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ControllerInterface: fix UpdateReferences() deadlock

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Removed useless locks to DeviceContainer::m_devices_mutex, as they were all already protected by m_devices_population_mutex.
We have no interest in blocking other threads that were potentially reading devices at the same time so this seems fine.
This simplifies the code, and I've adjusted a few comments which mentioned possible deadlock that should now be totally gone.

The deadlock could have happen if a thread directly called EmulatedController::UpdateReferences(), while another another thread also reached EmulatedController::UpdateReferences() within a call to ControllerInterface::UpdateDevices(), as the mentioned function locked both the DeviceContainer::m_devices_mutex and s_get_state_mutex at the same time.

The deadlock was frequent on game emulation startup on Android, due to the UpdateReferences() call in InputConfig::LoadConfig() and the UI thread triggering calls to ControllerInterface::UpdateDevices().
It could also have happened on Desktop if a user pressed "Refresh Devices" manually in the UI while the input config was loading.

Also brought some UpdateReferences() comments and thread safety fixes from https://github.com/dolphin-emu/dolphin/pull/9489
This commit is contained in:
Filoppi 2021-11-17 22:55:02 +02:00
commit 1badceb455
3 changed files with 21 additions and 36 deletions
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3
Source/Core/InputCommon/ControllerEmu/ControllerEmu.cpp
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@ -18,6 +18,8 @@
namespace ControllerEmu
{
// This should theoretically be per EmulatedController instance,
// though no EmulatedController usually run in parallel, so it makes little difference
static std::recursive_mutex s_get_state_mutex;
std::string EmulatedController::GetDisplayName() const
@ -77,6 +79,7 @@ void EmulatedController::UpdateSingleControlReference(const ControllerInterface&
{
ciface::ExpressionParser::ControlEnvironment env(devi, GetDefaultDevice(), m_expression_vars);
const auto lock = GetStateLock();
ref->UpdateReference(env);
env.CleanUnusedVariables();