Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Cache the local time zone calculation on Windows #1791

Closed
wants to merge 1 commit into from
Closed

Cache the local time zone calculation on Windows #1791

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
68 changes: 39 additions & 29 deletions absl/time/internal/cctz/src/time_zone_lookup.cc
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -67,7 +67,7 @@ namespace {
#if defined(USE_WIN32_LOCAL_TIME_ZONE)
// Calls the WinRT Calendar.GetTimeZone method to obtain the IANA ID of the
// local time zone. Returns an empty vector in case of an error.
std::string win32_local_time_zone(const HMODULE combase) {
static std::string win32_local_time_zone(const HMODULE combase) {
std::string result;
const auto ro_activate_instance =
reinterpret_cast<decltype(&RoActivateInstance)>(
Expand Down Expand Up @@ -138,6 +138,43 @@ std::string win32_local_time_zone(const HMODULE combase) {
calendar->Release();
return result;
}

static std::string get_once_win32_local_time_zone() {
// Use the WinRT Calendar class to get the local time zone. This feature is
// available on Windows 10 and later. The library is dynamically linked to
// maintain binary compatibility with Windows XP - Windows 7. On Windows 8,
// The combase.dll API functions are available but the RoActivateInstance
// call will fail for the Calendar class.
std::string winrt_tz;
const HMODULE combase =
LoadLibraryEx(_T("combase.dll"), nullptr, LOAD_LIBRARY_SEARCH_SYSTEM32);
if (combase) {
const auto ro_initialize = reinterpret_cast<decltype(&::RoInitialize)>(
GetProcAddress(combase, "RoInitialize"));
const auto ro_uninitialize = reinterpret_cast<decltype(&::RoUninitialize)>(
GetProcAddress(combase, "RoUninitialize"));
if (ro_initialize && ro_uninitialize) {
const HRESULT hr = ro_initialize(RO_INIT_MULTITHREADED);
// RPC_E_CHANGED_MODE means that a previous RoInitialize call specified
// a different concurrency model. The WinRT runtime is initialized and
// should work for our purpose here, but we should *not* call
// RoUninitialize because it's a failure.
if (SUCCEEDED(hr) || hr == RPC_E_CHANGED_MODE) {
winrt_tz = win32_local_time_zone(combase);
if (SUCCEEDED(hr)) {
ro_uninitialize();
}
}
}
FreeLibrary(combase);
}
return winrt_tz;
}

static std::string& cached_win32_local_time_zone() {
static std::string cached_time_zone = get_once_win32_local_time_zone();
Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Note that this is not safe for global destruction. See https://google.github.io/styleguide/cppguide.html#Static_and_Global_Variables.

Copy link
Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Good point! I wonder what else can be done here - maybe leaking the object? (Not ideal)

Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Yes that is what I would do, but I was just pointing that out. I think the approach here is wrong anyway. See above.

return cached_time_zone;
}
#endif
} // namespace

Expand Down Expand Up @@ -256,34 +293,7 @@ time_zone local_time_zone() {
}
#endif
#if defined(USE_WIN32_LOCAL_TIME_ZONE)
// Use the WinRT Calendar class to get the local time zone. This feature is
// available on Windows 10 and later. The library is dynamically linked to
// maintain binary compatibility with Windows XP - Windows 7. On Windows 8,
// The combase.dll API functions are available but the RoActivateInstance
// call will fail for the Calendar class.
std::string winrt_tz;
const HMODULE combase =
LoadLibraryEx(_T("combase.dll"), nullptr, LOAD_LIBRARY_SEARCH_SYSTEM32);
if (combase) {
const auto ro_initialize = reinterpret_cast<decltype(&::RoInitialize)>(
GetProcAddress(combase, "RoInitialize"));
const auto ro_uninitialize = reinterpret_cast<decltype(&::RoUninitialize)>(
GetProcAddress(combase, "RoUninitialize"));
if (ro_initialize && ro_uninitialize) {
const HRESULT hr = ro_initialize(RO_INIT_MULTITHREADED);
// RPC_E_CHANGED_MODE means that a previous RoInitialize call specified
// a different concurrency model. The WinRT runtime is initialized and
// should work for our purpose here, but we should *not* call
// RoUninitialize because it's a failure.
if (SUCCEEDED(hr) || hr == RPC_E_CHANGED_MODE) {
winrt_tz = win32_local_time_zone(combase);
if (SUCCEEDED(hr)) {
ro_uninitialize();
}
}
}
FreeLibrary(combase);
}
std::string winrt_tz = cached_win32_local_time_zone();
if (!winrt_tz.empty()) {
zone = winrt_tz.c_str();
}
Expand Down