From e81a2080ebf9712231dd29c081141780ffd46cfb Mon Sep 17 00:00:00 2001
From: Subv
Date: Fri, 20 Apr 2018 12:01:14 -0500
Subject: Kernel: Corrected the implementation of svcArbitrateLock and
 svcArbitrateUnlock.

Switch mutexes are no longer kernel objects, they are managed in userland and only use the kernel to handle the contention case.
Mutex addresses store a special flag value (0x40000000) to notify the guest code that there are still some threads waiting for the mutex to be released. This flag is updated when a thread calls ArbitrateUnlock.

TODO:
* Fix svcWaitProcessWideKey
* Fix svcSignalProcessWideKey
* Remove the Mutex class.
---
 src/core/hle/kernel/mutex.cpp | 94 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 94 insertions(+)

(limited to 'src/core/hle/kernel/mutex.cpp')

diff --git a/src/core/hle/kernel/mutex.cpp b/src/core/hle/kernel/mutex.cpp
index 0b9dc700c..50a9a0805 100644
--- a/src/core/hle/kernel/mutex.cpp
+++ b/src/core/hle/kernel/mutex.cpp
@@ -7,6 +7,7 @@
 #include <boost/range/algorithm_ext/erase.hpp>
 #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"
@@ -15,6 +16,30 @@
 
 namespace Kernel {
 
+/// Returns the number of threads that are waiting for a mutex, and the highest priority one among
+/// those.
+static std::pair<SharedPtr<Thread>, u32> GetHighestPriorityMutexWaitingThread(VAddr mutex_addr) {
+    auto& thread_list = Core::System::GetInstance().Scheduler().GetThreadList();
+
+    SharedPtr<Thread> highest_priority_thread;
+    u32 num_waiters = 0;
+
+    for (auto& thread : thread_list) {
+        if (thread->mutex_wait_address != mutex_addr)
+            continue;
+
+        ASSERT(thread->status == THREADSTATUS_WAIT_MUTEX);
+
+        ++num_waiters;
+        if (highest_priority_thread == nullptr ||
+            thread->GetPriority() < highest_priority_thread->GetPriority()) {
+            highest_priority_thread = thread;
+        }
+    }
+
+    return {highest_priority_thread, num_waiters};
+}
+
 void ReleaseThreadMutexes(Thread* thread) {
     for (auto& mtx : thread->held_mutexes) {
         mtx->SetHasWaiters(false);
@@ -135,4 +160,73 @@ void Mutex::SetHasWaiters(bool has_waiters) {
     Memory::Write32(guest_addr, guest_state.raw);
 }
 
+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 ResultCode(ErrorModule::Kernel, ErrCodes::MisalignedAddress);
+    }
+
+    SharedPtr<Thread> holding_thread = g_handle_table.Get<Thread>(holding_thread_handle);
+    SharedPtr<Thread> requesting_thread = g_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 == GetCurrentThread());
+
+    u32 addr_value = 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
+    requesting_thread->mutex_wait_address = address;
+    requesting_thread->wait_handle = requesting_thread_handle;
+
+    requesting_thread->status = THREADSTATUS_WAIT_MUTEX;
+    requesting_thread->wakeup_callback = nullptr;
+
+    Core::System::GetInstance().PrepareReschedule();
+
+    return RESULT_SUCCESS;
+}
+
+ResultCode Mutex::Release(VAddr address) {
+    // The mutex address must be 4-byte aligned
+    if ((address % sizeof(u32)) != 0) {
+        return ResultCode(ErrorModule::Kernel, ErrCodes::MisalignedAddress);
+    }
+
+    auto [thread, num_waiters] = GetHighestPriorityMutexWaitingThread(address);
+
+    // There are no more threads waiting for the mutex, release it completely.
+    if (thread == nullptr) {
+        Memory::Write32(address, 0);
+        return RESULT_SUCCESS;
+    }
+
+    u32 mutex_value = thread->wait_handle;
+
+    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.
+    Memory::Write32(address, mutex_value);
+
+    ASSERT(thread->status == THREADSTATUS_WAIT_MUTEX);
+    thread->ResumeFromWait();
+
+    thread->condvar_wait_address = 0;
+    thread->mutex_wait_address = 0;
+    thread->wait_handle = 0;
+
+    return RESULT_SUCCESS;
+}
 } // namespace Kernel
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