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// Copyright 2014 Citra Emulator Project
// Licensed under GPLv2 or any later version
// Refer to the license.txt file included.
#include <memory>
#include <utility>
#include <vector>
#include "common/assert.h"
#include "core/core.h"
#include "core/hle/kernel/errors.h"
#include "core/hle/kernel/handle_table.h"
#include "core/hle/kernel/kernel.h"
#include "core/hle/kernel/mutex.h"
#include "core/hle/kernel/object.h"
#include "core/hle/kernel/process.h"
#include "core/hle/kernel/scheduler.h"
#include "core/hle/kernel/thread.h"
#include "core/hle/result.h"
#include "core/memory.h"
namespace Kernel {
/// Returns the number of threads that are waiting for a mutex, and the highest priority one among
/// those.
static std::pair<std::shared_ptr<Thread>, u32> GetHighestPriorityMutexWaitingThread(
const std::shared_ptr<Thread>& current_thread, VAddr mutex_addr) {
std::shared_ptr<Thread> highest_priority_thread;
u32 num_waiters = 0;
for (const auto& thread : current_thread->GetMutexWaitingThreads()) {
if (thread->GetMutexWaitAddress() != mutex_addr)
continue;
ASSERT(thread->GetStatus() == ThreadStatus::WaitMutex);
++num_waiters;
if (highest_priority_thread == nullptr ||
thread->GetPriority() < highest_priority_thread->GetPriority()) {
highest_priority_thread = thread;
}
}
return {highest_priority_thread, num_waiters};
}
/// Update the mutex owner field of all threads waiting on the mutex to point to the new owner.
static void TransferMutexOwnership(VAddr mutex_addr, std::shared_ptr<Thread> current_thread,
std::shared_ptr<Thread> new_owner) {
const auto threads = current_thread->GetMutexWaitingThreads();
for (const auto& thread : threads) {
if (thread->GetMutexWaitAddress() != mutex_addr)
continue;
ASSERT(thread->GetLockOwner() == current_thread.get());
current_thread->RemoveMutexWaiter(thread);
if (new_owner != thread)
new_owner->AddMutexWaiter(thread);
}
}
Mutex::Mutex(Core::System& system) : system{system} {}
Mutex::~Mutex() = default;
ResultCode Mutex::TryAcquire(VAddr address, Handle holding_thread_handle,
Handle requesting_thread_handle) {
// The mutex address must be 4-byte aligned
if ((address % sizeof(u32)) != 0) {
return ERR_INVALID_ADDRESS;
}
const auto& handle_table = system.Kernel().CurrentProcess()->GetHandleTable();
std::shared_ptr<Thread> current_thread =
SharedFrom(system.CurrentScheduler().GetCurrentThread());
std::shared_ptr<Thread> holding_thread = handle_table.Get<Thread>(holding_thread_handle);
std::shared_ptr<Thread> requesting_thread = handle_table.Get<Thread>(requesting_thread_handle);
// TODO(Subv): It is currently unknown if it is possible to lock a mutex in behalf of another
// thread.
ASSERT(requesting_thread == current_thread);
const u32 addr_value = system.Memory().Read32(address);
// If the mutex isn't being held, just return success.
if (addr_value != (holding_thread_handle | Mutex::MutexHasWaitersFlag)) {
return RESULT_SUCCESS;
}
if (holding_thread == nullptr) {
return ERR_INVALID_HANDLE;
}
// Wait until the mutex is released
current_thread->SetMutexWaitAddress(address);
current_thread->SetWaitHandle(requesting_thread_handle);
current_thread->SetStatus(ThreadStatus::WaitMutex);
current_thread->InvalidateWakeupCallback();
// Update the lock holder thread's priority to prevent priority inversion.
holding_thread->AddMutexWaiter(current_thread);
system.PrepareReschedule();
return RESULT_SUCCESS;
}
ResultCode Mutex::Release(VAddr address) {
// The mutex address must be 4-byte aligned
if ((address % sizeof(u32)) != 0) {
return ERR_INVALID_ADDRESS;
}
std::shared_ptr<Thread> current_thread =
SharedFrom(system.CurrentScheduler().GetCurrentThread());
auto [thread, num_waiters] = GetHighestPriorityMutexWaitingThread(current_thread, address);
// There are no more threads waiting for the mutex, release it completely.
if (thread == nullptr) {
system.Memory().Write32(address, 0);
return RESULT_SUCCESS;
}
// Transfer the ownership of the mutex from the previous owner to the new one.
TransferMutexOwnership(address, current_thread, thread);
u32 mutex_value = thread->GetWaitHandle();
if (num_waiters >= 2) {
// Notify the guest that there are still some threads waiting for the mutex
mutex_value |= Mutex::MutexHasWaitersFlag;
}
// Grant the mutex to the next waiting thread and resume it.
system.Memory().Write32(address, mutex_value);
ASSERT(thread->GetStatus() == ThreadStatus::WaitMutex);
thread->ResumeFromWait();
thread->SetLockOwner(nullptr);
thread->SetCondVarWaitAddress(0);
thread->SetMutexWaitAddress(0);
thread->SetWaitHandle(0);
thread->SetWaitSynchronizationResult(RESULT_SUCCESS);
system.PrepareReschedule();
return RESULT_SUCCESS;
}
} // namespace Kernel
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