NVDA backend initialization failed

[small18]

summary

Called when I am running in NVDA initialize function, returns the Already initialized, then prism doesn't seem to recognize NVDA back end.

When I use the zdsr backend test, it is normal and can be initialized.

versions

prism0.17.3
nvda 2026.1.1 (2026.1.1.55980)

[ethindp]

@small18 Can you provide more detail? Like: what code were you using to produce this problem?

[small18]

@ethindp

hi

My nvgt project requires prism. Because I don't know much about c + +, I asked codex to write the prism plug-in integration.
Integrated in the plug-in initialize function, called automatically when the program starts,However, once NVDA is running, prism fails to initialize.

The following are the initialization functions that codex integrated for me:

static bool prism_initialize() {
	std::lock_guard<std::mutex> lock(g_mutex);
	if (g_backend) return true;
	g_last_error.clear();
	wchar_t plugin_path[MAX_PATH] = {};
	GetModuleFileNameW(g_plugin_module, plugin_path, MAX_PATH);
	std::wstring prism_path(plugin_path);
	size_t separator = prism_path.find_last_of(L"\\/");
	prism_path = (separator == std::wstring::npos ? L"" : prism_path.substr(0, separator + 1)) + L"prism.dll";
	g_library = LoadLibraryW(prism_path.c_str());
	if (!g_library) {
		g_last_error = "Unable to load prism.dll (Windows error " + std::to_string(GetLastError()) + ")";
		return false;
	}
	if (!load_symbol(p_config_init, "prism_config_init") || !load_symbol(p_init, "prism_init") ||
		!load_symbol(p_shutdown, "prism_shutdown") || !load_symbol(p_create_best, "prism_registry_create_best") ||
		!load_symbol(p_backend_free, "prism_backend_free") || !load_symbol(p_backend_initialize, "prism_backend_initialize") ||
		!load_symbol(p_backend_speak, "prism_backend_speak") || !load_symbol(p_backend_braille, "prism_backend_braille") ||
		!load_symbol(p_backend_stop, "prism_backend_stop") ||
		!load_symbol(p_backend_name, "prism_backend_name") || !load_symbol(p_error_string, "prism_error_string")) {
		unload_prism();
		return false;
	}
	PrismConfig config = p_config_init();
	g_context = p_init(&config);
	if (!g_context) {
		g_last_error = "Prism could not create a context";
		unload_prism();
		return false;
	}
	g_backend = p_create_best(g_context);
	if (!g_backend) {
		g_last_error = "No supported Prism speech backend was found";
		unload_prism();
		return false;
	}
	PrismError error = p_backend_initialize(g_backend);
	if (error != 0) {
		g_last_error = p_error_string(error);
		unload_prism();
		return false;
	}
	return true;
}

[ethindp]

@small18 Thanks, this is a pretty good reason why. I'll go through the code and point out the problems.

	wchar_t plugin_path[MAX_PATH] = {};
	GetModuleFileNameW(g_plugin_module, plugin_path, MAX_PATH);

Two problems here. First, do not assume windows APIs are wide-character. (AI models absolutely love doing this, but MS's own advice states that you should NOT do this, nor should you mix them.) Always always always use the macros (in this case, GetModuleFileName, LoadLibrary, etc.), which will resolve to the correct functions that you should call. Second, GetModuleFileNameA/GetModuleFileNameW return an error code, so check that! Literally all of your wide-character code which follows from this is just a follow-on to this particular problem. It will not bite you here because NVGT defines UNICODE and _UNICODE, but that doesn't mean you should do this.

Second, the problem causing your issue is this part:

	PrismConfig config = p_config_init();
	g_context = p_init(&config);
	if (!g_context) {
		g_last_error = "Prism could not create a context";
		unload_prism();
		return false;
	}
	g_backend = p_create_best(g_context);
	if (!g_backend) {
		g_last_error = "No supported Prism speech backend was found";
		unload_prism();
		return false;
	}
	PrismError error = p_backend_initialize(g_backend);
	if (error != 0) {
		g_last_error = p_error_string(error);
		unload_prism();
		return false;
	}

Going through this:

1. Initializing a Prism context with a config zero-initialized from prism_config_init doesn't give you any of the new features that Prism offers including availability polling. You should ask yourself if this is what you want. If you do want availability polling, you need to fill this out.
2. You are explicitly ignoring a paragraph of the manual when checking the return value of prism_backend_initialize. To be clear, AIs love doing this (because, for some reason, they never read the docs before implementing this, so this always trips them up.) To wit: "For backends obtained via prism_registry_create_best or prism_registry_acquire_best, the backend is already initialized when returned. Calling prism_backend_initialize on such a backend returns PRISM_ERROR_ALREADY_INITIALIZED. Applications MAY treat this error as non-fatal." Notice the "MAY": you don't have to treat this as non-fatal, but you should, as this is a non-fatal condition; calling prism_backend_initialize on an already-initialized backend is an idempotent operation and has no effect. As a consequence of this issue, the library is unloaded and Prism is not used.

You need only change the error check from:

	if (error != 0)

To:

	if (error != PRISM_OK && error != PRISM_ERROR_ALREADY_INITIALIZED)

And things should work.

[ethindp]

As a note, I have converted this into a discussion as it is not a bug report.

[small18]

Thanks you, this problem can be solved.