protected]>

* format verifyLoadedOnlyOnce

Signed-off-by: Dmitry Polyakovsky <[email protected]>

---------

Signed-off-by: Dmitry Polyakovsky <[email protected]>

Author: dmitrypol

vmsdk/src/module.h

@@ -23,6 +23,10 @@
   extern "C" {                                                              \
   int ValkeyModule_OnLoad(ValkeyModuleCtx *ctx, ValkeyModuleString **argv,  \
                           int argc) {                                       \
+    if (!vmsdk::verifyLoadedOnlyOnce()) {                                   \
+      VMSDK_LOG(NOTICE, ctx) << "Module cannot be loaded more than once";   \
+      return VALKEYMODULE_ERR;                                              \
+    }                                                                       \
     vmsdk::TrackCurrentAsMainThread();                                      \
     if (auto status = vmsdk::module::OnLoad(ctx, argv, argc, options);      \
         status != VALKEYMODULE_OK) {                                        \

vmsdk/src/utils.cc

@@ -53,6 +53,13 @@ int StopTimerFromBackgroundThread(
   });
 }
 
+bool verifyLoadedOnlyOnce() {
+  static bool prev_loaded = false;
+  if (prev_loaded) return false;
+  prev_loaded = true;
+  return true;
+}
+
 void TrackCurrentAsMainThread() {
   CHECK(!set_main_thread);
   is_main_thread = true;

vmsdk/src/utils.h

@@ -47,6 +47,7 @@ int StopTimerFromBackgroundThread(
     ValkeyModuleCtx *ctx, ValkeyModuleTimerID timer_id,
     absl::AnyInvocable<void(void *)> user_data_deleter);
 
+bool verifyLoadedOnlyOnce();
 void TrackCurrentAsMainThread();
 bool IsMainThread();
 inline void VerifyMainThread() { CHECK(IsMainThread()); }