46572d027d
Verified with a hwtest and implemented based on reverse engineering. Thread A's priority will get bumped to the highest priority among all the threads that are waiting for a mutex that A holds. Once A releases the mutex and ownership is transferred to B, A's priority will return to normal and B's priority will be bumped.
136 lines
4.6 KiB
C++
136 lines
4.6 KiB
C++
// Copyright 2014 Citra Emulator Project
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// Licensed under GPLv2 or any later version
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// Refer to the license.txt file included.
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#include <map>
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#include <vector>
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#include <boost/range/algorithm_ext/erase.hpp>
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#include "common/assert.h"
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#include "core/core.h"
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#include "core/hle/kernel/errors.h"
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#include "core/hle/kernel/handle_table.h"
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#include "core/hle/kernel/kernel.h"
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#include "core/hle/kernel/mutex.h"
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#include "core/hle/kernel/object_address_table.h"
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#include "core/hle/kernel/thread.h"
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namespace Kernel {
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/// Returns the number of threads that are waiting for a mutex, and the highest priority one among
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/// those.
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static std::pair<SharedPtr<Thread>, u32> GetHighestPriorityMutexWaitingThread(
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SharedPtr<Thread> current_thread, VAddr mutex_addr) {
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SharedPtr<Thread> highest_priority_thread;
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u32 num_waiters = 0;
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for (auto& thread : current_thread->wait_mutex_threads) {
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if (thread->mutex_wait_address != mutex_addr)
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continue;
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ASSERT(thread->status == THREADSTATUS_WAIT_MUTEX);
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++num_waiters;
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if (highest_priority_thread == nullptr ||
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thread->GetPriority() < highest_priority_thread->GetPriority()) {
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highest_priority_thread = thread;
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}
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}
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return {highest_priority_thread, num_waiters};
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}
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/// Update the mutex owner field of all threads waiting on the mutex to point to the new owner.
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static void TransferMutexOwnership(VAddr mutex_addr, SharedPtr<Thread> current_thread,
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SharedPtr<Thread> new_owner) {
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auto threads = current_thread->wait_mutex_threads;
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for (auto& thread : threads) {
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if (thread->mutex_wait_address != mutex_addr)
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continue;
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ASSERT(thread->lock_owner == current_thread);
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current_thread->RemoveMutexWaiter(thread);
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if (new_owner != thread)
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new_owner->AddMutexWaiter(thread);
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}
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}
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ResultCode Mutex::TryAcquire(VAddr address, Handle holding_thread_handle,
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Handle requesting_thread_handle) {
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// The mutex address must be 4-byte aligned
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if ((address % sizeof(u32)) != 0) {
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return ResultCode(ErrorModule::Kernel, ErrCodes::MisalignedAddress);
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}
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SharedPtr<Thread> holding_thread = g_handle_table.Get<Thread>(holding_thread_handle);
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SharedPtr<Thread> requesting_thread = g_handle_table.Get<Thread>(requesting_thread_handle);
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// TODO(Subv): It is currently unknown if it is possible to lock a mutex in behalf of another
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// thread.
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ASSERT(requesting_thread == GetCurrentThread());
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u32 addr_value = Memory::Read32(address);
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// If the mutex isn't being held, just return success.
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if (addr_value != (holding_thread_handle | Mutex::MutexHasWaitersFlag)) {
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return RESULT_SUCCESS;
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}
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if (holding_thread == nullptr)
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return ERR_INVALID_HANDLE;
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// Wait until the mutex is released
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GetCurrentThread()->mutex_wait_address = address;
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GetCurrentThread()->wait_handle = requesting_thread_handle;
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GetCurrentThread()->status = THREADSTATUS_WAIT_MUTEX;
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GetCurrentThread()->wakeup_callback = nullptr;
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// Update the lock holder thread's priority to prevent priority inversion.
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holding_thread->AddMutexWaiter(GetCurrentThread());
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Core::System::GetInstance().PrepareReschedule();
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return RESULT_SUCCESS;
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}
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ResultCode Mutex::Release(VAddr address) {
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// The mutex address must be 4-byte aligned
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if ((address % sizeof(u32)) != 0) {
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return ResultCode(ErrorModule::Kernel, ErrCodes::MisalignedAddress);
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}
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auto [thread, num_waiters] = GetHighestPriorityMutexWaitingThread(GetCurrentThread(), address);
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// There are no more threads waiting for the mutex, release it completely.
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if (thread == nullptr) {
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ASSERT(GetCurrentThread()->wait_mutex_threads.empty());
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Memory::Write32(address, 0);
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return RESULT_SUCCESS;
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}
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// Transfer the ownership of the mutex from the previous owner to the new one.
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TransferMutexOwnership(address, GetCurrentThread(), thread);
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u32 mutex_value = thread->wait_handle;
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if (num_waiters >= 2) {
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// Notify the guest that there are still some threads waiting for the mutex
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mutex_value |= Mutex::MutexHasWaitersFlag;
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}
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// Grant the mutex to the next waiting thread and resume it.
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Memory::Write32(address, mutex_value);
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ASSERT(thread->status == THREADSTATUS_WAIT_MUTEX);
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thread->ResumeFromWait();
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thread->lock_owner = nullptr;
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thread->condvar_wait_address = 0;
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thread->mutex_wait_address = 0;
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thread->wait_handle = 0;
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return RESULT_SUCCESS;
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}
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} // namespace Kernel
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